74. Walsh, B; Lormand, C; Procter, J; Williams-Jones, G.Characterizing the evolution of mass flow properties and dynamics through analysis of seismic signals: Insights from the 18 March 2007 Mt. Ruapehu lake-breakout lahar.Natural Hazards and Earth System Sciences, 2023, Characterizing the evolution of mass flow properties and dynamics through analysis of seismic signals: Insights from the 18 March 2007 Mt. Ruapehu lake-breakout lahar.
Monitoring for lahars on volcanoes can be challenging due to the ever-changing landscape which can drastically transform the properties and dynamics of the flow. These changes to the flows require the need for detection strategies and risk assessment that are tailored not only between different volcanoes, but at different distances along flow paths as well. Being able to understand how a flow event may transform in time and space along the channel is of utmost importance for hazard management. While visual observations and simple measuring devices in the past have shown how lahars transform along the flow path, these same features for the most part have not been described using seismological methods. On 18 March 2007 Mt. Ruapehu produced the biggest lahar in New Zealand in over 100 years. At 23:18 UTC the tephra dam holding the Crater Lake water back collapsed causing 1.3 x 10<sup>6</sup> m<sup>3</sup> of water to flow out and rush down the Whangaehu channel. We describe here the seismic signature of a lake-breakout lahar over the course of 85 km along the Whangaehu river system using three 3-component broadband seismometers installed < 10 m from the channel at 7.4, 28, and 83 km from the crater lake source. Examination of 3-componennt seismic amplitudes, peak frequency content, and directionality combined with video imagery and sediment concentration data were used. The seismic data shows the evolution of the lahar as it transformed from a highly turbulent out-burst flood (high peak frequency throughout), to a fully bulked up multi-phase hyperconcentrated flow (varying frequency patterns depending on the lahar phase) to a slurry flow (bedload dominant). Estimated directionality ratios show the elongation of the lahar with distance down channel, where each recording station shows a similar pattern, but for differing lengths of time. Furthermore, using directionality ratios shows extraordinary promise for lahar monitoring and detection systems where streamflow is present in the channel. DOI
73. Jones, TJ; Le Moigne, Y; Russell, JK; Williams-Jones, G; Giordano, D; Dingwell, DB.Inflated pyroclasts in proximal fallout deposits reveal abrupt transitions in eruption behaviour.Nature Communications, 2022, 13: 2832 Inflated pyroclasts in proximal fallout deposits reveal abrupt transitions in eruption behaviour.
volcano, explosive, eruption, pyroclast, Tseax
During explosive eruption of low viscosity magmas, pyroclasts are cooled predominantly by 1 forced convection. Depending on the cooling efficiency relative to other timescales, a spectrum of 2 deposits can be formed. Deposition of hot clasts, above their glass transition temperature, can form 3 spatter mounds, ramparts and clastogenic lava flows. Clasts may also be deposited cold, producing 4 tephra cones and blankets. Thus, the deposit and pyroclast type can provide information about 5 eruption dynamics and magma properties. Here we examine pyroclasts from Tseax volcano, 6 British Columbia, Canada. These newly identified inflated pyroclasts, are fluidal in form, have 7 undergone post-depositional expansion, and are found juxtaposed with scoria. Detailed field, 8 chemical and textural observations, coupled with high temperature rheometry and thermal 9 modelling, reveal that abrupt transitions in eruptive behaviour – from lava fountaining to low-10 energy bubble bursts – created these pyroclastic deposits. These findings should help identify 11 transitions in eruptive behaviour at other mafic volcanoes worldwide. Website DOI
71. Le Moigne, Y; Vigouroux, N; Russell, JK; Williams-Jones, G.Magmatic origin and storage conditions for the eruption of Tseax volcano, Northern Cordillera Volcanic Province, Canada.Chemical Geology, 2022, 588: 120648 Magmatic origin and storage conditions for the eruption of Tseax volcano, Northern Cordillera Volcanic Province, Canada.
Monogenetic volcano, Tseax volcano, Northern Cordilleran Volcanic Province, Basanite, Plumbing system
The Northern Cordilleran Volcanic Province (NCVP) is the most active volcanic belt in Canada, yet there are few detailed petrologic studies of the individual volcanoes. Tseax volcano is the southernmost volcanic centre of the NCVP, the second youngest (~ 1700 CE) eruption in Canada, and is one of Canada’s worst natural disasters killing up to ~ 2,000 Nisga’a First Nation people. We present a conceptual model for the origins, evolution and pre-eruptive storage of the Tseax magma which erupted ~ 0.5 km3 of volcanic material, mainly in the form of valley-filling lava flows. All Tseax products are alkali Fe- Ti- rich basanite-to-tephrite having trace element distributions similar to the other mafic NCVP lavas. Phenocrysts consist of plagioclase, olivine and titanomagnetite, often forming glomerocrysts suggesting co-crystallisation of these 3 mineral phases. Clinopyroxene is never observed as a phenocryst phase. The lavas have low Mg#’s implying they are fractionated relative to a mantle-derived ‘parent’ magma. Trace elements indicate the magma derives from melting of a fertile mantle source (i.e., (Nb/K)n ~1), most likely the upper asthenosphere. There is no evidence in the Tseax volcanic rocks for magma mixing or lithospheric contamination during ascent. The phenocryst assemblage suggests rapid ascent of a low viscosity magma to < 5.5 km where titanomagnetite becomes the first phase on the liquidus (~ 1133 °C). There the magma stalled for a very short period of time under P-T conditions where clinopyroxene did not reach saturation. Based on the size of the plagioclase phenocrysts, the magma stalled for less than a year and cooled down to 1094 - 1087 °C prior to eruption.Website DOI
70. Le Moigne, Y; Williams-Jones, G; Vigouroux, N; Russell, JK.Chronology and eruption dynamics of the historic ~ 1700 CE eruption of Tseax Volcano, British Columbia, Canada.Frontiers in Earth Science, 2022, 10: 910451 Chronology and eruption dynamics of the historic ~ 1700 CE eruption of Tseax Volcano, British Columbia, Canada.
Tseax volcano; Monogenetic volcanism; Lava flow; Eruption dynamics; Indigenous knowledge
The eruption of Tseax volcano in ~1700 CE, in north-western British Columbia, is the second youngest volcanic event in Canada. It is also one of Canada’s worst natural disasters as it killed up to 2,000 people of the Nisga’a First Nation living there at the time. The eruption also significantly impacted the local environment by diverting the Nass River (the 3rd largest river in British Columbia). Within the Nisga’a culture, Adaawak stories preserve an observational account of the Tseax eruption. In this study, we establish the chronology of the eruption by integrating field observations, petrophysical data and Nisga’a oral and written histories. The Nisga’a stories corroborate the short duration and exceptional intensity of the eruption as recorded in the volcanic products. The eruption was divided in two main periods: (1) Period A and (2) Period B. (1) The eruption started in a typical Hawaiian style with low levels of lava fountaining that built up a spatter rampart. This pyroclastic edifice was breached by voluminous pāhoehoe lava flows erupted at high discharge rates. We estimate that almost half of the erupted flow volume (0.20 km3) erupted in Period A was emplaced at 800-1000 m3/s. The lava reached the Nass Valley, 20 km downstream of the volcano, in “swift currents”, diverted the Nass River and engulfed the former Nisga’a villages in only 1 to 3 days, thus likely being responsible for the reported fatalities. The discharge rates progressively diminished to 10-200 m3/s until the end of this first eruptive period, which lasted a few weeks to a few hundred days. (2) During Period B, two ‘a‘ā flows were erupted with discharge rates < 50 m3/s. This period was also characterised by a more explosive eruption style that built a 70 m high tephra cone overlapping with spatter rampart. In total, Period B lasted approximately 20 days. In total, the eruption produced 0.5 km3 of volcanic materials (mostly in the form of lava flows) on the order of weeks to a few months. The short duration of the eruption was probably inherent to the limited amount of melt produced in the mantle. However, the eruption of Tseax was similar in magnitude to the flank eruption on larger shield volcanoes such as Kīlauea’s Fissure 8 in 2018 or Mauna Loa in 1984.PDF DOI
69. Muhammad, M, Williams-Jones, G, Stead, D, Tortini, R, Falorni, G, Donati, D.Applications of image-based computer vision for remote surveillance of slope instability.Frontiers in Earth Science, 2022, 10: 909078 Applications of image-based computer vision for remote surveillance of slope instability
InSAR, landslide, rockfall, computer vision, slope stability monitoring
Landslides and slope failures represent critical hazards for both the safety of local communities and the potential damage to economically relevant infrastructure such as roads, hydroelectric plants, pipelines, etc. Numerous surveillance methods, including ground-based radar, InSAR, Lidar, seismometers, and more recently computer vision, are available to monitor landslides and slope instability. However, the high cost, complexity, and intrinsic technical limitations of these methods frequently require the design of alternative and complementary techniques. Here, we provide an improved methodology for the application of computer vision in landslide and rockfall monitoring. The newly developed open access Python-based software, Akh-Defo, uses optical flow velocity, image differencing and similarity index map techniques to calculate land deformation including landslides and rockfall. Akh-Defo is applied to two different datasets, notably ground-based optical imagery for the Plinth Peak slope in British Columbia, Canada, and satellite optical imagery for Mud Creek landslide in California, USA. Ground-based optical images were processed to evaluate the capability of Akh-Defo to identify rockfalls and measure land displacement in steep-slope terrains to complement LOS limitations of radar satellite images. Similarly, satellite optical images were processed to evaluate the capability of Akh-Defo to identify ground displacement in active landslide regions a few weeks to months prior to initiation of landslides. The Akh-Defo results were validated from two independent datasets including radar-imagery, processed using state of the art SqueeSAR algorithm for the Plinth Peak case study and very high-resolution temporal Lidar and photogrammetry digital surface elevation datasets for Mud Creek case study. Our study shows that Akh-Defo software complements InSAR by mitigating LOS limitations via processing ground-based optical imagery. Additionally, if applied to satellite optical imagery, it can be used as a first stage preliminary warning system (particularly when run on the cloud allowing near real-time processing) prior to processing more expensive but more accurate InSAR products such as SqueeSAR.Website DOI
68. Sobolewski, L; Stenner, C; Williams-Jones. G; Anitori, R; Davis, RE; Pflitsh, A.Implications of the study of subglacial volcanism and glaciovolcanic cave systems.Bulletin of Volcanology,, 2022, 84 Implications of the study of subglacial volcanism and glaciovolcanic cave systems
Volcano-ice interactions, Cascade Volcanic Arc, Volcanoes
Glacial environments can have significant impacts on the surrounding landscape and nearby populations when affected by volcanic activity. As such, glaciovolcanic interactions and related hazards have received substantial attention during the last few decades. In contrast, the study of void spaces created by these interactions-glaciovolcanic cave systems-remains underrepresented. This review outlines the global distribution of glaciovolcanic caves and describes examples of both historical and ongoing research advances, most of which are limited to volcanoes of the Cascade Volcanic Arc and Antarctica. Examples range from a largely static fumarolic ice cave system in the crater of Mount Rainier to glaciovolcanic cave genesis and evolution in the crater of Mount St. Helens, where the advancing glacier ice is interacting with ongoing fumarolic activity and generating new cave systems. This review includes various volcanic subfields and also brings together additional disciplines including speleology, microbiology, and astrobiology. Due to the importance of glaciovolcanic caves in the hydrothermal cycle of volcanic systems, the global fight against antibiotic resistance, and their implications for understanding volcano-ice interactions beyond Earth, research on these systems is expanding. Kamchatka, Alaska, and Iceland have notable potential for further studies, while known research sites still hold open questions, including better understanding of the environmental parameters affecting cave genesis and persistence, the effect of glaciovolcanic cave development on underlying hydrothermal systems, and cataloging the biodiversity of glaciovolcanic cave environments.Website DOI
67. Warwick, R; Williams-Jones, G; Kelman, M; Witter, JB.A scenario-based volcanic hazard assessment for the Mount Meager Volcanic Complex, British Columbia.Journal of Applied Volcanology, 2022, 11:1-22 A scenario-based volcanic hazard assessment for the Mount Meager Volcanic Complex, British Columbia.
Mount Meager; Hazard scenarios; Pyroclastic density currents; Lahars; Tephra fall
The Mount Meager Volcanic Complex (Mount Meager) is a glacier-clad stratovolcanic system in southwestern British Columbia which last erupted over 2400 years ago (VEI 4). While this is Canada’s most recent major explosive eruption, most past research on Mount Meager has focused on its numerous and large volume landslides and thus the volcanic hazard characteristics remain understudied. Here we present a suite of scenario-based hazard maps and an assessment addressing a range of potential future explosive eruptions and associated hazards. In order to overcome limited knowledge of the eruptive history, numerical models have been used to simulate the primary syneruptive hazards of concern (dome-collapse pyroclastic density currents, lahars and tephra fallout) largely utilizing eruption parameters from analogous volcanoes, i.e., glacier-clad stratovolcanoes in a subduction zone setting. This study provides a framework for similar volcanic hazard studies where geologic data is limited, funds are minimal, and access is difficult. Furthermore, this sets the stage for recognizing volcanic hazards in the Canadian landscape, providing a resource to prepare for and mitigate potential impacts well in advance of a crisis situation. Website DOI
66. Anzieta, J; Williams-Jones, G; Bernard, B; Ortiz, H; Vallejo, S; Ruiz, M.Reviewing volcano hazard and risk communications in Ecuador: Experiences from a fast-format workshop.Volcanica, 2021, 4: 309–324 Reviewing volcano hazard and risk communications in Ecuador: Experiences from a fast-format workshop.
volcano, hazard communication, Ecuador
Hazard and risk communication requires the design and dissemination of clear messages that enhance people's actions before, during and after volcanic crises. To create effective messages, the communication components such as message format and content, must be considered. Technology is changing the way people communicate at an ever-increasing pace; thus, we propose revising the basic components of the communication process to improve the dialogue between scientists and the public. We describe communication issues during and outside the volcanic crises in Ecuador and assess possible causes and consequences. These ideas were discussed during the short-duration 2019 Volcano Geophysical Principles and Hazards Communications Workshop in Baños, Ecuador. We review and propose communication strategies for volcanic hazards and risks that resulted from the workshop discussions and experiences of experts from the Instituto Geofísico (IG-EPN), local and international professors involved in volcano research and communication, and students from universities across Ecuador.PDF DOI
65. Muhammad, M; Barendregt, RW; Williams-Jones, G.Structural geology constraints and its influence on geothermal systems, Mt. Meager, BC.Proceedings of the Canadian Geothermal Students' Day, Geothermal Canada, 2021, P2111: 1-15 Structural geology constraints and its influence on geothermal systems, Mt. Meager, BC.
volcano, geothermal, Mt. Meager
The Garibaldi Volcanic Belt (GVB), and particularly the Mount Meager Volcanic Complex (MMVC), has been identified as a region with significant geothermal potential (e.g., Ghomshei et al., 2004, 2005; Arianpoo, 2009). Although geothermal exploration at Mount Meager was carried out intermittently from the early 1970s through to 2009, the previous studies did not constrain the influence of major structural and tectonic features on the geothermal fluid pathways. In this study, we used classic structural field geology mapping of structures such as faults, folds, and other fractures along with paleomagnetic inclination of young volcanic units to constrain the neotectonic activity of structures at Mount Meager; the goal was to help define the current structural geology elements controlling geothermal pathways in the region. Our preliminary study indicates significant tilting and minor rotation of both older basement rocks and younger volcanic rocks as young as 300-700 ka or between
2-1.2 Ma. The tilting and rotation of basement and young volcanic rocks was most likely controlled by a newer fault strand of the Owl Creek fault and movement on the left lateral strike slip fault
between the east and west ridges of North Lillooet Ridge. Hence, potential geothermal fluid pathways, at least north of the Mount Meager complex, are controlled largely by kinematics of the Owl Creek fault and the mapped left-lateral strike slip fault between the east and west ridges of North Lillooet Ridge, north of the
Mount Meager massif. The current findings will significantly enhance our understanding of the geothermal reservoir at MMVC and can be used as essential input data for 3D reservoir modelling.PDF
64. Russell, JK; Stewart, M; Wilson, A; Williams-Jones, G.Eruption of Mount Meager, British Columbia during the early Fraser glaciation.Canadian Journal of Earth Science, 2021, 58: 1146-1154 Eruption of Mount Meager, British Columbia during the early Fraser glaciation
explosive volcanism, geochronometry, pyroclastic density current, glaciovolcanism
A new 40Ar/39Ar date from a pyroclastic density current deposit preserved on the northern slopes of the Lillooet River valley, British Columbia, indicates an explosive volcanic eruption of the Mount Meager Volcanic Complex (MMVC) at 24.3 +/- 2.3 ka. The age of this pyroclastic deposit is a record of the second youngest explosive volcanic event for the MMVC and indicates that Mount Meager has erupted, explosively, at least twice in the past ~25 000 years. The age of the volcanic eruption coincides with the early phase of growth of the late Wisconsin (Fraser) Cordilleran ice sheet. The deposit constrains the distribution and timing of glacier build-up in southwestern British Columbia over the last glacial cycle and suggests that the ice sheet was absent or thin in the upper Lillooet River valley at this time. Field evidence suggests the pyroclastic density current was sourced at high elevation near present-day Plinth Peak and was deposited and preserved on the adjoining Lillooet River valley wall. Coeval, proximal valley-filling glacial ice was up to ~120 m thick.PDF DOI
63. Le Moigne, Y, Zurek, JM, Williams-Jones, G, Lev, E; Calahorrano-Di Patre, A; Anzieta, JC.Standing waves in high speed lava channels: A tool for constraining lava flow dynamics and eruptive parameters.Journal of Volcanology and Geothermal Research, 2020, 401, 106944 Standing waves in high speed lava channels: A tool for constraining lava flow dynamics and eruptive parameters
Standing waves; Hydraulic jumps; Supercritical flow; Lava viscosity; Lava flow; Basalt; Real time monitoring
Estimates of the rheological properties of lava flows are essential for understanding their emplacement and for hazard assessment. Despite being a well-known phenomenon in water hydraulics, the formation and presence of standing waves in lava channels is poorly understood. Standing waves, generally located near the vent area, have been frequently described at high speed channelized lava flows. They are interpreted as hydraulic jumps indicating a flow under supercritical conditions. Identifying standing waves therefore offers an opportunity to apply open channel hydraulic theory for supercritical flows in order to determine important eruption parameters such as discharge rate and apparent viscosity. We use the length and amplitude of standing waves to reconstruct flow dynamics from both observational data and video analysis. The geometry of these standing waves allows us to extract the physical properties of the channelized lava (velocity, discharge rate, apparent viscosity), to estimate the channel depth and constrain the flow regime. With the rapid advances in technology, scientists can deploy equipment to enable low-cost real time monitoring of these phenomena and constrain eruption discharge rate and apparent viscosity, key parameters for volcanic hazard assessment and mitigation.PDF DOI
62. Le Moigne, Y; Williams-Jones, G; Russell, JK; Quane, S.Physical volcanology of Tseax volcano, British Columbia, Canada.Journal of Maps, 2020, 16(2), 363-375 Physical volcanology of Tseax volcano, British Columbia, Canada
Tseax volcano; lava flow; mapping; DEM; bathymetry
Tseax volcano erupted ∼ 250 years ago in NW British Columbia, Canada producing tephra deposits and lava flows. Field mapping has defined the stratigraphy of Tseax and the lava flow morphologies. Aerial photogrammetry and bathymetry surveys were used to create a high resolution digital elevation model of the volcano to facilitate mapping and estimates of erupted material volumes. Tseax volcano (∼ 10.4 ± 0.7 × 106 m3) comprises an outer
breached spatter rampart and an inner conical tephra cone. Tseax is associated with a 32 km long and 0.49 ± 0.08 km3 basanite-to-tephrite lava flow field covering ∼ 36 km2 and divided into 4 distinct lava flows with heterogeneous surface morphologies. We present a volcanological map of Tseax volcano at a scale of 1:22,500. This will serve as supporting information for further research on the eruptive history of Tseax volcano and the lava flow field emplacement.PDF DOI
61. Roberti, G; Ward, B; van Wyk de Vries, B; Le Corvec, N; Venugopal, S; Williams-Jones, G; Clague, JJ; Friele, P; Falorni, G; Baldeon, G; Perotti, L; Giardino, M; Menounos, B.Could glacial retreat-related landslides trigger volcanic eruptions? Insights from Mount Meager, British Columbia.In: Vilímek V., Wang F., Strom A., Sassa K., Bobrowsky P.T., Takara K. (eds) Understanding and Reducing Landslide Disaster Risk. WLF 2020. ICL Contribution to Landslide Disaster Risk Reduction. Springer, 2020, Could glacial retreat-related landslides trigger volcanic eruptions? Insights from Mount Meager, British Columbia
Mt Meager, glacier, volcano, landslides
Mount Meager, a glacier-clad volcanic complex in British Columbia, Canada, is known for its large landslides, as well as a major eruption about 2360 years ago. In 2010, after decades of glacier retreat, the south flank of Mount Meager collapsed, generating a huge (53 Mm3) landslide. In 2016, fumaroles formed ice caves in one of the glaciers on the complex. This glacier is bordered by a large unstable slope presently moving about 3.5 cm per month. If this slope were to fail, a long-runout debris avalanche would reach the floor of the Lillooet River valley, with possible destructive effects on downstream infrastructure. The unloading of the volcanic edifice from an abrupt failure would also have unknown effects on the magmatic plumbing system. From geochemical, geophysical, and petrological data, we infer the presence of a magmatic chamber at 3–16 km depth. Based on numerical model simulations carried out to constrain the stress change, the failure would affect the stress field to depths of up to ~6 km, with changes in effective stress of up to ~4 MPa. The change in effective stress following such a landslide might destabilize the magmatic chamber and trigger an eruption. This result also suggests that a previously documented major flank collapse may have had a role in the 2360 cal yr BP eruption.PDF DOI
60. Venugopal, S; Schiavi, F; Moune, S; Bolfan-Casanova, N; Druitt, T; Williams-Jones, G.Melt inclusion vapour bubbles: the hidden reservoir for major, trace and volatile elements.Nature Scientific Reports, 2020, 10, 9034 Melt inclusion vapour bubbles: the hidden reservoir for major, trace and volatile elements.
Olivine-hosted melt inclusions (MIs) provide samples of magmatic liquids and their dissolved volatiles from deep within the plumbing system. Inevitable post-entrapment modifcations can lead to signifcant compositional changes in the glass and/or any contained bubbles. Re-heating is a common technique to reverse MI crystallisation; however, its efect on volatile contents has been assumed to be minor. We test this assumption using crystallised and glassy basaltic MIs, combined with Raman spectroscopy and 3D imaging, to investigate the changes in fuid and solid phases in the bubbles before and after re-heating. Before re-heating, the bubble contains CO2 gas and anhydrite (CaSO4) crystallites. The rapid difusion of major and volatile elements from the melt during re-heating creates new phases within the bubble: SO2, gypsum, Fe-sulphides. Vapour bubbles hosted in naturally glassy MIs similarly contain a plethora of solid phases (carbonates, sulphates, and sulphides) that account for up to 84% of the total MI sulphur, 80% of CO2, and 14% of FeO. In both re-heated and naturally glassy MIs, bubbles sequester major and volatile elements that are components of the total magmatic budget and represent a “loss” from the glass. Analyses of the glass alone signifcantly underestimates the original magma composition and storage parameters.PDF DOI
58.Williams-Jones, G; Barendregt, RW; Russell, JK; Le Moigne, Y; Enkin, RJ; Gallo R.The age of the Tseax volcanic eruption, British Columbia, Canada.Canadian Journal of Earth Sciences, 2020, The age of the Tseax volcanic eruption, British Columbia, Canada
Tseax volcano; lava flow; tephra cone; paleomagnetism; radiocarbon dating; geochemistry
A recent volcanic eruption occurred at Tseax volcano that formed a series of tephra cones in northwestern British Columbia, Canada. The explosive to effusive eruption also formed a 32 km sequence of Fe-rich Mg-poor basanite–trachybasalt lavas covering 40 km2. Oral stories of the Nisg_a’a Nation report that the eruption may have caused as many as 2000 fatalities. The actual eruption date and question of whether there was one or multiple eruptive episodes in the 14th and 18th centuries are, as of yet, unresolved. New radiocarbon dating of wood charcoal from immediately beneath vent-proximal tephra deposits and complementary age information suggest an eruption in 1675–1778 CE (95.4% probability) was responsible for the formation of the tephra cone. New paleomagnetic and geochemical data from the tephra cone and lava flows suggest there is, in fact, no statistically significant difference in time between the explosive and effusive deposits and that they formed during a single eruptive episode.PDF DOI
57. Calahorrano-Di Patre, A; Williams-Jones, G; Battaglia, M; Mothes, P; Gaunt, E; Zurek, J; Ruiz, M; Witter, J.Hydrothermal fluid migration due to interaction with shallow magma: Insights from gravity changes before and after the 2015 eruption of Cotopaxi volcano, Ecuador.Journal of Volcanology and Geothermal Research, 2019, 387 Hydrothermal fluid migration due to interaction with shallow magma: Insights from gravity changes before and after the 2015 eruption of Cotopaxi volcano, Ecuador
Cotopaxi Volcano; Time-lapse gravity; Hydrothermal fluid migration; Volcanic unrest
On August 14, 2015 Cotopaxi Volcano (Ecuador) erupted with several phreatomagmatic explosions after nearly 135 years of quiescence. Unrest began in April 2015 with an increase in the number of daily seismic events and inflation of the flanks of the volcano. Time-lapse gravity measurements started at Cotopaxi volcano in June 2015. Although minor gravity changes were detected prior to eruptive activity, the largest gravity variations at Cotopaxi were measured between October 2015 and March 2016, when other geophysical parameters had reached background levels. Inverse modelling of GPS data suggests a deep intrusion prior to the eruptive activity, while inverse modelling of post-eruptive gravity changes suggests variations in the volcano hydrothermal system. Deformation, seismicity, and gravity changes are consistent with the intrusion of a deep magmatic source between April and August 2015. Part of the magma rose from depth and interacted with the hydrothermal system, causing the phreatomagmatic activity and pushing hydrothermal fluids from a deep aquifer into a shallow perched aquifer. (C) 2019 Elsevier B.V. All rights reserved.PDF DOI
56. Caravantes, G., Rymer, H., Zurek, J., Ebmeier, S., Blake, S. & Williams-Jones, G.Structures controlling volcanic activity within Masaya caldera, Nicaragua.Volcanica, 2019, Structures controlling volcanic activity within Masaya caldera, Nicaragua.
Masaya volcano; Structure; Ring fracture; Caldera; InSAR; VLF; Magnetics
Geophysical and geological observations collected in 2007-2012 shed light on the mechanisms controlling the style and location of eruptions within the Las Sierras-Masaya Caldera complex, Nicaragua. These results confirm a hypothesised ∼3.5 km diameter structure with features compatible with the presence of a ring fracture (50–65°, with inward-dipping bounding walls). A central block is bound by this fracture and defines an incipient nested caldera related to the emptying of the magma chamber following the last Plinian eruption (1.8 ka). The prolongation of the Cofradías fault from the Managua graben represents the most significant structure on the floor of Masaya caldera. Current activity, including a convecting lava lake, largely depends on the interplay between the extensional stress regime associated with the Managua graben and deformation along the inner caldera bounding fault. This high spatial resolution survey uses a novel combination of geophysical methodologies to identify previously overlooked foci for future volcanic activity at Masaya.PDF DOI
55. Rymer, H; Martinez, M; Brenes, J; Williams-Jones, G; Borgia, A.Geophysical and geochemical precursors to changes in activity at Poás volcano.In Tassi, F., Vaselli, O. & Mora-Amador, R. (Eds.) Poás volcano (Costa Rica): The pulsing heart of Central America Volcanic Zone, 2019, 203-211 Geophysical and geochemical precursors to changes in activity at Poás volcano
geophysics, geochemistry, volcano, precursory signals, Poas
Acidic crater lakes at persistently active volcanoes act as both a moderator and an index of volcanic processes. Poás exhibits cyclic behavior characterized by calm periods alternating with periods of phreatic eruptions that last 2–10 years, which roughly correspond to liquid or vapor dominance. However, what causes the system to move on from one phase to the other remains unclear. By integrating the insights gained from different methods of monitoring, a view of the physical and chemical changes occurring before, during and after alterations in activity can be gleaned.PDF DOI
54. Venugopal, S; Moune, S; Williams-Jones, G; Druitt, T; Vigouroux, N; Wilson, A; Russell, JK.Two distinct mantle sources beneath the Garibaldi Volcanic Belt: Insight from olivine-hosted melt inclusions.Chem. Geol., 2019, 532, 119346 Two distinct mantle sources beneath the Garibaldi Volcanic Belt: Insight from olivine-hosted melt inclusions
Melt inclusions; Garibaldi Volcanic Belt; Cascades; Trace elements; Two mantle sources
The nature of the magmatic source beneath the Garibaldi Volcanic Belt (GVB) in NW Washington (USA) and SW British Columbia (Canada) has been debated both due to its classification as the northern equivalent of the High Cascades and the alkaline nature of northern basalts. Whole rock studies have shown that the GVB does not share the same magmatic source as the High Cascades (Mullen and Weis, 2013, 2015). Nonetheless, the presence of alkaline basalts in this arc raises questions about the exact source of mantle enrichment and whether it is related to the young age of the downgoing Juan de Fuca Plate ( < 10 Ma) or the presence of a slab tear at the northern end of the arc. To gain insight into the source that underlies the GVB, we sampled olivine-hosted melt inclusions from each volcanic centre along the arc. Major, volatile and trace element data reveal a northward compositional trend from arc-typical calc-alkaline magma in the south to OIB-like melts in the north near the slab tear. Furthermore, contributions from the subducting slab are relatively high beneath the southern end of the arc (Cl/Nb > 80) but rapidly decreases to the north (Cl/Nb < 50). Finally, the significant differences in Zr/Nb from south to north (80 and 9, respectively) suggest two distinct mantle sources since one source cannot produce melts with such different ratios. As such, we propose the GVB should be segmented into the Northern and Southern groups, each having its own mantle source. Based on the geographic proximity, the enriched nature of the Northern group melt inclusions is likely controlled by the slab tear at the northern termination of the subducting Juan de Fuca Plate. Melt modelling results show that 3-7 % partial melting of the primitive mantle with a garnet lherzolite residue can reproduce the composition of the Northern group. Melt inclusions from the Southern group, on the other hand, imply a depleted MORB mantle that has been modified by fluids derived from the downgoing slab. Variability within the Southern group itself reflects the amount of hydrous fluids supplied beneath each centre and is correlated with slab age and subsequent degree of dehydration. This study addresses the compositional diversity along the arc and provides evidence that the age of the downgoing plate and the presence of a slab tear exert a strong compositional control over eruptive products within one arc.PDF DOI
53. Wespestad, CE; Thurber, CH; Andersen, NL; Singer, BS; Cardona, C; Zeng, XF; Bennington, NL; Keranen, K; Peterson, DE; Cordell, D; Unsworth, M; Miller, C; Williams-Jones, G.Magma Reservoir Below Laguna del Maule Volcanic Field, Chile, Imaged With Surface-Wave Tomography.Journal of Geophysical Research-Solid Earth, 2019, 124: 2858-2872 Magma Reservoir Below Laguna del Maule Volcanic Field, Chile, Imaged With Surface-Wave Tomography
Laguna del Maule; surface-wave tomography; magma reservoir; ambient noise
The Laguna del Maule (LdM) volcanic field comprises the greatest concentration of postglacial rhyolite in the Andes and includes the products of 40km(3) of explosive and effusive eruptions. Recent observations at LdM by interferometric synthetic aperture radar and global navigation satellite system geodesy have revealed inflation at rates exceeding 20cm/year since 2007, capturing an ongoing period of growth of a potentially large upper crustal magma reservoir. Moreover, magnetotelluric and gravity studies indicate the presence of fluids and/or partial melt in the upper crust near the center of inflation. Petrologic observations imply repeated, rapid extraction of rhyolitic melt from crystal mush stored at depths of 4-6km during at least the past 26ka. We utilize multiple types of surface-wave observations to constrain the location and geometry of low-velocity domains beneath LdM. We present a three-dimensional shear-wave velocity model that delineates a 450-km(3) shallow magma reservoir 2 to 8km below surface with an average melt fraction of 5%. Interpretation of the seismic tomography in light of existing gravity, magnetotelluric, and geodetic observations supports this model and reveals variations in melt content and a deeper magma system feeding the shallow reservoir in greater detail than any of the geophysical methods alone. Geophysical imaging of the LdM magma system today is consistent with the petrologic inferences of the reservoir structure and growth during the past 20-60kyr. Taken together with the ongoing unrest, a future rhyolite eruption of at least the scale of those common during the Holocene is a reasonable possibility.PDF DOI
52. Zurek, J; Moune, S; Williams-Jones, G; Vigouroux, N; Gauthier, PJ.Melt inclusion evidence for long term steady-state volcanism at Las Sierras-Masaya volcano, Nicaragua.Journal of Volcanology and Geothermal Research, 2019, 378: 16-28 Melt inclusion evidence for long term steady-state volcanism at Las Sierras-Masaya volcano, Nicaragua
Masaya volcano; Persistent degassing; Melt inclusion geochemistry; Volatile budgets; Magmatism and extensional tectonics
Las Sierras-Masaya volcanic system is a persistently active basaltic caldera complex in Nicaragua. While there has been almost no juvenile material erupted since 1772, Masaya volcano has been persistently degassing for >150 years. An additional unusual behaviour for the Las Sierras-Masaya volcanic complex is its ability to produce large caldera-forming basaltic Plinian eruptions with the most recent occurring about 1800 years ago. Here we present melt inclusion analyses that provide constraints on the magmatic system over time. Melt inclusions hosted in plagioclase and olivine crystals were analyzed for major, trace and volatile elements (S, Cl, F, H2O). The data supports a consistent parental magmatic source with restricted compositional variability explained by simple fractional crystallization of plagioclase, olivine, clinopyroxene and magnetite at a nearly constant temperature. This broadly agrees with previous whole rock geochemical studies showing that the overall chemical signature of volcanic products at Masaya has remained largely unchanged for similar to 60,000 years and that both shallow fractionation and degassing processes dominate the whole evolution of the magmatic series. Based on volatile element in melt inclusions and gas composition and flux measurements, we determine the magmatic flux to be similar to 0.19 km(3) yr(-1) implying that up to 47 km(3) of magma may have degassed since the last effusive eruption. As at other persistently active basaltic volcanoes (e.g., Mt. Etna, Italy; Kilauea, Hawaii, USA), this magmatic flux must involve significant endogenous storage which is likely accommodated by extensional tectonics. However, Masaya volcano differs in its apparent simplicity with respect to its stable chemistry and its fully interconnected magmatic system. (C) 2019 Elsevier B.V. All rights reserved.PDF DOI
51. Mauri, G; Saracco, G; Labazuy, P; Williams-Jones, G.Correlating hydrothermal system dynamics and eruptive activity - A case-study of Piton de la Fournaise volcano, La Reunion.Journal of Volcanology and Geothermal Research, 2018, 363: 23-39 Correlating hydrothermal system dynamics and eruptive activity - A case-study of Piton de la Fournaise volcano, La Reunion
Hydrothermal system; Volcanic activity; Wavelet analyzes; Volcano monitoring; Depth evolution of hydrothermal fluids
Piton de la Fournaise volcano, La Reunion Island, is a basaltic shield volcano, which underwent an intense cycle of eruptive activity between 1998 and 2008. Self-potential and other geophysical investigations of the volcano have shown the existence of a well-established hydrothermal system within the summit cone. The present study investigates the relationship between changes in the hydrothermal system and eruptive activity at the summit cone of Piton de la Fournaise. Here, we consider the depth of the hydrothermal activity section to be the area where the hydrothermal flow is the most intense along its path. Ten complete-loop self-potential surveys have been analyzed through multi-scale wavelet tomography (MWT) to characterize depth variations of the hydro thermal system between 1993 and 2008. Our MWT models strongly support the existence of six main hydrothermal flow pathways associated with the main edifice structure. Each of these pathways is part of the main hydrothermal system and is connected to the main hydrothermal reservoir at depth. In both 2006 and 2008, around Dolomieu crater, based on our results, the hydrothermal activity sections are located between 2300 and 2500 m a.s.l., which correlate well with the elevation of the observed fumarole belt within the post-2007-collapse crater wall. Our results show that the depths of the local hydrothermal activity sections change substantially over the investigated period. Vertical displacement of the main potential generation area, associated with these hydrothermal activity sections, is observed on the order of several hundred meters at the transition between the period of quiescence (1993-1997) and the resumption of eruptive activity in 1998 and 2007, respectively. From 1999 to March 2008, the hydrothermal system was consistently located at relatively shallow depths. By quantitatively determining the vertical displacement of hydrothermal fluids over 16 years, we identify a significant link between hydrothermal system and magmatic activity. Hydrothermal system depth below the surface is an indicator of the activity level (pressurization/depressurization of the volcano) within the shallow magmatic systems. Thus, when used in conjunction with long term volcano monitoring, this approach can contribute substantially to detection of the precursory signals of changes in volcanic activity. (C) 2018 Elsevier B.V. All rights reserved.PDF DOI
50. Miller, CA; Currenti, G; Hamling, I; Williams-Jones, G.Mass transfer processes in a post eruption hydrothermal system: Parameterisation of microgravity changes at Te Maari craters, New Zealand.Journal of Volcanology and Geothermal Research, 2018, 357: 39-55 Mass transfer processes in a post eruption hydrothermal system: Parameterisation of microgravity changes at Te Maari craters, New Zealand
Deformation; Hydrothermal system; Joint inversion; Microgravity; Phreatic eruptions; Volcano monitoring
Fluid transfer and ground deformation at hydrothermal systems occur both as a precursor to, or as a result of, an eruption. Typically studies focus on pre-eruption changes to understand the likelihood of unrest leading to eruption; however, monitoring post-eruption changes is important for tracking the return of the system towards background activity. Here we describe processes occurring in a hydrothermal system following the 2012 eruption of Upper Te Maari crater on Mt Tongariro, New Zealand, from observations of microgravity change and deformation. Our aim is to assess the post-eruption recovery of the system, to provide a baseline for long-term monitoring. Residual microgravity anomalies of up to 92 +/- 11 mu Gal per year are accompanied by up to 0.037 +/- 0.01 m subsidence. We model microgravity changes using analytic solutions to determine the most likely geometry and source location. A multiobjective inversion tests whether the gravity change models are consistent with the observed deformation. We conclude that the source of subsidence is separate from the location of mass addition. From this unusual combination of observations, we develop a conceptual model of fluid transfer within a condensate layer, occurring in response to eruption-driven pressure changes. We find that depressurisation drives the evacuation of pore fluid, either exiting the system completely as vapour through newly created vents and fumaroles, or migrating to shallower levels where it accumulates in empty pore space, resulting in positive gravity changes. Evacuated pores then collapse, causing subsidence. In addition we find that significant mass addition occurs from influx of meteoric fluids through the fractured hydrothermal seal. Long-term combined microgravity and deformation monitoring will allow us to track the resealing and re-pressurisation of the hydrothermal system and assess what hazard it presents to thousands of hikers who annually traverse the volcano, within 2 km of the eruption site. (C) 2018 Elsevier B.V. All rights reserved,PDF DOI
49. Roberti, G.; Ward, B.; van Wyk de Vries, B.; Falorni, G.; Menounos, B.; Friele, P.; Williams-Jones, G.; Clague, J.J.; Perotti, G.; Giardino, M.; Baldeon, G.;Freschi, S.Landslides and glacier retreat at Mt. Meager volcano: Hazard and risk challenges.Proceedings of the 7th Canadian Geohazards Conference: Engineering Resiliency in a Changing Climate., 2018, Landslides and glacier retreat at Mt. Meager volcano: Hazard and risk challenges.
Mt. Meager is a glacier-clad volcanic complex in southwest British Columbia. In the summer of 2010, melting snow and ice caused by warm weather triggered the collapse of 53 Mm3 of rock and debris from Mt. Meager's south flank, generating the largest historic landslide in Canada. In 2016 fumaroles formed ice caves in one of its glaciers, raising concern about the potential for eruptive activity. Following these events, we carried out a geomorphic study of the volcano. Employing satellite-based differencing methods, we measured movements on previously identified unstable
slopes and documented the recent retreat of glaciers on the volcanic complex. It is likely that glaciers will continue to thin
and recede, and that slopes will continue to deform, possibly leading to catastrophic collapses similar to the 2010 event.
Previous work concluded that the level of risk posed by large landslides at Mt. Meager is unacceptable. In spite of this conclusion, little has been done to manage the risk by local or provincial governments over the past decade. With new hydropower infrastructure near the volcano and continued population growth in the Lillooet River valley downstream, it is clear that the landslide risk is increasing.PDF
48. Miller, CA; Le Mevel, H; Currenti, G; Williams-Jones, G; Tikoff, B.Microgravity changes at the Laguna del Maule volcanic field: Magma-induced stress changes facilitate mass addition.Journal of Geophysical Research-Solid Earth, 2017, 122: 3179-3196 Microgravity changes at the Laguna del Maule volcanic field: Magma-induced stress changes facilitate mass addition
Time-dependent, or 4-D, microgravity changes observed at the Laguna del Maule volcanic field, Chile, since 2013, indicate significant (1.5 x 10(11) kg) ongoing mass injection. Mass injection is focused along the Troncoso fault, and subparallel structures beneath the lake at 1.5-2 km depth, and is best modeled by a vertical rectangular prism source. The low-density change (156 to 307 kg/m(3)) and limited depth extent suggest a mechanism of hydrothermal fluid intrusion into existing voids, or voids created by the substantial uplift, rather than deeper-sourced dike intrusion of rhyolite or basalt magma. Although the gravity changes are broadly spatially coincident with ongoing surface deformation, existing models that explain the deformation are deeper sourced and cannot explain the gravity changes. To account for this discrepancy and the correspondence in time of the deformation and gravity changes, we explore a coupled magmatectonic interaction mechanism that allows for shallow mass addition, facilitated by deeper magma injection. Computing the strain, and mean, normal, and Coulomb stress changes on northeast trending faults, caused by the opening of a sill at 5 km depth, shows an increase in strain and mean and normal stresses along these faults, coincident with the areas of mass addition. Seismic swarms in mid-2012 to the west and southwest of the mass intrusion area may be responsible for dynamically increasing permeability on the Troncoso fault, promoting influx of hydrothermal fluids, which in turn causes larger gravity changes in the 2013 to 2014 interval, compared to the subsequent intervals. Plain Language Summary Movement of liquid below the Earth's surface occurs in response to a variety of volcanic or tectonic processes and may result in changes that are measurable on the surface of the Earth. Understanding what causes these changes helps inform on the state of a volcanic system and how close it is to eruption. We present results of measurements showing changes in the Earth's gravity at the Laguna del Maule volcanic field, Chile. These measurements show small increases in gravity around the lake since 2013, coincident to where the ground is being uplifted by deep magma intrusion. Using computer simulations, we find that the location of the gravity changes is at 1.5 to 2km below the Earth's surface and is likely caused by the intrusion of water into an area of rock that is fractured by land movement. Flow of water into this fractured rock is facilitated by pressure exerted by deeper intruding magma, opening up the rock above and allowing water to flow into the space created. Our study provides important constraints on processes that are otherwise undetectable and allow us to better understand the dynamics of an active magma system. DOI
47. Miller, CA; Williams-Jones, G; Fournier, D; Witter, J.3D gravity inversion and thermodynamic modelling reveal properties of shallow silicic magma reservoir beneath Laguna del Maule, Chile.Earth and Planetary Science Letters, 2017, 459: 14-27 3D gravity inversion and thermodynamic modelling reveal properties of shallow silicic magma reservoir beneath Laguna del Maule, Chile
Bouguer gravity; inversion; MELTS; rhyolite; thermodynamics; volatiles
Active, large volume, silicic magma systems are potentially the most hazardous form of volcanism on Earth. Knowledge of the location, size, and physical properties of silicic magma reservoirs, is therefore important for providing context in which to accurately interpret monitoring data and make informed hazard assessments. Accordingly, we present the first geophysical image of the Laguna del Maule volcanic field magmatic system, using a novel 3D inversion of gravity data constrained by thermodynamic modelling. The joint analysis of gravity and thermodynamic data allows for a rich interpretation of the magma system, and highlights the importance of considering the full thermodynamic effects on melt density, when interpreting gravity models of active magmatic systems. We image a 30 km(3), low density, volatile rich magma reservoir, at around 2 km depth, containing at least 85% melt, hosted within a broader 115 km3 body interpreted as wholly or partially crystallised (>70% crystal) cumulate mush. Our model suggests a magmatic system with shallow, crystal poor magma, overlying deeper, crystal rich magma. Even though a large density contrast (-600 kg/m(3)) with the surrounding crust exists, the lithostatic load is 50% greater than the magma buoyancy force, suggesting buoyancy alone is insufficient to trigger an eruption. The reservoir is adjacent to the inferred extension of the Troncoso fault and overlies the location of an intruding sill, driving present day deformation. The reservoir is in close proximity to the 2.0 km(3) Nieblas (rln) eruption at 2-3 ka, which we calculate tapped approximately 7% of the magma reservoir. However, we suggest that the present day magma system is not large enough to have fed all post-glacial eruptions, and that the location, or size of the system may have migrated or varied over time, with each eruption tapping only a small aliquot of the available magma. The presence of a shallow reservoir of volatile rich, near liquidus magma, in close proximity to regional scale faulting, has important implications for volcano monitoring and hazard mitigation. (C) 2016 Elsevier B.V. All rights reserved. DOI
46. Caudron, C.; Mauri, G.; Williams-Jones, G.; Lecocq, T.; Syahbana, D.; De Plaen, R.; Peiffer, L.; Bernard, A.; Saracco, G.New insights into Kawah Ijen hydrothermal system from geophysical data.Special Issue on Volcanic Lakes, Geological Society Special Publication, 2016, 437 New insights into Kawah Ijen hydrothermal system from geophysical data.
The magmatic–hydrothermal system of Kawah Ijen volcano is one of the most exotic on Earth, featuring the largest acidic lake on the planet, a hyper-acidic river and a passively degassing silicic dome. While previous studies have mostly described this unique system from a geochemical perspective, to date there has been no comprehensive geophysical investigation of the system. In our study, we surveyed the lake using a thermocouple, a thermal camera, an echo sounder and CO2 sensors. Furthermore, we gained insights into the hydrogeological structures by combining self-potential surveys with ground and water temperatures. Our results show that the hydrothermal system is self-sealed within the upper edifice and releases pressurized gas only through the active crater. We also show that the extensive hydrological system is formed by not one but three aquifers: a south aquifer that seems to be completely isolated, a west aquifer that sustains the acidic upper springs, and an east aquifer that is the main source of fresh water for the lake. In contrast with previous research, we emphasize the heterogeneity of the acidic lake, illustrated by
intense subaqueous degassing. These findings provide new insights into this unique, hazardous hydrothermal system, which may eventually improve the existing monitoring system. DOI
45. MacQueen, P; Zurek, J; Williams-Jones, G.Connected magma plumbing system between Cerro Negro and El Hoyo Complex, Nicaragua revealed by gravity survey.Journal of Volcanology and Geothermal Research, 2016, 327: 375-384 Connected magma plumbing system between Cerro Negro and El Hoyo Complex, Nicaragua revealed by gravity survey
Gravity; Nicaragua; Cerro Negro; El Hoyo; Structure; Magmatic plumbing
Cerro Negro, near Leon, Nicaragua is a young, relatively small basaltic cinder cone volcano that has been unusually active during its short lifespan. Multiple explosive eruptions have deposited significant amounts of ash on Leon and the surrounding rural communities. While a number of studies investigate the geo-chemistry and stress regime of the volcano, subsurface structures have only been studied by diffuse soil gas surveys. These studies have raised several questions as to the proper classification of Cerro Negro and its relation to neighboring volcanic features. To address these questions, we collected 119 gravity measurements around Cerro Negro volcano in an attempt to delineate deep structures at the volcano. The resulting complete Bouguer anomaly map revealed local positive gravity anomalies (wavelength 0.5 to 2 km, magnitude +4 mGal) and regional positive (10 km wavelength, magnitudes +10 and +8 mGal) and negative (12 and 6 km wavelength, magnitudes 18 and 13 mGal) Bouguer anomalies. Further analysis of these gravity data through inversion has revealed both local and regional density anomalies that we interpret as intrusive complexes at Cerro Negro and in the Nicaraguan Volcanic Arc. The local density anomalies at Cerro Negro have a density of 2700 kg m(-3) (basalt) and are located between -250 and -2000 m above sea level. The distribution of recovered density anomalies suggests that eruptions at Cerro Negro may be tapping an interconnected magma plumbing system beneath El Hoyo, Cerro La Mula, and Cerro Negro, and more than seven other proximal volcanic features, implying that Cerro Negro should be considered the newest cone of a Cerro Negro-El Hoyo volcanic complex. (C) 2016 Elsevier B.V. All rights reserved.PDF DOI
44. Miller, CA; Williams-Jones, G.Internal structure and volcanic hazard potential of Mt Tongariro, New Zealand, from 3D gravity and magnetic models.Journal of Volcanology and Geothermal Research, 2016, 319: 12-28 Internal structure and volcanic hazard potential of Mt Tongariro, New Zealand, from 3D gravity and magnetic models
Gravity; Magnetic; 3D modelling; Volcanic hazard; Hydrothermal system; Volcanic structure
A new 3D geophysical model of the Mt Tongariro Volcanic Massif (TgVM), New Zealand, provides a high resolution view of the volcano's internal structure and hydrothermal system, from which we derive implications for volcanic hazards. Geologically constrained 3D inversions of potential field data provides a greater level of insight into the volcanic structure than is possible from unconstrained models. A complex region of gravity highs and lows (+/- 6 mGal) is set within a broader, similar to 20 mGal gravity low. A magnetic high (1300 nT) is associated with Mt Ngauruhoe, while a substantial, thick, demagnetised area occurs to the north, coincident with a gravity low and interpreted as representing the hydrothermal system. The hydrothermal system is constrained to the west by major faults, interpreted as an impermeable barrier to fluid migration and extends to basement depth. These faults are considered low probability areas for future eruption sites, as there is little to indicate they have acted as magmatic pathways. Where the hydrothermal system coincides with steep topographic slopes, an increased likelihood of landslides is present and the newly delineated hydrothermal system maps the area most likely to have phreatic eruptions. Such eruptions, while small on a global scale, are important hazards at the TgVM as it is a popular hiking area with hundreds of visitors per day in close proximity to eruption sites. The model shows that the volume of volcanic material erupted over the lifespan of the TgVM is five to six times greater than previous estimates, suggesting a higher rate of magma supply, in line with global rates of andesite production. We suggest that our model of physical property distribution can be used to provide constraints for other models of dynamic geophysical processes occurring at the TgVM. (C) 2016 Elsevier B.V. All rights reserved. DOI
43. Venugopal, S.; Moune, S.; Williams-Jones, G.Investigating the subsurface connection beneath Cerro Negro Volcano and the El Hoyo Complex, Nicaragua.Journal of Volcanology and Geothermal Research, 2016, 325 Investigating the subsurface connection beneath Cerro Negro Volcano and the El Hoyo Complex, Nicaragua.
Melt inclusions; Magmatic processes; Plumbing system; Cerro Negro; El Hoyo
Cerro Negro, the youngest volcano along the Central American Volcanic Belt (CAVB), is a polygenetic cinder cone with relatively frequent basaltic eruptions. The neighbouring El Hoyo complex, of which Las Pilas is the dominant edifice, is a much larger and older complex with milder and less frequent eruptions. Previous studies have suggested a deep link beneath these two closely spaced volcanoes (McKnight, 1995; MacQueen, 2013). Melt inclusions were collected from various tephra samples in order to determine whether a connection exists and to delineate the features of this link. Major, volatile, and trace elemental compositions reveal a distinct geochemical continuum with Cerro Negro defining the primitive endmember and El Hoyo representing the evolved endmember. Magmatic conditions at the time of melt inclusion entrapment were estimated with major and volatile contents: 2.4 kbar and 1170 °C for Cerro Negro melts and 1.3 kbar and 1130 °C for El Hoyo melts with an overall oxygen fugacity at the NNO buffer. Trace element contents are distinct and suggest Cerro Negro magmas fractionally crystallise while El Hoyo magmas are a mix between primitive Cerro Negro melts and residual and evolved El Hoyo magma. Modelling of end member compositions with alphaMELTS confirms the unique nature of El Hoyo magmas as resulting from incremental mixing between Cerro Negro and residual evolved magma at 4 km depth. Combining all available literature data, this study presents a model of the interconnected subsurface plumbing system. This model considers the modern day analogue of the Lemptégy cinder cones in Massif Central, France and incorporates structurally controlled dykes. The main implications of this study are the classification of Cerro Negro as the newest conduit within the El Hoyo Complex as well as the potential re-activation of the El Hoyo edifice. DOI
42. Singer, B., Andersen, N., Le Mével, H., Feigl, K., DeMets, C., Tikoff, B., Thurber, C., Jicha, B., Wespestad, C., Cardona, C., Córdova, L., Amigo, A., Unsworth, M., Cordell, D., Williams-Jones, G., Miller, C., Fierstein, J., Hildreth, W., Sruoga, P., Costa, F., Peterson, D., Keranen, K.The large, restless, rhyolitic magma system at Laguna del Maule, southern Andes: Its dynamics and hazards.Proceedings of the XIV Congreso Geologico Chileo., 2015, The large, restless, rhyolitic magma system at Laguna del Maule, southern Andes: Its dynamics and hazards.
Laguna del Maule, Chile, rhyolite, unrest
41. Van Hinsberg, V., Vigouroux, N., Palmer, S., Berlo, K., Mauri, G., Williams-Jones, A., Mckenzie, J., Williams-Jones, G., Fischer, T.Element flux to the environment of the passively degassing Kawah Ijen volcano, Indonesia, and implications for estimates of the global volcanic flux.Special Issue on Volcanic Lakes, Geological Society Special Publication, 2015, 437 Element flux to the environment of the passively degassing Kawah Ijen volcano, Indonesia, and implications for estimates of the global volcanic flux.
acid late, degassing, element flux, hydrothermal system
Volcanoes play an important role in the global cycling of elements by providing a pathway from the deep Earth to its surface. Here, we have constrained the flux to the environment for most elements of the periodic table for the passively degassing, crater lake-hosting Kawah Ijen volcano in the Indonesian arc. Our results indicate that emissions of Kawah Ijen are dominated by acid
water outflow, especially for the ligands (Cl, F, Br), with active fumaroles contributing significant (semi)metals (e.g. Se, As, Sb, Hg), as well as C and S. The compositional signature of emissions
from Kawah Ijen is similar to that of major volcanic emitters such as Etna, but element fluxes are smaller. This result provides the prerequisite foundation for extrapolating a small set of measured
volcanic gas emissions to a global volcanic flux estimate. However, the aqueous flux (i.e. seepage of volcanic hydrothermal fluids and volcano-influenced groundwater) is at least as important in terms of element release, and the consideration of the gaseous flux alone thus represents a significant underestimate of the impact of volcanoes on their environment and the contribution of volcanic hydrothermal systems to global element cycling. DOI
40.Williams-Jones, G.; Rymer, H.Hazards of Volcanic Gases.n H. Sigurdsson, B. Houghton, H. Rymer, J. Stix, S. McNutt (Eds.), The Encyclopedia of Volcanoes., 2015, 2nd Ed. Academic Press, 985-992 Hazards of Volcanic Gases.
hazards, volcanic gas
39. Zurek, J; Williams-Jones, G; Trusdell, F; Martin, S.The origin of Mauna Loa's Nnole Hills: Evidence of rift zone reorganization.Geophysical Research Letters, 2015, 42: 8358-8366 The origin of Mauna Loa's Nnole Hills: Evidence of rift zone reorganization
volcanology; gravity; Mauna Loa; geophysics
In order to identify the origin of Mauna Loa volcano's Nnole Hills, Bouguer gravity was used to delineate density contrasts within the edifice. Our survey identified two residual anomalies beneath the Southwest Rift Zone (SWRZ) and the Nnole Hills. The Nnole Hills anomaly is elongated, striking northeast, and in inversions both anomalies merge at approximately -7 km above sea level. The positive anomaly, modeled as a rock volume of similar to 1200 km(3) beneath the Nnole Hills, is associated with old eruptive vents. Based on the geologic and geophysical data, we propose that the gravity anomaly under the Nnole Hills records an early SWRZ orientation, now abandoned due to geologically rapid rift-zone reorganization. Catastrophic submarine landslides from Mauna Loa's western flank are the most likely cause for the concurrent abandonment of the Nnole Hills section of the SWRZ. Rift zone reorganization induced by mass wasting is likely more common than currently recognized. DOI
38. King, J; Williams-Jones, AE; van Hinsberg, V; Williams-Jones, G.High-Sulfidation Epithermal Pyrite-Hosted Au (Ag-Cu) Ore Formation by Condensed Magmatic Vapors on Sangihe Island, Indonesia.Economic Geology, 2014, 109: 1705-1733 High-Sulfidation Epithermal Pyrite-Hosted Au (Ag-Cu) Ore Formation by Condensed Magmatic Vapors on Sangihe Island, Indonesia
Although gold in high-sulfidation epithermal deposits generally occurs as the native metal or electrum, in some deposits, a significant proportion of the gold is hosted in pyrite. Here we use a combination of petrography, whole-rock geochemistry, pyrite chemistry, crystallography, and phase stability relationships to determine how gold was transported and incorporated into pyrite in two relatively young high-sulfidation epithermal deposits, where the gold occurs almost exclusively in solid solution or as nanoparticles in pyrite. The genetically related Bawone and Binebase Au (Cu-Ag) deposits, located 1 km apart on the volcanic island of Sangihe, northeastern Indonesia, are hosted by andesitic volcaniclastic rocks that were altered to a proximal advanced argillic association of quartz + pyrite (py I) + pyrophyllite + natroalunite + alunite + dickite + kaolinite and a more distal intermediate argillic association of quartz + pyrite (py I) + kaolinite + dickite + illite. The economic mineralization takes the form of multiple generations of auriferous pyrite, the first of which, pyrite I (py I), developed during advanced argillic alteration. Mass balance calculations show that all elements were mobile with the exception of Nb, Ti, some rare earth elements, and possibly Al. The highest gold concentration is in pyrite II (py II), which occurs in veins that cut pyrite I. This drusy variety of pyrite is characterized by complex growth and sector zoning, and contains as much as 6.0 wt % Cu. The elevated Cu concentrations correlate positively with Au and As concentrations, whereas the Ag concentration correlates strongly with Au but not Cu. Later barite-enargite mineralization exploited py II veins and vugs, and significant concentrations of Ag and Au are hosted by enargite, although the Au concentration in enargite is lower than in py II or py I. A model is presented in which the fluid responsible for advanced argillic and intermediate argillic alteration and associated stage 1 gold mineralization was a condensed magmatic vapor derived from an oxidized magma. The gold and other metals were transported as hydrated species that ascended through the volcanic pile via fractures and zones of enhanced permeability to a depth between 900 and 1300 m, where the vapor condensed at a temperature between 250 and 340 degrees C to form an acidic liquid with a pH of similar to 2.5; fo(2) ranged up to four log units above the hematite-magnetite buffer. Interaction of this liquid with the host andesites caused advanced argillic and intermediate argillic alteration, including sulfidation of mafic minerals to form py I. During crystallization of py I, Au, Cu and Ag were adsorbed onto the surface of the pyrite and deposited as nanoparticles, or were incorporated in the pyrite structure. Adsorption of Au, Cu, and Ag from the condensed vapor reached a peak during the crystallization of vein-hosted py II, and the uptake of Ag and minor Au continued during later crystallization of enargite. From the distribution of metals among growth and sector zones in py II, incorporation of gold and other metals appears to have been maximized when physicochemical conditions were relatively stable. This is in contrast to the requirement for native gold precipitation, namely that physicochemical gradients be steep to ensure supersaturation of gold in the ore fluid. DOI
37. Singer, B., Andersen, N., Le Mével, H., Feigl, K., DeMets, C., Tikoff, B., Thurber, C., Jicha, B., Cardona, C., Córdova, L., Gil, F., Unsworth, M., Williams-Jones, G., Miller, C., Fierstein, J., Hildreth, W., Vazquez, J.Dynamics of a large, restless, rhyolitic magma system at Laguna del Maule, southern Andes, Chile.GSA Today, 2014, 24: 4-10 Dynamics of a large, restless, rhyolitic magma system at Laguna del Maule, southern Andes, Chile
Laguna del Maule, rhyolite, magma, unrest
Explosive eruptions of large-volume rhyolitic magma systems
are common in the geologic record and pose a major potential
threat to society. Unlike other natural hazards, such as earthquakes and tsunamis, a large rhyolitic volcano may provide
warning signs long before a caldera-forming eruption occurs.
Yet, these signs—and what they imply about magma-crust
dynamics—are not well known. This is because we have learned
how these systems form, grow, and erupt mainly from the study of
ash flow tuffs deposited tens to hundreds of thousands of years
ago or more, or from the geophysical imaging of the unerupted
portions of the reservoirs beneath the associated calderas. The
Laguna del Maule Volcanic Field, Chile, includes an unusually
large and recent concentration of silicic eruptions. Since 2007, the
crust there has been inflating at an astonishing rate of at least
25 cm/yr. This unique opportunity to investigate the dynamics of
a large rhyolitic system while magma migration, reservoir growth,
and crustal deformation are actively under way is stimulating a
new international collaboration. Findings thus far lead to the
hypothesis that the silicic vents have tapped an extensive layer of crystal-poor, rhyolitic melt that began to form atop a magmatic
mush zone that was established by ca. 20 ka with a renewed phase
of rhyolite eruptions during the Holocene. Modeling of surface
deformation, magnetotelluric data, and gravity changes suggest
that magma is currently intruding at a depth of ~5 km. The next
phase of this investigation seeks to enlarge the sets of geophysical and geochemical data and to use these observations in numerical models of system dynamics. DOI
36. Scher, S; Williams-Jones, AE; Williams-Jones, G.Fumarolic Activity, Acid-Sulfate Alteration, and High Sulfidation Epithermal Precious Metal Mineralization in the Crater of Kawah Ijen Volcano, Java, Indonesia.Economic Geology, 2013, 108: 1099-1118 Fumarolic Activity, Acid-Sulfate Alteration, and High Sulfidation Epithermal Precious Metal Mineralization in the Crater of Kawah Ijen Volcano, Java, Indonesia
Opinion is divided over whether the fluid responsible for the formation of high sulfidation epithermal deposits is a vapor or a liquid, and whether it is entirely volcanic or of mixed volcanic-meteoric origin. Observations made at Kawah Ijen, an active stratovolcano (mainly andesitic in composition) located in the Ijen Caldera Complex in Java, Indonesia, are used to address these issues. The Kawah Ijen crater is approximately 1 km in diameter, and hosts one of the world's largest hyperacidic lakes (pH similar to 0). On the lake edge is a small and actively degassing solfatara field, which is surrounded by a much larger area of acid-sulfate alteration. This area was exposed during a phreatomagmatic eruption in 1817, which excavated the crater to a depth of 250 m, and comprises zones of residual silica, alunite-pyrite, and dickite/kaolinite. Based on the fractionation of S-34 and S-32 between alunite and pyrite, the acid-sulfate alteration occurred at a temperature between 200 degrees and 300 degrees C. High sulfidation epithermal mineralization accompanied the alteration in the form of massive and vein-hosted pyrite that contains up to 192 ppb Au, 9.2 ppm Ag, 6,800 ppm Cu, and 3,430 ppm As; these elements are invisible at the highest resolution of scanning electron microscopy, and thus either occur in the form of nanoparticles or are in solid solution in the pyrite. Condensed fumarolic gases released from the solfatara field and sampled at temperatures between 330 degrees and 495 degrees C contain up to 3 ppm Cu and 3.8 ppm As; the concentrations of Au and Ag are below detection. The pH of the condensed gas (water vapor) is similar to-0.5. The above observations support a model in which highly acidic gases condensed similar to 250 m beneath the floor of the crater. Depending on the fluid/rock ratio, the condensed liquids altered the andesitic host rocks by leaching them to leave behind a residue of "vuggy silica" (high fluid/rock ratio), by replacing the primary minerals with alunite and pyrite (intermediate fluid/rock ratio), or by converting them to dickite/kaolinite (lower fluid/rock ratio). Gold-, silver-, and copper-bearing phases were undersaturated in the condensed liquids. However, they were able to concentrate by adsorbing on the surfaces of the growing pyrite crystals, which developed p-type conductive properties as a result of the uptake of arsenic. The metals were incorporated in the pyrite either by their electrochemical reduction to form native metal nanoparticles or through coupled substitutions with arsenic for iron and sulfur. The results of this study provide compelling evidence that high sulfidation epithermal precious metal mineralization can form directly from condensed magmatic gases. DOI
35. Vigouroux, N.; Williams-Jones, G.; Hickson, C.Development of the MultiGAS for determining fumarole gas chemistry in geothermal systems.Transactions - Geothermal Resources Council, 2013, 37: 1-14 Development of the MultiGAS for determining fumarole gas chemistry in geothermal systems.
MultiGAS, gas emissions, exploration, Peru, Italy, gas geochemistry, real-time
Geothermal exploration relies in part on the gas geochemistry of fumaroles, bubbling springs and steaming ground to offer
insight into the nature of the fluids at depth, processes affecting them when rising to the surface, and provide estimates of the temperature of last equilibration of the gases within the reservoir.
Traditional measurements involve direct sampling of the gases
in pre-evacuated Giggenbach glass bottles before laboratory
chemical analysis. Gas component analysis, combined with the
isotope ratios of certain components (e.g., CO2, He), provides
insight into the proportion of magmatic, crustal, meteoric and
atmospheric components in the fluid, and the state of equilibrium
and temperature of these fluids at depth.
The Multi-component Gas Analyzing System (MultiGAS)
was developed by the volcanological community over 10 years
ago as a field-portable instrument for in-situ analysis of the major volcanic gas components in diffuse and dilute gas emissions. No two instruments are identical but all consist of various sensor
types now capable of simultaneously analyzing for H2O, CO2,
CO, SO2 and H2S.
In geothermal systems, surface manifestations are often comprised of gas emissions. In some cases, low temperatures and/or
low flow rates make traditional sampling of fumaroles difficult,
due to rapid vapor condensation (in water-rich fumaroles) and
atmospheric contamination. The MultiGAS is best suited to these
types of manifestations, providing a tool that can be used at a wide variety of locations with differing gas emission styles.
The MultiGAS has been field-tested in two very different
geothermal prospect areas: one characterized by cold, CO2-rich
gas seeps and bubbling springs, and the other characterized by
steaming ground and fumaroles with temperatures near the boiling
point of water. Results of the MultiGAS analysis are compared
with the equivalent ratios obtained from traditional sampling andanalytical procedures (where possible), in order to identify the advantages and disadvantages of this new technique. The MultiGAS allows for the rapid characterization of the gas geochemistry in the field, aids in mapping/targeting of fumaroles in a large field, and allows for the selection of the most ideal fumaroles to sample using the traditional Giggenbach method.
34. Zurek, J; Williams-Jones, G.The shallow structure of Kilauea caldera from high-resolution Bouguer gravity and total magnetic anomaly mapping: Insights into progressive magma reservoir growth.Journal of Geophysical Research-Solid Earth, 2013, 118: 3742-3752 The shallow structure of Kilauea caldera from high-resolution Bouguer gravity and total magnetic anomaly mapping: Insights into progressive magma reservoir growth
Bouguer gravity; potential fields; volcanology; total magnetic field; magma reservoir
We conducted total magnetic field and Bouguer gravity measurements to investigate the shallow structure beneath the summit caldera of Klauea Volcano, Hawai'i. Two significant and distinctive magnetic anomalies were identified within the caldera. One is interpreted to be associated with a long-lived prehistoric eruptive center, the Observatory vent, located similar to 1km east of the Hawaiian Volcano Observatory. The second magnetic anomaly corresponds to a set of eruptive fissures that strike northeast from Halema'uma'u Crater, suggesting this is an important transport pathway for magma. The Bouguer gravity data were inverted to produce 3-D models of density contrasts in the upper 2km beneath Klauea. The models detect 3.0km(3) of material, denser than 2800kgm(-3), beneath the caldera that may represent an intrusive complex centered northeast of Halema'uma'u. Recent temporal gravity studies indicate continual addition of mass beneath the caldera during 1975-2008 centered west of Halema'uma'u and suggest this is due to filling of void space. The growth of a large intrusive complex, apparent cyclical caldera formation, and continual mass addition without inflation, however, can also be explained by extensional rifting caused by the continual southward movement of Klauea's unstable south flank. DOI
33. Mauri, G; Williams-Jones, G; Saracco, G; Zurek, JM.A geochemical and geophysical investigation of the hydrothermal complex of Masaya volcano, Nicaragua.Journal of Volcanology and Geothermal Research, 2012, 227: 15-31 A geochemical and geophysical investigation of the hydrothermal complex of Masaya volcano, Nicaragua
Masaya; Hydrothermal; Self-potential; Wavelet; Groundwater; Volcano
Masaya volcano, Nicaragua, is a persistently active volcano characterized by continuous passive degassing for more than 150 years through the open vent of Santiago crater. This study applies self-potential, soil CO2 and ground temperature measurements to highlight the existence of uprising fluids associated to diffuse degassing structures throughout the volcano. The diffuse degassing areas are organized in a semi-circular pattern and coincide with several visible and inferred surface volcanic structures (cones, fissure vents) and likely consist of a network of buried faults and dykes that respectively channel uprising flow and act as barrier to gravitational groundwater flow. Water depths have been estimated by multi-scale wavelet tomography of the self-potential data using wavelets from the Poisson kernel family. Compared to previous water flow models, our water depth estimates are shallower and mimic the topography, typically less than 150 m below the surface. Between 2006 and 2010, the depths of rising fluids along the survey profiles remained stable suggesting that hydrothermal activity is in a steady state. This stable activity correlates well with the consistency of the volcanic activity expressed at the surface by the continuously passive degassing. When compared to previous structural models of the caldera floor, it appears that the diffuse degassing structures have an important effect on the path that shallow groundwater follows to reach the Laguna de Masaya in the eastern part of the caldera. The hydrogeological system is therefore more complex than previously published models and our new structural model implies that the flow of shallow groundwater must bypass the intrusions to reach the Laguna de Masaya. Furthermore, these diffuse degassing structures show clear evidence of activity and must be connected to a shallow magmatic or hydrothermal reservoir beneath the caldera. As such, the heat budget for Masaya must be significantly larger than previously estimated. (C) 2012 Published by Elsevier B.V. DOI
32. Vigouroux, N; Wallace, PJ; Williams-Jones, G; Kelley, K; Kent, AJR; Williams-Jones, AE.The sources of volatile and fluid-mobile elements in the Sunda arc: A melt inclusion study from Kawah Ijen and Tambora volcanoes, Indonesia.Geochemistry, Geophysics, Geosystems, 2012, 13: Q09015 The sources of volatile and fluid-mobile elements in the Sunda arc: A melt inclusion study from Kawah Ijen and Tambora volcanoes, Indonesia
H2O-rich fluid; Sunda arc; fluid-mobile element; melt inclusion; subduction zone; volatile element
Subduction zone recycling of volatiles (H2O, Cl, S, F) is controlled by the nature of subducted materials and the temperature-pressure profile of the downgoing slab. We investigate the variability in volatile and fluid-mobile trace element enrichment in the Sunda arc using melt inclusion data from Kawah Ijen and Tambora volcanoes, together with published data from Galunggung, Indonesia. Combining our results with data from other arcs, we investigate the mobility of these elements during slab dehydration and melting. We observe correlations between Sr, H2O and Cl contents, indicating coupling of these elements during subduction zone recycling. Sulfur is more variable, and fluorine contents generally remain at background mantle values, suggesting decoupling of these elements from H2O and Cl. Partial melting and dehydration models constrain the source of Sr and the volatiles and suggest that the altered oceanic crust (AOC) is the main source of the hydrous component that fluxes into the mantle wedge, in agreement with thermo-mechanical models. Sediment melt remains an important component for other elements such as Ba, Pb, Th and the LREE. The Indonesian volcanoes have variable concentrations of volatile and fluid-mobile elements, with Kawah Ijen recording higher AOC-derived fluid fluxes (Sr/Nd and H2O/Nd) compared to Galunggung and Tambora. Kawah Ijen has H2O/Ce ratios that are comparable to some of the most volatile-rich magmas from other cold slab subduction zones worldwide, and the highest yet measured in the Sunda arc. DOI
30. Mauri, G; Williams-Jones, G; Saracco, G.MWTmat-application of multiscale wavelet tomography on potential fields.Computers & Geoscience, 2011, 37: 1825-1835 MWTmat-application of multiscale wavelet tomography on potential fields
Wavelet; Signal processing; Potential field; Self-potential; Gravimetry; Geothermal
Wavelet analysis is a well-known technique in the sciences to extract essential information from measured signals. Based on the theory developed by previous studies on the Poisson kernel family, this study presents an open source code, which allows for the determination of the depth of the source responsible for the measured potential field. MWTmat, based on the Matlab platform, does not require the wavelet tool box, is easy to use, and allows the user to select the analyzing wavelets and parameters. The program offers a panel of 10 different wavelets based on the Poisson kernel family and the choice between a fully manual and a semiautomatic mode for selection of lines of extrema. The general equations for both horizontal and vertical derivative wavelets are presented in this study, allowing the user to add new wavelets. Continuous wavelet analyses can be used to efficiently analyze electrical, magnetic, and gravity signals; examples are presented here. The MWTmat code and the multiscale wavelet tomography approach are an efficient method for investigating spatial and temporal changes of sources generating potential field signals. (C) 2011 Elsevier Ltd. All rights reserved. DOI
29. Mauri, G; Williams-Jones, G; Saracco, G.Depth determinations of shallow hydrothermal systems by self-potential and multi-scale wavelet tomography.Journal of Volcanology and Geothermal Research, 2010, 191: 233-244 Depth determinations of shallow hydrothermal systems by self-potential and multi-scale wavelet tomography
hydrothermal; self-potential; wavelet; volcanoes
In hydrothermal studies, the depth of the hydrothermal system is always required, but rarely known via traditional geophysical exploration techniques. While previous studies have shown that continuous wavelet transform algorithms applied to self-potential data can theoretically determine the depth of the hydrothermal fluids, this study uses multi-scale wavelet tomography with multiple wavelets, field measurements and geophysical models to accurately determine this depth. On Stromboli, Waita and Masaya volcanoes, multi-scale wavelet tomography of field measurements gives reproducible depth results, supported by independent geophysical measurements and models, and accurately locates the main water flow paths at shallow depths. Unlike other traditional geophysical methods, multi-scale wavelet tomography using self-potential data is a low cost tool to rapidly determine depths of the shallowest hydrothermal structures. This approach has the potential to significantly enhance our ability to locate geothermal systems and monitor active volcanoes. (C) 2010 Elsevier RV. All rights reserved. DOI
28. Hickson, C.J.; Kelman, M.C.; Chow, W.; Shimamura, K.; Servranckx, R.; Bensimon, D.; Cassidy, J.F.; Trudel, S.; Williams-Jones, G.Nazko region volcanic hazard map.Geological Survey of Canada, Open File, 2009, 5978 Nazko region volcanic hazard map
Nazko, hazard map, volcano
27. Nadeau, PA; Williams-Jones, G.Apparent downwind depletion of volcanic SO2 flux-lessons from Masaya Volcano, Nicaragua.Bulletin of Volcanology, 2009, 71: 389-400 Apparent downwind depletion of volcanic SO2 flux-lessons from Masaya Volcano, Nicaragua
Masaya volcano; Persistent volcanic degassing; Sulfur dioxide; Topographic effects; Volcano monitoring; FLYSPEC
A series of 707 measurements at Masaya in 2005, 2006, and 2007 reveals that SO2 emissions 15km downwind of the active vent appear to be similar to 33% to similar to 50% less than those measured only 5km from the vent. Measurements from this and previous studies indicate that dry deposition of sulfur from the plume and conversion of SO2 to sulfate aerosols within the plume each may amount to a maximum of 10% loss, and are not sufficient to account for the larger apparent loss measured. However, the SO2 measurement site 15km downwind is located on a ridge over which local trade winds, and the entrained plume, accelerate. Greater wind speeds cause localized dilution of the plume along the axis of propagation. The lower concentrations of SO2 measured on the ridge therefore lead to calculations of lower fluxes when calculated at the same plume speed as measurements from only 5km downwind, and is responsible for the apparent loss of SO2. Due to the importance of SO2 emission rates with respect to hazard mitigation, petrologic studies, and sulfur budget calculations, measured fluxes of SO2 must be as accurate as possible. Future campaigns to measure SO2 flux at Masaya and similar volcanoes will require individual plume speed measurements to be taken at each flux measurement site to compensate for dilution and subsequent calculation of lower fluxes. This study highlights the importance of a comprehensive understanding of a volcano's interaction with its surroundings, especially for low, boundary layer volcanoes. DOI
26. Rymer, H.; Locke, C.A.; Borgia, A.; Martinez, M.; Brenes, J.; Van der Laat, R.; Williams-Jones, G.Long-term fluctuations in volcanic activity: implications for future environmental impact.Terra Nova, 2009, 21: 304-30 Long-term fluctuations in volcanic activity: implications for future environmental impact.
Poas, Costa Rica, acid lake, precursory signal
Acidic crater lakes at persistently active volcanoes act as both
an index and a moderator of volcanic processes. A catastrophic
drop in lake level can therefore lead to serious local environmental damage. In the early 1990s, the crater lake at Poas
volcano, Costa Rica diminished, and acid aerosols erupted with
devastating consequences for local health, environment and
economy. The first indications of this event can be retrospectively identified to have started from 1985, on the basis of our unique 20-year data time series, which provides evidence for the shallow intrusion of magma. New data presented in this
article show similar trends and we conclude that Poas has now
entered another active period with renewed intrusion. Severe
environmental damage in this region is expected within the
next few years if the current trend continues. DOI
25. Branan, YK; Harris, A; Watson, IM; Phillips, JC; Horton, K; Williams-Jones, G; Garbeil, H.Investigation of at-vent dynamics and dilution using thermal infrared radiometers at Masaya volcano, Nicaragua.Journal of Volcanology and Geothermal Research, 2008, 169: 34-47 Investigation of at-vent dynamics and dilution using thermal infrared radiometers at Masaya volcano, Nicaragua
persistent degassing; thermal; gas puff; gas/mass flux; Masaya
in order to develop a detailed understanding of the dynamics of gas puffing (gas release as a series of distinct pulses) and more sustained degassing (steady plumes of gas) during persistent volcanic degassing, measurements of gas mass flux are required in the vicinity of the volcanic vent. Masaya volcano (Nicaragua), a persistently degassing system, is an ideal location for measuring the dynamics of releases of volcanic gas in the first few seconds of their propagation. We carried out two field experiments during February 2002 and March 2003, during which thermal infrared thermometers were targeted into the degassing vent at Masaya to record thermal variations related to variations in the at-vent gas emission over short (on the order of seconds) time scales. The thermometers recorded an oscillating signal as gas puffs passed through the field of view, detailing variations in the degassing process developing over time scales of seconds. These data were processed to extract puff frequencies, amplitudes, durations, emission velocities and volumes. These data showed that, over time periods of hours, the total gas flux was stable with little variation in the puffing frequency. However, between the 2002 and 2003 data set we noted an increase in mean plume temperature, puffing frequency, puff emission velocity and puff volume, as well as a decrease in mean puff duration. These changes were consistent with a thermal data-derived increase in emitted gas flux from 4.2 x 10(7) m(3) d(-1) to 6.4 x 10(7) m(3) d(-1) between the two campaigns. Turbulent gas puffs entrain surrounding air, and quantifying the magnitude of air entrainment, or dilution, represents a major challenge for the measurement of total volcanic gas emissions. Our observations of small gas puffs suggest that they behave as turbulent buoyant thermals, and we use equations for mass, momentum and buoyancy, coupled with the standard entrainment assumption for turbulent buoyant flows, to estimate the gas puff dilution. The theoretically calculated dilution of 0.09 and 0.24 between emission and detection yields total SO2 mass fluxes of 209 t d(-1) and 864 t d(-1) for 2002 and 2003, respectively. This compares well with U-V-spectrometer SO2 fluxes of 470 and 680 t d(-1) for February 2002 and March 2003, respectively. (C) 2007 Elsevier B.V. All rights reserved. DOI
24. Crider, JG; Johnsen, KH; Williams-Jones, G.Thirty-year gravity change at Mount Baker Volcano, Washington, USA: Extracting the signal from under the ice.Geophysical Research Letters, 2008, 35:L20304 Thirty-year gravity change at Mount Baker Volcano, Washington, USA: Extracting the signal from under the ice.
Mount Baker in the Cascade Volcanic Arc displayed an unexplained period of increased fumarolic activity in 1975 and has since been quiescently degassing. We reoccupied gravity stations near the active crater and on the south flank of the volcano, initially measured in 1975 - 1981. We observe 1800 +/- 300 mu Gal gravity increase at the crater since 1977. Estimates of snow and ice volume change suggest these environmental factors significantly mask gravity change due to magmatic and hydrothermal sources; correcting for environmental factors could double the observed gravity increase. Hydrothermal recharge, magma intrusion, and significant deflation are rejected as explanations for the source of the gravity change. Densification of a magma body emplaced in 1975 is consistent with our gravity observations and with deformation and degassing data. Shallow pyrite precipitation may also contribute to the gravity increase. Citation: Crider, J. G., K. Hill Johnsen, and G. Williams-Jones (2008), Thirty-year change at Mount Baker Volcano, Washington, USA: Extracting the signal from under the ice, Geophys. Res. Lett., 35, L20304, doi: 10.1029/2008GL034921. DOI
23. Nadeau, P.A.; Williams-Jones, G.Beyond COSPEC - Recent advances in SO2 monitoring technology.In: Williams-Jones, G., Stix, J. & Hickson, C. (Eds.), The COSPEC Cookbook: Making SO2 Measurements at Active Volcanoes. IAVCEI Methods in Volcanology, 2008, 1: 219-233 Beyond COSPEC - Recent advances in SO2 monitoring technology.
COSPEC, SO2, degassing, volcano
22. Stix, J.; Williams-Jones, G.; Hickson, C.Applying the COSPEC at Active Volcanoes.In: Williams-Jones, G., Stix, J. & Hickson, C. (Eds.), The COSPEC Cookbook: Making SO2 Measurements at Active Volcanoes. IAVCEI Methods in Volcanology, 2008, 1: 121-167 Applying the COSPEC at Active Volcanoes
COSPEC, volcano, SO2, degassing
21. Vigouroux, N; Williams-Jones, G; Chadwick, W; Geist, D; Ruiz, A; Johnson, D.4D gravity changes associated with the 2005 eruption of Sierra Negra volcano, Galapagos.Geophysics, 2008, 73: WA29-WA35 4D gravity changes associated with the 2005 eruption of Sierra Negra volcano, Galapagos
Global Positioning System; gravity; remote sensing by radar; synthetic aperture radar; volcanology
Sierra Negra volcano, the most voluminous shield volcano in the Galapagos archipelago and one of the largest basaltic calderas in the world, erupted on October 22, 2005 after more than 25 years of quiescence. GPS and satellite radar interferometry (InSAR) monitoring of the deformation of the caldera floor in the months prior to the eruption documented extraordinary inflation rates (1 cm/day). The total amount of uplift recorded since monitoring began in 1992 approached 5 m at the center of the caldera over the eight days of the eruption the caldera floor deflated a maximum of 5 m and subsquently renewed its inflation, but at a decelerating rate. To gain insight into the nature of the subsurface mass/density changes associated with the deformation, gravity measurements performed in 2005, 2006, and 2007 are compared to previous measurements from 2001-2002 when the volcano underwent a period of minor deflation and magma withdrawal.The residual gravity decrease between 2001-2002 and 2005 is among the largest ever recorded atan active volcano (-950 mu Gal) and suggests that inflation was accompanied by a relative density decrease in the magmatic system. Forward modeling of the residual gravity data in 4D (from 2002 to 2005) gives an estimate of the amount of vesiculation in the shallow sill required to explain the observed gravity variations. Geochemical constraints from melt inclusion and satellite remote-sensing data allow us to estimate the pre-eruptive gas content of the magma and place constraints on the thickness of the gas-rich sill necessary to produce the gravity anomalies observed. Results suggest that reasonable sill thicknesses (700-800 m) and bubble contents (10-50 volume %) can explain the large decrease in residual gravity prior to eruption. Following the eruption (2006 and 2007), the deformation and gravity patterns suggest re-equilibration of the pressure regime in the shallow magma system via a renewed influx of relatively gas-poor magma into the shallow parts of the system. DOI
20.Williams-Jones, G; Rymer, H; Mauri, G; Gottsmann, J; Poland, M; Carbone, D.Toward continuous 4D microgravity monitoring of volcanoes.Geophysics, 2008, 73: WA19-WA28 Toward continuous 4D microgravity monitoring of volcanoes
geophysical techniques; gravity; hazardous areas; volcanology
Four-dimensional or time-lapse microgravity monitoring has been used effectively on volcanoes for decades to characterize the changes in subsurface volcanic systems. With measurements typically lasting from a few days to weeks and then repeated a year later, the spatial resolution of theses studies is often at the expense of temporal resolution and vice versa. Continuous gravity studies with one to two instruments operating for a short period of time (weeks to months) have shown enticing evidence of very rapid changes in the volcanic plumbing system (minutes to hours) and in one case precursory signals leading to eruptive activity were detected. The need for true multi-instrument networks is clear if we are to have both the temporal and spatial reso-lution needed for effective volcano monitoring. However, the high cost of these instruments is currently limiting the implementation of continuous microgravity networks. An interim approach to consider is the development of a collaborative network of researchers able to bring multiple instruments together at key volcanoes to investigate multitemporal physical changes in a few type volcanoes. However, to truly move forward, it is imperative that new low-cost instruments are developed to increase the number of instruments available at a single site. Only in this way can both the temporal and spatial integrity of monitoring be maintained. Integration of these instruments into a multiparameter network of continuously recording sensors is essential for effective volcano monitoring and hazard mitigation. DOI
19. de Zeeuw-van Dalfsen, E; Rymer, H; Williams-Jones, G; Sturkell, E; Sigmundsson, F.Integration of micro-gravity and geodetic data to constrain shallow system mass changes at Krafla Volcano, N Iceland.Bulletin of Volcanology, 2006, 68: 420-431 Integration of micro-gravity and geodetic data to constrain shallow system mass changes at Krafla Volcano, N Iceland
micro-gravity; deformation; Krafla; Askja; magma drainage; InSAR; reservoir
New and previously published micro-gravity data are combined with InSAR data, precise levelling and GPS measurements to produce a model for the processes operating at Krafla volcano, 20 years after its most recent eruption. The data have been divided into two periods: from 1990 to 1995 and from 1996 to 2003 and show that the rate of deflation at Krafla is decaying exponentially. The net micro-gravity change at the centre of the caldera is shown, using the measured free air gradient, to be -85 mu Gal for the first and -100 mu Gal for the second period. After consideration of the effects of water extraction by the geothermal power station within the caldera, the net gravity decreases are -73 +/- 17 mu Gal for the first and -65 +/- 17 mu Gal for the second period. These decreases are interpreted in terms of magma drainage. Following a Mogi point source model, we calculate the mass decrease to be similar to 2 x 10(10)kg/year reflecting a drainage rate of similar to 0.23m(3)/s,similar to the similar to 0.13m(3)/s drainage rate previously found at Askja volcano, N. Iceland. Based on the evidence for deeper magma reservoirs and the similarity between the two volcanic systems, we suggest a pressure-link between Askja and Krafla at deeper levels (at the lower crust or the crust-mantle boundary). After the Krafla fires, co-rifting pressure decrease of a deep source at Krafla stimulated the subsequent inflow of magma, eventually affecting conditions along the plate boundary in N. Iceland, as far away as Askja. We anticipate that the pressure of the deeper reservoir at Krafla will reach a critical value and eventually magma will rise from there to the shallow magma chamber, possibly initiating a new rifting episode. We have demonstrated that by examining microgravity and geodetic data, our knowledge of active volcanic systems can be significantly improved. DOI
18. Elias, T; Sutton, AJ; Oppenheimer, C; Horton, KA; Garbeil, H; Tsanev, V; McGonigle, AJS; Williams-Jones, G.Comparison of COSPEC and two miniature ultraviolet spectrometer systems for SO(2) measurements using scattered sunlight.Bulletin of Volcanology, 2006, 68: 313-322 Comparison of COSPEC and two miniature ultraviolet spectrometer systems for SO(2) measurements using scattered sunlight
ultraviolet spectroscopy; gas monitoring; SO(2) emissions; Kilauea volcano; COSPEC; DOAS; FLYSPEC
The correlation spectrometer (COSPEC), the principal tool for remote measurements of volcanic SO(2), is rapidly being replaced by low-cost, miniature, ultraviolet (UV) spectrometers. We compared two of these new systems with a COSPEC by measuring SO(2) column amounts at Kilauea Volcano, Hawaii. The two systems, one calibrated using in-situ SO(2) cells, and the other using a calibrated laboratory reference spectrum, employ similar spectrometer hardware, but different foreoptics and spectral retrieval algorithms. Accuracy, signal-to-noise, retrieval parameters, and precision were investigated for the two configurations of new miniature spectrometer. Measurements included traverses beneath the plumes from the summit and east rift zone of Kilauea, and testing with calibration cells of known SO(2) concentration. The results obtained from the different methods were consistent with each other, with < 8% difference in estimated SO(2) column amounts up to 800 ppm m. A further comparison between the COSPEC and one of the miniature spectrometer configurations, the 'FLYSPEC', spans an eight month period and showed agreement of measured emission rates to within 10% for SO(2) column amounts up to 1,600 ppm m. The topic of measuring high SO(2) burdens accurately is addressed for the Kilauea measurements. In comparing the foreoptics, retrieval methods, and resultant implications for data quality, we aim to consolidate the various experiences to date, and improve the application and development of miniature spectrometer systems. DOI
17. Horton, KA; Williams-Jones, G; Garbeil, H; Elias, T; Sutton, AJ; Mouginis-Mark, P; Porter, JN; Clegg, S.Real-time measurement of volcanic SO2 emissions: validation of a new UV correlation spectrometer (FLYSPEC).Bulletin of Volcanology, 2006, 68: 323-327 Real-time measurement of volcanic SO2 emissions: validation of a new UV correlation spectrometer (FLYSPEC)
FLYSPEC; volcanic emissions; ultraviolet correlation spectrometer
A miniaturized, lightweight and low-cost UV correlation spectrometer, the FLYSPEC, has been developed as an alternative for the COSPEC, which has long been the mainstay for monitoring volcanic sulfur dioxide fluxes. Field experiments have been conducted with the FLYSPEC at diverse volcanic systems, including Masaya (Nicaragua), Poas (Costa Rica), Stromboli, Etna and Vulcano (Italy), Villarica (Chile) and Kilauea (USA). We present here those validation measurements that were made simultaneously with COSPEC at Kilauea between March 2002 and February 2003. These experiments, with source emission rates that ranged from 95 to 1,560 t d(-1), showed statistically identical results from both instruments. SO2 path-concentrations ranged from 0 to > 1,000 ppm-m with average correlation coefficients greater than r(2)=0.946. The small size and low cost create the opportunity for FLYSPEC to be used in novel deployment modes that have the potential to revolutionize the manner in which volcanic and industrial monitoring is performed. DOI
16.Williams-Jones, G; Horton, KA; Elias, T; Garbeil, H; Mouginis-Mark, PJ; Sutton, AJ; Harris, AJL.Accurately measuring volcanic plume velocity with multiple UV spectrometers.Bulletin of Volcanology, 2006, 68: 328-332 Accurately measuring volcanic plume velocity with multiple UV spectrometers
FLYSPEC; plume velocity; volcanic emissions; ultraviolet correlation spectrometer
A fundamental problem with all ground-based remotely sensed measurements of volcanic gas flux is the difficulty in accurately measuring the velocity of the gas plume. Since a representative wind speed and direction are used as proxies for the actual plume velocity, there can be considerable uncertainty in reported gas flux values. Here we present a method that uses at least two time-synchronized simultaneously recording UV spectrometers (FLYSPECs) placed a known distance apart. By analyzing the time varying structure of SO2 concentration signals at each instrument, the plume velocity can accurately be determined. Experiments were conducted on Kilauea (USA) and Masaya (Nicaragua) volcanoes in March and August 2003 at plume velocities between 1 and 10 m s(-1)supercript stop. Concurrent ground-based anemometer measurements differed from FLYSPEC-measured plume speeds by up to 320%. This multi-spectrometer method allows for the accurate remote measurement of plume velocity and can therefore greatly improve the precision of volcanic or industrial gas flux measurements. DOI
15. Rymer, H; Locke, CA; Brenes, J; Williams-Jones, G.Magma plumbing processes for persistent activity at Poas volcano, Costa Rica.Geophysical Research Letters, 2005, 32: L08307 Magma plumbing processes for persistent activity at Poas volcano, Costa Rica
New microgravity data from the active crater of Poas volcano, Costa Rica, collected in 2002-2004 extends the existing dataset to provide a unique 20-year time series. These data show that gravity has decreased monotonically in the north and east of the crater over the last 5 years, whilst it has increased to the west and remained approximately constant in the south. These changes are interpreted in terms of convective recharge within dendritic intrusions beneath the crater, with overall down-welling in the north and up-welling in the west. The data reveal a 5-10 year periodicity in sub-crater mass movement, but overall, the upper part of the conduit system appears to have maintained a state of mass equilibrium. DOI
14. Fournier, N; Rymer, H; Williams-Jones, G; Brenes, J.High-resolution gravity survey: Investigation of subsurface structures at Poas volcano, Costa Rica.Geophysical Research Letters, 2004, 31: L15602 High-resolution gravity survey: Investigation of subsurface structures at Poas volcano, Costa Rica
Bouguer gravity surveys have long been used to investigate sub-surface density contrasts. The main sources of error in previous surveys have been the determination of relative elevations of stations and the effect of topography ( removed via the terrain correction). The availability of high precision Kinematic GPS data now facilitates generation of high-resolution Digital Elevation Models that can help to improve the accuracy of relative elevation determination and the terrain correction. Here we describe a high-resolution gravity survey at Poas volcano, Costa Rica. Our gravity modelling (i) identifies small pockets of magma at shallow depths which relate to successive magma intrusion through time and (ii) shows that the persistent degassing in the eastern part of the crater is related to local deformation at the top of the volcano and changes in the fracture network, rather than to the presence of a shallow magma intrusion. DOI
13. McGonigle, AJS; Delmelle, P; Oppenheimer, C; Tsanev, VI; Delfosse, T; Williams-Jones, G; Horton, K; Mather, TA.SO2 depletion in tropospheric volcanic plumes.Geophysical Research Letters, 2004, 31: L13201 SO2 depletion in tropospheric volcanic plumes
Ground based remote sensing techniques are used to measure volcanic SO2 fluxes in efforts to characterise volcanic activity. As these measurements are made several km from source there is the potential for in-plume chemical transformation of SO2 to sulphate aerosol (conversion rates are dependent on meteorological conditions), complicating interpretation of observed SO2 flux trends. In contrast to anthropogenic plumes, SO2 lifetimes are poorly constrained for tropospheric volcanic plumes, where the few previous loss rate estimates vary widely (from <<1 to >99% per hour). We report experiments conducted on the boundary layer plume of Masaya volcano, Nicaragua during the dry season. We found that SO2 fluxes showed negligible variation with plume age or diurnal variations in temperature, relative humidity and insolation, providing confirmation that remote SO2 flux measurements (typically of approximate to500-2000 s old plumes) are reliable proxies for source emissions for ash free tropospheric plumes not emitted into cloud or fog. DOI
12. Gottsmann, J.; Berrino, G.; Rymer, H.; Williams-Jones, G.Hazard assessment during caldera unrest at the Campi Flegrei, Italy: A contribution from gravity-height gradients.Earth and Planetary Science Letters, 2003, 211: 295-309 Hazard assessment during caldera unrest at the Campi Flegrei, Italy: A contribution from gravity-height gradients.
Hazard assessment and risk mitigation at restless calderas is only possible with adequate geophysical monitoring. We show here how detailed long-term micro-gravity and deformation surveys may contribute to hazard assessment at the Campi Flegrei caldera (CFc) in Italy by evaluating gravity^height change (vg/vh) gradients obtained during ground inflation and deflation between 1981 and 2001. Such gradients provide a framework from which to assess the likelihood and type of volcanic eruptions. Our new analysis of unrest at the CFc allows us to separate ‘noise’ during the gravity survey from the signal of deep-seated magmatic processes. This facilitates identification of the dynamics within the magma reservoir beneath the CFc. We found that magma replenishment during rapid uplift between 1982 and 1984 was insufficient, probably by one to two orders of magnitude, to trigger an eruption similar to the 1538 Monte Nuovo eruption, the most recent volcanic eruption within the CFc. Furthermore, our interpretation of vg/vh gradients for the ongoing period of deflation since 1984 suggests that eruptive volcanic activity is not imminent. Short periods of minor inflation associated with large gravity changes since 1981 are interpreted to reflect noise, which to some degree is probably due to sub-surface mass/density changes within shallow hydrothermal systems beneath the CFc, indicating no risk of eruptive volcanic activity. We propose that monitoring vg/vh gradients at restless calderas is essential as a caldera develops from a state of unrest to a state where volcanic eruptions have to be anticipated. Adoption of this method for the several tens of restless calderas world-wide will provide early warning of changes in or increase of activity at these supervolcanoes. DOI
11.Williams-Jones, G.; Rymer, H.; Rothery, D. A.Gravity changes and passive degassing at the Masaya caldera complex, Nicaragua.Journal of Volcanology and Geothermal Research, 2003, 123: 137-160 Gravity changes and passive degassing at the Masaya caldera complex, Nicaragua.
Masaya; micro-gravity; passive degassing; persistent activity; convection
An understanding of the mechanisms responsible for persistent volcanism can be acquired through the integration of geophysical and geochemical data sets. By interpreting data on micro-gravity, ground deformation and SO2 flux collected at Masaya Volcano since 1993, it is now clear that the characteristically cyclical nature of the activity is not driven by intrusion of additional magma into the system. Rather, it may be due in large part to the blocking and accumulation of gas by restrictions in the volcano
substructure. The history of crater collapse and formation of caverns beneath the crater floor would greatly facilitate the trapping and storage of gas in a zone immediately beneath San Pedro and the other craters. Another mechanism that may explain the observed gravity and gas flux variations is the convective overturn of shallow, pre-existing, degassed, cooled, dense magma that is replaced periodically by lower density, hot, gas-rich magma from depth. Buoyant gas-rich magma rises from depth and is
emplaced near the surface, resulting in the formation and fluctuation of a low-density gas-rich layer centred beneath
Nindir|¤ and Santiago craters. As this magma vigorously degasses, it must cool, increase in density and eventually sink. Five stages of activity have been identified at Masaya since 1853 and the most recent data suggest that the system may have been entering another period of reduced degassing in 2000. This type of analysis has important implications for hazard mitigation because periods of intense degassing are associated with poor agricultural yields and reduced quality of life. A better understanding of persistent cyclically active volcanoes will allow for more effective planning of urban development and agricultural land use. DOI
10.Williams-Jones, G.; Rymer, H.Detecting volcanic eruption precursors: A new method using gravity and deformation measurements.Journal of Volcanology and Geothermal Research, 2002, 113: 379-389 Detecting volcanic eruption precursors: A new method using gravity and deformation measurements.
volcano; magma physics; micro-gravity; deformation; caldera; eruption triggers
One of the fundamental questions in modern volcanology is the manner in which a volcanic eruption is triggered; the intrusion of fresh magma into a reservoir is thought to be a key component. The amount by which previously ponded reservoir magma interacts with a newly intruded magma will determine the nature and rate of eruption as well as the chemistry of erupted lavas and shallow dykes. The physics of this interaction can be investigated through a conventional monitoring procedure that incorporates the simple and much used Mogi model relating ground deformation (most simply represented by vh) to changes in volume of a magma reservoir. Gravity changes (vg) combined with ground deformation provide information on magma reservoir mass changes. Our models predict how, during inflation, the observed vg/vh gradient will evolve as a volcano develops from a state of dormancy through unrest into a state of explosive activity. Calderas in a state of unrest and large composite volcanoes are the targets for the methods proposed here and are exemplified by Campi Flegrei, Rabaul, Krafla, and Long Valley. We show here how the simultaneous measurement of deformation and gravity at only a few key stations can identify important precursory processes within a magma reservoir prior to the onset of more conventional eruption precursors. DOI
9.Williams-Jones, G.Integrated Geophysical Studies at Masaya Volcano, Nicaragua.Ph.D. Thesis, The Open University, UK., 2001, 237 Integrated Geophysical Studies at Masaya Volcano, Nicaragua.
Research into the mechanisms responsible for the lasting, cyclic activity at Masaya volcano can lead to a better understanding of persistently degassing volcanoes. This study is greatly enhanced by the integration of dynamic micro-gravity, deformation and gas flux measurements. The acquisition of extended temporal and spatial geophysical data will also allow for the development of robust models for the dynamics of magmatic systems. Masaya volcano, Nicaragua, is one of the most active systems in Central America, making it an excellent natural laboratory for this study. It is noted for repeated episodes of lava lake formation, strong degassing and subsequent quiescence.
Ground-based geophysical measurements show two episodes of similar magnitude gravity decreases in 1993-1994 and 1997-1999, separated by a period of minor gravity increase. A major increase in SO2 gas flux from 1997-1999 correlates well with the most recent episode of gravity decrease. The gravity changes are not accompanied by deformation in the summit areas and are interpreted in terms of sub-surface density changes. The persistent degassing at Masaya suggests that up to ~15 km3 of magma may have degassed over the last 150 years, only a minute fraction of which has been erupted. Furthermore, thermal flux calculations suggest that 0.5 km3 of magma (the estimated volume of the shallow reservoir) would cool from liquidus to just above solidus temperatures in only 5 years. The high rates of degassing and cooling at open-system volcanoes such as Masaya raise questions as to the ultimate fate of this degassed and cooled magma. A number of models have been proposed to explain this, but the most likely mechanism to explain persistent activity at Masaya and other similar volcanoes is convective removal of cooled and degassed magma and subsequent recharge by volatile-rich magma from depth.
Another fundamental question in modern volcanology concerns the manner in which a volcanic eruption is triggered; the intrusion of fresh magma into a reservoir is thought to be a key component. The amount by which previously ponded reservoir magma interacts with a newly intruded magma will determine the nature and rate of eruption as well as the chemistry of erupted lavas and shallow dykes. The physics of this interaction can be investigated through a conventional monitoring procedure that incorporates the Mogi model relating ground deformation (∆h) to changes in volume of a magma reservoir. Gravity changes (∆g) combined with ground deformation provides information on magma reservoir mass changes. Models developed here predict how, during inflation, the observed ∆g/∆h gradient will evolve as a volcano develops from a state of dormancy through unrest into a state of explosive activity.
7. Rymer, H.; Williams-Jones, G.Volcanic eruption prediction: Magma chamber physics from gravity and deformation measurements.Geophysical Research Letters, 2000, 27: 2389 Volcanic eruption prediction: Magma chamber physics from gravity and deformation measurements.
One of the greatest remaining problems in modern volcanology is the process by which volcanic eruptions are triggered. It is generally accepted that eruptions are preceded by magma intrusion [Sigurdsson and Sparks, 1978]. The degree of interaction between previously ponded magma in a chamber and newly intruded magma determines the nature and rate of eruption and also the chemistry of erupted lavas and shallow dykes. Here, we investigate the physics of this interaction. Volcano monitoring at its most effective is a synergy between basic science and risk assessment, while hazard mitigation depends on reliable interpretation of
eruption precursors. The simple and much used Mogi model relates ground deformation (∆h) to changes in magma chamber volume. Gravity changes (∆g) combined with ground deformation provide information on magma chamber mass changes. Our new models predict how the ∆g/∆h gradient will evolve as a volcano develops from a state of dormancy through unrest into a state of explosive activity. Thus by simultaneous measurement of deformation and gravity at a few key stations, magma chamber processes can be identified prior to the onset of conventional eruption precursors. DOI
6.Williams-Jones, G.; Stix, J.; Heiligmann, M.; Charland, A.; Sherwood Lollar, B.; Arner, N.; Garzón, G.V.; Barquero, J.; Fernandez, E.A model of diffuse degassing at three subduction-related volcanoes.Bulletin of Volcanology, 2000, 62: 130-142 A model of diffuse degassing at three subduction-related volcanoes.
Diffuse degassing; Radon; Carbon dioxide; Poas; Arenal; Galeras
Radon, CO2 and d13C in soil gas were measured at three active subduction-related stratovolcanoes (Arenal and Poµs, Costa Rica; Galeras, Colombia). In general, Rn, CO2 and d13C values are higher on the lower flanks of the volcanoes, except near fumaroles in the active craters. The upper flanks of these volcanoes have low Rn concentrations and light d13C values. These observations suggest that diffuse degassing of magmatic gas on the upper flanks of these volcanoes is negligible and that more magmatic degassing
occurs on the lower flanks where major faults and greater fracturing in the older lavas can channel magmatic gases to the surface. These results are in contrast to findings for Mount Etna where a broad halo of magmatic CO2 has been postulated to exist over much of the edifice. Differences in radon levels among
the three volcanoes studied here may result from differences in age, the degree of fracturing and faulting, regional structures or the level of hydrothermal activity. Volcanoes, such as those studied here, act as plugs in the continental crust, focusing magmatic degassing towards crater fumaroles, faults and the fractured lower flanks. DOI
5. Delmelle, P., Baxter, P., Beaulieu, A., Burton, M., Francis, P., Garcia-Alvarez, J., Horrocks, L., Navarro, M., Oppenheimer, P., Rothery, D., Rymer, H., St. Amand, K., Stix, J., Strauch, W., Williams-Jones, G.Origin, effects of Masaya volcano's continued unrest probed in Nicaragua.Eos, Transactions American Geophysical Union, 1999, 80 Origin, effects of Masaya volcano's continued unrest probed in Nicaragua.
4. Rymer, H.; van Wyk de Vries, B.; Stix, J.; Williams-Jones, G.Pit crater structure and processes governing persistent activity at Masaya Volcano, Nicaragua.Bulletin of Volcanology, 1998, 59: 345-355 Pit crater structure and processes governing persistent activity at Masaya Volcano, Nicaragua.
Masaya; Santiago; Pit; Structure; Microgravity; Magma; Gas
Persistent activity at Masaya Volcano, Nicaragua, is characterised by cycles of intense degassing, lava lake development and pit crater formation. It provides a useful site to study the processes which govern such activity, because of its easy accessibility and relatively short cycles (years to decades). An understanding of the present activity is important because Masaya is visited by large numbers of tourists, is located close to major cities and has produced voluminous lavas, plinian eruptions and ignimbrites in the recent past. We provide structural and geophysical data that characterise the “normal” present state of activity. These indicate that the ongoing degassing phase (1993 to present) was not caused by fresh magma intrusion. It was associated with hallow density changes within the active Santiago pit crater. The activity appears to be associated predominantly with shallow changes in the pit crater structure. More hazardous activity will occur only if there are significant departures from the present
gravity, deformation and seismic signatures. DOI
3.Williams-Jones, G.; Williams-Jones, A.E.; Stix, J.The nature and origin of Venusian canali.Journal of Geophysical Research - Planets, 1998, 103: 8545-8555 The nature and origin of Venusian canali.
Venusian canali have many characteristics of terrestrial rivers, notably cutoff meanders, braiding, point bars, and deltas, which required both erosion and sediment transport. This implies that the canali were not formed by construction but rather by thermal or mechanical erosion. We have evaluated the relative importance of these latter two mechanisms, assuming a basaltic substrate and a surface temperature similar to that currently prevailing, ∼470°C. In order to have thermally eroded the canali, the liquid must have been turbulent and at a temperature above that of the basalt solidus. The most plausible candidates for this liquid are basalt and komatiite lavas. However, at realistic flow rates and extrusion temperatures, flow of basaltic lava is laminar, and therefore basaltic lavas could not have thermally eroded the canali. Although komatiite flow is initially turbulent, the lava will cool in hours to its solidus temperature, whereas it will take months to thermally erode canali. By elimination, only mechanical erosion can adequately explain canali formation. Based on incision and lateral migration rates for terrestrial rivers, it could take from >5 years (in unconsolidated regolith) to 8×105 years (in solid basalt) to mechanically erode a typical Venusian canale. These estimates require that the eroding agent had a solidus temperature close to the Venusian surface temperature and that viscosities remained low until solidification. Only halogen‐rich, alkali carbonatite and sulfur lavas meet these criteria, and only the former could have been present in sufficient volumes to form the canali. We propose that the canali were mechanically eroded by such carbonatite lavas and that the latter originated from the fusion of anhydrous recycled crust, which had been altered by interaction with a CO2‐, SO2‐, and halogen‐rich atmosphere. DOI
2. Heiligmann, M; Stix, J; Williams-Jones, G; Sherwood Lollar, B; Garzón, GV.Distal degassing of radon and carbon dioxide on Galeras volcano, Colombia.Journal of Volcanology and Geothermal Research, 1997, 77: 267-283 Distal degassing of radon and carbon dioxide on Galeras volcano, Colombia.
degassing; soil gas; radon; carbon dioxide; Galeras volcano; Colombia
Diffuse degassing at Galeras volcano, Colombia, was studied during three consecutive field seasons from 1993 to 1995. Measurements of222Rn and CO2 were made at 30 stations which were distributed on the volcano and on regional faults intersecting the edifice. Time series data show a decline of radon soil gas of up to 50% prior to a M 2.8 earthquake on 12 August 1993 at stations located near the epicenter and on the volcano near the location of earthquake swarms which occurred in April 1993, November–December 1993 and March 1995. The onset of volcanic seismic activity (‘tornillos’) on 9 August 1994 was preceded by anomalous soil gas increases at six stations located on the flanks of the volcano. On the southwestern flank, radon increased from 51 to 130 pCi/1 between 7 and 14 August, while on the northern flank, radon concentrations began to increase 19 days before the appearance of tornillos. In general, stations close to the crater showed the largest radon increases. Soil gas distributions and carbon isotope data suggest that diffuse degassing on the volcano is structurally controlled and that the abundance of CO2 in soil gas on the edifice cannot be taken as an indicator for the presence of magmatic gases. Radon soil gas concentrations and the222Rn emanating226Ra concentration increase near faults, whereas CO2 concentrations are more variable but commonly are higher on the volcano than near faults. δ13C values in soil CO2 vary between −8.5 and −23.2‰, with δ13C values more enriched than −15‰ found only in the vicinity of faults or sites prone to earthquake swarms. This suggests a magmatic origin of CO2 soil gas only near faults and an almost impermeable edifice in unfractured areas. The observed correlations between seismic activity and soil degassing provide further evidence that soil gas studies, especially when correlated to other methods of volcano surveillance such as seismicity and deformation, may be useful in forecasting volcanic and seismic events.PDF DOI
1.Williams-Jones, G.The Distribution and Origin of Radon, CO2 and SO2 Gases at Arenal Volcano, Costa Rica.M.Sc. Thesis, Université de Montréal, 1996, 135 The Distribution and Origin of Radon, CO2 and SO2 Gases at Arenal Volcano, Costa Rica.
Volcanic gases are one of several important indicators used to better understand and forecast volcanic activity. However, direct sampling of these gases is often dangerous or impossible due to the high level of activity and the common inaccessibility of the crater areas of many volcanoes. Indirect methods such as the study of soil gases or the use of remote sensing techniques are thus required. Soil gases such as radon and carbon dioxide have been shown to correlate well with variations in volcanic activity. Similarly, the remote sensing of gases such as sulphur dioxide has proven significant in the geochemical characterisation of both passively and actively degassing volcanoes. Techniques such as these can now provide important clues to the behaviour and future
activity of the volcano.
This thesis investigates the degassing of Arenal volcano. A small stratovolcano in northwestern Costa Rica, Arenal is one of the most active volcanoes in Central America, having been in continuous eruption since its reactivation in July 1968. Estimates, using petrologic and remote sensing techniques, are made of the quantity of SO2 emitted from Arenal since 1968 and are related to a degassing model for the volcano. Observed spatial and temporal patterns of soil and plume gases are correlated to eruptive and seismic activity, and the origin and transport of these gases at Arenal is discussed. Measurements of seismicity, radon, CO2 and SO2 gas were made as (1) the results could be compared to other volcanoes where similar measurements have been
made, (2) it was comparatively simple to measure radon, CO2, and SO2, and (3) these gases are believed to respond to changes in activity and the stress-state of the volcano.