Submit to Geosciences Review for Geosciences Propose a Special Issue

Journal Menu

Journal Browser

► Journal Browser

Exploring and Modeling the Magma-Hydrothermal Regime

Special Issue Editors
Special Issue Information
Keywords
Published Papers

A special issue of Geosciences (ISSN 2076-3263). This special issue belongs to the section "Natural Hazards".

Deadline for manuscript submissions: closed (15 April 2020) | Viewed by 54215

Printed Edition Available!
A printed edition of this Special Issue is available here.

Special issue Exploring and Modeling the Magma-Hydrothermal Regime book cover image

Share This Special Issue

Special Issue Editors

Prof. Dr. John C. Eichelberger

E-Mail Website
Guest Editor

International Arctic Research Center, University of Alaska Fairbanks, Fairbanks, AK, USA
Interests: volcanology; igneous petrology; geothermal energy; scientific drilling; natural hazards; Arctic issues

Prof. Dr. Alexey Kiryukhin

E-Mail Website
Co-Guest Editor

Institute of Volcanology and Seismology, FEB RAS, Petropavlovsk-Kamchatsky, Russia
Interests: geothermal volcanology; hydrogeology
Special Issues, Collections and Topics in MDPI journals

Prof. Silvio Mollo

E-Mail Website
Co-Guest Editor

Department of Earth Sciences, Sapienza – University of Rome, Rome, Italy
Interests: igneous and experimental petrology
Special Issues, Collections and Topics in MDPI journals

Prof. Noriyoshi Tsuchiya

E-Mail Website
Co-Guest Editor

Graduate School of Environmental Studies, Tohoku University, Geomaterial and Energy Lab., Sendai, Japan
Interests: geology and petrology of supercritical hydrothermal systems

Dr. Marlène Villeneuve

E-Mail Website
Co-Guest Editor

Montanuniversität Leoben, Erzherzog Johann-Straße 3, A-8700 Leoben, Austria
Interests: rock mechanics; tunneling; drilling

Special Issue Information

Dear Colleagues,

Although associated volcanic and hydrothermal activity are presumed to be the surface expression of “magma–hydrothermal regimes” at depth, the number of papers that actually address the magma–hydrothermal connection is relatively small. Whether as large long-lived magma chambers or frequent small intrusions, nearby magma seems to be required to explain the existence of high-temperature hydrothermal systems. Conversely, because rocks are poor conductors of heat, hydrothermal convection around a magma body is the dominant control of heat loss, thereby influencing evolution and eruption of the magma. Direct interaction of magma and hydrothermal fluid is shown by eruptions that begin with ejection of hydrothermally altered rocks and are later joined by a fresh magmatic component. Whether a phreatic eruption progresses to a more violent magmatic one is a primary concern for volcanologists at observatories. Recently, inadvertent encounters with magma during geothermal drilling show that the magma-hydrothermal connection is closer than many researchers would have expected. We are only beginning to learn from these serendipitous events.

We invite papers that explore the relationship between magma and hydrothermal fluids. Topics will include interpretation of surface-detected geophysical and geochemical signals from active magma–hydrothermal regimes, modeling that treats coupling between magma and hydrothermal systems in terms of heat and mass transport, geologic evidence (“fossil systems”) of hydrothermal–magma relationships, and direct observations of the magma or near-magma environment through drilling. The goal of this Special Issue is to assemble as broad a view as possible about the dynamics of the magma–hydrothermal regime and thus accelerate research that is relevant to both volcanic hazards and geothermal energy.

Prof. John C. Eichelberger
Dr. Alexey Kiryukhin
Prof. Silvio Mollo
Prof. Noriyoshi Tsuchiya
Dr. Marlène Villeneuve
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Geosciences is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1800 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

Magma–hydrothermal
Geothermal energy
Volcanology
Hydrothermal convection
Magma convection
Heat transport
Gas and fluid geochemistry
Phreatomagmatic eruption
Volcano monitoring
Geophysical imaging

Published Papers (13 papers)

Download All Papers

Editorial

Jump to: Research

6 pages, 2229 KiB

Open AccessEditorial

Exploring and Modeling the Magma–Hydrothermal Regime

by John Eichelberger, Alexey Kiryukhin, Silvio Mollo, Noriyoshi Tsuchiya and Marlène Villeneuve

Geosciences 2020, 10(6), 234; https://0-doi-org.brum.beds.ac.uk/10.3390/geosciences10060234 - 18 Jun 2020

Cited by 10 | Viewed by 2336

Abstract

This special issue comprises 12 papers from authors in 10 countries with new insights on the close coupling between magma as an energy and fluid source with hydrothermal systems as a primary control of magmatic behavior. Data and interpretation are provided on the rise of magma through a hydrothermal system, the relative timing of magmatic and hydrothermal events, the temporal evolution of supercritical aqueous fluids associated with ore formation, the magmatic and meteoric contributions of water to the systems, the big picture for the highly active Krafla Caldera, Iceland, as well as the implications of results from drilling at Krafla concerning the magma–hydrothermal boundary. Some of the more provocative concepts are that magma can intrude a hydrothermal system silently, that coplanar and coeval seismic events signal “magma fracking” beneath active volcanoes, that intrusive accumulations may far outlast volcanism, that arid climate favors formation of large magma chambers, and that even relatively dry rhyolite magma can convect rapidly and so lack a crystallizing mush roof. A shared theme is that hydrothermal and magmatic reservoirs need to be treated as a single system. Full article

(This article belongs to the Special Issue Exploring and Modeling the Magma-Hydrothermal Regime)

► Show Figures

Figure 1

Research

Jump to: Editorial

26 pages, 6072 KiB

Open AccessArticle

Distribution and Transport of Thermal Energy within Magma–Hydrothermal Systems

by John Eichelberger

Geosciences 2020, 10(6), 212; https://0-doi-org.brum.beds.ac.uk/10.3390/geosciences10060212 - 01 Jun 2020

Cited by 15 | Viewed by 4330

Abstract

Proximity to magma bodies is generally acknowledged as providing the energy source for hot hydrothermal reservoirs. Hence, it is appropriate to think of a “magma–hydrothermal system” as an entity, rather than as separate systems. Repeated coring of Kilauea Iki lava lake on Kilauea Volcano, Hawaii, has provided evidence of an impermeable, conductive layer, or magma–hydrothermal boundary (MHB), between a hydrothermal system and molten rock. Crystallization on the lower face of the MHB and cracking by cooling on the upper face drive the zone downward while maintaining constant thickness, a Stefan problem of moving thermal boundaries with a phase change. Use of the observed thermal gradient in MHB of 84 °C/m yields a heat flux of 130 W/m². Equating this with the heat flux produced by crystallization and cooling of molten lava successfully predicts the growth rate of lava lake crust of 2 m/a, which is faster than simple conduction where crust thickens at

\sqrt{t}

and heat flux declines with

1 / \sqrt{t}

. However, a lava lake is not a magma chamber. Compared to erupted and degassed lava, magma at depth contains a significant amount of dissolved water that influences the magma’s thermal, chemical, and mechanical behaviors. Also, a lava lake is rootless; it has no source of heat and mass, whereas there are probably few shallow, active magma bodies that are isolated from deeper sources. Drilling at Krafla Caldera, Iceland, showed the existence of a near-liquidus rhyolite magma body at 2.1 km depth capped by an MHB with a heat flux of ≥16 W/m². This would predict a crystallization rate of 0.6 m/a, yet no evidence of crystallization and the development of a mush zone at the base of MHB is observed. Instead, the lower face of MHB is undergoing partial melting. The explanation would appear to lie in vigorous convection of the hot rhyolite magma, delivering both heat and H₂O but not crystals to its ceiling. This challenges existing concepts of magma chambers and has important implications for use of magma as the ultimate geothermal power source. It also illuminates the possibility of directly monitoring magma beneath active volcanoes for eruption forecasting. Full article

(This article belongs to the Special Issue Exploring and Modeling the Magma-Hydrothermal Regime)

► Show Figures

Figure 1

20 pages, 10945 KiB

Open AccessArticle

Transport and Evolution of Supercritical Fluids During the Formation of the Erdenet Cu–Mo Deposit, Mongolia

by Geri Agroli, Atsushi Okamoto, Masaoki Uno and Noriyoshi Tsuchiya

Geosciences 2020, 10(5), 201; https://0-doi-org.brum.beds.ac.uk/10.3390/geosciences10050201 - 25 May 2020

Cited by 4 | Viewed by 3736

Abstract

Petrological and fluid inclusion data were used to characterize multiple generations of veins within the Erdenet Cu–Mo deposit, Mongolia, and constrain the evolution of fluids within the magmatic–hydrothermal system. Three types of veins are present (from early to late): quartz–molybdenite, quartz–pyrite, and quartz. The host rock was emplaced at temperatures of 700–750 °C, the first quartz was precipitated from magma-derived supercritical fluids at 650–700 °C, quartz–molybdenite and quartz–pyrite veins were formed at ~600 °C, and the quartz veins were precipitated in response to retrograde silica solubility caused by decreasing temperatures at <500 °C. We infer that over-pressured fluid beneath the cupola caused localized fluid injection, or that accumulated stress caused ruptures and earthquakes related to sector collapse; these events disrupted impermeable layers and allowed fluids to percolate through weakened zones. Full article

(This article belongs to the Special Issue Exploring and Modeling the Magma-Hydrothermal Regime)

► Show Figures

Figure 1

25 pages, 14491 KiB

Open AccessArticle

Shallow Magmatic Hydrothermal Eruption in April 2018 on Ebinokogen Ioyama Volcano in Kirishima Volcano Group, Kyushu, Japan

by Yasuhisa Tajima, Setsuya Nakada, Fukashi Maeno, Toshio Huruzono, Masaaki Takahashi, Akihiko Inamura, Takeshi Matsushima, Masashi Nagai and Jun Funasaki

Geosciences 2020, 10(5), 183; https://0-doi-org.brum.beds.ac.uk/10.3390/geosciences10050183 - 14 May 2020

Cited by 21 | Viewed by 5777

Abstract

The Kirishima Volcano Group is a volcanic field ideal for studying the mechanism of steam-driven eruptions because many eruptions of this type occurred in the historical era and geophysical observation networks have been installed in this volcano. We made regular geothermal observations to understand the hydrothermal activity in Ebinokogen Ioyama Volcano. Geothermal activity resumed around the Ioyama from December 2015. A steam blowout occurred in April 2017, and a hydrothermal eruption occurred in April 2018. Geothermal activity had gradually increased before these events, suggesting intrusion of the magmatic component fluids in the hydrothermal system under the volcano. The April 2018 eruption was a magmatic hydrothermal eruption caused by the injection of magmatic fluids into a very-shallow hydrothermal system as a bottom–up fluid pressurization, although juvenile materials were not identifiable. Additionally, the upwelling of mixed magma–meteoric fluids to the surface as a kick was observed just before the eruption to cause the top–down flashing of April 2018. A series of events was generated in the shallower hydrothermal regime consisting of multiple systems divided by conductive caprock layers. Full article

(This article belongs to the Special Issue Exploring and Modeling the Magma-Hydrothermal Regime)

► Show Figures

Figure 1

23 pages, 18097 KiB

Open AccessArticle

A CO₂-Driven Gas Lift Mechanism in Geyser Cycling (Uzon Caldera, Kamchatka)

by Alexey V. Kiryukhin and Gennady Karpov

Geosciences 2020, 10(5), 180; https://0-doi-org.brum.beds.ac.uk/10.3390/geosciences10050180 - 14 May 2020

Cited by 5 | Viewed by 2597

Abstract

Here, we report on a new geyser (named Shaman) formed in the Uzon caldera (Kronotsky Federal Nature Biosphere Reserve, Russia) in autumn 2008 from a cycling hot Na-Cl spring. The geyser is a pool-type CO₂-gas lift driven. From 2012 to 2018, the geyser has shown a rather stable interval between eruptions (IBE) from 129 to 144 min with a fountain height up to 4 m, and the geyser conduit has gradually enlarged. In 2019, the Shaman geyser eruption mode significantly changed: cold water inflow from the adjacent stream was re-directed into the geyser conduit and the average IBE decreased to 80 min. We observed two eruptive modes: a cycling hot spring (June 2019) and a cycling geyser (after June 2019). Bottom-hole temperature recording was performed in the geyser conduit to understand its activity. The TOUGH2-EOS2 model was used to reproduce the obtained temperature records and estimate geyser recharge/discharge parameters in both modes. Modeling shows that a larger cold inflow into the conduit causes a switch from cycling geyser to hot cycling spring mode. It was also found that the switch to cycling geyser mode corresponds to a larger mass of CO₂ release during the time of the eruption. Full article

(This article belongs to the Special Issue Exploring and Modeling the Magma-Hydrothermal Regime)

► Show Figures

Figure 1

13 pages, 5507 KiB

Open AccessEditor’s ChoiceArticle

‘Silent’ Dome Emplacement into a Wet Volcano: Observations from an Effusive Eruption at White Island (Whakaari), New Zealand in Late 2012

by Arthur Jolly, Corentin Caudron, Társilo Girona, Bruce Christenson and Roberto Carniel

Geosciences 2020, 10(4), 142; https://0-doi-org.brum.beds.ac.uk/10.3390/geosciences10040142 - 14 Apr 2020

Cited by 17 | Viewed by 3604

Abstract

The 2012–2016 White Island (Whakaari) eruption sequence encompassed six small explosive events that included one steam driven and five explosive phreato-magmatic eruptions. More enigmatic, a dome was observed at the back of the vent and crater lake in November 2012. Its emplacement date could not be easily determined due to persistent steam from the evaporating crater lake and because of the very low levels of discrete volcanic earthquakes associated with its growth. During this period, seismicity also included persistent tremor with dominant frequencies in the 2–5 Hz range. Detailed assessment of the tremor reveals a very slow evolution of the spectral peaks from low to higher frequencies. These gliding spectral lines evolved over a three-month time period beginning in late September 2012 and persisting until early January 2013, when the tremor stabilised. As part of the dome emplacement episode, the crater lake progressively dried, leaving isolated pools which then promoted persistent mud/sulphur eruption activity starting in mid-January 2013. We interpret the emplacement of the dome as a non-explosive process where the hot, mostly degassed, magma intruded slowly through the hydrothermal system in late September 2012 and cooled in a relatively quiet state. The tremor evolution might reflect the slow contraction of subsurface resonant cavities, which increased the pitch of the peak resonant frequency through time. Alternatively, spectral evolution might reflect a ‘comb function’ due to clockwork beating of the slowly cooling dome, although direct evidence of clockwork beats is not seen in the waveform data. Finally, it might represent frothing of the hydrothermal system ahead of the slowly propagating magma. Full article

(This article belongs to the Special Issue Exploring and Modeling the Magma-Hydrothermal Regime)

► Show Figures

Graphical abstract

18 pages, 6206 KiB

Open AccessArticle

Pressure Controlled Permeability in a Conduit Filled with Fractured Hydrothermal Breccia Reconstructed from Ballistics from Whakaari (White Island), New Zealand

by Ben M. Kennedy, Aaron Farquhar, Robin Hilderman, Marlène C. Villeneuve, Michael J. Heap, Stan Mordensky, Geoffrey Kilgour, Art. Jolly, Bruce Christenson and Thierry Reuschlé

Geosciences 2020, 10(4), 138; https://0-doi-org.brum.beds.ac.uk/10.3390/geosciences10040138 - 11 Apr 2020

Cited by 45 | Viewed by 5436

Abstract

Breccia-filled eruption conduits are dynamic systems where pressures frequently exceed critical thresholds, generating earthquakes and transmitting fluids. To assess the dynamics of breccia-filled conduits, we examine lava, ash tuff, and hydrothermal breccia ballistics with varying alteration, veining, fractures, and brecciation ejected during the 27 April 2016 phreatic eruption of Whakaari/White Island. We measure connected porosity, strength, and permeability with and without tensile fractures at a range of confining pressures. Many samples are progressively altered with anhydrite, alunite, and silica polymorphs. The measurements show a large range of connected porosity, permeability, and strength. In contrast, the cracked samples show a consistently high permeability. The cracked altered samples have a permeability more sensitive to confining pressure than the unaltered samples. The permeability of our altered ballistics is lower than surface rocks of equivalent porosity, illustrating that mineral precipitation locally blocked pores and cracks. We surmise that alteration within the conduit breccia allows cracks to form, open and close, in response to pore pressure and confining pressure, providing a mechanism for frequent and variable fluid advection pulses to the surface. This produces temporally and spatially variable geophysical and geochemical observations and has implications for volcano monitoring for any volcano system with significant hydrothermal activity. Full article

(This article belongs to the Special Issue Exploring and Modeling the Magma-Hydrothermal Regime)

► Show Figures

Figure 1

12 pages, 4168 KiB

Open AccessArticle

The Granite Aqueduct and Autometamorphism of Plutons

by John M. Bartley, Allen F. Glazner, Michael A. Stearns and Drew S. Coleman

Geosciences 2020, 10(4), 136; https://0-doi-org.brum.beds.ac.uk/10.3390/geosciences10040136 - 10 Apr 2020

Cited by 15 | Viewed by 3444

Abstract

Ian Carmichael wrote of an “andesite aqueduct” that conveys vast amounts of water from the magma source region of a subduction zone to the Earth’s surface. Diverse observations indicate that subduction zone magmas contain 5 wt % or more H₂O. Most of the water is released from crystallizing intrusions to play a central role in contact metamorphism and the genesis of ore deposits, but it also has important effects on the plutonic rocks themselves. Many plutons were constructed incrementally from the top down over million-year time scales. Early-formed increments are wall rocks to later increments; heat and water released as each increment crystallizes pass through older increments before exiting the pluton. The water ascends via multiple pathways. Hydrothermal veins record ascent via fracture conduits. Pipe-like conduits in Yosemite National Park, California, are located in or near aplite–pegmatite dikes, which themselves are products of hydrous late-stage magmatic liquids. Pervasive grain-boundary infiltration is recorded by fluid-mediated subsolidus modification of mineral compositions and textures. The flood of magmatic water carries a large fraction of the total thermal energy of the magma and transmits that energy much more rapidly than conduction, thus enhancing the fluctuating postemplacement thermal histories that result from incremental pluton growth. The effects of water released by subduction zone magmas are central not only to metamorphism and mineralization of surrounding rocks, but also to the petrology and the thermal history of the plutons themselves. Full article

(This article belongs to the Special Issue Exploring and Modeling the Magma-Hydrothermal Regime)

► Show Figures

Figure 1

22 pages, 13950 KiB

Open AccessArticle

Simultaneous Magmatic and Hydrothermal Regimes in Alta–Little Cottonwood Stocks, Utah, USA, Recorded Using Multiphase U-Pb Petrochronology

by Michael A. Stearns, John M. Bartley, John R. Bowman, Clayton W. Forster, Carl J. Beno, Daniel D. Riddle, Samuel J. Callis and Nicholas D. Udy

Geosciences 2020, 10(4), 129; https://0-doi-org.brum.beds.ac.uk/10.3390/geosciences10040129 - 02 Apr 2020

Cited by 8 | Viewed by 3843

Abstract

Magmatic and hydrothermal systems are intimately linked, significantly overlapping through time but persisting in different parts of a system. New preliminary U-Pb and trace element petrochronology from zircon and titanite demonstrate the protracted and episodic record of magmatic and hydrothermal processes in the Alta stock–Little Cottonwood stock plutonic and volcanic system. This system spans the upper ~11.5 km of the crust and includes a large composite pluton (e.g., Little Cottonwood stock), dike-like conduit (e.g., Alta stock), and surficial volcanic edifices (East Traverse and Park City volcanic units). A temperature–time path for the system was constructed using U-Pb and tetravalent cation thermometry to establish a record of >10 Myr of pluton emplacement, magma transport, volcanic eruption, and coeval hydrothermal circulation. Zircons from the Alta and Little Cottonwood stocks recorded a single population of apparent temperatures of ~625 ± 35 °C, while titanite apparent temperatures formed two distinct populations interpreted as magmatic (~725 ± 50 °C) and hydrothermal (~575 ± 50 °C). The spatial and temporal variations required episodic magma input, which overlapped in time with hydrothermal fluid flow in the structurally higher portions of the system. The hydrothermal system was itself episodic and migrated within the margin of the Alta stock and its aureole through time, and eventually focused at the contact of the Alta stock. First-order estimates of magma flux in this system suggest that the volcanic flux was 2–5× higher than the intrusive magma accumulation rate throughout its lifespan, consistent with intrusive volcanic systems around the world. Full article

(This article belongs to the Special Issue Exploring and Modeling the Magma-Hydrothermal Regime)

► Show Figures

Figure 1

14 pages, 4255 KiB

Open AccessArticle

Climate and the Development of Magma Chambers

by Allen F. Glazner

Geosciences 2020, 10(3), 93; https://0-doi-org.brum.beds.ac.uk/10.3390/geosciences10030093 - 01 Mar 2020

Cited by 7 | Viewed by 4109

Abstract

Whether magma accumulating in the crust develops into a persistent, eruptible magma body or an incrementally emplaced pluton depends on the energy balance between heat delivered to the bottom in the form of magma and heat lost out the top. The rate of heat loss to the surface depends critically on whether heat transfer is by conduction or convection. Convection is far more efficient at carrying heat than conduction, but requires both abundant water and sufficient permeability. Thus, all else being equal, both long-term aridity and self-sealing of fractures should promote development of persistent magma bodies and explosive silicic volcanism. This physical link between climate and magmatism may explain why many of the world’s great silicic ignimbrite provinces developed in arid environments, and why extension seems to suppress silicic caldera systems. Full article

(This article belongs to the Special Issue Exploring and Modeling the Magma-Hydrothermal Regime)

► Show Figures

Figure 1

16 pages, 2891 KiB

Open AccessArticle

Magma Fracking Beneath Active Volcanoes Based on Seismic Data and Hydrothermal Activity Observations

by Alexey Kiryukhin, Evgenia Chernykh, Andrey Polyakov and Alexey Solomatin

Geosciences 2020, 10(2), 52; https://0-doi-org.brum.beds.ac.uk/10.3390/geosciences10020052 - 29 Jan 2020

Cited by 4 | Viewed by 2883

Abstract

Active volcanoes are associated with microearthquake (MEQ) hypocenters that form plane-oriented cluster distributions. These are faults delineating a magma injection system of dykes and sills. The Frac-Digger program was used to track fracking faults in the Kamchatka active volcanic belt and fore-arc region of Russia. In the case of magma laterally injected from volcanoes into adjacent structures, high-temperature hydrothermal systems arise, for example at Mutnovsky and Koryaksky volcanoes. Thermal features adjacent to these active volcanoes respond to magma injection events by degassing CO₂ and by transient temperature changes. Geysers created by CO₂-gaslift activity in silicic volcanism areas also flag magma and CO₂ recharge and redistributions, for example at the Uzon-Geyserny, Kamchatka, Russia and Yellowstone, USA magma hydrothermal systems. Seismogenic faults in the Kamchatka fore-arc region are indicators of geofluid fracking; those faults can be traced down to 250 km depth, which is within the subduction slab below primary magma sources. Full article

(This article belongs to the Special Issue Exploring and Modeling the Magma-Hydrothermal Regime)

► Show Figures

Figure 1

27 pages, 8524 KiB

Open AccessArticle

New Conceptual Model for the Magma-Hydrothermal-Tectonic System of Krafla, NE Iceland

by Knútur Árnason

Geosciences 2020, 10(1), 34; https://0-doi-org.brum.beds.ac.uk/10.3390/geosciences10010034 - 19 Jan 2020

Cited by 19 | Viewed by 7114

Abstract

The complexity of the Krafla volcano and its geothermal system(s) has puzzled geoscientists for decades. New and old geoscientific studies are reviewed in order to shed some light on this complexity. The geological structure and history of the volcano is more complex than hitherto believed. The visible 110 ka caldera hosts, now buried, an 80 ka inner caldera. Both calderas are bisected by an ESE-WNW transverse low-density structure. Resistivity surveys show that geothermal activity has mainly been within the inner caldera but cut through by the ESE-WNW structure. The complexity of the geothermal system in the main drill field can be understood by considering the tectonic history. Isotope composition of the thermal fluids strongly suggests at least three different geothermal systems. Silicic magma encountered in wells K-39 and IDDP-1 indicates a hitherto overlooked heat transport mechanism in evolved volcanos. Basaltic intrusions into subsided hydrothermally altered basalt melt the hydrated parts, producing a buoyant silicic melt which migrates upwards forming sills at shallow crustal levels which are heat sources for the geothermal system above. This can explain the bimodal behavior of evolved volcanos like Krafla and Askja, with occasional silicic, often phreatic, eruptions but purely basaltic in-between. When substantial amounts of silicic intrusions/magma have accumulated, major basalt intrusion(s) may “ignite” them causing a silicic eruption. Full article

(This article belongs to the Special Issue Exploring and Modeling the Magma-Hydrothermal Regime)

► Show Figures

Figure 1

25 pages, 5168 KiB

Open AccessEditor’s ChoiceArticle

Spatio-Temporal Relationships between Fumarolic Activity, Hydrothermal Fluid Circulation and Geophysical Signals at an Arc Volcano in Degassing Unrest: La Soufrière of Guadeloupe (French West Indies)

by Giancarlo Tamburello, Séverine Moune, Patrick Allard, Swetha Venugopal, Vincent Robert, Marina Rosas-Carbajal, Sébastien Deroussi, Gaëtan-Thierry Kitou, Tristan Didier, Jean-Christophe Komorowski, François Beauducel, Jean-Bernard De Chabalier, Arnaud Le Marchand, Anne Le Friant, Magali Bonifacie, Céline Dessert and Roberto Moretti

Geosciences 2019, 9(11), 480; https://0-doi-org.brum.beds.ac.uk/10.3390/geosciences9110480 - 15 Nov 2019

Cited by 26 | Viewed by 3643

Abstract

Over the past two decades, La Soufrière volcano in Guadeloupe has displayed a growing degassing unrest whose actual source mechanism still remains unclear. Based on new measurements of the chemistry and mass flux of fumarolic gas emissions from the volcano, here we reveal spatio-temporal variations in the degassing features that closely relate to the 3D underground circulation of fumarolic fluids, as imaged by electrical resistivity tomography, and to geodetic-seismic signals recorded over the past two decades. Discrete monthly surveys of gas plumes from the various vents on La Soufrière lava dome, performed with portable MultiGAS analyzers, reveal important differences in the chemical proportions and fluxes of H₂O, CO₂, H₂S, SO₂ and H_2, which depend on the vent location with respect to the underground circulation of fluids. In particular, the main central vents, though directly connected to the volcano conduit and preferentially surveyed in past decades, display much higher CO₂/SO₂ and H₂S/SO₂ ratios than peripheral gas emissions, reflecting greater SO₂ scrubbing in the boiling hydrothermal water at 80–100 m depth. Gas fluxes demonstrate an increased bulk degassing of the volcano over the past 10 years, but also a recent spatial shift in fumarolic degassing intensity from the center of the lava dome towards its SE–NE sector and the Breislack fracture. Such a spatial shift is in agreement with both extensometric and seismic evidence of fault widening in this sector due to slow gravitational sliding of the southern dome sector. Our study thus provides an improved framework to monitor and interpret the evolution of gas emissions from La Soufrière in the future and to better forecast hazards from this dangerous andesitic volcano. Full article

(This article belongs to the Special Issue Exploring and Modeling the Magma-Hydrothermal Regime)

► Show Figures