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Causes of unrest at silicic calderas in the East African Rift: new constraints from InSAR and soil-gas chemistry at Aluto volcano, Ethiopia

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Hutchison_et_al_2016_G3_CausesOfUnrest_CCBY.pdf (2.351Mb)
Date
08/2016
Author
Hutchison, William
Biggs, Juliet
Mather, Tamsin A.
Pyle, David M.
Lewi, Elias
Yirgu, Gezahegn
Caliro, Stefano
Chiodini, Giovanni
Clor, Laura E.
Fischer, Tobias P.
Keywords
Geothermal resources
InSAR
Degassing
Continental rifting
Magmatic processes
GE Environmental Sciences
DAS
Metadata
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Abstract
Restless silicic calderas present major geological hazards, and yet many also host significant untapped geothermal resources. In East Africa this poses a major challenge, although the calderas are largely unmonitored their geothermal resources could provide substantial economic benefits to the region. Understanding what causes unrest at these volcanoes is vital for weighing up the opportunities against the potential risks. Here we bring together new field and remote sensing observations to evaluate causes of ground deformation at Aluto, a restless silicic volcano located in the Main Ethiopian Rift (MER). Interferometric Synthetic Aperture Radar (InSAR) data reveal the temporal and spatial characteristics of a ground deformation episode that took place between 2008 and 2010. Deformation time-series reveal pulses of accelerating uplift that transition to gradual long-term subsidence, and analytical models support inflation source depths of ∼5 km. Gases escaping along the major fault zone of Aluto show high CO2 flux, and a clear magmatic carbon signature (CO2–δ13C of −4.2 to −4.5 ‰). This provides compelling evidence that the magmatic and hydrothermal reservoirs of the complex are physically connected. We suggest that a coupled magmatic-hydrothermal system can explain the uplift-subsidence signals. We hypothesize that magmatic fluid injection and/or intrusion in the cap of the magmatic reservoir drives edifice wide inflation while subsequent deflation is related to magmatic degassing and depressurization of the hydrothermal system. These new constraints on the plumbing of Aluto yield important insights into the behaviour of rift volcanic systems and will be crucial for interpreting future patterns of unrest.
Citation
Hutchison , W , Biggs , J , Mather , T A , Pyle , D M , Lewi , E , Yirgu , G , Caliro , S , Chiodini , G , Clor , L E & Fischer , T P 2016 , ' Causes of unrest at silicic calderas in the East African Rift: new constraints from InSAR and soil-gas chemistry at Aluto volcano, Ethiopia ' , Geochemistry, Geophysics, Geosystems , vol. 17 , no. 8 , pp. 3008-3030 . https://doi.org/10.1002/2016GC006395
Publication
Geochemistry, Geophysics, Geosystems
Status
Peer reviewed
DOI
https://doi.org/10.1002/2016GC006395
ISSN
1525-2027
Type
Journal article
Rights
Copyright 2016. The Authors. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Description
This work is a contribution to the Natural Environment Research Council (NERC) funded RiftVolc project (NE/L013932/1, Rift volcanism: past, present, and future). W.H., J.B., T.A.M., and D.M.P. are supported by and contribute to the NERC Centre for the Observation and Modelling of Earthquakes, Volcanoes, and Tectonics (COMET). Envisat data were provided by ESA. ALOS data were provided through ESA third party mission. W.H. funded by NERC studentship, NE/J5000045/1. Additional funding for fieldwork was provided by University College (University of Oxford), the Geological Remote Sensing Group, the Edinburgh Geological Society, and the Leverhulme Trust. Analytical work at the University of New Mexico was supported by the Volcanic and Geothermal Volatiles Lab at the Center for Stable Isotopes and an NSF grant EAR-1113066 to T.P.F.
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URL
http://onlinelibrary.wiley.com/doi/10.1002/2016GC006395/full#footer-support-info
URI
http://hdl.handle.net/10023/9338

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