144 research outputs found
Benchmarking and developing numerical Finite Element models of volcanic deformation
This is the final version of the article. Available from the publisher via the DOI in this record.Volcanic deformation during an unrest episode can provide valuable insights into potential magmatic plumbing
system dynamics. Paramount to this is a model linking the recorded ground movement to the causative source at
depth. Most models employ analytical techniques due to their simplicity, but these are limited in their approach
due to a number of necessary assumptions, and restricted to crude subsurface representations. We address this
problem by providing guidelines and example model files to benchmark against a simple, analytical model
with a numerical Finite Element approach using COMSOL Multiphysics. The boundary conditions should also
be applicable to other Finite Element modeling packages. Then, due to the flexibility of the Finite Element method,
this allows a progression of adding increasing complexities to reproduce the likely intricacies of the subsurface.
We thus provide further guidelines and accompanying model files to incorporate subsurface heterogeneity,
benchmarked viscoelastic rheology and temperature-dependent mechanics. In doing so, we highlight that setting
up more integrated geodetic models is not particularly difficult and can alter inferred source characteristics and
dynamics. The models are applied to Uturuncu volcano in southern Bolivia to demonstrate the approach.This work was supported by the European Union, Framework Program
7 (grant #282759, “VUELCO”, and grant #308665, “MEDSUV”),
the Natural Environmental Research Council (NE/G01843X/1) and the
Royal Society (UF090006). We thank Maurizio Battaglia, an anonymous
reviewer and editor Joan Martí for their constructive reviews
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A stress-controlled mechanism for the intensity of very large magnitude explosive eruptions
Large magnitude explosive eruptions are the result of the rapid and large-scale transport of silicic magma stored in the Earth's crust, but the mechanics of erupting teratonnes of silicic magma remain poorly understood. Here, we demonstrate that the combined effect of local crustal extension and magma chamber overpressure can sustain linear dyke-fed explosive eruptions with mass fluxes in excess of 10^10 kg/s from shallow-seated (4–6 km depth) chambers during moderate extensional stresses. Early eruption column collapse is facilitated with eruption duration of the order of few days with an intensity of at least one order of magnitude greater than the largest eruptions in the 20th century. The conditions explored in this study are one way in which high mass eruption rates can be achieved to feed large explosive eruptions. Our results corroborate geological and volcanological evidences from volcano-tectonic complexes such as the Sierra Madre Occidental (Mexico) and the Taupo Volcanic Zone (New Zealand)
Estimating volcanic deformation source parameters with a Finite Element inversion: the 2001-2002 unrest at Cotopaxi volcano, Ecuador
This is the final version of the article. Available from the publisher via the DOI in this record.Deformation at Cotopaxi was observed between 2001 and 2002 along with recorded seismicity
beneath the northeast (NE) flank, despite the fact that the last eruption occurred in 1942. We use electronic
distance meter deformation data along with the patterns of recorded seismicity to constrain the cause of
this unrest episode. To solve for the optimum deformation source parameters we employ inverse finite
element (FE) models that account for material heterogeneities and surface topography. For a range of source
shapes the models converge on a shallow reservoir beneath the southwest (SW) flank. The individual best fit
model is a small oblate-shaped source, approximately 4–5 km beneath the summit, with a volume increase
of roughly 20 × 106 m3. This SW source location contrasts with the NE seismicity locations. Subsequently,
further FE models that additionally account for temperature-dependent viscoelasticity are used to reconcile
the deformation and seismicity simultaneously. Comparisons of elastic and viscous timescales allude to
aseismic pressurization of a small magma reservoir in the SW. Seismicity in the NE is then explained through
a mechanism of fluid migration from the SW to the NE along fault systems. We extend our analyses to
further show that if future unrest crises are accompanied by measurable seismicity around the deformation
source, this could indicate a higher magma supply rate and increased likelihood of a forthcoming eruption.The data informing this paper is
available upon request to the lead
author. This work was supported by
the European Commission, Framework
Program 7 (grant 282759, VUELCO,
and grant 308665, MEDSUV), the
Natural Environmental Research
Council (NE/G01843X/1), and the
Royal Society (UF090006). We thank
reviewers A. Gudmundsson and
L. Crescentini, and Editor A. Revil,
for their comments which helped to
improve the paper. We also thank Mark
Jellinek for thoughtful discussions
during manuscript preparation
The large-scale surface uplift in the Altiplano-Puna region of Bolivia: A parametric study of source characteristics and crustal rheology using finite element analysis
PublishedThis is the final version of the article. Available from the publisher via the DOI in this record.This paper focuses on the driving mechanism behind a 70 km wide region of ground uplift centered on
Uturuncu volcano, in the Altiplano-Puna region of southern Bolivia. We present a series of forward models
using finite element analysis to simultaneously test for first-order parameters that help constrain a viable
model for the observed maximum line of sight uplift rate of 1–2 cm/yr between 1992 and 2006. Stresses
from pressure sources with finite geometries are solved numerically, accounting for both homogeneous
and heterogeneous mechanical rock properties in elastic and viscoelastic rheologies. Crustal heterogeneity
is constrained by seismic velocity data that indicate the presence of a large low-velocity zone, the AltiplanoPuna
magma body, at depths of ~17 km below the surface. A viscoelastic rheology is employed to account
for time-dependent deformation and an inelastic crust. Comparing homogeneous and heterogeneous
models demonstrates the significant impact of a mechanically weak, source-depth layer, which alters
surface displacement patterns by buffering subsurface deformation. Elastic model results guide the source
parameters tested in the viscoelastic models and demonstrate a range of possible causative source
geometries. Our preferred model suggests that pressurization of a magma source extending upward from
the Altiplano-Puna magma body is causing the observed surface uplift and alludes to a continued increase
in this pressure to explain both the spatial and temporal patterns. We also demonstrate how a pressure-time
function plays a first-order role in explaining the observed temporal deformation patternThis work was supported by the Natural Environmental
Research Council (grant NE/G01843X/1), the European Union
Framework Program 7 (grant 282759, “VUELCO”) and the
Royal Society (University Research Fellowship). We thank
Matthew Pritchard, Ciro Del Negro and editor James Tyburczy
for their constructive review
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On the interpretation of gravity variations in the presence of active hydrothermal systems: Insights from the Nisyros Caldera, Greece
We report on short-term (over tens of minutes) residual gravity changes recorded at the restless Nisyros caldera in Greece via a series of discrete measurements at benchmarks within or in proximity to a hydrothermal area located along the caldera floor. The obtained time series reveal sinusoidal gravity variations with amplitudes of up to 25 μGal and wavelengths of 40–50 min. Degassing of a magmatic source coupling into (shallow) hydrothermal systems including the ascent of steam pockets and transient pressure variations during steam/liquid interface propagation appear to be the most likely causative process for the observed short-term variations. We assess standard protocols of microgravity surveys for hazard assessment in volcanic areas in the light of these findings and propose additional techniques, such as continuous gravimetry, for the discrimination of hydrothermal signals from deeper-seated, i.e. magmatic, signals during gravity monitoring of restless volcanoes hosting active hydrothermal systems
Thermomechanical controls on magma supply and volcanic deformation: application to Aira caldera, Japan
ArticleGround deformation often precedes volcanic eruptions, and results from complex interactions between source processes and the thermomechanical behaviour of surrounding rocks. Previous models aiming to constrain source processes were unable to include realistic mechanical and thermal rock properties, and the role of thermomechanical heterogeneity in magma accumulation was unclear. Here we show how spatio-temporal deformation and magma reservoir evolution are fundamentally controlled by three-dimensional thermomechanical heterogeneity. Using the example of continued inflation at Aira caldera, Japan, we demonstrate that magma is accumulating faster than it can be erupted, and the current uplift is approaching the level inferred prior to the violent 1914 Plinian eruption. Magma storage conditions coincide with estimates for the caldera-forming reservoir ~29,000 years ago, and the inferred magma supply rate indicates a ~130-year timeframe to amass enough magma to feed a future 1914-sized eruption. These new inferences are important for eruption forecasting and risk mitigation, and have significant implications for the interpretations of volcanic deformation worldwide.This work was supported by the European Commission, Framework Program 7 (grant 282759, “VUELCO”, and grant 308665, “MEDSUV”), the Natural Environmental Research Council (NE/G01843X/1, “STREVA”, and “COMET”), the Royal Society (UF090006), the University of Bristol International Strategic Fund, and the MEXT project (Ministry of Education, Culture, Sports, Science and Technology). We thank Paul Alanis for the seismic tomography data, Keigo Yamamoto for the levelling data, and Takeshi Tameguri for the VT data. We thank Jon Blundy and Kathy Cashman for feedback on an early version of the manuscript
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