The effects of topography on magma chamber deformation models: Application to Mt. Etna and radar interferometry

<p>Deformation models are an important tool to study and monitor active volcanoes. However, in many cases models are strongly simplified either due to a lack of data or for the sake of speed and computational demands. The assumption of a magma body embedded in a homogeneous elastic half-space for example neglects the topography and heterogeneous crustal structures found at some volcanoes. This oversimplification can lead to a poor representation of individual systems and result in erroneous estimates of deformation source parameters like the location and geometry of a magma chamber. &#160;The Finite Element Method (FEM) is a powerful tool to include complex heterogeneous structures and existing data sets into deformation models in order to create more realistic representations of individual volcanic systems. <br>In this study, the FEM-software COMSOL was used to build a three-dimensional elastic model of the subglacial volcano Gr&#237;msv&#246;tn, Iceland, accounting for the steep topography at the caldera rim, using a digital elevation model, as well as crustal heterogeneity. The elastic structure developed for this model is based on a density-structure, a seismic-velocity-structure and a pressure-dependent relation between the dynamic and static elastic moduli. The main feature of the elastic structure is a weak material (static shear modulus of G<sub>stat</sub>=0.6-9.8 GPa from 1 km above to 2 km below sea level) filing the caldera, which is surrounded by a stiffer, ring-like structure underneath the caldera rim (G<sub>stat</sub>=1.6-18 GPa from 1 km above to 2 km below sea level). The source parameters and geometry of forward models including the topography and elastic structure (individually and combined) were varied to fit the deformation observed at the nunatak GPS station GFUM, located at the caldera rim, during the last eruption (2011). While the topography has limited influence at the deformation at GFUM, the elastic structure requires the magma chamber to be significantly deeper than previous models suggested.</p>

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A model for gravity changes induced by lava fountaining at Mt Etna

10.5194/egusphere-egu21-9186 ◽

2021 ◽

Author(s):

Luigi Passarelli ◽

Mehdi Nikkhoo ◽

Eleonora Rivalta ◽

Corine Frischknecht ◽

Costanza Bonadonna ◽

...

Keyword(s):

Magma Chamber ◽

Foam Layer ◽

Lava Fountain ◽

Gas Accumulation ◽

Lava Fountaining ◽

Gravity Changes ◽

Gravity Measurements ◽

Mt Etna ◽

Lava Fountains ◽

Gravity Signal

<div> <p><span>Lava fountains represent a common eruptive phenomenon at basaltic volcanoes, which consist of jets of fluid lava ejected into the atmosphere from active vents or fissures. They are driven by rapid formation and expansion of gas bubbles during magma ascent. The dynamics of lava fountains is thought to be controlled by the gas accumulation in the foam layer at the top of a shallow magmatic reservoir, which eventually collapses triggering the lava fountaining. Gravity measurements taken from a location close to summit of Mt. Etna during the 2011 lava fountain episodes showed a pre-fountaining decrease of the gravity signal. The interplay between gas accumulation in the foam layer and its subsequent exsolution in the conduit has been interpreted as the mechanism producing the gravity decrease and eventually leading to the foam collapse and onset of the lava fountaining activity. Gravity measurements have proved helpful in recording the earliest phases anticipating the lava fountain episodes and inferring the amount of gas involved. However, more accurate estimates of the accumulating and ascending gas volume and total magma mass require considering the possible effect of non-spherical magma chamber geometries and magma compressibility. </span></p> </div><div> <p><span>Under task 4.4 of the H2020 NEWTON-g project, we are accomplishing a detailed study aimed to simulate the gravity signal produced in the stage prior to a lava fountain episode, through a magma chamber - conduit model. We use a prolate ellipsoidal chamber matching the inferred shape of the shallow chamber active at Mt. Etna during the lava fountain episodes, and calculate the surface gravity changes induced by inflow of new magma into the chamber-conduit system. We use a two-phase magma with fixed amount of gas mass fraction and account for magma compressibility. We find that a realistic chamber shape and magma compressibility play a key role and must be considered to produce realistic gravity changes simulations. We combine our physical model with empirical distributions of recurrence time and eruption size of the past lava fountains at Mt. Etna to stochastically simulate realistic time series of gravity changes. The final goal of this study is to develop a prediction model for the amount of magma and duration of lava fountains at Mt. Etna.</span></p> </div>

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Inversion of SAR data in active volcanic areas by optimization techniques

Nonlinear Processes in Geophysics ◽

10.5194/npg-12-863-2005 ◽

2005 ◽

Vol 12 (6) ◽

pp. 863-870 ◽

Cited By ~ 16

Author(s):

G. Nunnari ◽

G. Puglisi ◽

F. Guglielmino

Keyword(s):

Optimization Problem ◽

Ground Deformation ◽

Optimization Techniques ◽

Radar Interferometry ◽

Synthetic Aperture ◽

Inversion Problem ◽

Synthetic Aperture Radar Interferometry ◽

Volcanic Source ◽

Mt Etna ◽

Sar Data

Abstract. The inversion problem concerns the identification of parameters of a volcanic source causing observable changes in ground deformation data recorded in volcanic areas. In particular, this paper deals with the inversion of ground deformation measured by using SAR (Synthetic Aperture Radar) interferometry and an inversion approach formulated in terms of an optimization problem is proposed. Based on this inversion scheme, it is shown that the problem of inverting ground deformation data in terms of a single source, of Mogi or Okada type, is numerically well conditioned. In the paper, two case studies of inverting actual SAR data recorded on Mt. Etna during eruptions occurring in 1998 and 2001 are investigated, showing the suitability of the proposed technique.

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Radar Interferometry Time Series to Investigate Deformation of Soft Clay Subgrade Settlement—A Case Study of Lungui Highway, China

Remote Sensing ◽

10.3390/rs11040429 ◽

2019 ◽

Vol 11 (4) ◽

pp. 429 ◽

Cited By ~ 4

Author(s):

Xuemin Xing ◽

Hsing-Chung Chang ◽

Lifu Chen ◽

Junhui Zhang ◽

Zhihui Yuan ◽

...

Keyword(s):

Time Series ◽

Ground Deformation ◽

Soft Clay ◽

Velocity Model ◽

Radar Interferometry ◽

Suitable Model ◽

Seasonal Model ◽

Soft Clay Subgrade ◽

Sbas Insar ◽

Deformation Models

Monitoring surface movement near highways over soft clay subgrades is fundamental for understanding the dynamics of the settlement process and preventing hazards. Earlier studies have demonstrated the accuracy and cost-effectiveness of using time series radar interferometry (InSAR) technique to measure the ground deformation. However, the accuracy of the advanced differential InSAR techniques, including short baseline subset (SBAS) InSAR, is limited by the temporal deformation models used. In this study, a comparison of four widely used time series deformation models in InSAR, namely Multi Velocity Model (MVM), Permanent Velocity Model (PVM), Seasonal Model (SM) and Cubic Polynomial Model (CPM), was conducted to measure the long-term ground deformation after the construction of road embankment over soft clay subgrade. SBAS-InSAR technique with TerraSAR-X satellite imagery were conducted to generate the time series deformation data over the studied highway. In the experiments, three accuracy indices were applied to show the residual phase, mean temporal coherence and the RMS of high-pass deformation, respectively. In addition, the derived time series deformation maps of the highway based on the four selected models and 17 TerraSAR-X images acquired from June 2014 to November 2015 were compared. The leveling data was also used to validate the experimental results. Our results suggested the Seasonal Model is the most suitable model for the selected study site. Consequently, we analyzed two bridges in detail and three single points distributed near the highway. Compared with the ground leveling deformation measurements and results of other models, SM showed better consistency, with the accuracy of deformation to be ±7 mm.

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