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Rust, Alison C.
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Rust, Alison C.
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- PublicationOpen AccessNumerical models for ground deformation and gravity changes during volcanic unrest: simulating the hydrothermal system dynamics of a restless caldera(2016)
; ; ; ; ; ; ; ;Coco, A.; Bristol University ;Gottsmann, J; Bristol University ;Whitaker, F; Bristol University ;Rust, A; Bristol University ;Currenti, G; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia ;Jasim, A; Bristol University ;Bunney, S; Bristol University; ; ; ; ; ; Ground deformation and gravity changes in restless calderas during periods of unrest can signal an impending eruption and thus must be correctly interpreted for hazard evaluation. It is critical to differentiate variation of geophysical observables related to volume and pressure changes induced by magma migration from shallow hydrothermal activity associated with hot fluids of magmatic origin rising from depth. In this paper we present a numerical model to evaluate the thermo-poroelastic response of the hydrothermal system in a caldera setting by simulating pore pressure and thermal expansion associated with deep injection of hot fluids (water and carbon dioxide). Hydrothermal fluid circulation is simulated using TOUGH2, a multicomponent multiphase simulator of fluid flows in porous media. Changes in pore pressure and temperature are then evaluated and fed into a thermo-poroelastic model (one-way coupling), which is based on a finite-difference numerical method designed for axi-symmetric problems in unbounded domains. Informed by constraints available for the Campi Flegrei caldera (Italy), a series of simulations assess the influence of fluid injection rates and mechanical properties on the hydrothermal system, uplift and gravity. Heterogeneities in hydrological and mechanical properties associated with the presence of ring faults are a key determinant of the fluid flow pattern and consequently the geophysical observables. Peaks (in absolute value) of uplift and gravity change profiles computed at the ground surface are located close to injection points (namely at the centre of the model and fault areas). Temporal evolution of the ground deformation indicates that the contribution of thermal effects to the total uplift is almost negligible with respect to the pore pressure contribution during the first years of the unrest, but increases in time and becomes dominant after a long period of the simulation. After a transient increase over the first years of unrest, gravity changes become negative and decrease monotonically towards a steady-state value. Since the physics of the investigated hydrothermal system is similar to any fluid-filled reservoir, such as oil fields or CO2 reservoirs produced by sequestration, the generic formulation of the model will allow it to be employed in monitoring and interpretation of deformation and gravity data associated with other geophysical hazards that pose a risk to human activity.277 148 - PublicationOpen AccessPhreatic eruptions at crater lakes: occurrence statistics and probabilistic hazard forecastPhreatic eruptions, although posing a serious threat to people in crater proximity, are often underestimated and have been comparatively understudied. The detailed eruption catalogue for Ruapehu Volcano (New Zealand) provides an exceptional opportunity to study the statistics of recurring phreatic explosions at a crater lake volcano. We performed a statistical analysis on this phreatic eruption database, which suggests that phreatic events at Ruapehu do not follow a Poisson process. Instead they tend to cluster, which is possibly linked to an increased heat flow during periods of a more shallow-seated magma column. Larger explosions are more likely to follow shortly after smaller events, as opposed to longer periods of quiescence. The absolute probability for a phreatic explosion to occur at Ruapehu within the next month is about 10%, when averaging over the last 70 years of recording. However, the frequency of phreatic explosions is significantly higher than the background level in years prior to magmatic episodes. Combining clast ejection simulations with a Bayesian event tree tool (PyBetVH) we perform a probabilistic assessment of the hazard due to ballistic ejecta in the summit area of Ruapehu, which is frequently visited by hikers. Resulting hazard maps show that the absolute probability for the summit to be affected by ballistics within the next month is up to 6%. The hazard is especially high on the northern lakeshore, where there is a mountain refuge. Our results contribute to the local hazard assessment as well as the general perception of hazards due to steam-driven explosions.
312 97 - PublicationOpen AccessMeMoVolc consensual document: a review of cross-disciplinary approaches to characterizing small explosive magmatic eruptions(2015)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;; ; ; ; ; ;; ; ; ; ; ;; ; ; ; ; ; ; ; ; ; ; ;; ; ; ; ; ; ; ; ;; A workshop entitled “Tracking and understanding volcanic emissions through cross37 disciplinary integration: A textural working group.” was held at the Université Blaise Pascal (Clermont-Ferrand, France) on the 6-7th November 2012. This workshop was supported by the European Science Foundation (ESF). The main objective of the workshop was to establish an initial advisory group to begin to define measurements, methods, formats and standards to be applied in the integration of geophysical, physical and textural data collected during volcanic eruptions so as to homogenize procedures to be applied and integrated during both past and ongoing events. The working group comprised a total of 35 scientists from six countries (France, Italy, Great Britain, Germany, Switzerland and Iceland). The group comprised eleven advisors from the textural analysis field, eleven from deposit studies, seven geochemists and six geophysicists. The four main aims were to discuss and define: 1) Standards, precision and measurement protocols for textural analysis; 2) Identify textural, field deposit, chemistry and geophysical parameters that can best be measured and combined; 3) Agree on the best delivery formats so that data can be sheared between, and easily used by, each group; 4) Review multi-disciplinary sampling and measurement routines currently used, and measurement standards applied, by each community. The group agreed that community-wide cross-disciplinary integration, centered on defining those measurements and formats that can be best combined, is an attainable but key global focus. Consequently, we prepared a final document to be used as the foundation for a larger, international textural working group to serve as the basis of fully realizing such a pandisciplinary goal in volcanology. Thus, we here report our initial conclusions and recommendations.605 267