Volcano deformation in different tectonic settings using InSAR and modeling

Abstract

Magma movements from reservoir toward the surface are responsible for volcanic unrest. Unrest can culminate with an eruption or the volcanic system can return to quiescence if magma fails to reach the surface. However, magma movements produce effects that can be observed and measured at the surface: seismicity, ground deformation and gas emission; monitoring these geo-indicators at unresting volcanoes allow to evaluate the probability of occurrence of an eruption and which type of eruption is expected in order to define the hazard. It is also necessary to monitor these geo-indicators between unrest periods in order to define the background behavior of the volcano. Space geodesy techniques allow to monitor ground deformation. In particular InSAR technique allow to measure mm-scale surface displacements over time spans of days to years and over wide areas. Inverting these data using analytical or numerical models allow to obtain information about the deformation source. I studied ground deformation using InSAR technique and I evaluated the deformation sources parameters with analytical models at two magmatic systems located in extensional and compressional settings. The first target area is Dallol, a proto-volcano located along the Afar rift axis; here I studied deformation associated to the October 2004 dyke intrusion that highlighted the presence of magma at shallow depth below the hydrothermal field, in an area without evidence of volcanism, and provided new information about the extension mechanisms along rift segments. Furthermore, I produced ground deformation time series between 2005-2010 for an area that cover Dallol and the Erta Ale Ridge, another volcanic segment located along the Afar rift axis. This data suggest that Dallol subsided after the dyke intrusion whereas Alu Dalafilla and Erta Ale caldera uplifted. Data inversion for the subsidence at Dallol suggest the presence of a shallow deflating source. The second target area is Aso Caldera that belongs to the Japanese South West volcanic arc. I studied ground deformation between 1993-2011 using different SAR sensors. I observed small displacement associated to eruptions. In particular I inverted InSAR data for a subsidence period 2 between 1996-1998 caused by a deflation of a deep magmatic source just after the last phreato-magmatic eruption. Finally I compared results on the magmatic sources at Dallol and Aso with those of volcanic systems located along divergent plate boundary and intra-arc volcanoes to verify if there are similarities between volcanoes that belong to the same tectonic setting.