Hunting the missing shallow hydrothermal reservoir prior to the 2011 Shinmoe-dake, Kirishima eruption with satellite radar interferometry
Abstract
Phreatic eruptions are thought to be related to the pressure change of the subsurface hydrothermal system at shallow levels. Compared with typical magmatic eruptions, phreatic eruptions are relatively small, but can be very hazardous. However, due to the small and localized signal, geophysical monitoring is difficult. Here we show the detection of a localized ground deflation after a series of small phreatic events at Shinmoe-dake, Kirishima volcano through interferometric synthetic aperture radar (InSAR) time series analysis with ALOS-1 data from 2006-2011. The ground deflation started right after the first phreatic event at 22 August 2008 at a steady speed of ~4 cm/year with a spatial size of ~1.3 km until the last phreatic event at 10 July 2010, half a year before the VEI=2 magmatic eruption. This deformation can be well explained by the decompression of a prolate cuboid source underneath the crater with a depth of 150 m above sea level. The source location is consistent with the one from explosive earthquakes measured by the seismic array in 2011 after the magmatic eruption (Nakamichi et al., 2013, EPS). The post-eruptive inflation from ALOS-2 data during 2015-2016 reveals a slightly deeper (~100 below sea level) source at the same horizontal location. Combined with the resistivity structure from broadband magnetotelluric data (Aizawa et al., 2014, JGR), we infer the shallow source represents a zone with hydrothermal fluids at temperatures over 400 °C, which served as the end part of a magma path formed before the 2011 magmatic eruption. Our results demonstrate that high spatial resolution InSAR deformation data can be a good indicator of the subsurface pressure conditions of phreatic eruptions with pinpoint spatial accuracy.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.G31A..04Z
- Keywords:
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- 1240 Satellite geodesy: results;
- GEODESY AND GRAVITY;
- 1295 Integrations of techniques;
- GEODESY AND GRAVITY;
- 8485 Remote sensing of volcanoes;
- VOLCANOLOGY