Deformation of a Basaltic Shield Volcano: Uplift, Trapdoor Faulting, Eruption Triggering and Subsidence associated with the 2018 eruption of Sierra Negra Volcano, Galapagos
Abstract
Recent well monitored eruptions of basaltic to basaltic andesite calderas have greatly improved our observations of the mechanisms of caldera formation and growth. The 2000 Miyakejima (piecemiel), 2007 Piton de la Fournaise (trapdoor), 2014 Bardarbunga (trapdoor) and 2018 Kilauea (piecemiel) volcano, eruptions were stunning examples of caldera formation related to withdrawal of magma from sub-volcanic reservoirs. Sierra Negra, Galapagos Islands, Ecuador is a large (40 km diameter) basaltic shield volcano with a large (9.5 by 7.5 km) summit caldera. Historical eruptions at Sierra Negra were preceded by extensive uplift of the caldera floor, deformation on intra-caldera trapdoor and ring faults, and eruption along ring faults and through the flanks of the volcano. These eruptions have resulted in net uplift of the caldera, instead of the subsidence observed at the volcanoes listed above. The penultimate eruption of Sierra Negra was the 2005 VEI 3, which erupted ~0.15 km3 of basaltic lavas. This eruption was preceded by ~4.9 m of vertical uplift of the caldera floor since at least 1992, and was followed by rapid co-eruptive deflation of approximately the same amount. Modeling of the pre-eruptive inflation signal observed in GPS and InSAR data indicate a pressurized magmatic body (sill) at 2 km depth. The eruption was also preceded by trapdoor faulting events along intra-caldera faults six-months and ~3 hrs prior to the eruption. We present geodetic (cGPS and tilt) and seismic observations of the June 26 - August 30, 2018 eruption of Sierra Negra volcano indicating extensive pre-eruption uplift of the caldera (>5.2 m), seismicity on intracaldera trapdoor faults, including co-seismic uplift of a trapdoor fault during a M5.3 earthquake that preceded the eruption by ~8 hrs, magma injection, rapid co-eruptive subsidence and trapdoor faulting earthquakes, and post-eruptive re-inflation. As observed in previous eruptions, the 2018 eruption resulted in net growth uplift of the caldera floor.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.V11B..01L
- Keywords:
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- 1295 Integrations of techniques;
- GEODESY AND GRAVITY;
- 7280 Volcano seismology;
- SEISMOLOGY;
- 8178 Tectonics and magmatism;
- TECTONOPHYSICS;
- 8485 Remote sensing of volcanoes;
- VOLCANOLOGY