From major caldera subsidence to quiescence at the world's top volcanic degassing source (Ambrym, Vanuatu): the influence of regional tectonics
Abstract
In the past 30 years, magmatic activity at the basaltic volcano of Ambrym (Vanuatu), which hosts a 12-km-diameter caldera and two 20-km-long rift zones, has been characterized by intra-caldera strombolian activity restricted to the semi-permanent lava lakes. Little is known about the interaction between the rift zones and caldera of this volcano, due to its remote location (lack of instrumentation) and the absence of rift zone intrusions since the last event in 1937. Using satellite remote sensing of deformation, gas emissions and thermal anomalies, combined with seismicity and ground observations, we show that in December 2018 an intra-caldera eruption preceded more than 2.5 m of caldera-wide subsidence. In particular, InSAR ground deformation measurements during this eruption show a lateral migration of >0.4 cubic kilometers of magma from within the caldera to more than 20 km into the SE rift zone, extinguishing the lava lakes, and feeding a submarine eruption.
The extinction of the five lava lakes was associated with multiple crater collapses, ash clouds, and followed by a drastic decrease in degassing. We also use InSAR ground deformation measurements from ALOS-2, Sentinel-1, and Cosmo-SkyMed to track the decaying subsidence signal during the weeks following the rift zone intrusion, concluding that the submarine eruption lasted for more than a month. A similar event has not occurred at Ambrym since the 1930's. This is thus the first opportunity to investigate the mechanism of caldera formation and development, driven silently and episodically by magma emplacement into the volcano's well-defined rift zone. We propose that the stress induced by the D'Entrecasteaux Ridge collision against the New Hebrides arc drives the persistence of Ambrym's caldera-rift system.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.V51A..03S
- Keywords:
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- 8419 Volcano monitoring;
- VOLCANOLOGY;
- 8439 Physics and chemistry of magma bodies;
- VOLCANOLOGY;
- 8440 Calderas;
- VOLCANOLOGY;
- 8488 Volcanic hazards and risks;
- VOLCANOLOGY