Inter-eruptive spatiotemporal variation of caldera contraction on Miyakejima volcano revealed by PALSAR and PALSAR-2 time-series data

Monitoring caldera deformation helps improve the understanding of pressure conditions within a volcanic conduit beneath the caldera. Miyakejima volcano in Japan experienced a caldera collapse associated with an eruption in 2000, which included dike intrusions. Although a previous InSAR study suggested deceleration of caldera subsidence in 2009, few observations on the caldera deformation have been reported. We applied SAR time-series analysis to Phased Array-type L-band Synthetic Aperture Radar (PALSAR) and PALSAR-2 data to investigate spatiotemporal variations of ground deformations at Miyakejima volcano during 2006-2011 and 2014-2019. The spatial characteristics of the caldera contraction transformed from a concentric pattern into a north-south asymmetric pattern in mid-2009, implying migration of a deformation peak from the central aspect to the southern edge of the caldera floor. These peaks of the caldera contraction are located at the initial position of the caldera collapse on the central caldera floor, and at an active fumarole on its southern edge. The asymmetric pattern of the caldera contraction continued during 2014-2019 based on PALSAR-2 data. Using the results of numerical modeling and earthquake distribution beneath the caldera, we interpreted that the continuous asymmetric caldera contraction was driven by brittle failures induced by continuous hydrothermal alterations. Although a previous study proposed deceleration of caldera subsidence in mid-2009, we believe that their findings revealed only a snapshot of the spatial variation of the caldera contraction detected in this study.

Automated summary

This study used synthetic aperture radar (SAR) data to analyze the ground deformation at Miyakejima volcano and identified asymmetric collapse patterns. It was found that continuous brittle failures induced by hydrothermal alterations were responsible for the ongoing collapse.