Abstract
Post-eruptive destabilization of volcanic edifices by gravity driven debris flows or erosion can catastrophically impact the landscapes, economies and human societies surrounding active volcanoes. In this work, we propose cosmic-ray muon imaging (muography) as a tool for the remote monitoring of hydrogeomorphic responses to volcano landscape disturbances. We conducted the muographic monitoring of Sakurajima volcano, Kyushu, Japan and measured continuous post-eruptive activity with over 30 lahars per year. The sensitive surface area of the Multi-Wire-Proportional-Chamber-based Muography Observation System was upgraded to 7.67 m^2; this made it possible for the density of tephra within the crater region to be measured in 40 days. We observed the muon flux decrease from 10 to 40% through the different regions of the crater from September 2019 to October 2020 due to the continuous deposition of tephra fallouts. In spite of the long-term mass increase, significant mass decreases were also observed after the onsets of rain-triggered lahars that induced the erosion of sedimented tephra. The first muographic observation of these post-eruptive phenomena demonstrate that this passive imaging technique has the potential to contribute to the assessment of indirect volcanic hazards.
Highlights
Post-eruptive destabilization of volcanic edifices by gravity driven debris flows or erosion can catastrophically impact the landscapes, economies and human societies surrounding active volcanoes
Volcano vegetation has already been damaged on the volcanic edifice due to deposition and transportation of volcanic ejecta
Lahar sensors are applicable to characterize these events, muography has potential to complement the conventional lahar sensors by measuring the amount of tephra deposition and topographical changes that controlling the onset of post-eruptive lahars
Summary
Post-eruptive destabilization of volcanic edifices by gravity driven debris flows or erosion can catastrophically impact the landscapes, economies and human societies surrounding active volcanoes. Continuous monitoring of the amount of sedimented volcanic ejecta would allow researchers to observe the occurrence of erosion processes before the destabilization of the volcanic edifice and onset of post-eruptive lahars. Various remote sensing techniques, such as airborne synthetic aperture r adar[18] or airborne laser s canning[19], are utilized for measurement of long-term changes (from few months to few years) in the thickness of volcanic ejecta deposits, the monitoring of short-term (from few hours to few weeks) erosion processes has not yet been realized due to the constraints on observational time and cost
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