Muographic Monitoring of Hydrogeomorphic Changes Induced by Post-Eruptive Lahars and Erosion of Sakurajima Volcano

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 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 m2 ; 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.

Hidden chamber discovery in the underground Hellenistic necropolis of Neapolis by muography

“…• No structural model of the nearby buildings, including their load-bearing walls, basements or other massive elements is available. • The empty space is described with a null density while the rock with the constant value of 2.0 g/cm 3 . This is a rough approximation as some underground regions are dominated by volcanic tuff, others by diluvial material while buildings basements are made of concrete.…”

Muon Imaging of Volcanic Conduit Explains Link Between Eruption Frequency and Ground Deformation

“…Improving on the earlier work (Oláh et al., 2019), threshold energies were calculated by taking into account the stochastic energy loss processes of muons (Lipari & Stanev, 1991) via Monte Carlo simulation instead of using an analytical approach based on the continuous slowing down approximation (Groom et al., 2002). Here GEANT4 framework (Agostinelli et al., 2003) was used to simulate the energy deposit of muons in silicon dioxide and parametrize the threshold energies as a function of thickness (Oláh et al., 2021).…”

“…We note that the vertical angle region of 0–150 mrad (see under the OP line) was also covered by the MMOS, but the excessive (>2.5 km) rock thickness did not allow us to measure the density in this angular region beneath the crater. The MMOS measured the muon tracks continuously from January 2017 with only a few technical stops of a few days each during installation of new MMOS modules or maintenance work (Oláh et al., 2019, 2021; Varga et al., 2020). Upgrading the MMOS allowed to observe muons across the upper plumbing system of the Minamidake crater and monitor the changes in mass density through this region which was not yet possible in our earlier work (Oláh et al., 2019).…”