Model of Surface Subsidence of Pyroclastic Flow: the August 29, 2019 Shiveluch Volcano Eruption, Kamchatka

Abstract—Possible causes of surface subsidence of the pyroclastic flow formed on the slopes of the Shiveluch volcano, Kamchatka, during the eruption on August 29, 2019 are studied. A series of InSAR (Interferometric Synthetic Aperture Radar) images from acquisitions by the European Space Agency Sentinel-1A satellite for a period from May to October in 2020 and 2021 are used to construct maps of the displacement rates of the volcano surface. An area with large subsidence coinciding with the area of pyroclastic flow is revealed on the volcano’s southeastern slope. The maximum subsidence rates are found to be 385 mm/year in 2020 and 257 mm/year in 2021. The thickness of the pyroclastic deposits is estimated from radar images for 2020. The dependence of the subsidence rate on flow thickness has a significant scatter with a rather high correlation coefficient (‒0.69). A thermomechanical model has been constructed, which takes into account compaction of the deposited material due to changes in porosity and density over time. According to the model, to explain the dependence of the subsidence rate of the flow surface on the thickness of rocks, it is sufficient to assume that in addition to surface subsidence, flow cooling was accompanied by a small change in porosity occurred, which, depending on the initial flow temperature, made up to 1.5 to 1.7% for the period from 2019 to 2021. The scatter in the relationship “subsidence rate versus flow thickness” is explained for by the erosion of pyroclastic deposits.