ANALYSIS OF DISPLACEMENTS OF THE LAVA FLOW SURFACE OF THE 2012–2013 TOLBACHIK FISSURE ERUPTION BY SAR INTERFEROMETRY
Résumé
The Tolbachik fissure eruption, named after the 50th anniversary of the Institute of Volcanology and Seismology of the Far East Branch RAS (TFE-50), occurred from November 27, 2012 to September 15, 2013 in the area of the Plosky Tolbachik volcano. During the eruption, a large lava field was formed with area of about 45.8 km2 and total lava volume ~0.6 km3. The application of the method of persistent scatterers to the satellite Sentinel-1A SAR images made it possible to estimate the rates of the lava field surface displacement in 2017–2019. The surface mainly subsides in the direction from the satellite, with the exception of the periphery of the Toludsky and Leningradsky lava flows, where small uplifts are observed. Assuming that the displacements occur mainly along the vertical, the maximum average displacement rates for the snowless periods of 2017–2019 were 285, 249, and 261 mm/year, respectively. The maximum subsidence was registered in areas with the maximum lava thickness on the Leningradsky and Toludsky lava flows.
The estimates of the thermal subsidence of the lava surface during its cooling are generally close to the subsidence values over a significant part of the lava field, but in a number of areas in its central part, the actual subsidence values are several times higher. According to the thermal model when lava thickness exceeds 40 m, there can be a hot moving layer under the solidified surface, which temperature exceeds 2/3 of the melting point. Since on the Leningradsky flow, the maximum subsidence is observed in the area of the fissure along which the eruption took place, it can be assumed that the retreat of lava down the fissure contributed to the observed displacements of the flow surface. Subsidence can also be associated with degassing of the molten part of the lava, compaction of rocks under the weight of the overlying strata and the migration of non-solidified lava under the hard cover.
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