Fabien Albino "How active volcanism changes topography" [31 mars 2022]

Over the past three decades, satellite radar interferometry (InSAR) has shown its ability to detect ground deformation and topographic changes associated with volcanic activity. Although InSAR has a much better spatial resolution than ground instrumentation, most of the InSAR ground deformation signals are still detected a-posteriori due to delays for acquiring and processing the data. Thanks to the Sentinel-1 mission, the near real-time monitoring of volcanic ground deformation is now achievable with InSAR, as data are freely available only 1-2 hours after acquisitions. Using the automated InSAR processing chain LïCSAR, we are able to produce time series of ground deformation to response rapidly to ongoing volcanic crisis such as the 2017 seismic crisis at Agung volcano. For this tropical volcano, we first show that the corrections of atmospheric signals in the interferograms are crucial to extract ground deformation signals. We then detect a persistent 5 km radius uplift signal of 8-10 cm on the north flank of Agung volcano prior to the 2017 November eruption. Numerical inversion of InSAR data using 3D FEM models indicates that the ground deformation signal is consistent with a deep sub-vertical magma intrusion located at midway between Agung and its neighbor, Batur caldera. 

Bi-static missions such as TanDEM-X are designed for the production of high-resolution Digital Elevation Model (DEM), as phase changes are only dependent on terrain. Although TanDEM-X DEMs have been widely used to quantify the thicknesses of lava flows, until now, the method had not been applied to pyroclastic flows, because the thin deposits are often emplaced in steep-sided valleys where DEM accuracy is expected to be low. Here, we demonstrate the benefit of TanDEM-X DEMs to characterize the spatial distribution of the topographic changes associated with the emplacement of the Pyroclastic Density Currents (PDC) during the 2018 Fuego eruption. Erosion and collapses of 30 m occurred close to the summit whereas the deposits (up to 25 meters) mainly accumulated inside the main channel of the SE flank. Analysis of the volume budget indicates that a large proportion of the PDC volume originated from the summit collapse, which confirms that bulking increases the run-out distance of pyroclastic flows and explains why the 2018 eruption was particularly destructive.