IDYST Seminar: "Rock glacier activity and distribution in the semi-arid Andes of Chile and Argentina detected from dInSAR"
Rock glaciers in the semi-arid Central Andes of Chile and Argentina (approx. 28-34°S) are widespread elements of the high mountain landscape. The presence and activity of this type of ice-rich creeping permafrost have potential consequences for the hydrological functioning of the watersheds as well as for the stability of the debris slopes. The assessment of the activity status of those landforms, which is of crucial importance for further studying their sensitivity to climate- and human-induced impacts, is generally done thanks to expert knowledge. Based on visual interpretation of optical imagery, sometimes combined with in situ observations, this approach induces subjectivity-related biases and a limited reliability of the analysis. To overcome those limitations, the differential radar interferometry (d-InSAR) can be used to produce interferograms that can, under certain assumptions, be interpreted in terms of surface changes over large areas and for periods covering a few days to some months. In our work, we used 17 TerraSAR-X images acquired between April 2014 and January 2015 over two zones of the Central Andes (Cordón del Plata: 33°S; El Tapado: 30°S) to generate 15 interferograms (8 in descending mode and 7 in ascending mode) with a pixel size of 10 m, at 11, 22 and 33-day intervals and a baseline of the SAR pairs ranging from a few meters to some hundreds of meters. The d-InSAR dataset has been locally validated thanks to in situ dGPS measurements (Tapado rock glacier site) performed between 2010 and 2014. We were able to evidence several areas of distinct velocity patterns, depending on the glacio-geomorphological activity (glacier/debris-covered glacier/rock glacier) for which a clear d-InSAR signal could be associated, as also observed in other high mountain sites in the Alps where such approach has been previously used. The dataset covers a surface of almost 5100 km², with a median elevation of 4120 m asl (25-75% quantiles = 3464-4606 m asl) and several hundreds of fresh rock glaciers inventoried. We present here a synthetic overview of the regional rock glacier's activity based on the interpretation of the TSX interferograms. The kinematic characteristics of some interesting rock glaciers is further presented and discussed, especially in terms of the correspondence between geomorphological observations and d-InSAR signal, as well as future research directions.
Tuesday 14 November 2017 (17h15 - 18h00) - Géopolis - 1620