Terrestrial Radar Interferometry Monitoring During a Landslide Emergency 2016, Ghirone, Switzerland

Abstract

In early spring 2016 an exceptionally high rock-fall activity in a slope above the Village of Ghirone, Blenio-Valley Ticino, Switzerland was observed. Constant rock-fall activity was induced by toppling movement of the very thin-layered metamorphic rock. At this time, there was no information on the actual extent and the deformation rates of the landslide instability. Due to the rock-fall and failure related risk, no instrumentation on-site was possible. Local authorities then decided setting up a monitoring campaign using terrestrial radar interferometry that does not need installations in the target area. A campaign was started in the morning of 22 March 2016. Shortly after the beginning of the measurements, the extent of the active area could be determined, showing a total affected area of 5300 m2. The displacement velocity was in the range of 0.02--0.05 m/h, showing an increasing trend. Using inverse velocity extrapolations, a failure forecast could be done pointing to a potential failure event in the late afternoon of the same day. At 16:45 UTC+1 a major part of the slope failed. It was only 1/3 of the expected volume. Landslide activity continued and a second major failure was recorded in the night. The emergency campaign ended on 24 March 2016 after the deformation was decreasing to a level without imminent threat to the village. A refined post-processing of the radar data showed that the simplified real-time processing approach was suitable for the situation. Additionally, information on the 2d direction of the landslide movement could be obtained using intensity image pixel tracking technique. Finally, maps of volume differences could be created using the interferometric baseline, showing a difference of 33,900 m3 between 22 March and a later campaign performed on 31 May 2016.