LiDAR and geomorphic characterisation of landslide-induced liquefaction deposits in the eastern Swiss Alps

The Flims rockslide, located in the eastern Swiss Alps, is the largest postglacial landslide in Europe. About 9400 years ago, 10-12 km3 of limestone detached from the north wall of the Vorderrhein River valley and rapidly fragmented, impacting and liquefying approximately 1 km3 valley-fill sediments. A slurry of liquefied sediment, the “Bonaduz gravel”, traveled 16 km downvalley and up the Hinterrhein valley, carrying huge fragments of rockslide debris (tumas). The sheet of liquefied sediments is >60 m thick and fines upward from cobble gravel at the base to sand at the top. Another large, slightly older rockslide (Tamins rockslide) blocked the Vorderrhein River and impounded a lake into which the Flims rockslide fell, increasing the mobility of the Bonaduz flow and affecting its flow path. I used field observations and a LiDAR-based DEM to map the Bonaduz gravel and infer its mechanism of emplacement.