THE FLIMS ROCKSLIDE: HISTORY OF INTERPRETATION AND NEW INSIGHTS

Abstract

© 2006 Springer. Printed in the Netherlands. A chronological review illustrates the evolution of the geological interpretation of the Flims rockslide event and leads to new field evidences and dating results. Fundamental is the new dating of the rockslide event to the Boreal time of about 8,200-8,300 yBP (uncalibr.). During that time, the climate excluded any direct glacial influence on the rockslide mechanisms and on the surface morphology. All the supposedly “clear” evidences for glacial influences during or after the Flims event therefore must and can be explained by other processes. The main rockslide body has moved by a slab by slab mode with extreme deformation along the bedding planes, responsible for a high mobility. Nevertheless the sedimentary rock structure was well preserved. Despite the good stability conditions of the material the rockslide dam has broken. The extreme long runout distance of the most distal parts of the rockslide material can be attributed to secondary effects. The impact of the rockslide on the valley bottom, occupied presumably by a pre-existing lake, displaced the alluvial sediments and transported large parts of the Flims rockslide and of the nearby and older Tamins rockslide material far into the Hinterrhein valley. The displaced alluvium resedimented as “Bonaduz gravels”, a characteristic graded but unstratified sediment.