Spatial distribution of rockslide deposits and their morphological features suggest timing and palaeo-environmental conditions for rock slope failures in innerdalen and INNFJORDDALEN, MØRE OG ROMSDAL COUNTY, WESTERN NORWAY

Abstract

Rock avalanches dropping into a fjord or lake, initiating displacement waves or damming narrow valleys, are severe hazard scenarios in glacial overprinted mountain areas and have strong influence on the quaternary valley development. Several investigations show, that the collapse of a rock avalanche increases the probability for prospective similar events at the same rock slope. Moreover, data for the Storfjord area in Western Norway indicates that catastrophic rockslides were more frequent during late Pleistocene than in Holocene. This study is to test these hypotheses, to reconstruct the palaeo-environmental conditions of multiple landslide deposits, and to study the effect of rock avalanches on decaying ice bodies and landforms influenced by isostatic rebound. For investigation, the two valleys of Innerdalen and Innfjorddalen in Western Norway were chosen, where multiple landslide deposits have developed on the valley floor. Its spatial and temporal distribution is studied by detailed field investigations, including morphological and sedimentological analyses. In Innerdalen glacial and postglacial rock avalanches have occurred, whereas the first was partly deposited on the decaying ice body. In Innfjorddalen several post glacial rock avalanches occurred, whereas the first was deposited on highly water saturated valley fill sediments. In both valleys distinct morphological features have developed.