"On-zone" and "off-zone" geomorphic features for multirisk assessment related to slope dynamics in the Icelandic fjords

Abstract

Geomorphological studies are a useful tool for risk analysis in mountainous areas, as most of the vulnerable settlements are located within the deposit zones of various processes acting on slopes. Risk assessment related to slope dynamics in the Icelandic fjords, such as snow avalanches and debris flows, often consider the geomorphic characteristics "on-zone", i.e. in the slope above the inhabited area, from the starting zone to the first houses. However, most of the useful extreme runout distance features are no longer visible in built areas, as slope deposits have been removed from the residential areas during the building time, and later on. Indeed, these landforms are of great significance in risk analysis. Therefore, inquiries into "off-zone" geomorphic evidences, in unspoiled areas with similar lithologic, topographic and meteorologic conditions to inhabited surroundings, reveal the missing information "on-zone". Based on field investigations and using dendrogeomorphologic opportunities, it especially indicates the potential runout distance of slope dynamics that are lacking in built areas. Consequently, by transferring the data from unspoiled areas to inhabited areas, geomorphic investigations are an indicator for damage potential analysis in areas subjected to devastating multi-slope dynamics. Furthermore, the specific topography of the Icelandic fjords is prone to unexpected risk, such as local snow-avalanche induced tsunamis. This process has not yet been taken in account in risk analysis, originating "off-zone". However, it caused severe damages and loss of lives during the last century in the Icelandic fjords.