Debris flow triggered by rapid snowmelt: A case study in the Gleidarhjalli area, northwestern Iceland

Debris flows in the Gleivarhjalli area in northwestern Iceland occurred after a sudden and intensive snowmelt period during 10-12 June, 1999. The area, in the northwestern part of the town of Isafjorvur, was chosen for a detailed study. Meteorological data and bedrock conditions, triggering mechanisms and geomorphological and human impacts were examined. This paper describes and emphasises the role of rapid snowmelt as a mechanism for the release of debris flows in a subpolar basaltic fjord setting. Post-event mapping of erosional and depositional landforms showed strong geomorphic impacts of debris flows and their role in mass transfer in a mountainous environment. The estimated denudation rate for the singleevent is 0.29 mm/km(2). The use of a new lichen growth curve provides relative dating of previous unreported events. Finally, the paper estimates the mean return period for debris-flow events in the Gleivarhjalli area as 4-5 years, thus constituting a serious threat to the community.