Holocene climate fluctuations and geomorphic impact of extreme events in Svalbard

Geomorphological investigations, detailed mapping and lichenometrical surveys carried out at 27 sites located in northwest and central Spitsbergen provide new insight into the history of major slush stream and debris flow events. Recurrence intervals are estimated at 80-500 yr for debris flows and ca. 500 yr for slush avalanches, which is consistent with previous estimates from other Scandinavian mountains. The life-expectancy of resulting landforms is estimated to be 2000 yr for avalanche boulder tongues which are protected from active slope processes by their distance from adjacent rockwalls. In contrast, except for some restricted sites, the fragile debris flow levees are rarely preserved for more than30-40 years and the terminal lobes do not for much more than 100 years. The short lifespan of these features is due to their small size (limited by the thinness of the active layer), by the erosive effects of spring snow avalanches and by reworking by subsequent debris flow events. Correlating extreme events and climate fluctuations in the Scandinavian mountains is difficult because of the low frequency of major slush stream events and of the brief lifetime of debris flow features. Even ii the increase of debris flow episodes after 1950 reported in the literature may partly result from improved observations, field evidence suggests that debris flows, combined with slope wash and active throughflow, have replaced pressure release and frost related mechanisms as the most prominent component of contemporary morphogenesis in arctic environments.