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In Northwestern and Central Spitsbergen geomorphological and botanical data were collected on slope deposits associated with infrequent meteorological events. In hillslope debris flows triggered by heavy rainfall, compact volumes of debris range from 1 to 600 m3 . Recurrence intervals of major episodes are tentatively estimated from lichenometry at 80 to 500 years. Such debris flows are widespread in Spitsbergen and induce conspicuous geomorphological effects. Nevertheless, typical levees and lobes are small-sized because of the thinness of permafrost and they rarely survive more than one century. In contrast, catastrophic slush avalanches mobilize 1300 to 7000 m3 of rock debris every 500 years, forming long boulder tongues and fans. Such accumulations can been observed in much more restricted sites. In Central Spitsbergen at least three generations of slush avalanche deposits have been identified and lichenometry suggests that such boulder tongues survive for at least 2000 years. So the geomorphic impact of sporadic slush avalanches appears much more important than the effects of recurrent spring snow avalanches which do not generate original and long-lasting landforms. Botanical studies show that investigations of saxicolous lichen communities allow more reliable chronological reconstructions than observations of phanerogamic and bryophytic vegetation cover. Rhizocarpon diameters are partly interpreted from growth curves from Baffin Island and North Alaska. The results will be refined when a curve is published for Spitsbergen. Nevertheless, recurrence intervals proposed here seem to be consistent and are fruitfully compared with previous evaluations from Swedish Lappland and Colorado.
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