Present-Day Periglacial Environments in Central Spitsbergen, Svalbard

抄録

This report overviews observations on periglacial geomorphology in central Spitsbergen, which have been undertaken by the Japanese geomorphological groups. Focus is given to permafrost-related processes, including solifluction, thermal contraction cracking and pingo growth. Annual freeze-thaw action dominates the ground, resulting in extensive occurrence of solifluction and shallow landslides on soil slopes. Solifluction shows low surface velocity but large volumetric transport, which respectively reflects infrequent diurnal frost creep and deep movement. The latter partly originates from plug-like flow in the basal active layer, where permafrost temperature is low and muddy sediment is thick. Non-sorted polygons with a wide range of diameters develop on lowlands. In colder inland terrains, large polygons (>7m) have ice wedges, whereas smaller polygons have only soil wedges or cracks confined to the active layer. Significant ice-wedge cracking occurs during rapid and intensive cooling in midwinter. In warmer coastal terrains, ice wedges are not common even below large polygons, because higher winter temperature can produce only shallow cracks. Open-system pingos occur in valley bottoms and near shores. Some pingos are still growing under a low artesian pressure fed by constant supply of sub-permafrost water. Following lateral river erosion, a new frost mound emerged at a side of a pingo, reaching 3m high during three years. The observations demonstrate that central Spitsbergen is situated in a High Arctic but relatively warm permafrost environment. The transitional condition between cold and warm permafrost allows diverse periglacial features to coexist within a small area. Even minor climatic change can switch the two thermal regimes, affecting significantly the type and magnitude of periglacial processes.