Ground Ice Distribution, Cryostratigraphy and Sedimentation in Longyeardalen Valley, Svalbard

ABSTRACT Ground ice, cryostratigraphical and sediment analyses have been done on samples from 16 boreholes covering the different landforms in the lower part of the valley Longyeardalen, where the largest settlement in Svalbard, Longyearbyen, is located. This allows the production of the first ever top 1 m permafrost ice content map showing the spatial distribution of ground ice (excess ice content) for the Longyearbyen area based on the collected ground ice data and the quaternary geology map of the valley. The valley was infilled since deglaciation with up to 45 m of mainly alluvial sediment and marine mud, whereas colluvial and till deposits with thicknesses from less than 1 m to more than 7 m are dominating the hillsides surrounding the valley. Rock glaciers and ice cored moraines are the landforms with the highest ice content, with assumed over 20% excess ice in the top metre of permafrost. Till and solifluction material has a medium ice content with 10%–20% excess ice content, whereas colluvial deposits have a low ice content with 5%–10% excess ice content. These landforms all have an active layer thickness between 1.6 and 2.2 m. Alluvial deposits in the valley floor has the lowest ice content with 0%–2% excess ice content. Pore ice, suspended ice and reticulate cryostructures dominates the ground ice types, with layered, lenticular and porphyritic cryostructures also present. Marine sediments are widespread and only found in the lower parts of the valley beneath the marine limit. These findings are important to understand and to be prepared for increased landslide risk that is expected due climate warming thawing the top of permafrost and bringing more rainfall in the near future.