Hummocky moraine landscape on Jæren, SW Norway—implications for glacier dynamics during the last deglaciation

Abstract

The Jæren area, SW Norway, can topographically be divided in two regions, Lågjæren and Høgjæren. Høgjæren is a plateau > 120 m a.s.l. covered by Quaternary sediments. The stratigraphically youngest deposit is a sandy diamicton, which accumulated in ridges and hummocks during the last deglaciation. This hummocky moraine landscape has previously been interpreted as the record of a stagnant glacier. Detailed morphological mapping and sedimentological investigations have revealed that various glacigenic elements exist and dominate different areas of the Høgjæren plateau. Glacigenic elements formed by an active wet-based glacier characterize the southern central hummocky area and include marginal moraine ridges and drumlins, while circular moraine ridges and glaciofluvial features formed in a stagnant glacial regime dominate the northern central hummocky area. The distribution of glacigenic elements within the hummocky moraine landscape shows that active and stagnant ice coexisted on Høgjæren during the last deglaciation, and that actively flowing ice was focused through eastward extending valleys. It is not possible to determine whether ice flow was kept active in the southern area throughout the deglaciation or if the glacier was reactivated. A possible readvance is suggested to have happened simultaneous to a readvance previously suggested based on the morphology on Lågjæren.