Deglaciation of the Drangajökull ice cap, NW Iceland: preliminary results from 36Cl cosmogenic exposure dating

Monday, 15 December 2014
Anders Schomacker1,2, Skafti Brynjolfsson1, Olafur Ingolfsson3 and Jakob K Keiding4, (1)Norwegian University of Science and Technology, Trondheim, Norway, (2)Geological Museum – University of Copenhagen, Copenhagen, Denmark, (3)University of Iceland, Reykjavik, Iceland, (4)Geological Survey of Denmark and Greenland, Copenhagen, Denmark
The Drangajökull ice cap is situated over the glacially eroded Tertiary plateau basalt landscape of NW Iceland, and currently covers an area of approximately 145 km2. Late Holocene glacier marginal fluctuations are known from earlier studies, and older, well preserved moraine ridges and glacial landforms have also been mapped and described. Presently, outlet glaciers drain into the valleys Leirufjörður and Reykjarfjörður at the northwest and east side of the ice-cap, respectively. Samples for cosmogenic exposure dating (36Cl) were collected from erratics and striated bedrock in order to date the last deglaciation and to determine ages of terminal moraines.

Preliminary results suggest that the valleys were still glaciated during the early Holocene. Lateral and terminal moraines at the mouth of Leirufjörður were dated to 9-10 kyr BP, indicating the main outlets of the ice-cap were calving glaciers at that time. Erratics dated to 20-37 kyr BP indicate that at least some coastal capes and plateaux were ice-free much earlier. However, erratics from similar elevations, 300-500 m a.s.l., but located more proximal to the ice cap have average exposure ages about 10 kyr. The 20-37 kyr old erratics could also be older rocks preserved under less active or even cold based ice.