A 300 Year Surge History of the Drangajökull Ice Cap, Northwest Iceland: Surge Frequency and Little Ice Age Maximum

Monday, 15 December 2014
Skafti Brynjolfsson1,2, Anders Schomacker1,3, Olafur Ingolfsson2,4 and Esther Ruth Gudmundsdottir2, (1)Norwegian University of Science and Technology, Trondheim, Norway, (2)University of Iceland, Institute of Earth Sciences, Reykjavik, Iceland, (3)Geological Museum – University of Copenhagen, Copenhagen, Denmark, (4)University Centre in Svalbard, Geology, Longyearbyen, Norway
Over the last 300 years, each of the three surge-type outlet glaciers of the Drangajökull ice cap in north-west Iceland has surged 2-4 times. There is valuable historical information available on the surge frequencies since the Little Ice Age (LIA) maximum because of the proximity of the surging outlets, Reykjarfjarðarjökull, Leirufjarðarjökull and Kaldalónsjökull to farms and pastures. We have reconstructed the surge history of the Drangajökull ice cap, based on geomorphological mapping, sedimentary studies and review of historical records. Geomorphological mapping of the glacier forefields revealed twice as many end-moraines than previously recognized. This indicates a higher surge frequency than previously perceived. A clear relationship between the surge frequency and climate cannot be established, however, surges were more frequent during the 19th century and the earliest 20th century compared to the cool 18th century and the warmer late part of the 20th century.

We have estimated the magnitude of the LIA maximum surge events by reconstruction of Digital Elevation Models (DEMs) that can be compared with modern DEMs. As reference points for the digital elevation modelling we used the recently mapped lateral moraines and historical information on the exposure timing of nunataks. During the LIA maximum surge events the outlet glaciers extended 3-3.5 km further down-valley than at present. Their ice volumes were at least 2-2.5 km3 greater than after their most recent surges in the beginning of the 21st century.