2003 Seattle Annual Meeting (November 2–5, 2003)

Paper No. 9
Presentation Time: 3:30 PM


PRINCIPATO, Sarah M.1, GEIRSDÓTTIR, Áslaug2, ANDREWS, John T.3 and JÓHANNSDÓTTIR, Gudrún2, (1)Enivornmental Studies, Gettysburg College, 300 N Washington St, Box 2455, Gettysburg, PA 17325, (2)Department of Geosciences, Univ of Iceland, Reykjavik, 101, Iceland, (3)INSTAAR and Geological Sciences, Univ of Colorado, CB 450, Boulder, CO 80309, principa@colorado.edu

The late glacial and deglacial history of Vestfirdir, NW Iceland is interpreted from terrestrial geomorphic mapping, marine cores, and seismic studies. Understanding the timing of deglaciation is complicated by a lack of dateable organic material, the uncertainties associated with interpretation of diamictons, and ambiguities in radiocarbon dating. New 36Cl exposure ages of boulders and bedrock surfaces suggest that at least part of the coastal uplands were ice free by 20.5 cal ka B.P. Deglaciation of the valleys followed. Boulders from the crests of end moraines in the valley of Laugaland correspond to a mean age of 14.6±0.8 cal ka B.P. (n=4), and the outermost moraine in Kaldalón has an average age of 10.6± 0.9 cal ka B.P. (n=3).

Tephrochronology provides a link between the terrestrial and marine sequences around Vestfirdir. The Vedde tephra (~12 cal ka B.P.) is present in some offshore cores, but it is absent from terrestrial sites, suggesting that its distribution might provide a constraint on ice extent. The Saksunarvatn tephra (10.2±0.6cal ka B.P.) is present in at least three terrestrial locations on eastern Vestfirdir and in many cores from the fjords and shelf, which is confirmed by geochemical analyses and radiocarbon dating. Its presence further constrains early Holocene ice extent. Ice rafted debris in cores from the inner shelf and fjords ceases by ~9.6 cal ka B.P., suggesting that the ice had withdrawn from the fjord heads by this time.

In the northwest and southeast regions of the study area, distinct erosive glacial landforms including, cirques, arêtes, horns, and u-shaped valleys are present. A GIS analysis of these features is combined with the calculation of lake-density. In general, there is an inverse relationship between lake density and presence of alpine-style, erosive glacial landforms. Lake density is the highest in the regions of former ice centers over Glama and on the upland from Steingrimsfjardarheidi to Ofeigsfjardarheidi. This contrasts with findings from the Canadian Arctic, where there is no erosion underneath the position of former ice divides. Possible explanations for the lake density distribution on Vestfirdir include ice divide migration, erosion under the ice divide, or incorrect placement of the ice divide.