HR: 0800h
AN: H51G-0450    [Abstracts]
TI: High-Resolution Multibeam Survey of glacier-dominated lake Hvitarvatn in Central Iceland
AU: * Geirsdottir, A
EM: age@hi.is
AF: Institute of Earth Sciences and Dept. of Geosciences, University of Iceland, Askja, Sturlugata 7, Reykjavik, Iceland, 101 Iceland
AU: Miller, G H
EM: gmiller@colorado.edu
AF: INSTAAR and Dept. of Geological Sciences, University of Colorado, 1560 30th Street, Boulder, CO 80309 United States
AU: Wattrus, N
EM: nwattrus@d.umn.edu
AF: Large Lake Observatory, University of Minneapolis, 220S E 5th St, Duluth, MN 55812 United States
AU: Thors, K
EM: kthors@centrum.is
AF: Kjartan Thors Jardfraedistofa, Borgartun 18, Reykjavik, Iceland, 105 Iceland
AB: Historical records document the dramatic impact of the Little Ice Age (LIA) cooling on Iceland where in most cases the LIA moraines represent the most advanced ice margins since regional deglaciation. One of the sites reflecting this cooling is lake Hvarvatn, which sits beneath Langjökull the second largest ice cap in Iceland. Little Ice age moraines are prominent around two Langjokull outlet glaciers that calved into the lake at the peak of the LIA. Long cores recovered from the lake with the GLAD-200 drill rig in 2003 show abundant ice-rafted debris during the latest Holocene, and seismic profiles surveyed in 2001 show evidence of large-scale mass movement associated with the LIA moraines. To better evaluate the impact of LIA outlet glaciers on sedimentation in the lake we collected high-resolution multibeam bathymetric data from Hvarvatn in 2005. Combined with seismic reflection profiles and sediment core data from the lake, the multibeam data enhance our understanding of sediment distribution and processes in the lake during the Holocene and particularly during the Little Ice Age. In the primary depositional center in the lake 55 m of sediment have accumulated since deglaciation. The Little Ice Age moraines form prominent ridges into the mid lake extending approx. 1500 m away from the current margin. The deepest part of the lake is between the extant glacier margin and the LIA moraines, although also featuring several morainal ridges, which reflect the stepwise retreat of the outlet glaciers in the 20th century. Packets of sediment gravity flows not present in the more distant deeper basin characterize the lake-ward side of the moraines. Beyond the moraines several bedrock ridges protrude from the lake bottom up to ca. 30 m water depth, and they are capped by 15 m of stratified sediment. The multibeam survey shows ice-berg scour marks, some up to 5 m deep in the upper sediment layers. The relatively smooth sediment cover of the shallower basin near the southern outlet is molded into long north-south striking bedforms. These are presumably the expression of strong ice scouring of the lake bottom.The seismic reflection profiles and sediment cores from the lake suggest the most intense ice scouring and glacier calving took place during the latter part of the Little Ice Age.
DE: 1621 Cryospheric change (0776)
DE: 1807 Climate impacts
DE: 1863 Snow and ice (0736, 0738, 0776, 1827)
DE: 4558 Sediment transport (1862)
DE: 9345 Large bodies of water (e.g., lakes and inland seas) (0746)
SC: Hydrology [H]
MN: Fall Meeting 2005