Jökull - 01.01.2004, Page 38

Jessica Black et al.
Figure 1. A Landsat 7 satellite image of central Iceland, from the year 2000, showing Langjökull and Hvítárvatn,
the largest lake at the perimeter of the ice cap. – Gervitunglamynd af Langjökli og Hvítárvatni.
sequences, and 4) the ice-cap profile of Langjökull
is relatively flat; consequently, small changes in
the equilibrium line altitude (ELA) results in large
changes in accumulation area. These changes are ex-
pected to produce large oscillations in outlet glaciers,
which will impact sedimentation in Hvítárvatn. Two
of Langjökull’s outlet glaciers that advanced into the
lake during the late Holocene disturbed the sediment
distribution in the lake. Consequently, before attempt-
ing to recover sediment cores from Hvítárvatn, the
character of the sediment needed to be defined.
In this paper we document more than 100 km of
seismic profiling across the main depositional basin
in Hvítárvatn, and present the interpretation of the
seismic reflection data. Five distinctive seismostrati-
graphic units can be mapped across the Hvítárvatn
basin. Isopach maps of sediment thickness for each
unit, derived using GIS software, show that sediment
is not uniformly distributed across the basin. These
maps imply substantial changes in the dominant sedi-
ment sources during the Holocene. Sediment volume
inferred from the seismic data, combined with sus-
pended load and discharge records from the out-flow
stream, provide constraints on average Holocene ero-
sion rate across the Hvítárvatn catchment.
38 JÖKULL No. 54