Jökull - 01.01.2004, Blaðsíða 47

Sediment thickness and erosion rates within Hvítárvatn, central Iceland
Figure 8. Seismic profile across the Northern Flats (see Figure 2 for location), illustrating the layer-cake stratig-
raphy of this portion of the basin, and lack of disturbance. – Endurvarpslína eftir nyrsta hluta Hvítárvatns sem
sýnir beina og óhreyfða lagskiptingu í þessum hluta setfyllunnar.
crude stratigraphy in the Basal Unit. The occurrence
of faint strata in this otherwise massive unit indicates
the Basal Unit is likely a glacial deposit. However, in
some areas the Basal Unit is exclusively massive or
opaque, and probably represents bedrock at the base
of the sediment fill, for example at the Bedrock Ridge
(Figure 5).
Seismic Unit 1 has a stratified appearance char-
acterized by multiple strong internal reflections (e.g.
Figure 8). The sediment in Unit 1 has a variable thick-
ness (1.4 m to 21.0 m; Figure 9a) and fills in the un-
even basal topography, smoothing out the lake sedi-
ment surface. The thickest deposits of Unit 1 are in
the Central Deep and the thinnest deposits are on the
Bedrock Ridge, as is the case in all four units. The
rest of the lake basin is fairly evenly draped with Unit
1 sediment. The isopach map of Unit 1 suggests that
there is no diagnostic sedimentation pattern. The vol-
ume of sediment deposited in this unit is 11.7x107 m3,
and the calculated mass is 19.9x1013 g (Table 1). We
interpret Unit 1 to represent rapid sedimentation at the
margin of the main Icelandic ice cap as it receded to
the east from the lake basin in the early Holocene.
We subdivided the sediments overlying Unit 1 by
matching the acoustic signal to the major lithostrati-
graphic units visible in two cores recovered from the
Bedrock Ridge in 2002, cores 02HVT-04 and 02HVT-
05. An iceberg furrow, apparent in the bathymetric
JÖKULL No. 54 47