Jökull - 01.01.2004, Page 45

Sediment thickness and erosion rates within Hvítárvatn, central Iceland
Figure 6. Seismic profile from the Central Deep (see Figure 2 for location), illustrating the 5 primary seis-
mostratigraphic units. In the Central Deep, Unit 4 contains evidence of ponded sediment. In this section three
lenses (a to c) of acoustically transparent sediment within Unit 4 are interpreted to be sediment gravity flows
originating along the over-steepened and unstable LIA moraines of Suðurjökull and Norðurjökull. This inter-
pretation was verified for unit a in core 02HVT-06. – Endurvarpslína frá miðdæld Hvítárvatns (sjá staðsetningu
á 2. mynd). Eining 4 sýnir nokkur aurflóð (a til c) sem myndast hafa vegna óstöðugleika við framrás Suðurjökuls
og Norðurjökuls. Hægt er að greina aurflóðin í setkjarna 02HVT-06.
ure 5), and scour marks are present in the shallow por-
tions of the Southern Shallows. Scours are not seen in
seismic lines at water depths >35 m, suggesting the
maximum keel depth of icebergs was <35 m.
The Northern Flats comprises a long, gently slop-
ing shelf in northeastern Hvítárvatn (Figures 3 and 8).
The sediments do not appear to be affected strongly
by sediment gravity flows from the prograding delta
to the east or the steep sides of the northern margin of
the lake. The seismic reflectors in this area are rela-
tively flat. The sediment is approximately 25 m thick.
We interpret this to be the best area to obtain an undis-
turbed extended record of Holocene sediment deposi-
tion in Hvítárvatn that rely on proxies other than lam-
inae thickness.
Seismic units linked to lithostratigraphy
Five seismostratigraphic units are identified in the
seismic profiles. To subdivide the seismic record, we
rely on systematic differences in the acoustic charac-
ter of the sediment fill, and on a direct comparison of
JÖKULL No. 54 45