Jökull - 31.12.2001, Blaðsíða 56

Guðmundsson et al.
Figure I. Iceland, the main sandur areas in South Iceland, glaciers and the survey area. The area shown on
Figures 2 and 5 is framed. - Helstu sandar á Suðurlandi. Kassinn afmarkar svœðið á 2. og 5. mynd.
SURVEY AREA
Skeiðarársandur (Figures 1 and 2) lies between Lóma-
gnúpur in the west and the district of Öræfi in the east.
To the north is the broad lobe of Skeiðarárjökull, one
of the largest outlets of Vatnajökull. Skeiðarárjökull
has retreated 2-3 km from its Little Ice Age maximum
extent, reached in the nineteenth century (Jóhannes-
son, 1984; Sigurðsson, 1995), leaving a moraine com-
plex to the south of the present location of the ter-
minus. Three main rivers drain from Skeiðarárjök-
ull across the sandur. These are Núpsvötn-Súla in
the west, Gígjukvísl on the central western part and
Skeiðará in the east. Skeiðarársandur has over several
centuries been swept by jökulhlaups from Grímsvötn
in Vatnajökull that have occurred on average at 5 to
10 year intervals (Þórarinsson, 1974, Guðmundsson et
al., 1995). Some of these jökulhlaups have been very
large, with peak discharges of 40-50x 103 m3s_1; in-
undating most of the sandur and bringing abundant
sediments that have been deposited on the sandur and
in the sea (Þórarinsson, 1974; Russell and Knudsen,
1999; Smith et al., 2000; Maria et al., 2000; Snorra-
son et al, 2002). Thus Skeiðarársandur is, at least
partly, built up of repeated large magnitude jökul-
hlaups (Maizels, 1991).
In 1991 a small outcrop of crystalline bedrock
was observed close to the terminus of Skeiðarárjök-
ull, near the water divide between the rivers Gígju-
kvísl and Sæluhúsavatn. This outcrop is now covered
by sediments from the 1991 surge of Skeiðarárjök-
ull and the 1996 jökulhlaup (Óskar Knudsen, pers.
comm., 2002).
SEISMIC MEASUREMENTS
In 1997 three seismic profiles were surveyed close to
the glacier Svínafellsjökull. Svínafellsjökull has re-
treated several hundred metres from the moraine com-
plex formed during the Little Ice Age (LIA) maxi-
mum. Two of the profiles were located on the allu-
vium plain west of the terminal moraines while the
54 JÖKULLNo. 51