Jökull - 01.01.2012, Síða 159

Surge fingerprinting of cirque glaciers
Figure 4. Teigarjökull during the 1971 surge. The glacier is about 1200 m long on the photograpm but its
length increased from about 1100 to 1500 meters during its only reported surge. Photo:/Ljósm. Helgi Hall-
grímsson, July 1971. – Teigarjökull í hlaupfasa sumarið 1971. Á myndinni er jökullinn um 1200 m langur en í
framhlaupinu lengdist hann úr u.þ.b. 1100 m í um 1500 m.
glaciers of Icelandic ice caps. Periodically, exhaustive
rock falls from the steep mountain slopes above many
of the glaciers cause coarse-grained and angular rock
fragments to be prominent in the glacier forefields.
Because debris from rock fall lands on the ice sur-
face close to the equilibrium line altitude (ELA) of the
glaciers, most of the debris is transported englacially
and supraglacially rather than basally. As the glacier
melts in the ablation area, englacial sediment becomes
exposed at the surface and, together with supraglacial
sediments, gradually covers the glacier margin. Fin-
ally, after all the glacial ice has melted, most of the
subglacial sediments are blanketed by the englacial
and supraglacial drift (Benn and Evans, 2010; Ham-
brey et al., 1999), This process explains why coarse
grained and angular rock fragments are so prevalent in
the Búrfellsjökull and Teigarjökull forefields as well
as in front of most cirque glaciers on the Tröllaskagi
peninsula.
Sediments at Búrfellsjökull
Sediments from the 1912 surge of Búrfellsjökull are
exposed in a small river-cut section about 50 m from
the present glacier margin. Three distinct sediment
layers are present (Figure 5). The lowermost layer is
20–30 cm thick, brownish, and very compact. It is
a diamicton with a silty to sandy matrix, supporting
numerous subangular pebbles and cobbles. Its upper
contact is sharp and erosional. Layer 1 is interpreted
to be subglacial till formed during a surge of Búrfells-
jökull, most likely in 1890.
Figure 5. Three different diamict layers can be seen
in river-cut sections by the present margin of Búrfells-
jökull, the scale is 1 metre. – Í árfarvegi skammt fram-
an við núverandi jaðar Búrfellsjökuls eru greinanleg
þrjú jökulruðningslög. Mælistikan er 1 m að lengd.
JÖKULL No. 62, 2012 157