Jökull - 01.01.2012, Blaðsíða 163

Surge fingerprinting of cirque glaciers
For comparison, the forefield of a non-surge type
glacier, the Deildardalsjökull glacier (Figure 8) was
examined. There were no exposures in the Deildar-
dalsjökull forefield where stratigraphy and sedimen-
tology of drift could be studied in sections. However,
judging from shallow surface pits, the sediments seem
to be mainly diamicton, with cobbles and boulders in
a clayey-silty matrix. The proglacial surface carries
scattered subangular cobbles and boulders. In gen-
eral, the sediments are richer in fine grains sizes and
angular rocks are relatively rare, compared to the Búr-
fellsjökull and Teigarjökull forefields. A well-defined
terminal moraine marks the maximum extent of the
glacier at the end of its advance due to positive mass
balance between 1980 and 1995 (Figure 8A) (Sig-
urðsson, 2005; Jóhannesson and Sigurðsson, 1998).
Distinct small annual (retreat) moraines (Figure 8B)
reveal responses to the winter accumulation of the
glacier.
Older moraines further out in the valley indicate
former stages of the glacier, but the age of these is not
known. Flutes extend from below the present glacier
margin out to the 1995 moraine. The flutes consist
of diamicton, similar to the diamicton in the drift de-
scribed above, and are often overprinted by the annual
moraines. Neither hummocky terrain nor crevasse-fill
ridges were observed. The sedimentary environment
of this non-surge type cirque glacier is also charac-
terized by short transport distances. However, the ge-
omorphology differs from the surge-type glaciers at
Tröllaskagi.
DISCUSSION
Conceptual model of changes in the marginal zone
of surge-type cirque glaciers
A conceptual model for the geomorphological devel-
opment at surge-type glaciers in Tröllaskagi is out-
lined in Figure 9. The development is divided into
three phases based on observations in front of Búr-
fellsjökull which surged from 2001–2004 and Teigar-
jökull which surged in 1971.
In phase A, as a surge terminates, an end moraine
consisting of ice and debris has formed in front of the
glacier. At this time the glacier is heavily crevassed,
the margin is steep and supraglacial debris is promi-
nent in the stagnant marginal zone.
Phase B is characterized by downwasting of the
stagnant glacier snout. When the dead-ice melts, the
supraglacial and englacial debris gradually emerges
and covers the ice surface. The melt rate of the
ice gradually decreases as debris accumulates on the
ice surface, which results in formation of hummocky
moraines. In 3–5 years the glacier margin separates
from its moraine, which at first is relatively big due
to the ice-core. In a few years the moraine becomes
smaller as the ice-core melts.
Figure 8. Moraines in front of Deildardalsjökull. A) End moraine from 1995. B) Annual moraines formed
in the years 2007 and 2008, which are characteristic for non-surge type glaciers. – Jökulgarðar framan við
Deildardalsjökul. A) Endagarður frá 1995. B) Árgarðar myndaðir 2007 og 2008 en þeir eru dæmigerðir fyrir
jafngangsjökla, þ.e. jökla sem hlaupa ekki.
JÖKULL No. 62, 2012 161