Jökull - 01.01.2012, Blaðsíða 157

Surge fingerprinting of cirque glaciers
The recent surge history of the Búrfellsjökull
glacier is known (Figure 3) whereas less is known
about the Teigarjökull glacier (Brynjólfsson, 2009).
The first known surge of Búrfellsjökull occurred in
1912 (Björnsson, 1991; Hallgrímsson, 1972). At first,
local farmers noticed how the color of the river com-
ing from the glacier changed from being relatively
clear to brownish, and remained so through the sum-
mer. The farmers discovered that the muddy coloring
of the water was caused by a rapid advance (surge) of
Búrfellsjökull.
A small terminal moraine shows on aerial pho-
tographs from 1960, where as this moraine does not
show on aerial photographs from 1946. Licheno-
metric dating of moraines in front of Búrfellsjökull
(Kugelmann, 1991) dates this moraine back to about
1955. On the photograph from 1960, it is clear that the
glacier margin has separated from the moraine, indi-
cating some years of glacier retreat since the moraine
was formed. Monitoring of Búrfellsjökull since the
last surge terminated in 2004 suggests that it takes 3–
5 years before the glacier margin separates from the
surge moraine. Based on this, we believe the moraine
to have formed by surge between 1950 and 1955.
The Búrfellsjökull glacier surged in 2001–2004
and overrode the 1950–1955 moraine. The surge oc-
curred few years subsequent to a period, 1970–1995,
when most glaciers in Iceland advanced or were in
balance (Jóhannesson and Sigurðsson, 1998; Sigurðs-
son, 2005). These three surges of Búrfellsjökull in-
dicate a quiescent period of approximately 50 years
between surges. There are two older moraines outside
the 1912 moraine (Figure 3), dated from around 1825
and 1890 (Kugelmann, 1991). Due to reported surge
activity and similar geomorphology as the younger
moraines, we consider the older moraines also to have
been formed by surges.
The only surge reported from Teigarjökull (Figure
4) occurred in 1971 (Hallgrímsson, 1972), early in the
1970–1995 period of generally advancing glaciers in
Iceland (Jóhannesson and Sigurðsson, 1998; Sigurðs-
son, 2005). There are four moraines outside the 1971
moraine. Two of them, dated to approximately 1870–
1890 (Kugelmann, 1991), have comparable geomor-
phology to the moraines in front of Búrfellsjökull that
was formed by surges. Therefore these moraines are
considered to have been formed by a surge around
1870–1890.
METHODS
Geomorphological and sedimentological data on the
Búrfellsjökull and Teigarjökull glaciers were col-
lected by remote sensing methods and field obser-
vations. Landforms such as terminal moraines, me-
dial moraines and hummocky moraines are distin-
guishable on aerial photographs and their distribution
was verified in the field. Distribution of crevasse-fill
ridges and flutes were mapped in the field. Dead-ice
is widespread in the glacier forefields, and it is diffi-
cult, with surface exploration only, to identify dead-
ice within the sediments in front of the glaciers. How-
ever, by evaluating the stability of the surface and map
landforms that indicate dead-ice melting, e.g. cracks,
backslumping, furrows and troughs, sinkholes, and
hummocky surfaces, it was possible to estimate the
extent of the dead-ice. By studying time series of
aerial photographs, we improved the existing surge
history of the glaciers. A geomorphological map, in
the scale 1:13 000, of the forefield of Teigarjökull
and Búrfellsjökull glaciers was produced in a Geo-
graphical Information System (GIS) using aerial pho-
tographs as base.
To investigate the differences between surge-type
and non-surge type cirque glaciers, the forefield of the
non-surge- type glacier Deildarjökull (Figure 1) was
also explored. The observational data was used for
constraining a conceptual landsystem model for surg-
ing cirque glaciers, explaining how the glacier snout
and forefield developed over a surge cycle.
The Kugelmann (1991) lichenometric dating of
terminal moraines was used for better constraining the
chronology of the different surges.
RESULTS
Sediments and landforms
The alpine landscape setting of the cirque glaciers
on the Tröllaskagi peninsula causes the debris cas-
cade and sedimentary environments there to differ
considerably from those prevailing at the major outlet
JÖKULL No. 62, 2012 155