Jökull - 01.01.2012, Blaðsíða 154

S. Brynjólfsson et al.
to be triggered from within or under a glacier rather
than to be externally forced (Kamb, 1987; Björnsson,
1998; Kjær et al., 2006; Benn and Evans, 2010), al-
though a recent study by Striberger et al. (2011) sug-
gests that surge periodicities of the Eyjabakkajökull
glacier, eastern Iceland may have been forced by cli-
matically driven mass balance changes.
Thórarinsson (1964, 1969) compiled historical
records and reviewed the state of knowledge on
surging glaciers in Iceland with emphasis on outlet
glaciers draining the Vatnajökull ice cap. He con-
cluded that surging glaciers in Iceland were character-
ized by a smooth ablation zones and shallow spoon-
shaped basins that widened towards the glacier ter-
minus. Later, Björnsson et al. (2003) extended Thór-
arinsson’s work and gave an overview of surging
glaciers in Iceland and their activity. They suggested
that surges affect about 70% of glaciers in Iceland,
and that steep-sloped glaciers typically do not surge.
Búrfellsjökull and Teigarjökull, located in the moun-
tainous Tröllaskagi peninsula, northern Iceland, are
surge-type cirque glaciers with mean slopes about 11–
14◦, which make them the steepest surge-type glaciers
in Iceland. Judging from the last surge of Búrfells-
jökull which lasted for four years, 2001–2004, the
surging phase seems to last longer in north Iceland
compared to the larger outlet glaciers in south Iceland
where surges usually last from a few months to one or
two years.
Palaeoclimate and glacier fluctuations over time
have been reconstructed from marginal moraines and
glacial deposits in the Tröllaskagi peninsula, assum-
ing that the Tröllaskagi glaciers generally are in equi-
librium with climate (Kugelmann, 1991; Caseldine
and Stötter, 1993; Stötter et al., 1999). Only three
glaciers among more than 150 glaciers in the Trölla-
skagi peninsula have been known for surge activity,
but a preliminary study by Brynjólfsson (2009) sug-
gested that there might be more surge type glaciers in
the area.
In this study we explore the geomorphology and
sedimentology of the forefield of two surge-type
cirque glaciers and one non-surging cirque glacier at
Tröllaskagi peninsula. Different geomorphological
and sedimentological signatures of the surge-type and
the non-surging glacier were used to identify specific
characteristics of the surge type glacier forefield.
Here we describe the geomorphology of the surge-
type Búrfellsjökull and Teigarjökull cirque glaciers in
Tröllaskagi, explore their dynamics and reconstruct
the recent surge history. Our study of those two
glaciers results in a new landsystems model for surge-
type cirque glaciers in alpine environments.
SETTING AND KNOWN SURGE
EVENTS
The Tröllaskagi peninsula is a mountainous area in
central northern Iceland, extending from the central
highlands, north out into the North Atlantic Ocean
(Figure 1). The glacially sculptured landscape, mostly
heavily eroded and dissected Tertiary plateau basalts,
ranges in altitude from sea level to more than 1500 m
a.s.l. (Björnsson, 1979; Pétursson and Jónsson, 2006).
There are more than 150 small glaciers in the moun-
tain range (Figure 1), located in cirques and valley
bottoms between 700 and 1400 m a.s.l. (Sigurðsson
and Williams, 2008). Approximately 40 km2 of the
area is covered by glaciers. In most cases, glaciers
face north and are sheltered by steep mountain slopes
which reduce the incoming solar radiation. Most of
the glaciers have surface areas of 0.5–2 km2 and only
a few of the glaciers are larger than 2 km2 (Björns-
son, 1979; Björnsson, 1991; Björnsson and Pálsson,
2008). The precipitation in the high mountains of
Tröllaskagi is estimated to be 2000–2500 mm/year
of which the majority falls as snow on the glaciers
(Ólafsson and Ólafsson, 2004; Lippert et al., 2006;
Brynjólfsson and Ólafsson, 2008). In addition, the
glaciers receive accumulation from avalanches and
snowdrift (Björnsson 1991, Björnsson and Pálsson,
2008). Studies on mountain permafrost conditions in
Iceland and local climate of the Tröllaskagi peninsula
show that sporadic permafrost occurs above 800–900
m a.s.l. which is consistent with the occurrence of
rock glaciers at high elevation in Tröllaskagi (Farbrot
et al., 2007a, 2007b).
The study area consists of two small glacially
eroded hanging valleys, the Búrfellsdalur and Teigar-
dalur that are southern tributaries to the main valley
152 JÖKULL No. 62, 2012