Jökull - 01.12.1978, Blaðsíða 55

Rock Glaciers in Esjufjöll Nunatak Area,
South-East Iceland
N. EYLES,
Department of Geology, University of Newcastle upon Tyne
In South-east Iceland heavily debris laden
glaciers, such as the termini of Öræfajökull’s
southern outlet glaciers, can be related to easi-
ly weathered volcanic bedrock. Another
related manifestation of high rates of debris
production are rock glacier tongues observed
in August 1977 at Skálabjörg ridge, in Esju-
fjöll, 25 km upglacier of the terminus of
Breidamerkurjökull (64°15’N; 16°30’W; Fig.
1). These rock glacier lobes retain an ice-core,
appear to be active and have developed in an
area with a present mean annual temperature
of +1°C. This is the first report of rock
glaciers in southern Iceland. Previous reports
of rock glaciers indicate their rarity in
maritime areas; their formation at Esjufjöll is
therefore of general climatic interest and may
reflect the more severe continental climatic
conditions that prevailed during the
Neoglacial (c. 1150—1900 AD) climatic
deterioration.
Esjufjöll nunatak area (20 km2) consists of
parallel bedrock ridges up to 11 km long,
trending northwest-southeast in the ablation
zone of Breidamerkurjökull (Fig. 1). The
ridges project up to 450 m above the ice sur-
face culminating in the firn-covered peak of
Snæhetta (1700 m). The nunatak ridges of
Esjufjöll were first mapped in 1904 (Danish
General Staff map; Blad 87; 1:50 000 Esju-
fjöll) when they extended over 6 km2 and were
visited by Koch and Wegener in 1912 in their
journey south across Vatnajökull. A map
made by Durham University Exploration
Society in 1951 serves to indicate the broad
extent of deglaciation since the turn of the
century. Sigbjarnarson (1970) has estimated
that' the ice surface in the area has fallen at
least 70 m since 1904.
Skálabjörg ridge is asymmetric in cross
profile, westerly facing slopes contrast with
steeper slopes and frost-riven cliffs of the east
facingslopes side of which Steinthórsfell (1190
m) is the most prominent. On the western
slopes a mosaic of sparsely vegetated nivation
hollows, solifluxion lobes, terraces and dry
valley systems only occupied during spring
snow melt, contrast with unvegetated scree
slopes and snow patches on the east side of the
ridge where large protaius ramparts, indicat-
ing the free fall of debris onto snow, are com-
mon.
Fig. 2 and 1961 aerial photography show
rock glacier tongues on the eastern side of
Skálabjörg ridge below the imposing and ex-
tremely active backwall of Steinthórsfell. The
site lies 150 m above the surface of the Esju-
dalur tributary of Breidamerkurjökull. Three
well-defined arcuate lobes termining at 875 m
extend downslope from a large snow patch
though the debris lobes are separated from the
latter by a complex belt of snowbank ice-cored
debris ridges and mounds — similar mounds
separate the tongues. The largest tongue is 50
m wide (Fig. 3) and is composed of super-
imposed, ice-cored arcuate ridges of scree debris
such that a steeply-dipping crenulate long
profile is exhibited typical of rockglaciers
reported elsewhere (Corte 1976). Ridge height
is 1.5—2 m above the surface of the rock
glacier which in turn lies up to 9 m above the
surrounding surface. The frontal ridge is steep
JÖKULL 28. ÁR 53