Jökull - 01.12.1978, Blaðsíða 58

fore that the rock glaciers are relict Breida-
merkurjökull ice surviving under a thick
debris cover. In addition there is no evidence
that the rock glaciers are of the so-called
'transitional type’, i. e. a continuum from a
heavily debris-laden cirque glacier to ice-
cored moraines to rock glaciers described by
Foster and Holmes (1965) in Alaska. Thus the
superimposed arcuate ridges of the rock
glaciers are not simply closed spaced ice-cored
terminal moraine ridges. Furthermore the
mean annual temperature of the rock glacier
site is +1°C with a yearly precipitation of at
least 1700 mm (extrapolation from data from
Fagurhólsmýri, 30 km to the south-west, in
Eythorsson and Sigtryggsson 1971). Rock glaciers
with a glacier ice-core are rare in maritime
environments such as Esjufjöll and are more
commonly found in areas of more continental
regime of lower precipitation such as the Ak-
ureyri area in Northern Iceland (Whalley
1974).
The alternate possibility that both the rock
glacier and glacierette are relict and date from
the late Neoglacial climatic deterioration, that
in Iceland extended from c. 1150 to 1900 AD,
is unlikely. The site of the rock glacier lobes
and the glacierette is 200 m below the present
regional snowline and the north easterly
aspect of the site is clearly of importance in the
formation of the rock glaciers and glacierette.
Around the North Atlantic, snow patches
survive in favourable locations up to 450 m
below the firn line (Manley 1949) and it is
likely that the rock glacier lobes at Eyjafjöll
have formed by the dumping of large volumes
of debris onto snowpatches below very active
easily eroded backwalls. Wahrhaftig and Cox
(1959) have stressed the importance of easily
weathered bedrock lithologies in deforming
the location of rock glaciers. Immediately
outside the limits of the rock glacier lobes (Fig.
2) an old protalus rampart composed of large
boulders can be identified over which the rock
glacier lobes are encroaching. .This would
suggest that the ice-core of the lobes is snow
bank ice, a remnant of a much larger snow
patch or a glacierette that extended out to the
protalus rampart and was subsequently
buried by scree. This would explain the un-
usual maritime development of rock glaciers
at Esjufjöll.
ÁGRIP
ÞELAURÐIR I ESJUFJÖLLUM
Höfundur lýsir þelaurðum (grjótjöklum)
við Steinþórsfell austan í Skálabjörgum í
Esjufjöllum (sjá myndir). Þelaurðir eru al-
gengar á Norðurlandi, t. d. á Tröllaskaga, en
sjaldgæfar sunnanlands. I Esjufjöllum sunn-
antil er meðalhiti árs um 1 °C. Telur höfundur
ólíklegt að þelaurðirnar hafi myndast á síð-
astliðnum öldum þegar kaldara var en nú.
Hann telur að fannir eða ís úr Breiðamerkur-
jökli hafi grafist undir urð.
REFERENCES
Corte, A. E. 1976: Rock glaciers. Biuletyn
Peryglacjalny 26: 175—198.
Eythorsson, J. and H. Sigtryggsson 1971: The
climate and weather of Iceland. Zoology of
Iceland 1 (3) Munksgaard, Copenhagen.
Foster, H. L. and G. W. Holmes 1965: A large
transitional rock glacier in the Johnson
River area, Alaska Range. United States
Geological Survey Professional paper 525
B ppB 112-1.
Manley, G. 1949: The snow line in Britain.
Geogr. Ann. 31: 179—193.
Sigbjarnarson, G. 1970: On the recession of
Vatnajökull. Jökull 20: 50—61.
Wahrhaftig, C. andA. Cox 1959: Rock glaciers in
the Alaska Range. Geological Society of
America, Bulletin. 86: 737 — 748.
Whalley, W. B. 1974: Rock glaciers and their
formation. Geographical papecs no. 24.
Department of Geography, University of
Reading, U. K. 60 pp.
Manuscript received September 1978.
56 JÖKULL 28. ÁR