Jökull - 01.12.1987, Blaðsíða 52

Figure 2: Aerial photograph (1960), of Nautadalur
and its neighbouring rock glacier. © Copyright: Ice-
land Geodetic Survey.
2. mynd. Flugmynd frá 1960 af Nautadal, sem sýnir
grjótjökul (þelaurð). © Utgáfuréttur: Landmælingar
íslands.
Figure 3: Nautadalur rock glacier, as viewed from the
corrie backwall.
3. mynd. Grjótjökullinn (þelaurðin) I Nautadal. Horft
frá efstu rótum.
glaciers formed and, as a result, they are a subject of
some argument and conflicting interpretation.
There have been few reports of rock glaciers in Ice-
Iand (Einarsson 1968; Eyles 1978; Escritt 1976;
Whalley 1974). Whalley (1974) suggested that the rock
glaciers of Tröllaskagi shed much light on the forma-
tion and significance of such features. This paper con-
siders one rock glacier, located in Skjóldalur, Trölla-
skagi (figure 1) on which monitoring has been in oper-
ation over a period of eight years.
ROCK GLACIER DEFINITION
Martin and Whalley (in press) discuss the disputed
terminology concerning the delimitation of rock gla-
ciers and conclude that a morphological (hence non-
genetic) definition is most consistent with existing
literature and a general basis for definition is sug-
gested as follows;
1. Rock glaciers are found in mountain regions which
have, or have had, glacial/periglacial conditions.
2. they have an outward appearance of being com-
posed of rock debris.
3. the extent of this rock debris is distinct both mar-
ginally and terminally (though sometimes less so at
its head).
4. they have a source area (or areas) i.e. a head, and a
distinct snout which marks its maximum extent
downslope.
5. they have, in many cases, flow-Iike features on
their surface. The rock glacier is supposed to flow
(or have flowed in the case of relict features) as a
result of ice contained in some manner within the
rock debris.
6. they may move; for active rock glaciers, at rates of
approximately 2 — 3 orders of magnitude slower
that for true glaciers (usually < 1 m/year).
ROCK GLACIERS IN SKJÓLDALUR,
TRÖLLASKAGI
Mountains rising to 1300—1500m a.s.l. are found
in Tröllaskagi which lies between Skagafjördur and
Eyjafjördur. Much of the peninsula consists of basalt
plateaux dissected by glacially modified valleys (Sig-
bjarnarson 1983). Some of these valleys contain rock
glaciers, identified by Griffey (in Escritt 1976). Many
are located in corries with glacierettes at their heads
suggesting that their origin may be related to glacial
activity.
Skjóldalur lies in the south of Tröllaskagi, running
almost west—east, from the central watershed of the
peninsula to the farm of Ysta-Gerði, 20km south of
Akureyri (figure 1). On the southern side of Skjóldalur
are four tributary valleys heading in corries. The west-
ern most two contain both glaciers and rock glaciers.
Nautadalur is the Iargest of these (figure 2) being
deeply incised into the plateau which rises to just over
1300m at this point. The corrie is occupied by a small
glacier (approx. area 0.28km2), that appears to merge
downstream with a rock glacier, which resembles a
heavily debris-covered glacier snout. In rock glacier
terminology, it may be described as tongue-shaped
(Wahrhafting and Cox, 1959) or valley floor (Outcalt
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