Jökull - 01.12.1988, Blaðsíða 19

Historical Development of the Proglacial Landforms of
Svínafellsj ökull and Skaftafellsj ökull,
Southeast Iceland
ALAN THOMPSON
Department ofEarth Sciences, Liverpool University,
Liverpool L69 3BX, England
ABSTRACT
This paper examines the origin and development
of proglacial landforms associated with the histori-
cal recession of two adjacent valley glaciers in
southeast Iceland.
The two glaciers have displayed contrasting
behaviour in response to recent climatic change
(1870 to 1984), as afunction of differences in source
area conditions on the Orœfájökull icecap, and this
in turn has been reflected in contrasting styles of
glacial and fluvioglacial outwash deposition.
The rapid recession of Skaftafellsj ökull since
1870 has revealed an extensive area of subglacial
ground moraine, moulded by minor oscillations of
the retreating ice-front into a series of low concen-
tric ridges. At Svínafellsjökull by contrast, alternate
episodes of slow recession and readvance have pro-
duced a more complex series of higher push-
moraines, composed largely of englacial and
supraglacial debris.
Outwash deposits at Skaftafellsjökull are gen-
erally preserved as discrete units between the arcu-
ate moraines, whilst those at Svínafellsjökull are
almost entirely developed outside the moraines,
forming dissected outwashfans.
Approximate dating of these landforms has been
achieved by reconstructing stages in the recession
ofthe two glaciers,from cartographic, photographic
and documentary evidence, coupled with field inves-
tigation of geomorphic relationships and
lichenometry.
INTRODUCTION
The historical recession of Svínafellsjökull and
Skaftafellsjökull, adjacent outlet glaciers from the
Öræfajökull icecap (Fig. 1), has revealed two con-
trasting landform assemblages in a complex progla-
cial area. This study employs documentary, carto-
graphic, aerial photographic, lichenometric and
morphological field evidence to examine the origin
and development of these landforms over the last
one hundred and fifteen years.
EVIDENCE AND CAUSES OF
GLACIER FLUCTUATIONS
Prior to 1935, the snouts of the two glaciers were
united in front of the mountain Hafrafell,
(Thorarinsson, 1943, p. 33), forming an extensive
piedmont ice lobe which spread out onto the coastal
outwash plain (Fig. 2). The maximum extent of this
ice-front during Postglacial time is represented by
the ancient "Stóralda" moraine in front of Svína-
fellsjökull. From tephrochronological evidence this
moraine is known to predate the 1362 eruption of
the Öræfajökull volcano,* and may therefore date
* Note added in proof. Recent sampling of tephra layers on
various parts of the Stóralda moraine complex has shown that
the 1362 Öræfajökull pumice is not found on the main
(innermost) ridge, except as a constituent of the underlying
till, implying a more recent age for this part of the moraine.
Evidence for a pre-1362 ice advance is found only on the
subdued outer ridges where the pumice is found in situ within
the soil.
JÖKULL, No. 38, 1988 17