ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

The slopes have an estimated mean annual air temperature
of-7°C to -5 °C, and an estimated mean annual precipitation
of under 300 mm/a. Most of the latter falls in summer,
often as snow. The few plants that grow on the surface of
the diamicton forming the landform exhibit elongation of
stems and/or roots to accommodate congelifluction. The
surrounding slopes have a more verdant meadow tundra
which would form alpine meadow if not so heavily grazed.
The surface of the mass is inclined at an average of about
19°, while the mean slope of the fronts is 21°. With one exception,
the slope of the fronts does not exceed 25°, unlike
true rock glaciers. The diamicton mantles the north slope
of the ridge but splits into at least 16 separate tongues which
are moving down fluvially graded valleys. The lowest
front lies at 4630 m, but varies in thickness up to 40 m in
valley number 4. The active layer was found to be between
12 and 30 ern in July at 4780 m, but increases to 1.5 to
2 m. at about 4650 m. Ice contents have been measured at
up to 57 % but they are usually under 30 % in the upper
layers of permafrost.
The larger boulders act as braking blocks on the upper slops
of the landform and are frozen into the permafrost. The
rates of advance of the lower parts of the landform measured
by surveying range up to 3 ern/a, whereas the rate of
movement of the fine-grained material in the active layer
past braking blocks on the upper slopes ranges up to
30 ern/a. It is therefore concluded that the excess material
moving down the steeper upper slopes must be causing
thickening of the deposit on the more gentle lower slopes.
There is no direct evidence for flowage of the icy diamicton
forming the deposit.
This landform has been referred to by various names such
as rock ice-cap, periglacial boulder tongue and Kunlunshan-type
rock glaciers. Its dominant mode of downslope
movement of material (congelitluction) distinguishes it
from true rock glaciers (which move by flowage of the permafrost
layer due to the presence of excess ice). It also
lacks the over-steepened front which is a consequence of
that movement, but exhibits braking blocks. None of the
other terms have been properly defined and described. It
is therefore best referred to as a massive congelifluction
deposit, and is the longest and most spectacular of these
deposits described so far in the world.
JANE K. HART
The deforming bed / debris-rich basal ice continuum
and its implications for Glacial Geology
Department of Geography, University of Southampton, Southampton,
SOI7 IB}, UK
It is shown that there are many similarities in processes
between the subglacial deforming bed and the debris-rich
200
basal ice layer, including: compression at the margin; longitudinal
extension and simple shear upglacier; similar styles
of shear zone and associated fabric development; and
similar incorporation, transport and depositional processes.
These have an important effect on glacier dynamics.
However, the resultant layers will depend on the nature of
the bedrock, the sediment supply and the thermal characteristics
of the glacier. These ideas will be illustrated from
contrasting glaciers in Greenland, Alaska and the European
Alps.
The main differences include, rates of sediment movement
processes and preservation potential. It is argued that there
is little chance of the debris-rich basal ice layer being
preserved, and this is demonstrated from modern examples,
flutes studies and studies of Pleistocene «melt-out»
tills from the UK, USA and Germany. It is argued instead
that the debris-rich basal ice layer will melt-out to form a
deforming layer, which will in turn be preserved once the
ice sheet retreats.
ADRIAN M. HARVEY\ J. GOy 2 , A.E. MATHER\
P.G. SILVA 4, M. STOKES 3 & C. ZAZo 5
The impact of Quaternary sea level andclimate change
on coastal alluvial fans in the semi-arid Cabo de Gata
ranges, southeast Spain
1Department of Geography, University of Liverpool, p.o. box 147,
Liverpool, L69 3BX, UK
2 Departamento de Geologia, Facultad de Ciencias,
Universidad de Salamanca, 37008, Salamanca, Spain
3 Department of Geographical Sciences, University of Plymouth,
Drake Circus, Plymouth, PL4 8AA, UK
4 Departamento de Geologia, Universidad de Salamanca,
E.U. Politecnica de Avila, 05003 Avila, Spain
5 Departamento de Geologia, Museo Nacional CC. Naturales (CSIC),
CI}ose Gutierrez Abascal, 2.28006 Madrid, Spain
Conventionally, base-level fall is seen as stimulating incision
in the distal zones of alluvial fans. In the Cabo de Gata
ranges of semi-arid southeast Spain there is evidence to
the contrary. There, two sets of Quaternary alluvial fans
demonstrate the interaction between climatically driven variations
in sediment supply and eustatically driven base-level
change. Both fan sets are fed by Miocene volcanic terrain
within which there is no evidence for tectonic deformation
during the period of fan development. The evolution
of the east-coast fans has been affected by variations
in both sediment supply and sea level change. The westcoast
fans were buffered from the effects of sea level change
by coastal barriers.
Two major phases of fan sedimentation can be identified,
apparently coincident with global glacials (>£135 ka and