Glacial Erosion/Sedimentation of the Baltic Region and the Effect on the Postglacial Uplift - The Baltic Sea Basin - page 55

the last glaciation were still sufficient to induce isostatic movements comparable to
those caused by glacial loading. The analysis suggests interesting phenomenological
connections.
The purpose of this chapter is to present and describe the results of this new kind
of analysis. We motivate the methods used with a fairly extensive review of geolog-
ical observations that provide insight into the processes that are occurring and the
parameters that appear to be important and then give a fairly brief discussion of the
methods themselves. The results of our analysis are then given in reasonable detail.
Although physically based, our methods remain largely empirical algorithms.
As such they are difficult to fully describe in any reasonable space, and, in any
case, their validity rests largely in their predictions. We will describe the methods
in full detail in subsequent publications. Here we hope mainly to show that the
sediment redistributions that result from the analysis we describe are reasonable
and interesting.
3.2 Glacial Erosion and Sedimentation
Rates of glacial erosion have been estimated between 0.1 and 10 mm/year. Erosion
of glaciated catchments of fjords of southern Alaska exceeds 10 mm/year (Hallet
et al. 1996 ) . Long-term averaged exhumation rates are 3 mm/year in the Chugach-
St. Elias Range, Alaska, where the maximum rates of denudation are thought to be
limited by rates of tectonic uplift (Spotila et al. 2004 ) . In Western Nunavut, 6-20 m
of rock is believed to have been eroded during the last glacial cycle (Kaszycki and
Shilts 1980 ) .
In Northeast Scotland, where both glacial and preglacial landforms exist in close
proximity, the expansion of ice sheets across the area in the middle Quaternary was
associated with a sharp increase in the rates of erosion (>0.13 mm/year), but the last
(Late Devensian) ice sheet in the area was less erosive (<0.095 mm/year) (Glasser
and Hall 1997 ) .
On the assumption that the erosional work was achieved over 10,000-
20,000 years of each 100,000 year glacial cycle, the rates of surface lowering
during glaciations in Britain fall in the range of 11-23 mm/year (Clayton 1996 ) .
The average erosion rate over the full glacial cycle is comparable to the 1 mm/year
figure regarded as “typical” by Boulton et al. ( 1991 ) for glacial erosion of resistant
rocks. Erosion in Britain is several times faster for weaker rocks flooring major
lowlands and much of the shelf (Clayton 1996 ) . Average erosional rates of the
sedimentary bedrock of the Barents Sea during the last ~2.5 million years were esti-
mated to be between 0.1 and 1.1 mm/year (Faleide et al. 1996 ) or 0.2-0.6 mm/year
(Solheim et al. 1996 ) .
Assuming glacial erosion for 1 million years over the past 2.57 million years, the
average rate of glacial erosion in the Sognefjord drainage basin, western Norway,
was ~0.4 mm/year by subtracting the present topography from a reconstructed
preglacial (paleic) surface. Considering the selective nature of glacial erosion along