Darter, J.R.,
2004. Constraining the geometry of the Scandinavian Ice Sheet
at the last glacial maximum, Nordland,
Norway. M.S. Thesis, University of Wisconsin-Madison, 102 pp.(04-10)
CONSTRAINING
THE GEOMETRY OF THE SCANDINAVIAN ICE SHEET AT THE LAST GLACIAL MAXIMUM,
NORDLAND, NORWAY
The thickness of the
Scandinavian Ice Sheet (SIS) during the Last Glacial Maximum (LGM) has
been the topic of debate for decades. Some
studies using isostatic and modeling
reconstructions predict ice thickness well above the highest peaks in
regions of Scandinavia, while other studies use observations of highly
weathered blockfields and cosmogenic dating to suggest that the highest
peaks remained as nunataks during the LGM. Consolidation testing was performed on 10
fine-grained samples from 5 sites. The samples were collected from
units underlying late Weichselian till, and
thus, should have experienced the full load of the ice sheet. However, the preconsolidation
pressures result in ice thickness estimates that are too small to be
reasonable. A combination of excessive pore
water pressure during consolidation, and low permeability of the
substratum is the likely cause for low preconsolidation
pressures for two of the three sites in Norway, whereas permafrost and
frozen glacier bed are the probable cause for low preconsolidation
pressures for the site in Sweden. The samples
from Finland have a high degree of disturbance due to insufficient
sample cohesion, and thus are inconclusive. Although
consolidation testing did not offer reasonable ice thickness estimates,
it did provide insight for the thermal regime during the last glaciation.
Another approach used to
determine ice thickness during the late Weichselian
is cosmogenic dating, and lower extent of blockfields and related geomorphic observations. Five mountain summits were sampled for cosmogenic dating, and an additional five were
analyzed for geomorphic indications (upper limits of striations, chattermarks, till and glacial sculpting, and
changes in degree of weathering) of ice coverage during the last glaciation. The two peaks with blockfields at their summits are believed to
represent peaks that remained ice free during the last glaciation, whereas four of the peaks have clear
evidence that they were ice-covered. The
remaining four peaks require further cosmogenic
dating of boulders in order to distinguish between the peaks covered by
thin or cold-based ice, and the peaks that remained as nunataks.