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RESEARCH |
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Timothy F.
Johnsen (2004)
Abstract During the decay of
the Cordilleran Ice Sheet (CIS), ~10 to 12 ka 14C BP, numerous ribbon lakes
developed within the moderately deep valleys of the Interior Plateau of British
Columbia. A rich geomorphic and sedimentary record of these lakes remains. This
study integrates geomorphology, sedimentology, aerial photographs, differential
global positioning system data, ground penetrating radar data and a digital elevation
model (DEM) in a geographic information system (GIS) to (i) investigate, survey
and correlate paleolake levels, (ii) reconstruct paleolake geography, evolution
and environment, and (iii) reconstruct glacio-isostatic rebound.
Two definable
glacial paleolake levels were identified, associated with Glacial Lake Thompson
and Glacial Lake Deadman. DEMs of paleolake levels, inferred lake bottom and modern
topography were integrated in a GIS to quantify lake parameters. Lakes were ribbon-shaped
(width to length ratio of ~3:100), deep (~140 and ~50 m, respectively), and of
significant volumes (84 and 24 km3, respectively). Glacio-isostatic tilts of
these lake shorelines (1.8 - 1.7 m km-1) are among the highest measured in the
world and are related to a thin lithosphere, a low viscosity mantle and rapid
deglaciation. Glacioisostatic depression in the interior was likely hundreds of
metres.
The sedimentary
record of these lakes reflects the adjustments of a landscape undergoing
deglaciation. Seventeen glaciolacustrine lithofacies were identified and record
deltas, subaqueous fans, high rates of sedimentation, numerous hyperpycnal
flows and a diversity of sediment dispersal and deposition processes. High
sedimentation rates and numerous hyperpycnal flows suggest that ribbon lakes
likely received their meltwater and
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