Variability of the Earth’s climate - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 102

Figure 2.48. Example of polishing of bedrock by glacial silt (UWESS).
More recently, the University of Washington Earth and Space Sciences
Department (UWESS) has produced a number of excellent presentations on ice
ages that are very descriptive and instructive. The entire structure of the great
valley in Yosemite National Park is presented as an example of a classic alpine
glaciated landscape.
Glacial erosion occurs by abrasion, crushing and fracturing, and quarrying of
joint blocks. Ice is not hard enough to abrade rocks, but rock fragments imbedded
in the base of the glacier can abrade rocky terrain below, leaving characteristic
striations (see Figure 2.47 ) .
The UWESS described how glacier action can pluck large blocks leaving
characteristic scalloped terrain. Fine silts suspended in glacial melt water can
polish underlying bedrock (see Figure 2.48 ) .
In addition, the UWESS provided many more examples and illustrations of
past glacial action.