Geology of Urban Watersheds - Urban Watersheds: Geology, Contamination, and Sustainable Development - page 55

FIGURE 2.33
Extent of Pleistocene Age glaciers (From Chamberlin, T.C. and Salisbury, R.D., A College Textbook of Geology , The
Lakeside Press, Chicago, IL, 1909.)
Figures 2.34a and b show the variety of glacial deposits as they are formed in the glacial
sedimentary environment (modified from Farrand 1988).
The following discussion refers to Figures 2.34a and b and is based on the description of
glacial deposits found in Bennett and Glasser (1996) and Benn and Evans (1999):
• Moraines—are formed by the deposition of material from a glacier and are
exposed after the glacier has receded. These features usually are referred to as
glacial till. Glacial till is material directly deposited from glacial ice, and usually
appears as linear mounds of unsorted material, or as a very poorly sorted mixture
of rock, gravel, and boulders within a matrix of a fine-grained silt- and clay-sized
material. There are three main types of moraines:
• Lateral moraine: formed on the sides of glaciers.
• End moraine: formed at the end of a glacier or at locations where the glacier
had been stagnant during a retreating or regressive phase.
• Ground moraine: formed under the ice between the lateral moraine. Deposits
of the ground moraine variety tend to be fine-grained than lateral or end
moraines. Ground moraines may also be termed lodgment tills.
• Kames—Ice contact features shaped by glacial meltwater; these form conical-
shaped masses of course-grained sand and gravel with little or no fine-grained
material.