Geology of Urban Watersheds - Urban Watersheds: Geology, Contamination, and Sustainable Development - page 56

Esker

Lobe of
ice cap

Drumlins

Stagnant
ice

Kames

Crevasse
fillings

End moraine

Crevasses

End
moraine

Ice tunnel

Pro-glacial lake

Glacial
lake plain

Ground moraine

Outlet channel

End moraine

Ice
block pits

Outwash
plain

Ground moraine Stagnant ice blocks

Till Outwash

(a) (b)

FIGURE 2.34
Glacial deposits formed in the glacial sedimentary environment.

• Kettles—Depressions formed when portions of ice from the glacial front become
partially or wholly buried with glacial outwash. Groundwater fills the depres-
sions to form kettle lakes. Many of the inland lakes in Michigan are kettle lakes.
• Eskers—Formed beneath glaciers in ice-walled tunnels of outwash; they typi-
cally deposit coarse-grained gravel deposits in an irregular pattern, deposited by
streams flowing under the ice.
• Outwash—Glacial sediments deposited by the action of meltwater transporting
glacial till away from the glacier front. Glacial meltwater streams from a glacial
front may form a type of pattern called braided streams consisting of a maze of
interconnected channels with high sediment loads.
• Drumlins—Elongated hills composed of glacial till; they are much steeper on
one side than the other. The steeper slope indicates the direction of ice movement
(Figure 2.34b).
• Glacial lakes—Many glacial lakes form between the ice front and end moraines of a
retreating glacier. The end moraines form an effective barrier for glacial meltwater
to form. Deposits in glacial lakes tend to be fine-grained and may contain varves.

Glacial lacustrine lakes or pro-glacial lakes as shown in Figure 2.34a were very common
throughout North America during the Late Pleistocene (Benn and Evans 1998). Many
urban areas such as Chicago, Detroit, Cleveland, and Buffalo are located along or near the
shoreline of these glacial lakes (Farrand 1988; Rogers 1996; Benn and Evans 1998). Other
notable large Pleistocene glacial lakes include Lake Bonneville, which occupied the area
where Salt Lake City in Utah is located (Green and Currey 1988; Morrison 1991); Lake
Missoula and others that were located in Montana, Idaho, and eastern Washington (Alt
2001); and Lake Agassiz in the northern United States and southern Canada (Imbrie and
Imbrie 1979). Many of these Pleistocene glacial lakes were as large as the current Great
Lakes and they form, or have influenced, many of the landscapes of urban areas in the
northern United States.