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Unformatted text preview: anced over northern New Jersey at least three
times (fig. 10). From oldest to youngest, these glaciations are named
the pre-Illinoian, Illinoian, and late Wisconsinan. Glaciers are large
bodies of ice that form over long periods from the gradual buildup of
compacted and recrystallized
snow. Eventually, the ice
becomes thick enough to
flow under the stress of its
own weight. Ice sheets are
thick glaciers that cover large
parts of continents. In North
America the Laurentide and
Cordilleran ice sheets grew
to enormous sizes.
estimated that their centers
were as much as 10,000
feet thick. At High Point,
the ice may have been 2000
feet thick when the North
American ice sheets were at
their maximum size.
ice sheets were centered
Figure 10. Limits of glaciations in New in the subarctic regions of
Jersey. The trace of the lw limit generally Canada and grew and spread
marks the Terminal Moraine. Key: lW - late
outward during periods when
Wisconsinan, I - Illinoian, and pI - prethe northern hemisphere was
13 colder than it is now. Current ideas are that small changes in the
earth’s orbit, tilt of its axis, direction of ocean currents and storms,
and volcanic dust in the atmosphere may have all contributed to
global cooling. The geologic record shows that the growth and decay
of continental ice sheets in the northern hemisphere was cyclic. In
New Jersey, the climate varied from arctic or boreal during glacial
periods to temperate or subtropical during interglacial periods.
Today we are considered to be in an interglacial stage.
A precise age of the oldest glacial deposits is uncertain. Their
extensive weathering and poor preservation suggest they were laid
down more than 800,000 years ago. Later, during the Illinoian
stage about 150,000 years ago, an ice sheet again covered northe...
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