GEOPHYSICS OF THE GEOID
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"More than any other data set of the Earth the Geoid shows us the
dynamic structure of the Earth's deep interior. The most dramatic
feature in the Geoid of North American is the Yellowstone Hot Spot,
believed to be a plume structure rising through the mantle and the main
contributor to the Geoid high over Montana. Details of the topographic
anomalies of the Western Rockies can be seen superimposed upon this
anomaly, although with much less magnitude. The Great San Joaquin Valley
of California, formed through the tectonics of the earlier subduction of
the Pacific plate by North America is outlined in detail in the Geoid.
Comparison with this feature can be made with those smaller yet similar
Geoid lows to the north in Oregon and Washington state. In the mid
continent an ancient rift or suture zone can be seen in sharp outline
running from the tip of Lake Superior through Minnesota and continuing
to Texas.
The Eastern offshore shows some of the oldest portions of the Atlantic
Ocean formed some 120 million years ago with its now characteristic
Geoid low centered off the Carolinas. Seen also is a deep suture
structure running the length of the Hudson River Valley to the opening
of the Gulf of Saint Laurence. At the very top of the figure on the
right can be seen the outline of the most recently formed feature of
Geoid of North America. This is the postglacial Geoid low caused by
the depression of the continent under the ice load from the last Ice
Age some 20,000 years ago. Because of the viscous nature of the
Earth's Mantle this feature will slowly disappear until the end of the
next Ice Age when the process will repeat itself again."
By:
Allen Joel Anderson
Department of Physics
University of California
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