between 16,000 and 12,000 years ago, when average global temperatures
increased about 5 degrees Celsius to nearly present-day levels. A renewal of the
deep-ocean circulation system, which was shut off or severely weakened during
the Ice Age, might have thawed out the planet from the deep freeze.
A gigantic ice dam on the border between Idaho and Montana held back
a huge lake hundreds of miles wide and up to 2,000 feet deep. Around 13,000
years ago, the sudden bursting of the dam sent waters gushing toward the Pacific
Ocean.Along the way, the floodwaters carved out one of the strangest landscapes
known, called the Channel Scablands (Fig. 195). Lake Agassiz, a vast reservoir of
Figure 195The Grand
Coulee Dam on the
Columbia River in
northwest Washington,
showing tortured scablands
terrain.
(Courtesy USGS)QUATERNARY GLACIATION