LAKE WASHINGTON AREA
2001; Using a high-powered computer and millions of bits of data from geological and oceanographic surveys over the past 100 years, University of Washington staffers produced this digital image of the city. The result is a picture that strips away most of man's interventions, laying bare the landscape carved by the Vashon Glacier some 14,000 years ago. (Data from Lake Washington and Lake Union had not been incorporated into the system.)
Ice Age Floods in Washington: A Cyber tour
Imagine Puget Sound under a mile of ice. 20,000 years ago, glaciers covered everything in between the Olympics and the Cascade mountains and spread as far south as Olympia.
ice over Seattle was higher than
five Space Needles (3,412 feet.) Glaciers
advanced from Canada
and retreated four or more times.
Over a few million years, Puget Sound was
carved and scoured by glaciers.
the ice finally retreated to the north, it left
behind deeply gouged channels, north-and-south oriented passages and
Weather, waves, and gravity reworked the glacial sediment, molding
landforms and shorelines like frosting on a
cake. The results are the beaches and bluffs that now edge the Sound
About 15,000 years ago, the Vashon glacier begins to melt and recede from lands that will come to be known as the Puget Sound region and the Columbia Basin region. By 11,000 years ago, the glacier has retreated to the border of present-day Canada. During its advance, the glacier had carved out Lake Washington, Lake Tapps, Lake Sammamish, Puget Sound, and Hood Canal. The other major shaper of the land -- the pushing of the Pacific Plate underneath the North American plate, and the docking of terranes (fragments of continents) had already occurred long ago.
The Vashon glacier was the last "stade" (a glacial advance and retreat) to cover the region. It was the last glacier of the Pleistocene Epoch, which lasted from 2 million years b.p. (before present) to about 10,000 years b.p. As far south as the Seattle area to the west and the Spokane area to the east, the glacier, at its thickest, reached 3,000 feet of ice. To give a comparison, the Pacific Northwest's tallest skyscraper (as of 2003), Seattle's Bank of American Tower (Columbia Tower), is about 997 feet tall. See: Link