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As summer looms ahead, the season of beaches begins! But enjoy it while you can. To a geologist, beaches are very temporary things.
Every modern beach in the world today did not exist twenty thousand years ago!
At the peak of the last Ice Age, sea level was at least 90 meters (300 feet) lower than it is today. Ice Age beaches would have been miles farther out to sea! Los Angeles, Sarasota, Myrtle Beach - any city famous for its fun in the sun - would have been landlocked completely. There was no such thing as an English Channel, a Bering Strait, or even the Great Lakes.
Going to the lake this summer? Modern lakes didn’t exist during the last Ice Age. Most lakes in the Midwest are “kettle lakes”, lakes created by great chunks of retreating glaciers that broke off and melted in place.
But the Ice Age did have some enormous lakes! They just don't exist anymore. A glacial dam in Montana would create the legendary Lake Missoula. Lake Missoula at its peak covered 2,000 square miles and contained over 500 cubic miles of water - half the volume of modern Lake Michigan!
Glacial Lake Wisconsin was born when the Green Bay Lobe (a glacial lobe over present-day Green Bay) created a dam on the Wisconsin River. Glacial Lake Wisconsin would eventually grow as large as the Great Salt Lake.
However, glacial dams are made of ice. Since ice has only nine-tenths of water’s density, rising water levels will create a buoyant force that tries to lift an ice dam, like how ice cubes float in your ice tea.
When that happens, glacial lakes will empty violently!
When the dam broke on Lake Missoula, over 500 cubic miles of water suddenly raced to the ocean! This created the eerie landscape known as the Channeled Scablands of the Columbia Plateau. When the southern moraine collapsed, the explosive draining of Glacial Lake Wisconsin carved out the Wisconsin Dells, which today are a major tourist attraction.
Some Ice Age lakes were created by climate changes. Lake Bonneville was a lake that covered over 20,000 square miles - almost as big as Lake Michigan - and stretched from Idaho through Utah. Lake Lahontan in Nevada’s Great Basin Range grew to cover 8,570 square miles (bigger than Lake Ontario’s 7,540 square miles). Both Bonneville and Lahontan were over 900 feet deep, deeper than any Great Lake except Lake Superior.
What created these monsters? It was Ice Age weather! The jet stream is a zone of high-velocity wind that carries moist air from the Pacific into the American Northwest and Canada. This wind pattern strongly influences the humid climate in coastal Washington and Oregon, making it quite different from the arid Southwest. But during the Ice Age, the fierce cold of the continental ice sheet split the jet stream and established a strong region of high pressure, called an anticyclone.
This anticyclone drove part of the jet stream north and the other part south – a deflection of as much as three degrees of latitude. This detour brought the moisture-laden jet stream into the arid Great Basin, which created huge pluvial lakes. But with the ice sheet’s retreat, precipitation decreased. Lakes Bonneville and Lahontan slowly shriveled up. The Great Salt Lake – and its little sister, Utah Lake – is all that remains of the mighty Lake Bonneville. Tiny Lake Walker in Nevada is all that remains of Lake Lahontan.
Beaches may come and go, but these processes take thousands of years.
Maybe it’s all relative. After all, doesn’t every summer go by in a blink too?
Alt, David. Glacial Lake Missoula and its Humongous Floods. Missoula, MT: Mountain, 2001.
Dott, Richard H., and John W. Attig. Roadside Geology of Wisconsin. Missoula, MT:Mountain, 2004.
Orndorff, Richard L., Robert W. Wieder, and Harry F. Filkorn. Geology Underfoot in Central Nevada. Missoula, MT: Mountain, 2001.
Orndorff, Richard L., Robert W. Wieder, and David G. Futey. Geology Underfoot in Southern Utah. Missoula, MT: Mountain, 2006.
Hello! My name is Heath Shive, content manager at ScholarFox. I'll be the author of most of the blog posts. I'm a former geologist and currently a freelance writer. The world is complex and seemingly crazy. Good! Because when you love to learn, you'll never be bored.