Boulder Park

Boulder Park National Natural Landmark, along with the nearby Natural Landmarks McNeil Canyon Haystack Rocks and Sims Corner Eskers and Kames comprise several of the best examples of Pleistocene ice stagnation landforms in Washington. Feature include numerous glacial erratics near and on the terminal moraine. Boulder Park is located on the Waterville Plateau of the Columbia Plateau in north central Washington state in the United States. The boulders provide important evidence for glacial erosion and transport, as well as marking the direction of movement and the terminus of the Okanogan lobe on the southern margin of the Cordilleran ice sheet during the last glaciation.cite book|author=Mueller, Marge & Ted|title=Fire, Faults and Floods|publisher=University of Idaho Press, Moscow, Idaho|year=1997|id=ISBN 0-89301-206-8 ]

Geologic History

The plateau

Boulder Park National Natural Landmark is located on the Waterville Plateau, which lies in the northwest corner of the Columbia River Plateau. The plateau is formed on top of the Columbia River Basalt Group, a large igneous province that lies across parts of the states of Washington, Oregon, and Idaho. During late Miocene and early Pliocene times, one of the Earth's largest flood basalts engulfed about 163,700 km² (63,000 mile²) of the Pacific Northwest, forming a large igneous province with an estimated volume of 174,300 km3. Eruptions were most vigorous from 17—14 million years ago, when over 99% of the basalt was released. Less extensive eruptions continued from 14—6 million years ago.

These lava flows have been extensively exposed by the erosion resulting from the Missoula Floods, which laid bare many layers of the basalt flows on the edges of the plateau at Grand Coulee and Moses Coulee. cite book|first=David|last=Alt|id=ISBN 0-87842-415-6|location= |title=Glacial Lake Missoula & its Humongous Floods|publisher=Mountain Press Publishing Company ] cite book|author=Bjornstad, Bruce|title=On the Trail of the Ice Age Floods: A Geological Guide to the Mid-Columbia Basin |publisher=Keokee Books; Sand Point, Idaho |year=2006|id=ISBN 978-1-879628-27-4] ["Portions of this article, including a figure, are adapted from works of the United States Government, which are in the public domain"] cite book|author=Alt, David & Hyndman, Donald|title=Northwest Exposures: a Geologic Story of the Northwest |publisher= Mountain Press Publishing Company |year=1995|id=ISBN 0-87842-323-0] cite book|author=Carson, Robert J. and Pogue, Kevin R.|title=Flood Basalts and Glacier Floods:Roadside Geology of Parts of Walla Walla, Franklin, and Columbia Counties, Washington |publisher=Washington State Department of Natural Resources (Washington Division of Geology and Earth Resources Information Circular 90)|year=1996|id=ISBN none ]

The glacial history

Two million years ago the Pleistocene epoch began and the Okanogan lobe of the Cordilleran Ice Sheet flowed southward through the Okanogan trough from the Interior Plateau of British Columbia blocking the course of the Columbia River and ending on the elevations of the Waterville Plateau. Glacial ice scoured the Columbia River Plateau, reaching as far south as the middle of the Waterville Plateau highlands above the Grand Coulee and south to the head of Moses Coulee. In some areas north of the Grand Coulee the glaciers were as much as 3 km (10000 feet) thick. Grooves in the exposed granite bedrock scraped by the movement of glaciers are still visible in the area, and numerous glacial erratics remain in the elevated regions to the northwest of the coulee.

Creation of the Boulder Park

As the glacier filled the Columbia River depression to the north and flowed out onto the Waterville Plateau, it stripped basalt from the plateau. Because of the dramatic gain in elevation, the glacier's southward motion stalled on the plateau. At the end of the ice age, as the Okanagan Lobe's leading edge stalled, debris was dropped in intense concentrations; near those locations glacial erosion was most intense, including the Boulder Park.

ee also

* List of National Natural Landmarks in Washington State

External links

* [http://www.nps.gov/ccso/nnl/nnlw.htm U.S. National Park Service on Sims Corner Eskers and Kames]

References

Photo gallery