It’s fairly quiet now, but central Washington has a tumultuous past. The past scarred its landscape multiple times. Last weekend, I took a field trip of the Geology of Grant County, Washington. It painted a picture of numerous, massive volcanic eruptions burying entire ecosystems with basalt rock and fire; and multiple episodes of equally massive ice age floods, spreading enormous walls of water over the region, carving through the newly-laid rock, drowning a multi-state area underneath a huge lake.
And that’s just what we covered on the middle day of the tour.
Below are some photographs of the field trip, led by geoscientist Mark Amara, organized by Association of Women Geoscientist – Pacific Northwest Chapter board members Theresa Burton and Marcia Knadle, with geological explanations.
Wanapum Basalts: Volcanoes
Wanapum Basalts by Shari Maria Silverman is licensed under a Creative Commons Attribution 3.0 Unported License. The lava that formed these basalts flowed from a vent in Idaho westward into Washington between 15.6 and 14.5 million years ago. They were in a middle of a series of lava flows, which occurred between 17.5 and 6 million years ago (Bjornstad et al. 1997:211, Fig. 2). This photo was taken by Banks Lake.
Dry Lake: Ice Age Floods
Dry Lake by Shari Maria Silverman is licensed under a Creative Commons Attribution 3.0 Unported License. When they flowed over basalt rock 14,000 years ago, these falls dwarfed Niagara. They spanned 3.5 miles and plummeted 350 feet. The water may have been 300 feet deep before cascading over the cliffs. The water originated from an ice dam break, which released glacial Lake Missoula to pour over central Washington. The gargantuan glacial river carried huge icebergs and boulders, as as sands, mud, and gravel. All these scoured the landscape (Amara and Neff 2008).
Erratic on Steamboat Rock: Ice Age Floods
Erratic on Steamboat Rock by Shari Maria Silverman is licensed under a Creative Commons Attribution 3.0 Unported License. This is a crumpled, granite boulder on top of Steamboat Rock. It probably landed here during one of the great floods from glacial Lake Missoula began to peter out, stranding an iceberg. As the iceberg melted, it settled here. These foreign rocks are called erratics. Some come from as far away as Canada and exhibit features of Rocky Mountain granites (Amara and Neff 2008:11-12, 21).
Two Erratics on Steamboat Rock: Ice Age Floods
Two Erratics on Steamboat Rock by Shari Maria Silverman is licensed under a Creative Commons Attribution 3.0 Unported License. Erratics dot the entire top of Steamboat Rock. However, they’re pretty far away from each other. This is a view from one granite erratic looking northish to another one.
East – West Coulee on Steamboat Rock: Ice Age Floods
According to the Ice Age Institute, a coulee is defined as follows:
“A long, dry, steep-walled, trench-like gorge or valley representing an abandoned river channel. In south central Washington, the term coulee is mostly used for an abandoned ice-age flood channel,” (Ice Age Flood Institute 2002-2011). Coulees formed throughout central Washington and neighboring areas as the huge floods from glacial Lake Missoula poured from the narrow opening of the broken Ice Dam along the Clark Fork River. Some were large, like the ones formed by the Dry Falls photograph. Others were smaller, such as the East – West Coulee on top of Steamboat Rock.
East – West Coulee on Steamboat Rock by Shari Maria Silverman is licensed under a Creative Commons Attribution 3.0 Unported License. A trail connecting the top and the bottom of Steamboat Rock briefly runs through the East – West Coulee near its mouth. The mouth appears to be a hanging valley, through which streams fall to depths below during spring runoff. The sage grows tall and abundant here compared to many other parts of Steamboat Rock.
Playa on Steamboat Rock: Ice Age Floods
The tall grasses growing in this shallow depression may indicate that this spot on top of Steamboat Rock may be a playa. A playa is a “dry lake basin found in a desert,” (Chernicoff and Venkatakrishnan 1995:G-12). When an iceberg was stranded on top of Steamboat Rock during a receding flood, its meltwater could have formed a shallow lake (Amara 2013).
Link to Part Two of Field Trip
Basalt Monocline and Ice-age Grand Coulee
Amara, Mark S.
2013 My (Shari Silverman’s) field notes taken during a geological field trip (April 13, 2013) that Mark Amara led. They are field notes. They capture general items said, but I can only write so fast while taking pictures, so take them with that note.
Amara, Mark S. and George E. Neff
2008 Banks Lake to Soap Lake. In Geologic Road Trips in Grant County, Washington. Moses Lake Museum and Art Center, Moses Lake, Washington.
Bjornstad, Bruce N., R. Scott Babcock, and George V. Last
2007 Flood Basalts and Ice Age Floods: Repeated Late Cenozoic Cataclysms of Southeastern Washington. In Floods, Faults, and Fire: Geological Field trips in Washington State and Southwest British Columbia, Stilling, Pete and David S. Tucker, editors. In The Geological Society of America: Field Guide 9, 2007. The Geological Society of America, Inc., Boulder, Colorado.
Chernicoff, Stanley and Ramesh Venkatakrishnan
1995 Glossary. In Geology. Worth Publishers, New York, New York.
Ice Age Floods Institute
2002-2011 Glossary of Technical Terms Related to the Ice Age Floods. Within Ice Age Floods Institute website. Electronic document, http://www.iceagefloodsinstitute.org/glossary.html, accessed April 21, 2013.
Basalts and Ice Age Floods of Grant County, Washington by Shari Maria Silverman is licensed under a Creative Commons Attribution 3.0 Unported License.