Folded Mountains and Fiery Floods
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From this vantage point, you can view evidence of the following geologic phenomena: one of the largest lava fields in the world, the result of an uplift that created an anticline, and a steep, narrow river gorge exposing the basalt record of the lava floods. You also have the opportunity to find yakimacacher's very nearby Fiery Floods geocache while you're here.
Until the first lava flow 25 million years ago, this area was a land of meandering streams and lush, rolling hills. Long vents opened in the earth’s surface and lava spread through the land like water. After the lava cooled and solidified into basalt, lakes, swamps and streams reformed on the new, relatively flat surface. Then lava flooded the land again. The time between lava flows was sometimes months, sometimes hundreds, even thousands of years. Each eruption reset the clock in a cycle that continued for 15 to 20 million years. The layers of basalt visible in these valley walls are part of one of the largest lava fields in the world. It covers over 200,000 square miles in Washington, Oregon, and Idaho and is astonishingly thick in some places.
Untanum Anticline: Folded Mountains
Toward the end of the lava flow cycle, the land began to rise, forming the Cascade Mountains. Over millions of years, tremendous pressure from beneath the earth’s crust warped the flat basalt layers of this area into hills. The Untanum Ancline, the geologic feature at this location, was formed when the basalt layers were folded by this immense, slow pressure. As a result, the Cascade Mountains changed the climate of the Columbia Basin into a semi-arid plain.
Yakima River: Older Than the Hills
Before the uplift of the Cascade Mountains, the Yakima River was a peaceful, meandering stream. The land rose across the river’s path, but so slowly that the rate of erosion by the river equaled the rate of uplift. Although slow by human standards, the erosion was swift by geological standards, as is evident by the steep, narrow gorge cut by the river. The layers of basalt exposed by the river cutting through are part of the rock record of the lava flood that created the Columbia Basin.
To log this earthcache, please email me (through my gc.com profile) the answers to the following questions. You will be able to find the information at the roadside marker. Once you've sent the email, go ahead and log your find without waiting for a reply from me. I will contact you if there are any problems with your log entry. (It is difficult to keep track of log entries when there is a substantial gap in time between the email and the log entry, so please send the email and then log the cache at the same time.)
1. In some places, what is the reported thickness of this lava field?
2. How do the Cascade Mountains affect the climate of the Columbia Basin?
3. Why did the Yakima River retain its early meanders during the uplift?
4. Optional (but appreciated): Post photos of yourself with the view, being sure to not reveal any answers to the questions in your photographs.