Spokane to Davenport 2

Basalt, Buttes and Channeled Scablands
Continued

[5.0 MM 278]
Look for giant ripple marks in the fields to the north near Airway Heights. In the photo of the ocean beach at right, the sand ripples are smaller versions of these giant ripples. Most ripples are usually less than an inch high and a few inches between the tops (crests) of each ripple. Large ripple marks like these are found elsewhere in the Channeled Scablands and were the most convincing evidence for the Glacial Lake Missoula floods.

In the photos below you can see fields and these giant ripples from the air. Note that the image is made from several photos and that the dark gray circular areas are irrigated crops.

Giant Ripples from the air. Close up of ripples (on right). USGS aerial photos.

"This mega-ripple field covers an area of approximately 60 square kilometers (23 square miles). The wavelength (length of each ripple) of these ripple bedforms range approximately from 60 to 120 meters! Amplitudes (height of ripple) range from 2 to 9 meters. Their stratigraphy (layers) and coarse-grained texture suggests a flood origin...clearly the product of floodwaters moving through the region." [Buchanan]

[10.5 MM 273]
Loess, extremely fine sand particles blown by the wind in arid or glacial areas, covered the basalt layers and provides the fertile soil in the Palouse hills where dry land farms grow wheat, barley, lentils, bluegrass for lawns, and other farm crops.

Beneath the golden brown loess on this road cut is a sand and fine gravel deposit. We will see this tawny soil in road cuts in a number of places as we travel.

In the NASA image of Mars at right there are shaped islands and channels that are thought to have been caused by a great flood. These shaped channels are similar to those we will be passing through in this part of our trip.

The Mars Pathfinder landed in the Ares Vallis area (center of picture) that has flood channels and flood plains like those we will see later.

As we continue on US 2 for a few more miles we will be on the edge of the Channeled Scablands. At the town of Davenport we will turn south to drive through a flood channel and onto one of these islands.

[24.8 MM 258]
We see basalt exposures in the Scabland channelway. During the Ice Age floods, basalt was ground into depressions where pools now form. This scouring of the basalt can also be seen in and around Spokane as seen in the photo at right. This basalt knob is about 5 feet across.

Giant Floods and Channeled Scablands

When Ice Age glaciers blocked the Columbia River, the Spokane River and the Clark Fork river in Montana they formed Glacial Lake Columbia, Glacial Lake Spokane and Glacial Lake Missoula. The evidence of these lakes can be seen in the lakebeds visible in various road cuts in eastern Washington and lap marks on hills and gravel deposits in Montana. Glacial Lake Missoula, the largest lake, covered some 3000 square miles and was about 2000 feet deep. What happens when 500 cubic miles of water is suddenly released? Find out more on the Channeled Scablands page or continue on to the NEXT page.

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Geology Terms

Here are some basic terms used on this page. Find more geology terms in the Glossary.

Basalt

Volcanic rock caused by partial melting of the Earth's crust.

Catastrophic Principle

A concept proposing that all geological features were formed by sudden, catastrophic events like volcanoes, earthquakes, floods and even asteroid hits. Most geologists today believe that certain catastrophic events may form features but most are formed by slow processes that happened in the past just as they do today (uniformitarianism). Also, Catastrophism.

Channeled Scabland

Area in Washington state where huge floods made channels in a large, deep basalt flow. Named by J Harlan Bretz during the 1920's in various publications. See also Channeled Scablands and Glacial Lake Missoula.

Geomorphology

The study of the changes in landforms due to volcanoes,
earthquakes, weather, floods, etc.

Granite

Coarse-grained igneous rock usually without obvious bands or markings.

Ice Age

A period in Earth's history when much of the continents are covered with ice sheets and glaciers.

Uniformitarian Principle

A concept proposing that all geological features were formed just as features are formed today. Sudden events like volcanoes, earthquakes, floods and asteroid hits are not to be considered when describing how features are formed. Also, Uniformitarianism.

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