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The Webfooted Astronomer - August 1999

 

Bus Tour to Mars

by Mary Ingersoll

In the early hours of Thursday, about 30 "AstroConers" boarded a bus bound for Mars. Actually, the air-conditioned bus carried us to the Columbia Plateau and Channeled Scablands of Eastern Washington for a field trip led by Dr. John P. Buchanan (professor of geology at Eastern Washington University, and amateur astronomer).

Our first stop off of Interstate 90 was a long wall of six-sided columns of basalt. It was here that Dr. Buchanan began telling us the history of the formation of the Columbia Plateau, a land covered numerous times by lava that had extruded through a series of vents and fissures located in southeastern Washington and northeastern Oregon. "Each individual flow consisted of a tripartite cooling unit with a characteristic colonnade (large columns), entablature, and vesicular zone, from bottom to top." There were more than 300 flows that covered the plateau region, the thickest portion is near Tri-Cities and is about 4,000 meters thick.

Armed with this information we then headed down the road looking for walls of basalt, attempting to count the separate flows. The second stop however, had nothing to do with basalt. We stopped in a field and walked toward a long lump of sandy dirt where we found ourselves standing in the middle of a giant ripple of a 40-mile flood channel. The mega-ripple field covers an area of approximately 60 sq. km (23 sq. miles). Their coarse-grained texture reveals a flood origin rather than eolian (blown there by wind). Dr. Buchanan told us of the floodwaters that rushed through this area from the outburst of Glacial Lake Missoula from behind an ice dam in northern Idaho during the last glacial epoch (Pleistocene). Multiple floods scoured the area with peak flows reaching 17 million cubic meters per second (surf's up, dude!)

The flood origin for the Channeled Scablands was originally proposed by J. Harlan Bretz in 1923. He drew maps of the topography of the area that are almost identical to present aerial photographs. The catastrophic flood proposal was dismissed by his contemporaries, but today is not only confirmed by scientists, but also taught in college geology courses.Stop number three was at the pillow lavas near Grand Coulee. An exposed road cut revealed a pillow pattern made by the oozing lava when it had entered water on land (such as a lake or stream channel), or directly into water from below (submarine). Quick cooling from the water created the bulbous forms of fractured basalt looking very much like a large cluster of tortoises with their backs to us.

Next stop—lunch! At the Crown Point Vista above the Grand Coulee Dam we were treated to a buffet lunch hosted by Jay Cousins of the Spokane Astronomical Society. The granite around the covered eating area had been worn smooth by a glacier many years before our visit. We were now at the very edge of the lava flows, which made it easy for engineers to expose the granite below the layers of basalt for the foundation for the great dam. Except that there were fractures in the granite beneath the dam that had to be grouted before it could become fully functional (much like many a bathroom in the Seattle area).

After a drive over the dam, we headed south through the Grand Coulee, past Steamboat Rock (standing high above the water of Lake Banks, looking much like a flattened pyramid) and on to Dry Falls. Dr. John told of the racing floodwaters (reaching nearly to the rim of the canyon for a flood depth of 500 feet). The water and ice deposited granite boulders on Steamboat Rock, rushing southward at 110 km/hr (68 mph). It chewed away at the basalt, digging down and picking up boulders the size of Uncle Bob’s van, and then pouring down what was once the largest waterfall in the world (four miles wide). In trying to image the scene, I was almost sure that I could hear the ear-piercing roar of the falling water, but it turned out to be the bus starting up and preparing to take us to the next stop.

As the sun was edging toward the west, and we knew we were going to miss dinner, we skipped two sites (Sun Lakes State Park and Lane Lenore Caves) and hurried on to the Ephrata Fan. Here the boulders were strewn about in a debris field left by the floodwater as it slowed and diminished. Dr. Buchanan then brought out his motorized model of the Mars Pathfinder to illustrate how NASA and JPL scientists had brought a prototype rover here for testing. We were now in Ares Vallis, the Pathfinder landing site, crawling over our own "Yogi" and "Casper" rocks. Occasionally a grasshopper would leap in front of the rover and bring us back to reality. It was not difficult to imagine being on the surface of Mars in that setting.

We hopped again into our transport and headed back to EWU, just in time to for the 8 p.m. social hour. Some of us opted to chew on a few gingersnaps and head for bed instead of attending the star party, as our heads were "waterlogged" with data, and we just wanted to "rock" ourselves to sleep.

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