Sunday, May 17, 2009

The Story of Sand: Ripples large and small

Today’s Through the Sandglass blog shows some cigarette cards from about 90 years ago that told the story of sand. Imagine thinking of cigarette cards as the blogs of their day! But since manufacturers were always looking for interesting gimmicks, a series on the history of sand would do. Inset picture: Cigarette card showing ripples from Through the Sandglass Blog.

In addition to being an adorable picture, “Ripple Marks” brought a tantalizing memory. We have all seen ripple marks just like those. At the beach where water has briefly stood, or even at the foot of the driveway when we’ve washed the car. The ripple marks I recalled were those near the “channeled scablands” in eastern Washington state, where water covered the land during and after the Spokane Floods.

The Spokane Floods! As briefly as I can tell it: after the last glaciation, melting glaciers left a vast deep lake, today called ancestral Lake Missoula. At the west end, a plug was created by a lobe of a glacier. During a thaw cycle, lake water would reach a depth of about 2000 feet, and the glacial plug would become weak enough that the flood would push it out of the way and race westward … at about 65 mph (also described as a force greater than the combined force of all the world’s rivers). Inset: a NASA photograph of a mountain wall in the Missoula valley, showing lateral wave lines left by varying water levels in ancestral Lake Missoula.

Freeze-thaw cycles turned every couple decades, and geologists reckon this cataclysm happened fifty or so times. The water’s journey depended on where glaciers currently blocked gorges. Everywhere it ran, it stripped at least a thousand feet of rich topsoil off the underlying rock and then carved the rock. From Spokane to the southwest, the water moved, down the Columbia. It flooded the Willamette Valley, leaving the rich soil behind before finally escaping to sea and carving the river’s deep entry into the Pacific.

I first read about the channeled scablands about twenty years ago and wouldn’t rest until we had taken a family vacation there. It would include four days of Lydia and her dad being bored to tears, while I had perpetual chills down my spine from viewing on every side the true force of nature. The trip’s final thrill came on the flight back, viewing the ripple marks below and recognizing in their hugeness the same energy that creates the small ones, grain by grain, at the beach. Inset image: from Google satellite, showing ripple marks in southeast Washington state. The dark area at the top left and around Rock Lake, bottom right, is scarred by the floods and has no topsoil remaining.

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