Science writer answers rock mysteries

Williams tracked down statistics of historic floods

Two weeks ago I raised the question of the argument over the source of water for creating the landforms in the channeled scablands in southeastern Washington.

The argument was finally resolved by aerial photography.

But my sources differed with each other, and I set out to resolve the question of how much water was built up in Glacial Lake Missoula, as the huge body of water came to be called.

And I set out to find whether it was 50 cubic miles, as one source said, or more than 500 as memory kept tugging at me.

That’s a substantial difference.

After a long search I found the answer in a small book by Hill Williams, a scientific writer for a Seattle newspaper for more than 20 years and with other writing to his credit. He said it was in excess of 500.

As the ice age waned, shorelines were left by impounded water behind the ice dam, which made its way down the Purcell trench and into the Clark Fork River.

The shorelines of the lakes, each a bit smaller than the ones before it, left unmistakable marks of their existence, and can be seen to this day. Scientists studying the telltale marks say this happened at least 50 times, or about every 200 years.

I wanted statistics, and Williams gave them. The ice dam in the Clark Fork valley was 30 miles thick and almost half a mile high.

But ice is not good building material for a dam. It floats. And ultimately, as the weather warmed, it weakened.

Finally, says science, it developed tunnels through the ice mass, and warmer water went through. The dam began to disintegrate.

Then came the moment when it collapsed, and a wall of water mixed with trees, with great hunks of ice and huge rocks, swept out over the landscape.

Stream beds were completely inundated, new channels were cut, water rushed into existing stream beds, causing them to flow upstream, and rocks were torn out of their places and tumbled along in the gargantuan rush of water, carrying them sometimes hundreds of miles from their sources.

Temporary lakes, lasting only weeks, formed and drained. Water at the site of Portland was 400 feet deep.

Then, in about 200 years, it happened again, and again. That land would never be the same.

And J. Harlan Bretz correctly read the story of the action of all this water in the unlikely locale of a desert.

Hill Williams was the one who tracked down some of the statistics for us, for often we want to know how long? How much?

I repeat: What a story!

Elizabeth Widel is a columnist for

The Chronicle. This is the 2,846th column in a series. She may be reached at 509-826-1110.

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