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Aerial photographs verify historic floods

Big water carved out much of the state’s landscape

When J. Harlan Bretz claimed that the channel scablands were formed by flood waters, he was not believed.

Where, they asked, will you get that in a desert?

For a time he could not answer that question. But aerial photographs proved that water had, indeed, created these great forms.

Finally the story came out. During the ice ages thousands of years ago, a great glacier had slowly moved down the Purcell Valley, finally stabilizing east of Spokane. Water accumulated behind the ice dam, back into every valley until a lake of some 504 cubic miles had formed.

Icebergs are thought to have floated on its surface.

But ice is not good dam material.

It floats.

After the pressures rose beyond what it could hold, the dam broke.

A wall of water perhaps a half mile high roared across the landscape, bearing huge hunks of rock from as far away as the northern Rockies, tumbling them over anything in their path, cutting great channels, piling up gravel bars hundreds of feet in length and scores of feet high.

The torrent rushed over the landscape, which would never be the same. It topped ridges and divides, cutting new channels and rushing up pre-existing streams and causing them to flow upstream in the rush.

It formed great temporary lakes where it could not find a channel. Often they were named, though

photo

The Palouse Falls, one of scores of waterfalls created by the huge floods, is one of only a few to survive to this day. Much of the state’s landscape has been carved by these massive floods, which are believed to have happened as many as 50 times.

they were temporary. One of these, called Lake Columbia, is thought to have helped carve the Grand Coulees as it drained vigorously.

Waters impounded temporarily at place after place in the course of the Columbia River, Wallula Gap, possibly the best known. It was a tumultuous time, and nothing in its path was safe.

Ultimately, in a time said to be two weeks, the huge lake behind the ice dam drained, leaving a scarred and altered landscape behind.

But about 50 years later, say researchers, it happened again, and yet again.

It is believed that this happened at least 50 times, deepening channels and cutting new ones each time.

The monster lake behind the series of failed ice dams has been named Glacial Lake Missoula, and it left, in the waning years of the ice age, the now silent shorelines.

The repeated lines of the successive lakes show through the landscape, which they formed and drained catastrophically.

Ultimately, the ice ages ended, and the silent and forever scarred landscape still bears testimony to their being and passing.

How the ground must have shaken under the onslaught of this flood, which has been termed the greatest the world has ever known.

And the multitude of coulees, two huge ones (Grand and Moses) and scores, perhaps hundreds, of smaller ones bear witness to the drama that happened here.

Bretz was vindicated in his explanation of this landscape and deforming of a quarter of the state. He lived to see his explanation of the landscape accepted by most (though not quite all) of those who followed his lead.

There is an old saying, “Nothing on earth can stop an idea whose time has come.” It took the better part of a century – and those aerial photographs – to prove Bretz’s contention that it was water, big water, that carved out the southeast portion of this state.

What a story it makes!

Elizabeth Widel is a columnist for

The Chronicle. This is the 2,845th column in a series. She may be reached at 509-826-1110.

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