Geologist tells dramatic story

Not only did dozens of gigantic floods shape the local landscape thousands of years ago, they raced across the solid-rock remains of hundreds of layers of lava flows that built the local bedrock millions of years earlier.

So said Geologist Nick Zentner to roughly 130 people at the Grand Coulee Dam Visitor Center on Saturday, brought to town by the Grand Coulee Dam Rotary Club.

Zentner, who hosts the video series "Nick on the Rocks," spoke for over an hour in the upstairs theater in the Visitor Center, presenting interested facts and a slideshow, then fielding questions from the audience that included members of all ages.

Zentner detailed the lava flows that formed the basalt of the "Channeled Scablands" and the Grand Coulee, and the Ice Age glaciers and floods that carved the basalt into the shape they have today.

The lava flows stacked up on each other, in about 300 layers Zentner explained, erupting out of cracks in the earth, rather than mountain volcanoes, about 16 million years ago. Imagine a 300-layer cake, he said.

Zentner said that the lava flows were about three miles thick in the Tri-Cities area.

The weight of the basaltic lava affected the slope of the land in Washington, changing the direction that water, such as the Columbia River, flowed, Zentner explained.

Maps of what Washington and the Pacific Northwest looked like following the Missoula Floods showed the area where dozens of Ice Age floods changed the landscape between 13,000 and 15,000 years ago when an ice dam, where the Grand Coulee Dam is now, diverted the Columbia south through the coulee.

Zentner showed simulations of what Dry Falls would have looked like during the floods, emphasizing that it wasn't a peaceful looking waterfall like Niagara Falls, but a much more violent and intense flow of water, dirty with the loess, or the flour-like dirt of granite ground up by nearby glaciers, that covered the land and formed the Palouse Hills, even the farmland around Wilbur.

Zentner said that the edges of the cliffs at Dry Falls carved by the floods were likely nearer to Soap Lake, but as the floods plucked away the basalt, the edges eventually ended up being at present day Dry Falls. One more flood, he noted, would have brought the falls even closer to where Grand Coulee is today.

Many questions still need to be answered, Zentner said, noting his recent fascination with the fact that scientists have relatively recently confirmed that humans were in the region during the latest Ice Age floods.

Zentner recommended http://www.hugefloods.com for finding good details on the Missoula Floods and some of his videos.

Upper right, Nick Zentner displays a slide of lava erupting in Iceland in 2014 to show how lava came from cracks in the Earth in this region to form the layers of basalt we see on the coulee walls. - Scott Hunter photos

Zentner, left, chats with people after his presentation at the USBR VC.