Thompson hunts for signs of past floods through her work with the Ice Age Floods Institute.
Sylvia Thompson is a flood devotee. The Portland photographer rambles all over the Pacific Northwest looking for signs of some of the greatest deluges in the planet’s history, part of her role as secretary of the Lower Columbia Chapter of the Ice Age Floods Institute. gigaflood.com .
Q The Ice Age floods—really that big a deal?
A Incredible. An ice dam holding back Glacial Lake Missoula collapsed many times during the last ice age, unleashing walls of water hundreds of feet deep that rolled from Montana to the Pacific Coast. That all ended less than 13,000 years ago.
Q What’s special about the aftermath?
A Finding a granite boulder that shouldn’t be there. Or a giant ripple on floodplain. It’s a treasure hunt. Once you understand the floods, you don’t look at the land the same way again.
Q What did the floods look like?
A Giant rivers of sludge. Uprooted trees, boulders, soil. More debris than water.
Q Where can we see clear evidence?
A The most obvious places are in the scablands of eastern Washington, but there are great flood sites in Oregon. The water deepened the Columbia River Gorge, leaving waterfalls behind. The 40-ton boulder at Erratic Rock State Park east of Sheridan rafted in on an iceberg.
Q Other Oregon sites?
A There are interpretive kiosks at Fields Bridge Park in West Linn, and the Tualatin Heritage Center has a display that includes two boulders from the floods. My husband and I guide field trips every May.
Photography by Robbie McClaran 
This article was first published in May 2012. Some facts may have aged gracelessly. Please call ahead to verify information.