Digging in a Geologist's Playground

Oregon's natural wonders double as teaching tools for Liz Safran. Last semester, she ferried students from her spatial analysis class to two well-known destinations--the Columbia River Gorge National Scenic Area and the Deschutes River--to dig for clues about when the landslides they mapped in class actually occurred.

In February, they traveled east along the Columbia River just past the Bridge of the Gods, the 80-year-old steel crossing that geologic evidence and Native folklore suggest was once the site of a natural rock bridge. Safran says geologists are fairly certain when landslides created the bridge, but less sure about when and how it was breached.

Since the bridge would have backed up the Columbia River into a "Lake of the Gods," Safran says finding and dating sediments from that lake could yield valuable evidence. So the class spent a day shoveling and breaking apart rocks at riverside gravel pits and road cuts, looking for evidence that those deposits might once have formed a delta at the lake's edge. "I wanted to show students how geologists gather information they need to tell a story about an event," Safran says.

Then, on a Friday in March, five students accompanied Safran to a spot along the Deschutes River about 50 miles south of The Dalles. They spent a frigid night camping beside the river before scouring the landslides along the river canyon for evidence of their age.

One way to roughly date a landslide, Safran says, is by examining layers of sediment that accumulate in depressions created by the blocky topography within the landslide deposit. After locating one sufficiently deep depression, the students used two 9-foot-long augers to extract a cross section of sediment and look for the fine gray material that distinguishes volcanic ash from other deposits.

Scientists can chemically fingerprint the ash to determine its age. This information, coupled with the ash's proximity to the bottom of the sediment pile, is used to estimate when the landslide occurred.

Safran hasn't gotten the results back yet, but she suspects some of the ash the students dug up was from Mount Mazama--the peak whose violent eruption 7,700 years ago led to the creation of Oregon's Crater Lake.

Students were impressed. "It's research in action," says Caitlin Sampson '06, an environmental studies major from La Grande. "We did a lot on the computer, but the fun stuff is going out to the field. It makes the work come alive."