Portland State Magazine Spring 2013

SPRING 2013 PORTLAND STATE MAGAZINE 15 a depth of 2,100 feet and contained the equivalent of half of Lake Michigan. The ice dam broke, creating a flood of biblical proportions. It scoured the eastern half of Washington, then filled up the Columbia Gorge, traveling at speeds of up to 60 miles an hour. “If you take the flows of all the rivers in the world measured in cubic meters per second, add them up and multiply by 10, you have the flow rate of the Missoula Floods,” Burns says. The floodwaters filled the Willamette Valley to a depth of 400 feet all the way to present-day Eugene, and then receded north, joined the Columbia River, and drained into the Pacific. The water carried granite sediment from Montana, and deposited it at various spots along its course. All rocks are radioactive to some extent, because they all contain trace levels of uranium, but some have more than others. Basalt, coming from the Northwest’s volcanoes, doesn’t have much; granite does. Radon is a product of the breakdown of that uranium. A house built on soils containing granite sediments— especially porous soils that allow the radon gasses to rise and dissipate—is subject to dangerous levels of radon exposure. Portland’s Alameda Ridge is one such place, and has one of the highest radon levels in the city. The ridge was formed when the Missoula floodwaters encountered Rocky Butte. There, the waters slowed and changed course, depositing several cubic miles of granite-rich sediment. Burns has known about radon levels on Alameda Ridge since his first study came out 20 years ago, and his most recent study backed it up. The surprises came when areas that were not really affected by the Missoula Floods cropped up as being high in radon: Sandy, for example. “Sandy is my mystery city. It was above the Missoula Floods, so I can’t figure out why the levels are high.” Newberg also doesn’t fit the same profile as other high-radon areas. The soils there are not very porous—which seems to be a prerequisite for high readings. However, it sits on top of major faults, which enable the release of radon from deep in the earth, Burns says. DATA FOR THE STUDY came from tests people through- out the state performed in their homes. For as little as $12, you can get a test kit from your local hardware or home Washington Portland Gresham Beaverton Hillsboro Oregon PORTLAND AREA RADON LEVELS RADON POTENTIAL High Moderate Low Uncategorized Rn Radon 86