PSU Magazine Spring 1999

Today's troubles arise because the fickle Troutdale Formation never had time to settle down. Made up of a mix of different soils and gravels-what geologists call "poorly consolidated material"-the Troutdale tends to slide when saturated with rain, espec ially where it rests on its hard , slick Cowlitz base, as in Kelso. The more fine-grained the soil, the more easily it shifts. "The whole area from Oregon C ity to Kelso is like a big bowl, filled up with these kind of deposits," Bums says. In places like east Multnomah County, where the sediments are larger, the Troutdale is well-drained and less of a hazard. Portland's West Hills also rest on larger sediments. After a day of dry weather, their soils quickly drain, Bums says. But when a lot of rain fa lls without letup , the steep ground can still lose its grip . L ike it or not, we have to live with our geologic history. We can 't fight the bas ic forces of nature. And with global warming, meteorolo– gists predict those forces will get nastier: more intense storms, more hurricanes and tornadoes-and so, more landslides. But Bums points out three things that can mitigate future tragedy: better surveys of hazardous sites and condi– tions, more public education , and stronger regulations. PSU's geology faculty and students are engaged in a number of studies to better map the area's risks and dangers, including compilation of a home– owner's guide for the Federal Emergency Management Agency. In their studies, Bums says, they look to the past for telltale signs of future trouble. Where land has fa iled before, for instance, it's likely to fa il again. "One thing we need to do is delin– eate where these ancient landslides are and avoid building on them, whenever possible," he says, citing the Aldercrest development in Kelso as a "classic example of a reactivation of an old landslide." S ince human development, as we ll as nature, can trigger an ancient slide, assessing the hazards in advance is 16 PSU MAGAZINE SPRI NG I999 critical. Cutting off the base , or toe, of a slope can set it in motion. Poorly compacted fill , or bad grading, can destabilize a hillside. Without adequate dra inage, water saturates the earth, loosening the soil. In helping ra ise awareness in the community, Bums is frequently on the go, speaking to Rotary clubs and other groups, offering sound bites for televi– sion news, and granting interviews to newspapers and magazines. Geology graduate students serve as free consul– tants to area businesses and govern– ments, learning by doing while at the same time providing a vital service. M eanwhile, the O regon Legislature is grappling with the tricky task of regulation in a state where land use planning delegates a lot of dec isions to local governments and where homeowners and builders alike chafe at meddling bureaucrats. Currently, different counties have differen t requirements for assessing hazardous sites. Even with proper geologic surveys in hand, loca l offi cials may lack the expertise to eva luate them. Senate Bill 12, now under consider– ation, would first of all restrict logging, especially around streams at their sources high up on slopes. Logging there creates dams which burst during storms, unleashing huge landslides of slurry-a mixture of water and soil– downstream, like those during the 1996 storm, which killed several people and tossed houses about like toys. The bill would also instruct the Department of Land Conservation and Development to require local govern– ments to identify landslide hazard areas and regulate the building of homes in these areas. It proposes amending state building codes to require geotechnical reports for areas at high risk of slipping, and include landslide dangers on a list of items that must be disclosed to a potential buyer. Whatever the shape of the final bill, Bums believes such changes are badly needed. "It's a question of balance," he says. "We need to save lives and prop– erty, without treading too much on people's property rights." D For the high-end Cape Meares town– houses on the Oregon coast, devel– opers thought they were doing all the right things-but they got it all wrong. The project, known as The Capes, should never have been built. First-rate geologists, hired by the developer, did a careful study of the 89-aae site on a huge forested dune, concluding that it was stable-an 80,000- to 100,000-yeafoOld-fixture. Tillamook County planning commis– sioners who approved the project had no reason to doubt this conclu– sion. They were wrong, though they had no way of knowing it at the time, according to Professor Curt Peterson. Recent research of the Oregon and Washington coastline, which Peterson and others have carried out over the last decade, has found the Cape Meares dune to be much younger-and much less stable. Instead of being thrust up by tectonic heavings tens of thousands of years ago, the cape Meares dunes formed out of windblown sand a mere few thousand years back. That mistake in the dune's age is only the beginning of the story, which involves tectonic plates under the oceans, giant tsunamis, El Nino, and the movement of sand out of curious things geologists call littoral cells-actually, stretches of beach bounded at both ends by protruding headlands. Start with the Juan de Fuca plate along the Northwest coast, •subduct– ing" or sliding under the North American plate. The trouble is, •it's sliding under in jerks,• says Peterson. Think of an ocean liner crashing full speed into another one, then magnify that 10,000 times and you begin to get the picture. The force of impact churns up giant tsunamis. The last big one, in 1700, crashed against the Oregon coast with 30-foot-high waves and swept a mile or so inland in lower-lying areas.