In most of the U.S., landslides would be considered an odd and unlikely disaster to worry about. But as almost everyone who lives in the Columbia-Pacific region knows, around here they are an expensive, destructive and potentially dangerous part of everyday life for most years.
Although our own winter of 2012-13 wasnt that bad, the Pacific Northwest as a whole experienced a rainy season that was among the worst on record for landslides. A massive 200,000-cubic-yard hillside collapse on Whidbey Island in Puget Sound was sufficiently eye-catching to grab national headlines in March. Interruptions of passenger and freight rail service have been commonplace throughout the region.
The trend is interesting enough to attract attention from national media and university experts. In Clatsop and nearby counties, it is familiar news. A few years ago, the slide between Westport and Clatskanie on U.S. Highway 30 disrupted travel for months. Slippages large and small are an unavoidable part of life in Astoria. Across the river in Pacific County, slides have closed all state highways at some point in recent years. Twenty years ago, one on KM Mountain between Naselle and Longview was fabulously costly to the local economy and dazzlingly expensive to fix. There have been many more in the years since, including one this winter on State Route 100 between Ilwaco and Cape Disappointment.
Whats going on? Is this a trend, or simply an instance of news organizations looking for a story?
The usual suspect, global warming, certainly has been mentioned. In the Pacific Northwest, long-term trends are for wetter winters. In Washington the average annual precipitation has increased by about one-third of an inch each decade since the beginning of the 20th century, according to National Public Radio.
A U.S. Geological Survey scientist who studies slides in our region notes that gravity is what ultimately causes them. This is so obvious as to invite ridicule, but the deeper point is soils that have become saturated with rain are both heavier and weaker, their particles pushed apart by the water. They are prone to come tumbling down.
UW weather expert Cliff Mass, always refreshingly skeptical about attributing near-term changes to long-term climate shifts, is more inclined to look at local human-related factors as the cause for slides. He notes ...the substantial disturbance to the slopes by development on its crest and folks mucking about on the slopes. Do vibrations from the trains have an effect or the drainage from impermeable surfaces on the top? Mass wonders how proposed coal trains more than a mile in length would add to this problem.
As land values and growth management rules shoehorn more homes into remaining undeveloped areas near shorelines, its inevitable that innocent mistakes will be made. For another thing, it has been pointed out that old-growth cedar and fir roots that knitted some hillsides together are finally giving out. The land here on the West Coast is still adapting to the heavy-duty demands of 21st century humanity. It may take centuries for everything to reach a new equilibrium.
What all this means in terms of policy is for experts to figure out. Clearly, Astorias concept of placing known slide-prone areas off limits for building is sensible. Forest-practice rules must similarly keep pace with increasing precipitation, perhaps by adopting more conservative rules for acceptable grades and increasing setbacks anywhere near highways, homes or vital infrastructure like railways. Catchment walls, retaining walls and slide-detection fences are some of the other tools available to get ahead of landslides.
Property developers and homeowners are well advised to seek the advice of a qualified geotechnical engineer before upsetting the status quo of slopes. It is important to deal with these risks up front openly and professionally before approving new subdivisions or other major changes in land use.
Avoiding landslides is expensive. Unfortunately, allowing them to happen can be much more so.