Landslides in the Columbia Gorge and Portland-Vancouver Area

January 1997

Heavy precipitation occured in the Portland-Vancouver area between late December 1996 and early January 1997 resulting in local landslide activity. On Friday 10 January Richard Waitt and Roger Denlinger of the USGS Cascades Volcano Observatory drove up the Columbia Gorge from Vancouver to Hood River, to observe recent landslides. They each made 1-2 separate additional trips up the Columbia Gorge January 11 to 13. Their observations follow:

The western part of the Columbia Gorge on the Oregon side, had numerous small debris flows down small gullies off very steep slopes, most or all of them in the trouble spots of last Febuary. These flows covered the UnionPacific - Southern Pacific Railroad in a few places. but obstructions were cleared by 10 January. In this section of the Gorge two ice (freezing-rain) storms on 26 and ~28 December 1996 had stripped limbs off thousands of trees, adding to the debris flows in early January.
In side channels at Dodson Oregon, where destructive debris flows occurred in February 1996, there had been recent high water in the two main channels but flow remained entirely within banks, nothing unusual, certainly nothing like last February 3. From Latourelle Falls to Viento, the freezing rain of the December storms had been replaced by ice-pellet snow, which shed down into several scores of great snow fans that blocked the Columbia Gorge Scenic Highway as deep as 4-m and in places extended out onto the railroad tracks. As of Monday the 13th of January this highway remains blocked East of Multnomah Falls, but has been cleared to the west. One of these great snow fans built into Multnomah Creek below lower Multnomah Falls, filling the channel, and the creek overflowed 0.6-m deep into the historic Multnomah Falls lodge, damaging the lower floor and US Forest Service exhibits. The building remains closed.
The February 1996 slide on bluffs near Stevenson, Washington has not changed much. Waitt and Denlinger saw minor sloughing and perhaps evidence of small movement on 1 or 2 of the February '96 scarplets. Skamania County has hired a geotechechnical consultant to monitor the slide.
On State Highway 14, a few miles below Skamania, Washington the highway sheared along the margin of a creeping slide that damaged the highway last February. Only a few inches of movement is evident in new pavement laid in the spring or summer 1996. In February, 1996 an upslope part of this slide had toppled into a debris flow, which blocked and closed the highway for a few days.
On the Washington side of the Columbia Gorge the same sequence of events from the late December storms occurs: thick snow fans in the west-central portion and broken trees from freezing rain in the west-most portion.
There are several small moving slides in the lowlands reported in the newpapers and (or) TV which Waitt and Denlinger have not yet visited. The two most newsworthy are near Camas, Washington and near Oregon City, Oregon. Both are shallow slides on steep slopes. At Oregon City a few houses are built on a slide that has flowed some meters; at least 3 and perhaps 5. The houses are now abandoned. The Camas situation seems like that near Stevenson but smaller, with meter-deep headscarp grabens opening in yards, but no houses abondoned as of yet.

Roger P. Denlinger
USGS
Cascades Volcano Observatory
roger@usgs.gov (roger@asopus.wr.usgs.gov)
5400 MacArthur Blvd :
Vancouver, WA 98661

Richard B Waitt
USGS
Cascades Volcano Observatory
waitt@usgs.gov (waitt@asopus.wr.usgs.gov)
5400 MacArthur Blvd :
Vancouver, WA 9866