On February 8, 1996 a massive landslide gave way on the south side of the valley. Actually it began the day before with slides coming down all over the gorge. It had been raining hard for several days. The snow had melted at the top of the cliff which was unusual, adding even more water. Around noon on February 8th, a 2,000 feet vertical cliff gave way. The earth shook as the huge wall of mud, water, rocks and trees roared down toward Carol & Hersh Royse’s farmhouse on the frontage road along Highway 84. They ran out in the front yard, crawled through the board fence and down through the field to the frontage road.
The slide engulfed the farmhouse, filling the basement and first floor with water, mud and rocks up to the kitchen counter tops and tore out the living room on the west side. It pushed their earth stove about 100 feet out in front of the house. Four to 15 feet of mud, boulders and trees completely covered their property down to the Frontage Road.
Bonneville School, located on the alluvial fan at elevation 55 m and about 1,500 m northwest of the steep gorge slopes, incurred damage to fencing and partial burial of the school’s parking area with muddy debris from an overflow lobe. The Bonneville School District subsequently retained GRI to evaluate the potential for future debris flows to affect the school. GRI observed that subsequent erosion in the main channel of the debris flow stranded the initial overflow lobe, which provided additional catchment space for subsequent flows and diminished the immediate hazard to the school. GRI provided recommendations for debris flow risk management procedures to the school district.
An upstream reconnaissance of the Tumalt Creek drainage in 1996 documented areas with sharp, V-shaped channels, erosion and exposure of older debris flow deposits, and large transported boulders up to 3 m in diameter. Re-examination of these areas in 2002 documented channel migration patterns, redistribution of channel sediment, erosion of channel side slopes, and stream downcutting. Alder regrowth and other vegetation patterns also provide useful markers for the 1996 erosional and depositional surface. Several examples of comparative ground photography from 1996 and 2002 will be presented and reviewed.
The school was closed in late 1996 in response to long-term changes in student enrollment patterns, not because of the debris flow hazard.
In this imagery from Google Earth, the Royse farm house and other structures are visible in the lower left corner, slowly being consumed by the forest over the years... The first image is from 1993, before either slide.
First the effects of the 1996 Leveens Creek slide becomes visible, then the 2001 slide appears on the next creek over to the west.
Portland State University Page on the 1996 Event:
Follow the link below for some great before and after photos of the farmhouse.
Waymarking.com: Massive Landslide, Dodson, Oregon
http://www.waymarking.com/waymarks/WM16PD_Massive_Landslide_Dodson_Oregon
Portland Hikers: The Landslide House
http://www.portlandhikers.org/forum/viewtopic.php?f=30&t=10862
Portland State University Page on the 2001 Event:
http://geomechanics.geol.pdx.edu/Projects/Dodson/2001_Flow/default.html