|A currently active landslide at The Capes, in Tillamook County near Netarts, was first noticed in 1997 by local home owners. A small slope failure on the seaward side of a steep hill indicated that minor but steady movement was accelerating.
The slide began with small problems when a stairway to the beach was damaged and had to be removed. Ground cracks opened, and lawns dropped vertically some 18 inches in January 1998. Five more feet of drop were added a few weeks later, and fresh slumping was visible downslope.
The main area of movement is presently 900 feet long and 500 feet wide, endangering 10 houses, with 10 more at risk. Because the slide is now moving so rapidly, assessment of hazards is ongoing.
The situation at The Capes could have been easily prevented if an existing geologic assessment had been used by planners and developers. The landslide is an old structure that cuts through a 100-foot-thick body of Holocene (less than 10,000 years old) dune sand lying over muddy debris and, together with it, filling an ancient valley. Groundwater saturated the valley lined by the impermeable muds, but a contributing factor to reactivation of the landslide was the erosion of a high modern dune which had supported the toe of the landslide.
A large coastal landslide near Netarts continues to
threaten homes and property.
|Learn more about landslide hazards in Oregon: Department of Land Conservation and Development landslide hazards website
Special Paper 34 - Slope Failures in Oregon, GIS Inventory for three 1996/1997 storm events
Oregon Department of Geology and Mineral Industries
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