Landslide of the Week – Ribbon Cliff Landslide

July 20, 2009

Each week we will feature a new landslide in Washington State. Washington State is covered with dynamic and sometimes quirky landslides.

Ribbon Cliff Landslide, Chelan County

The Ribbon Cliff landslide moved on December 14th, 1872, during (or shortly following) the 1872 earthquake. The landslide moved into the Columbia River and blocked it for several hours.
The earthquake location has been sort of a mystery until recently, as paleoseismic scientists have tracked down an approximate location for the landslide. The landslide was centered somewhere near Lake Chelan and caused some fairly interesting stories. Excerpted from the USGS website:

“Most of the ground fissures occurred at the east end of Lake Chelan in the area of the Indian camp; in the Chelan Landing-Chelan Falls area; on a mountain about 19 kilimeters west of the Indian camp area; on the east side of the Columbia River (where three springs formed); and near the top of a ridge on a hogback on the east side of the Columbia River. These fissures formed in several localities of differing physiographic environments. Slope failure or settlements or slumping in water-saturated unconsolidated sediments may have produced the fissures in areas on steep slopes or near bodies of water. Sulfurous water was emitted from the large fissures that formed in the Indian camp area. At Chelan Falls, “a great hole opened in the earth” from which water spouted as much as 9 meters in the air. The geyser activity continued for several days, and, after diminishing, left permanent springs.”

It would take some time, but it would be interesting to try and find the locations of slope failures from this landslide.

Ribbon Cliffs Landslide Location Map

Ribbon Cliffs Landslide Location Map

Ribbon Cliff Landslide

Ribbon Cliff Landslide

The landslide toe is a bit difficult to determine. The Rocky Reach Dam, built in 1962, formed Lake Entiat, which inundated the toe of the Ribbon Cliff Landslide. Older topographic maps indicate a probable toe (which is the loosely drawn toe on the map above). The landslide was drawn to the area mapped out in Madole et al, 1995.

The landslide location is along the Columbia River and was probably subjected to undercutting and oversteepening from erosion. Evidence of landslides (one just north of the Ribbon Cliff Landslide) is evident when looking at aerial photos of DEMs. The landslide itself was probably not a rock fall/topple event, but more of a translational landslide, that carried the mass relatively intact.

One of the more interesting summaries of the landslide can be found on this website. It gives a general summary of the landslide (plus some amazing oblique pictures of the landslide).

Controversy
It turns out (like most things in science) that not everyone agrees the Ribbon Cliffs Landslide is from the 1872 earthquake. The 1872 date, beyond the account of the 15-year old youth living in a cabin 3 km up stream, is also based on the presence of Mt. St. Helens Volcanic ash (set W) near the top of the undisturbed talus deposit (absolute maximum date). However, a dendrochronology study by Kienle et al (1978) reported that two of the oldest trees examined and three younger trees examined pointed to a failure date prior to 1872. No evidence was found within the tree rings of disturbance. This could be explained by the mass of the landslide did considerably disturb the trees (if the landslide mass moved as a whole).

Reference

Kienle, Clive F., Jr.; Farooqui, Saleem M.; Strazer, Robert J.; Hamill, Molly L., 1978, Investigation of the Ribbon Cliff landslide, Entiat, Washington: Shannon & Wilson, Inc., 26 p., 23 figs., 2 plates.

Madole, Richard F.; Schuster, Robert L.; Sarna-Wojcicki, Andrei M., 1995, Ribbon Cliff landslide, Washington, and the earthquake of 14 December 1872: Seismological Society of America Bulletin, v. 85, no. 4, p. 986-1002.

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