Located three miles north of the town of Entiat along the shore of the Columbia River Ribbon Cliff landslide has an interesting history. The personal recollections collected from local newspaper archives are a record of a night of horror during and after the landslide on the memorable night of December 14, 1872. They were published as The Night the Mountain Fell and Other Stories. It was a frightening night that was spawned by what geologists have described as probably the largest earthquake in the Northwest. Some reports credit it with a near total blockage of the Columbia River.
Travelers speed along 97W passing by this noticeable scalping of the hillside but few stop to learn of what it is all about. The State Highway Department created a small pullout and posted a display explaining what transpired. The massive slide can also been viewed by travelers on the east side of the river on 97E.
Estimates of the epicentral location and maximum intensity of the earthquake are controversial largely because the estimates are based on ground effects. The Ribbon Cliff landslide is one of the more critical ground effects used to argue that the epicenter was in the vicinity of Lake Chelan in central Washington. Sketchy historical accounts link the Ribbon Cliff landslide to the 1872 earthquake, but a subsequent study disputed the historical accounts and, on the basis of dendrochronology, concluded that the landslide occurred more than 100 yr prior to the earthquake. However, Quaternary stratigraphic relations and the results of multiple dating techniques reported here indicate that the main Ribbon Cliff landslide probably occurred within a 14-yr period that includes the time of the 1872 earthquake. Although our study supports the historical accounts that link the landslide to the December 1872 earthquake, it does not prove that seismic shaking triggered the landslide.
Geomorphic and stratigraphic relations show that Ribbon Cliff has a long and complex history and that the landslide was not primarily a rockfall-rockslide that originated from the cliff itself, as some believe, but rather that the main failure occurred in colluvium that had accumulated beneath the cliff. Four colluvial units and two volcanic ash deposits, the (Mt) Mazama ash bed (erupted about 6.8 ka), and the Mount St. Helens set W (erupted about 1480 A.D.), underlie the slopes below Ribbon Cliff. Most of the colluvium involved in the landslide accumulated after deposition of the Mazama ash bed. Loss of support at the foot of the colluvial wedge because of undercutting by the Columbia River probably was an important contributing factor to slope failure.
While the state mentions that the volcanic ash at the base of the slide blew in from Glacier Peak some 50 miles northeast. Seismologists make no such claims only mentioning Mt. St. Helens and Mt. Mazama.
An impressive view of the massive slide made be had from the opposite shore of the Columbia River at Daroga State Park. A loop drive through Chelan or Wenatchee provides a more graphic view. Either drive provides beautiful views of the Columbia Rivers and adjacent hillsides.
To claim this Earthcache answer the following questions before listing the find
1. Name the two components believed involved in the landslide.
2. What is the elevation at the base of the slide.
3. Approximately how high is the landslide.
4. Include a photo of you holding your GPSr in front of the sign.
5. This cache was adopted over to Mr. Gadget #2. Your answers will be evaluated and IF THEY ARE NOT satisfactory or incorrect, I will be contacting you.
Sources
Richard F. Madole, Robert L. Shuster and Andrew M. Sama-Wojcicki Seismological Society of America. "The Night the Mountain Fell and Other Stories" by KPQ radio
THANKS - Much thanks to Patudles for allowing me to place an Earthcache at the same site as her traditional cache - "'The Night the Mountain Fell," GCJG35.