Bonneville Landslide
What is it and why visit?
Most people driving through the Columbia Gorge don’t realize that hundreds of landslides have shaped this beautiful scenery. More than 500 years ago, an entire hillside collapsed near modern-day Cascade Locks. The open, un-vegetated faces of nearby Greenleaf Peak and Table Mountain hint at the area’s violent past. The Bonneville landslide was so huge that it dammed the Columbia River, forming a temporary lake that stretched 150 miles upriver to Wallula Gap. The landslide’s size makes it difficult to appreciate from the ground. Looking downriver from the Cascade Locks Marine Park on the Oregon side of the river, you can begin to comprehend the sheer size of the headscarp and hummocky landslide deposit. Both the Bonneville Dam and the modern Bridge of the Gods are built on the landslide. On your next trip through the Gorge, look at the landscape with the eyes of geologist and you will see this massive landslide too.
Geologic story
The Bonneville landslide is one of the more impressive landslides in Washington, covering an area of about 6 square miles. Although sizeable on its own, this huge slide is just the most recent of four overlapping landslides within the much larger Cascade landslide complex.
The main scarp of the landslide, an 800-foot-tall cliff, is located adjacent to Table Mountain. Table Mountain is composed of
The slide sent an estimated 1.2 billion dump trucks’ worth of material roaring down into the valley. The water impounded by the landslide dam pooled upstream and flooded the nearby forest, drowning the trees and preserving them. This “submerged forest” was noted by Lewis and Clark, who passed through the area in 1805.
When did this huge landslide happen? Scientists have several ways of finding out. Methods like radiocarbon dating, lichenometry, and dendrochronology can tell us that the landslide occurred about 580 years ago. However, parts of the slide may have been active at different points in time, and areas of the Cascade landslide complex are still moving today. A satellite imaging technique known as Interferometric Synthetic Aperture Radar (InSAR) can measure tiny movements in Earth’s surface. Using this method, researchers determined that a section of the Cascade landslide complex had moved 2.3 feet downslope between 2007 and 2011. Though this is not a lot of motion, it means that this area is still moving—which could impact structures built on the slide deposit.
LEARN MORE ABOUT:
See the Nick on the Rocks video below to learn more about the Bonneville Landslide!
Fun Fact
Prior to construction of the Bonneville Dam in 1938, the Cascade Rapids formed a treacherous area along the river. During the 1800s, pioneers traveling through the area along the Oregon Trail were forced to choose between taking a dangerous route over Mount Hood or paying a hefty toll to raft down the river.
What to see and do
Access passes you may need:
A national forest day-use permit, Northwest Forest Pass, or America The Beautiful Pass is required for the Bonneville trailhead.
Click here to open full sized image
Getting There
The Bonneville Landslide is on the Washington side of the Columbia River Gorge. It is accessible via Washington State Route 14 from the east or west, or from Oregon via I-84. There is a modern-day bridge called The Bridge of the Gods that spans the river at Cascade Locks, Oregon. It costs $2 to cross. The landslide is visible from parts of Cascade Locks as well as the Bonneville Dam area. You can also see it in profile from the top of Beacon Rock.
Nearby Amenities
Photo gallery
Bibliography
Cascade Locks Tourism Committee: The History of Cascade Locks [webpage]: Cascade Locks Tourism Committee. [accessed Aug. 10, 2018, at http://www.cascadelocks.com/about-cascade-locks/cascade-locks-history/]
Hu, Xie; Wang, Teng; Pierson, T. C.; Lu, Zhong; Kim, Jinwoo; Cecere, T. H., 2016, Detecting seasonal landslide movement within the Cascade landslide complex (Washington) using time-series SAR imagery: Remote Sensing of Environment, vol. 187, p. 49–61. [https://doi.org/10.1016/j.rse.2016.10.006]
Miller, M. B.; Cowan, D. S., 2017, Roadside geology of Washington, second edition: Mountain Press Publishing Company, 378 p.
Pierson, T. C.; Evarts, R. C.; Bard, J. A., 2016, Landslides in the western Columbia Gorge, Skamania County, Washington: U.S. Geological Survey Scientific Investigations Map 3358, scale 1:12,000, 22 p. [http://dx.doi.org/10.3133/sim3358]
Pringle, Patrick, 2009, The Bonneville slide: Columbia Gorge Interpretive Center Museum Explorations, Fall–Winter 2009, p. 2–3.
Schuster, R. L.; Pringle, P. T., 2002, Engineering history and impacts of the Bonneville landslide, Columbia River Gorge, Washington–Oregon, USA. In Rybar, Jan; Stemberk, Joseph; Wagner, Peter, editors, Landslides—Proceedings of the First European Conference on Landslides: A. A. Balkema, p. 689–699.
The Oregonian, 2016, Geologists track ancient Columbia River Gorge landslides: The Oregonian. [accessed Dec. 26, 2018, at https://www.oregonlive.com/pacific-northwest-news/index.ssf/2016/11/geologists_track_ancient_colum.html]
Tong, Xiaopeng; Schmidt, David, 2016, Active movement of the Cascade landslide complex in Washington from a coherence-based InSAR time series method: Remote Sensing of Environment, 186, p. 405–415. [https://doi.org/10.1016/j.rse.2016.09.008]