Savage Island Landslide
June 6, 2009
Savage Island, Franklin County
One of the interesting things about working here at the Washington Geological Survey is you never know what you are going to find. Last week as I was trying to find information on environmental impacts of landslides, I came across a large landslide along the Columbia River at Savage Island. The landslide did fail on the island itself, but the shoreline along the river did.
Savage Island is located in on a stretch of the Columbia River known as the Hanford Reach. Geologically, this area is know as the White Cliffs and across the way is the Hanford Dunes.
This area was originally inhabited by the Wanapum tribe prior to European settlers entering the area in the 1860’s. European settlements established farms, orchards, vineyards, similar to what we see today. However, in 1943, during the Manhattan Project, the Department of Energy confiscated the land and removed many of the established towns and forming the Hanford Site.
In modern times, agriculture still exists on the eastern side of the Columbia River (with the Hanford on the West). Thick loess deposits make up most of the area (hence the White Cliffs) and create the rich soil for agriculture. Loess can also be sensitive to large amounts of water, since Loess is a fine grained (silty) sediment. Water(from agriculture) + silt(loess) = landslides(usually earthflows).
So, it should be no surprise that in 1981 a section of the cliff east of Savage Island started to become active, catastrophically failing as a large earthflow in April of 1981. This landslide, besides clearing away farmland, also killed a large amount of swallows nesting in the cliff side (undoubtedly taking a large amount of rattlesnakes and rodents as well). Agriculture still plays a big role in instability along these cliffs and we continue to see many smaller landslides. Newer watering techniques and technology has helped reduce the amount of water needed (and hence, less water in the subsurface) and this has lead to a reduction in catastrophic landslides such as the Savage Island Landslide.