Flooding in the Columbia River and landslides off the White Bluffs are combining to erode an island so rich in archeological treasures that it’s listed on the National Register of Historic Places.
At its midpoint, Locke Island is about 35 feet narrower than it was two weeks ago, said Paul Nickens, archeologist for the Pacific Northwest National Laboratories. The island, which is a half-mile wide and 3 miles long, has lost 85 feet of width since 1995.
Nickens said the causes are two-fold.
From the early 1970s until the mid-1980s, a series of slides sloughed off the fragile White Bluffs. In recent years, the debris has slid into the Columbia, cutting the width of the channel between the bluffs and the island from 1,500 feet to about 500.
With upstream dams open to prevent flooding, the river is flowing at about 10 times the strength of the Spokane River. When the water hits the slide, it’s deflected against the island, where the sandy soil can’t handle the beating.
The island has been used by Native Americans for at least 2,000 years. The Wanapum tribe gathered there to catch salmon as recently as 1943, when the federal government took over the island, the river and surrounding land to build atomic bombs.
Nickens said the slides were caused by irrigation.
Excess water follows a layer of underground clay, said the Bureau of Reclamation’s Jim Blanchard. That clay becomes so slick, the soil slides off the top.