White Bluffs Landslides

White Bluffs Landslide

The White Bluffs along the Columbia River are the signature visual feature of the Monument; unfortunately, they are also the most endangered feature.

Over the past two decades, the natural erosion rate has been greatly accelerated, in all likelihood due to irrigation waters from the Central Columbia Basin Irrigation Project saturating soils that are naturally unstable. The sediments comprising the White Bluffs are from an ancestral river and are nearly two miles wide within the Monument. These sediments are unconsolidated silts and sands, which promote the percolation of water until an impermeable stratum captures the flow and causes it to seep out, causing extreme slope instability, deep fissures, and water-filled pockets.

Apart from the obvious damage to a unique geologic feature, sloughing of the White Bluffs has several other impacts. Although exposure of the Ringold Formation and fossil localities is a useful aspect of the landslide for geologists and paleontologists, these resources are being lost to the river with every landslide. While all the slides are detrimental, the most prominent and controversial slide is the one above Locke Island. Here, continual hydration of the fragile sediments has resulted in the slide of an estimated twelve million cubic yards of sediment into the modern-day river channel. The movement of the landslide into the river has forced the river to shift its flow, eating into Locke Island and eroding cultural sites on the island. Other impacts from the landslides include siltation of salmon redds. Sloughing threatens the rare White Bluffs bladderpod, which grows along the cliff edges. The Savage Island slide (ten million cubic yards) is located near the Ringold area, an area of heavy public use, raising concerns over public safety due to unstable soils and deep, water-filled pockets.