A Refuge of Fire, Ice, Flood and Volcano


The Columbia Refuge is in the middle of Washington's famous Channelled Scablands and has a rich geologic history highlighted by periods of extreme violence. Fire, Ice, flood, and volcano all played major roles in shaping the area, and the process goes on today.

Lava Flows

All of the native rock in the refuge area is basalt, a dense crystalline lava that covers more than 100,000 square miles in Washington, Oregon, and Idaho. Most of this lava erupted between 30 million and 10 million years ago. At times one flow followed another at short intervals, but at other times, tens of thousands of years intervened between flows. Erupting from long, wide fissures, early flows filled the valleys and subsequent flows covered most of the high hills as layer upon layer eventually formed a solid sea of basalt, in places more than 10,000 feet thick. Slowly a covering of windblown silt or loess and ash from Cascade volcanoes built up over the basalt, eventually producing fertile soils covered with grasses that nurtured the wildlife of the times.

Ice Dams

Beginning 100,000 years ago, glaciers crept south from British Columbia into northern Washington, Idaho, and Montana. Many times the advances of glacial ice blocked the Clark Fork River near the Idaho-Montana border and water blacked up behind the ice dam.

The lake that was formed [Glacial Lake Missoula] at its highest level covered an area of about 3,000 square miles and contained an estimated 500 cubic miles of water. Its maximum depth of nearly 2,000 feet was more than twice the depth of Lake Superior.

Huge Floods

Eventually, the rising water began to overflow its ice dam. The flowing water eroded the dam within a very short time - perhaps no more than a day or two - releasing the tremendous volume of the lake. As the lake drained, the maximum rate of flow is estimated to have been 9 1/2 cubic miles per hour - a rate of 386 million cubic feet per second, or about 10 times the combined flow of all the rivers on Earth.

Evidence indicates that glaciers advanced and blocked the Clark Fork River as many as 85 times in the last 16,000 years. Although there were many episodes of glacial flooding, so far as geologists can tell, the largest lake was formed 12,000 years ago and its sudden draining produced the last and greatest flood.

When the flood reached the Columbia Basin, the enormous volume, velocity, and turbulence of the water eroded away the surface soils and exposed the basalt underneath. Deep canyons were eroded into the basalt forming the Channeled Scabland terrain of which the refuge is a part. The northern half of the refuge south of Potholes Reservoir is a rugged jumble of cliffs, canyons, lakes, and remnants of lava flows. This part of Drumheller Channels, is the most spectacularly eroded area of its size in the region and was designated a National Natural Landmark in 1986.























Volcano's

Not all notable geologic changes happened thousands or millions of years ago. On May 18, 1980, Mount St. Helens, 150 miles southwest of the refuge, erupted violently and sent a cloud of volcanic ash over eastern Washington that turned day into night. A heavy layer of powdery ash, up to 2 inched thick at the north end of the refuge, buried vegetation, disrupted wildlife and generally made life miserable. The compacted ash layer is still very evident but is eroding from high spots and elsewhere is being incorporated into the soil through natural processes.