The Columbia National Wildlife Refuge reveals a dynamic geologic story. The refuge is located in the southwest part of the Columbia Basin in an area known as the Channeled Scablands. Each butte, coulee and lake tells of a chapter in the geologic history of this unique landscape. A series of forceful geologic events shaped the area over the past million years and even through the last century. Today, the area is characterized by isolated cliffs and hills, surrounded by braided channels or coulees.
The foundation of the Columbia Basin, including the area around the refuge, primarily formed 17 million to 6 million years ago. During this time, more than 300 flows of lava erupted from long fissures in the earth’s surface. These flows formed a broad plateau of basalt, eventually covering 63,000 square miles and accumulating to a thickness of 6,000 feet in places. As some flows cooled, the lava cracked in the form of hexagonal columns, known as columnar basalt.
Ice Age Floods
A series of events that significantly defined the geology of the refuge and surrounding area occurred in the last Ice Age, between 18,000 and 12,000 thousand years ago. During numerous cooling periods, glaciers advanced southward into the Idaho Panhandle, damming the Clark Fork River and creating Glacial Lake Missoula. This lake often covered 3,000 square miles and could reach a depth of 2,000 feet deep at the ice dam.
Periodic warming phases would cause the ice dam to weaken and suddenly fail, sending the lake waters rushing through the Columbia Basin and towards the Pacific Ocean at a rate of 15 cubic miles per hour. The volume of water was immense—over 10 times the combined flow of all the rivers on earth today. Repeated dozens of times—possibly hundreds of times—these massive floods cut deep canyons and created buttes and cliffs in the basalt bedrock forming the Channeled Scabland terrain of the refuge.
Not all of the events shaping the landscape of the refuge occurred thousands or millions of years ago. Just last century, the Columbia Basin Irrigation Project was constructed, altering the landscape of the refuge once again. Prior to this project, there were only a few shallow lakes and wetlands on what is now the refuge. The elevated water table from the irrigation project and seepage from O’Sullivan Dam created over 3,800 acres of lakes and wetlands throughout the refuge.
Mount St. Helens
The most recent event to dramatically shape the geology and landscape of the refuge occurred just a few decades ago. On May 18, 1980, Mount St. Helens, located 150 miles southwest of the refuge, erupted violently, sending a cloud of volcanic ash over eastern Washington and turning day into night. A heavy layer of powdery ash settled on the refuge, varying in depth from 1 inch on the southern areas to 2 inches near the north. The ash flattened vegetation and suffocated many terrestrial insects, creating food shortages for other wildlife. Over the years, the ash layer has eroded and been incorporated into the soil but is still evident throughout the refuge.