Updated: Jul 14, 2021
Palouse Falls, Washington's state waterfall, was created when a series of massive Ice Age floods rearranged the landscape and altered the course of the ancient Palouse River.
Palouse Falls, born of a "stolen river", drops 80 feet over a ledge of basalt and wends its way down the deep canyon it carved, Photo: © Donald J. Rommes
During the last ice age, enormous sheets of ice moved south from Canada while also forming at higher elevations. Tongues of that ice sheet slowly flowed into the areas of lower elevation, occupying ancient river valleys and creating ice dams that could block the river's flow. One such ice dam was formed on the Clark Fork River as it entered present day Idaho from Montana.
The extent of glacial ice during the last ice age. One lobe of ice (Purcell Trench Lobe) blocks the Clark Fork River, causing water to back up as Lake Missoula (green). Another, similarly-formed glacial lake is seen in green. The brown color indicates the course of the flood waters when the ice dams broke.
River water accumulated behind the dam to depths of more than 2000 feet, forming a massive lake. This glacial lake—Lake Missoula—was the size of Lakes Ontario and Erie—combined. Inevitably, the enormous weight of the water in the lake undermined and lifted the ice dam. The resulting collapse was sudden and released a cataclysmic outburst of water that raced towards the Columbia River valley at speeds of upwards of 50 miles per hour.
This series of events happened repeatedly—perhaps as many as 40 times.
During one event, scouring floods cut across the ancient valley of the Palouse River, creating a new and deeper channel, forcing the river to forever alter its course and flow over a series of basaltic ledges, forming waterfalls. The lovely Palouse Falls is thus one product of that cataclysm and chaos.
Palouse River flowing over basalt and through its flood-created channel, a couple hundred yards upriver from Palouse Falls. Photo: © Donald J. Rommes
Palouse River canyon just below (downstream from) Palouse falls. Click on the photo to go to its location on our companion website—Iris Arts. Photo: © Donald J. Rommes
Waterfall meets plunge pool. Palouse Falls. Photo: © Donald J. Rommes.