A Turbulent Sea of Icebergs Pouring Over a 400-Foot Ridge - the Scale of the Missoula Floods

Standing at a ridge in the Columbia Valley, Randall Carlson describes what this landscape looked like at the peak of the Ice Age floods - a churning, turbulent mass of water approximately 200 feet deep, choked with thousands of icebergs, moving toward you with enough force to pour over a ridge flanked by 400-foot walls. The scale is almost impossible to hold in the mind. This was not a river in flood. It was an inland sea in violent motion, ripping through the landscape at a speed and volume that left permanent marks on the geology of the entire Pacific Northwest.

The key to reading flood geology, Randall explains, is understanding that erosion and deposition are two halves of the same process. The floodwaters excavated material from one location - tearing up bedrock, stripping soil, carving channels - and that material had to go somewhere. Learning to correlate what was ripped from a given location with where it eventually settled is how geologists reconstruct the path, the volume, and the violence of a flood that left no human witnesses.

Join Randall for his upcoming Finger Lakes Tour, Aug 30 Sep 5, 2026