Ice Age Floods National Geologic Trail

The Ice Age Floods National Geologic Trail is a network of routes connecting natural sites and facilities that provide interpretation of the geological consequences of the Glacial Lake Missoula floods of the last glacial period that occurred about 18,000 to 15,000 years ago.

There it formed a 2,000 ft (610 m)-high ice dam that blocked the mouth of the Clark Fork River, creating glacial Lake Missoula, which impounded greater than 2,000 km3 (480 cu mi) of water.

The flood front swept in a wave across Idaho and Washington at speeds approaching 100 km/h (62 mph), and Glacial Lake Missoula drained in periods as short as 2 days.

The cumulative effect of the floods was to excavate 210 km3 (50 cu mi) of loess, sediment and basalt from the channeled scablands of eastern Washington and to transport it downstream.

[2] Over a period of 2,000 to 2,500 years, the repetition of ice dam failure and flood was repeated 40-60 times, leaving a lasting mark on the landscape.

Glacial Lake Columbia (west) and Glacial Lake Missoula (east) are shown south of the Cordilleran Ice Sheet . The areas inundated in the Columbia and Missoula floods are shown in red.
Glacial Lake Missoula high-water mark, 4200 ft.
Illustration of the glacial flows leading to formation of several parts of the trail
Moses Coulee at mid canyon
View from trail near Glacial Lake Missoula high-water mark, 4200 ft.