Along the ICE AGE FLOODS
NATIONAL GEOLOGIC TRAIL

Glacial Lake Missoula National Natural Landmark Ice Age Floods National Geologic Trail Glacial Lake Missoula was the largest of several lakes impounded by the Cordilleran Ice Sheet in the Northern Rocky Mountains during the Quaternary period. The lake was approximately 2,900 square miles in size and contained more than 500 cubic miles of water. It occupied the Mission, Jocko and Little Bitterroot valleys, drained by the Flathead River; and the Missoula, Ninemile and Bitterroot valleys, drained by the Clark Fork River. The lake was formed by an ice dam across the mouth of the Clark Fork River at Lake Pend Oreille, Idaho, a result of successive advances of a lobe of the Cordilleran Ice Sheet. The site is located 12 miles north of Perma, Montana. At least three and possibly more than 100 separate collapses of the ice dam, possibly coincident with periods of ice retreat, caused the lake to drain, producing catastrophic floods across the Columbia Plateau and down the Columbia River Basin. It is estimated that the waters of Glacial Lake Missoula, 1,000 feet deep at Eddy Narrows, were withdrawn at a peak discharge rate of 10 cubic miles per hour. Approximately 550 cubic miles of water passed through those narrows during withdrawal. Evidence of this catastrophic withdrawal can be found in scourings, high eddy deposits of flood debris, flood bars of boulders and course gravel, and successions of giant arcuate ripples or ridges of gravel resting on bedrock surfaces. Ripples appear as ridges 15 to 50 feet high, 100 to 250 feet wide, and from 300 feet to a half-mile long. While the form, structure and arrangement of these features are similar to that of ordinary current ripple marks, they are termed giant flood ripples, due to their large size. The giant flood ripples at this site are unusual due to their being on the down-current side of notches in a ridge separating two basins that were both subsidiary to the main course of Lake Missoula in the Clark Fork Valley. The best examples of giant flood ripples are found in Camas Prairie. Quick Facts Designation:National Natural Landmark OPEN TO PUBLIC:Private Land, closed to the public, but features throughout the area are visible from many vantage points.

Montana Natural History Center Ice Age Floods National Geologic Trail  The mission of the Montana Natural History Center is to promote and cultivate the appreciation, understanding, and stewardship of nature through education. Founded in 1991, MNHC was the brainchild of a group of educators who were involved in various efforts to educate both kids and adults about the natural history of western Montana, and who decided to unite those efforts into one environmental education organization. MNHC provides nature education programming for people of all ages through summer camps, kids’ activities, Visiting Naturalist in the Schools, Master Naturalist certification courses and Field Days, evening programs, Field Notes on Montana Public Radio, museum tours, and more.  We have a variety of exhibits that focus on the flora, fauna, geology, and ecology of our beautiful state. Please stop by and visit! MNHC often partners with the Ice Age Floods Institute to share fields trips and lectures about the Ice Age Floods.   MNHC has exhibits that help visitors explore the Glacial Lake Missoula and Ice Age Floods. Learn more at:Explore Glacial Lake Missoula | Montana Natural History Center (montananaturalist.org) The Glacial Lake Missoula Chapeter of the Ice Age Floods Institue also produced a short movie about Glacial Lake Missoula. You can find a link here. Quick Facts Location:120 Hickory Street, Suite A, Missoula, Montana