Along the ICE AGE FLOODS
NATIONAL GEOLOGIC TRAIL

Lake Pend Oreille Ice Age Floods National Geologic Trail  The Purcell Lobe of the Cordilleran Ice Sheet repeatedly formed a 2000′ tall ice dam in this area, which backed up Glacial Lake Missoula and eventually burst catastrophically, releasing Ice Age Floods as often as about every ~10-60 years. Lake Pend Oreille is the largest lake in Idaho. The lake level is 2062 ft above sea level, with the surrounding terrain as high as 6002 ft. With a maximum depth of 1150 ft, this lake is the 5th deepest in the US. The location of the lake is probably related to an old river valley controlled by faults. The Lake Pend Oreille basin was carved by the repeated advances of Pleistocene ice and scoured by Ice Age Floods. With the waning of flood waters, the basin was filled with glacial out-wash and flood deposits. The lake is dammed at the south end by thick glacial and flood deposits that mark the beginning of the “Outburst Deposits”Quick Facts MANAGED BY:US Forest Service

Museum of North Idaho IceAgeFloods National GeologicTrail “The Museum of North Idaho collects, preserves and interprets the history of the Coeur d’Alene Region. to foster appreciation of the area’s heritage.” In the 1960s, the North Idaho Hoo Hoo Club, an organization of loggers, lumbermen and foresters, first entertained the idea of establishing a museum. They incorporated on May 1, 1968 for a museum focusing on the history of the Coeur d’Alene Region (Kootenai, Benewah and part of Shoshone counties). Through the efforts of volunteers and community support, the Museum opened its doors on the North Idaho College campus on July 28, 1973. In 1979, they remodeled a City-owned building and relocated to its current location. Quick Facts Location: 115 Northwest Blvd, Coeur d’Alene, ID 83814Phone: (208) 664-3448 The Museum is open Tuesday to Saturday from 11 am – 5 pm.

Ice Age Floods National Geologic Trail 12,000 to 17,000 years ago a 4000′ tall ice dam blocked the path of the Clark Fork River creating glacial Lake Missoula. At the end of the last ice age this ice dam failed, releasing more water than is held in modern day Lake Ontario and Lake Erie combined. 600 cubic miles of water rushed through this area and down Lake Pend Oreille destined for the Pacific Ocrean.One of the most intriguing questions about the catastrophic flooding is how the ice dam failed. Various mechanisms for glacial outburst floods have been proposed: Ice erosion by overflow water, subglacial failure by flotation, deformation of ice by water pressure, and erosion of subglacial tunnels by flowing water. One model suggests a self-dumping phenomenon. In this mechanism, floodwaters are released when the lake level reaches nine-tenths the height of the ice. At this depth the ice becomes buoyant, subglacial tunnels form and enlarge, and drainage occurs until hydrostatic pressure is decreased and the ice again seals the lake. The self-emptying model is used to explain the numerous cycles in the rhythmite deposits and to interpret each cycle as a separate flood. Even so, only the total collapse of the ice dam can explain the largest of the catastrophic foods. Sub-glacial tunneling and enlargement due to thermal erosion progressing to collapse have also been proposed, as well as catastrophic failure due to water pressure. All are dependent on the configuration of the ice dam and structure of the ice. Quick Facts Location:Clark Fork, Idaho