It’s generally accepted that the Clark Fork River was dammed during the last ice age by a glacier at the current location of Lake Pend Oreille near the Idaho/Montana border. The lake rose and fell multiple times. At its maximum, the lake was 2000 feet (610 m) deep at the ice dam, 1000 feet (305 m) deep at Missoula, and extended up multiple valleys in Montana.
Larry Smith of Montana Tech will present evidence of multiple fillings of Glacial Lake Missoula near the end of the last Ice Age. Everyone is invited at 7:00 pm on Thursday, April 6, in CWU’s Science II Building room 103,
Glaciolacustrine sediments in the Clark Fork River valley at Garden Gulch, near Drummond, MT allow for documenting highstand positions in glacial Lake Missoula and repeated subaerial exposure of the lake bottom. Sandy alluvial sediment below the glaciolacustrine section locally interfingers with the lowermost lake-bottom sediments, showing concurrent deposition of the alluvium with the transgressing lake. Cycles of lake deepening, subaerial exposure, and periglacial modification are represented in a 9 m-thick section.
Optical dating of quartz show that glacial Lake Missoula reached >65% of maximum capacity by 17-24 ka and either partially or completely drained twelve times from this position. Others have inferred that the lake rose and fell 35-90 times, but many of those events possibly did not reach the maximum elevation seen near Drummond.
Larry Smith is an associate professor in the Department of Geological Engineering at Montana Tech. He has been studying glacial Lake Missoula for about 17 years. He got interested in the lake deposits while working at the Montana Bureau of Mine and Geology. He studied the huge gravel deposits in the Alberton Gorge are, which were moved during cataclysmic lake drainages. The gravels host the aquifers that residents use for groundwater. Larry has Bachelor’s, Master’s, and Ph.D degrees in geology from University of California, Santa Cruz and the University of New Mexico. He has lived in Butte for 23½ years.
Lecture sponsored by the Ellensburg Chapter of the Ice Age Floods Institute.