Breakout Area of Glacial Lake Missoula

November 05, 2019


Photographer: Bruce Bjornstad 
Summary Author: Bruce Bjornstad 

Shown above is the breakout area for the Ice Age megafloods from Glacial Lake Missoula. Today the valley is occupied by idyllic Lake Pend Oreille, but as recently as 15,000 years ago a massive glacier, thousands of feet (over 1,000 m in thickness) thick, occupied the valley. To the north, near Sandpoint, Idaho, the valley glacier split into two sub-lobes. One lobe flowed east to block the Clark Fork River, creating the ice dam for Glacial Lake Missoula. A second ice lobe continued south terminating near the present town of Bayview, shown at right. Evidence for glacial scouring is apparent along the leading edge of the former glacier at upper left.

Periodically, Ice Age megafloods burst forth when the ice dam failed -- suddenly releasing up to 500 cubic miles (2,085 cubic km) of water from the 2000 ft (610 m) deep Lake Missoula. After each ice dam failure, flood deposits spread out creating the expansive, flat and streamless Rathdrum Prairie outburst plain, seen in the distance. Image was collected on July 3, 2019 using a DJI Phantom 4 quadcopter.