Lake Pend Oreille: Historic Site of a Glacial Ice Dam

August 07, 2014


Photographer: Robert Farrimond
Summary Authors: Robert Farrimond; Jackie Phillips

Lake Pend Oreille in Northern Idaho is the site of an ice dam created over 12,000 years ago by the Purcell Lobe of the Cordilleran Ice Sheet. The dam blocked the Clark Fork River, forming Glacial Lake Missoula and filling it with an estimated 500 cu mi (2,000 cu km) of water. That’s nearly the equivalent of Lake Erie and Lake Ontario combined. Periodically the dam burst sending massive amounts of water towards the Pacific Coast and carving out the Columbia River Gorge. The photo above shows the modern-day Lake Pend Oreille. Historically, the Purcell Lobe of the Cordilleran Ice Sheet flowed from the right side of the photograph to the left, where it impounded the Clark Fork River and its tributaries. At left, note the sundog, segment of a 22 degree halo and portion of a parhelic circle. Photo taken on June 20, 2014.

Photo Details: Camera: Canon EOS REBEL T1i; Focal Length: 28.0mm; Aperture: f/5.6; Exposure Time: 0.0003 s (1/4000); ISO equiv: 400.