Earthquake Lake

August 18, 2006


Provided by: Matthew d'Alessio, US Geological Survey
Summary authors & editors: Matthew d'Alessio

At first glance, this photo looks like just another lake along a Montana highway. A closer look reveals that dead trees are still standing, but partially submerged in the lake. To the left of the far end of the lake, the entire hillside is bare and brown -- little vegetation. Forty-seven years ago today (August 18, 1959), Mother Nature built a new dam on the Madison river. The Magnitude 7.3 Hebgen Lake earthquake shook loose 30 million cubic yards of rock and soil that tumbled down and blocked the Madison River. It would take about a million dump trucks over 100 days of round-the-clock work to move that much dirt (at ten seconds per truck). Earthquake Lake's dam formed in just a few seconds. As the river backed up behind the new dam, it formed a lake and drowned the trees near the valley floor. The hillside that was the source of all the rock remains un-vegetated even today -- fifty years isn't long enough to develop a good layer of soil in this area. Photo taken in July of 2004.

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