Quake Lake

August 17, 1959:

Quake Lake (officially Earthquake Lake) is a lake in southwestern Montana, United States. It was created after a massive earthquake struck on August 17, 1959, which killed 27 people. Today, Quake Lake is 190 feet (58 m) deep (150 feet as of July 2009) and six miles (10 km) long. US 287 follows the lake and offers glimpses of the effects of the earthquake and landslide and allows access to a visitor center. The lake is mostly within Gallatin National Forest.
Hebgen Dam, built in 1917, is a concrete core and rock fill faced structure that sustained severe damage but continued to hold. Repairs were completed on the dam spillway in a few weeks. The landslide, which occurred downstream from the dam, blocked almost all the flow of the Madison River which began to fill in the void upstream from the slide. In less than a month, the waters had created what is now known as Quake Lake. The lack of a reliable water outlet for this new lake forced one of the largest mobilizations of the U.S. Army Corps of Engineers ever commenced in the western U.S. Before the new landslide was breached by the quickly rising waters, a spillway was constructed to ensure erosion and potential failure of the natural dam would be minimized. Within the immediate vicinity of the earthquake and resultant landslide a few dozen cabins and homes were destroyed. Overall damages to buildings and roads were minor with damage costs placed at 11 million dollars in 1959. Aftershocks up to 6.5 on the Richter scale continued for several months.