![]() 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. Army Corps of Engineers ever commenced in the western U.S. The lack of a reliable water outlet for this new lake forced one of the largest mobilizations of the U.S. In less than a month, the waters had created what is now known as Quake Lake. 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. Repairs were completed on the dam spillway in a few weeks. Hebgen Dam, built in 1917, is a concrete core and rock fill faced structure that sustained severe damage but continued to hold. At the time, the quake was the second largest to occur in the continental US during the 20th century. Aftershocks up to 6.5 on the Richter magnitude scale continued for several months. Overall damages to buildings and roads were minor with damage costs placed at 11 million dollars in 1959. Within the immediate vicinity of the earthquake and resultant landslide, a few dozen cabins and homes were destroyed. Several geysers in the northwestern sections in Yellowstone National Park erupted and numerous hot springs became temporarily muddied. 32,000 acres (50 sq mi 130 km 2) of the area near Hebgen Lake subsided more than ten feet (3 m). The earthquake created fault scarps up to twenty feet (6 m) high in the area near Hebgen Lake and the lake bottom itself dropped the same distance. A seiche, a wave effect created by wind, atmospheric pressure, or seismic activity on water, crested over Hebgen Dam, causing cracks and erosion. Upstream the faulting caused by the earthquake forced the waters of Hebgen Lake to shift violently. The landslide traveled down the north flank of Sheep Mountain, at an estimated 100 miles per hour (160 km/h), killing 28 people who were camping along the shores of Hebgen Lake and downstream along the Madison River. The earthquake was the most powerful to hit the state of Montana in historic times. The earthquake measured 7.5 on the Richter magnitude scale (revised by USGS to 7.3) and caused an 80-million ton landslide, which formed a landslide dam on the Madison River. Main article: 1959 Hebgen Lake earthquake The lake is mostly within Gallatin National Forest. Route 287 follows the lake and offers glimpses of the effects of the earthquake and landslide, and a visitor center is just off the road. Northwest of West Yellowstone, Quake Lake is six miles (10 km) in length with a maximum depth of 125 feet (38 m). It was created after an earthquake struck on August 17, 1959, with 28 fatalities. Western United States, on the Madison River in southwestern Montana. Quake Lake (officially Earthquake Lake) is a lake in the Geological Survey Quake Lake from overlook
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