HEGBEN LAKE EARTHQUAKE & MADISON RIVER CANYON LANDSLIDE
FIELD TRIP STOPS – THE 1959 HEGBEN LAKE EARTHQUAKE AND THE RESULTING MADISON CANYON LANDSLIDE.
LOCATION: The epicenter of the quake is about 20 miles northwest of West Yellowstone. The Madison River Canyon slide is found about 5 miles west of the epicenter.
GEOLOGIC FEATURES: Landslides (Mass Wasting); Epicenter; Normal Fault; Fault Scarp; Seiche
DESCRIPTION: On August 17, 1959, the 7.5 Hegben Lake Earthquake occurred in southwestern Montana, just west of Yellowstone N.P. The earthquake occurred mainly along a couple of normal faults located near the north end of Hegben Lake. Displacement along fault scarps was about 20 ft. Tilting of the Earth’s crust towards the north created a seiche within Hegben Lake that sloshed back and forth for half a day reaching vertical displacements of up to 8 ft destroying cabins and property along the lake’s edge and killing 9.
The earthquake caused a landslide in Madison River Canyon about 5 miles to the west of the epicenter. About 40 million cubic meters (75 million metric tons) of earth was moved downslope blocking the Madison River creating Quake Lake. The landslide created 100 mph winds as the loosened material plowed through the air burying 19 campers.
STUDENT QUESTIONS:
(1) What is an Epicenter?
(2) Define, and illustrate using a cross-section, a Normal Fault.
(3) What is a Fault Scarp and how is it related to a Fault Plane?
(4) Define Mass Wasting.
(5) CHALLENGE: Define a Seiche and explain its origin. Include the concept of Standing Waves. Describe how this phenomenon affected the waters of Hegben Lake.
SELECTED REFERENCES:
-"Madison River Canyon Earthquake - One of the Largest in US History." National Museum of Forest Service History (Virtual Exhibit). Accessed on 4/26/2020: https://forestservicemuseum.org/exhibits/madison-river-canyon-earthquake/
-“Today in Earthquake History: Hegben Lake, 1959.” UC Berkeley, Berkeley Seismology Lab - Seismo Blog. (Aug. 17, 2019). Accessed on 4/26/20: https://seismo.berkeley.edu/blog/2019/08/17/today-in-earthquake-history-hebgen-lake-1959.html
PHOTOS:
.jpg)
Figure 1 - The Cabin Creek Fault Scarp exposed at Hebgen Lake resulting from a 20 ft drop along a normal fault. (Photo 1983)
.jpg)
Figure 2 - A house along the shore of Hebgen Lake that was damaged during the earthquake and subsequent water motion. (Photo 1983)
.jpg)
Figure 3 - The Madison River Canyon Landslide. Triggered by the Hebgen Lake Earthquake, Nearly 80 million metric tones of earth slid down into the valley-bottom blocking the flow of the Madison River and creating Earthquake Lake. 16 people were buried by the land movement. (Photo 1983)