Hebgen Lake Landslide

1
Hebgen Lake Landslide
2
1959 Yellowstone Earthquake

• August 17, 1959 _at_ 1137 in Southwestern Montana
• Strongest and deadliest earthquake to hit Montana
  since 1935

3
Epicenter

• Epicenter was located just outside of Yellowstone
• 7.5 Magnitude
• Earthquake was felt in 9 states and aftershocks
  were felt for several months after.

4
The Earthquake

• Extensive fault scarps, subsidence and uplift, a
  massive landslide, and a seiche in Hebgen Lake.
• A maximum MM intensity X was assigned to the
  fault scarps in the epicentral area.
• Area of perceptibility, maximum intensity, and
  Richter magnitude all were larger for this
  earthquake than for any earlier earthquake on
  record in Montana (from May 1869).

5
The Slide

• The largest effect that caused the most disaster
  was the huge avalanche of rock, soil and trees.
• Cascaded from the steep south wall of the Madison
  River Canyon
• 2,000 ft. long, 1,300 ft. wide ridge section

6
Creation of the Lake

• The slide formed a natural dam that blocked the
  gorge and stopped the flow of the Madison River.
• Volume of material that blocked the river below
  Hebgen Dam was around 28-33 million cubic meters.
• Within a few weeks, a lake was created almost 53
  meters deep.
• Earthquake Lake - reached back many miles toward
  Hebgen Lake.

7
Damages

• 28 total deaths (most of which were caused by
  rockslides that covered the Rock Creek public
  campground on the madison river, about 9.5
  kilometers below Hebgen Dam).
• 11 million in damages
• Numerous roads and building structures were ruined

8
(No Transcript)