Hebgen Lake Fault Scarp

July 04, 2012

Hebgen Fault Scarp (2) (3)

: Russell Losco
Summary Author: Russell Losco

The photo above shows a scarp that resulted from the largest earthquake ever recorded within the Rocky Mountain Intermountain Seismic Belt. This quake occurred at 11:37 p.m. on August 17, 1959 when a fault near Hebgen Lake, Montana ruptured. It's been discovered that there were actually two discrete large earthquakes registering magnitudes of 6.3 and 7.5 on the Richter scale. These quakes were felt throughout a 600,000 sq mi (1,555,000 sq km) area. The initial fault rupture is believed to have begun 6-9 mi (10-14 km) below the surface. Twenty-two aftershocks were recorded; four that were greater than magnitude 6.0. This event produced fault scarps ranging up to 22 ft (6.7 m) high and producing a total of 18-22 mi (29-35 km) of scarps. The scarp shown above formed astride an occupied campground, stranding many campers. Not far away, in the Madison River Canyon, approximately 28 million cu yd (21.4 million cu m) of rock slid into the Madison River, falling over 1,000 ft (300 m). The debris was traveling at nearly 100 mph (160 km/h) -- momentum carried it 400 ft (120 m) up the opposite canyon wall. Twenty-eight people were killed, 19 of which remain entombed under the Madison Landslide. Dozens more were injured or left homeless and damage was estimated at $13,000,000 (in 1959 dollars). Photo taken in August of 2007.

Photo Details: Camera: FUJIFILM FinePix A340; Focal Length: 5.7mm; Aperture: f/2.8; Exposure Time: 0.0031 s (1/320); ISO equiv: 100; Software: Paint Shop Photo Album v5.22.