The night the mountain fell in Yellowstone

Springtime snow collects on the slide scar left by the 1959 Hebgen Lake earthquake.

Photo courtesy of Annie Jehle

By Annie Jehle

 

 

One late summer night, thousands awoke to a horrific nightmare: an enormous force rattling the ground beneath them. At 11:37 p.m. on Aug. 17, 1959, the 7.5-magnitude Hebgen Lake Earthquake hit southwest Montana. At its time, it was the second-largest recorded earthquake in the continental United States in the 20th century. It still is among the largest recorded in the United States, and the effects of the quake are still observed today.

Today, the Madison River Canyon stretches for several miles west of Hebgen Lake, a large, manmade reservoir. The Hebgen Dam, completed in 1914, sits at the head of the canyon barely out of sight of Highway 287. Flowing both in and out of the lake is the Madison River, world renowned for its blue-ribbon fly-fishing.

Prior to the quake, the Madison flowed from the dam outlet through a tucked-away canyon of the Madison range toward Ennis. On either side of the timber-laden valley sat steep slopes coated with rocky outcroppings and dense forest. At the foot of the canyon, the river dropped in elevation, entering the expansive Madison Valley. Just before the foot of the canyon sat Rock Creek Campground, a then-popular resting ground for tourists visiting Yellowstone National Park.

The initial quake lasted less than a minute. Within mere seconds, the ground plunged downwards along the fault line, leaving behind a sheer 20-foot wall of exposed earth. Shortly following the massive quake, an immense slab of weakly affixed material detached from the canyon’s north-facing slope and slid swiftly into the valley, snapping trees and tossing thousand-pound boulders in fierce disarray. As debris plummeted to the canyon floor, a new natural dam formed at the foot of the canyon several miles downstream from Hebgen Dam. Behind the slide, the Madison River flooded the canyon, engulfing trees and campgrounds alike and forming the beginnings of what is now known as Earthquake Lake.

Meanwhile, sizable waves, or seiches, spilled over the Hebgen Dam, threatening to fracture the dam’s already weakened infrastructure. Residents downstream feared that the dam would fail, causing the community of Ennis to evacuate shortly thereafter. Highway 287 plunged into Hebgen Lake along the scarp. The Hillgard Fishing Lodge, located on the north shore of Hebgen Lake, fell into a gaping fissure caused by the displacement and plummeted into the lake – just moments after owner Grace Miller jumped from inside the building.

Following the quake, officials rescued hundreds of trapped victims from Refuge Point, a high but accessible promontory. The state cleared debris and repaired damaged roads and bridges. Within a couple of days, the majority of roads were reopened. The Hebgen Dam held and was repaired within several weeks. In total, 28 perished in the quake, slide and aftermath.

In Yellowstone National Park, thermal features experienced changes, including Old Faithful geyser, the park’s most visited attraction. Prior to the quake, Old Faithful’s average eruption interval was 65 minutes. Within two to three years following the earthquake, Old Faithful’s average eruption interval increased to 74 minutes.Within a few days of the quake, Sapphire Pool, a previously quiet hot spring in Yellowstone’s Biscuit Basin, began erupting over 200 feet high. The eruptions destroyed the biscuit-like formations, the basin’s namesake. Steamboat, the world’s tallest geyser, located in Yellowstone’s Norris Geyser Basin, awoke from its 50-year dormancy when it erupted in 1961, less than three years after the 1959 earthquake.

Eight years after the earthquake, the U.S. Forest Service opened the Earthquake Lake Visitor Center. The center is located on Highway 287, directly across from the original slide, which is still visible today. The center is about 27 miles from West Yellowstone and is open from May through September.

Today, the fault scarp may be viewed north of Highway 287 at the Cabin Creek Scarp Area, which is 23 miles northwest of West Yellowstone, and in Red Canyon, about 17 miles northwest of the town. From the turnoff to Red Canyon, it is about a 10-minute drive to the trailhead and about a 20-minute hike to view the scarp.

Along the north shore of Hebgen Lake, the Building Destruction site is located 21 miles northwest of West Yellowstone. This under-frequented site offers a short drive on the old highway and a short walk to view the remnants of the sunken Hillgard Fishing Lodge.

A prominent spectacle of the canyon, the slide is still mostly barren with only dispersed tree regrowth. The raw, barren slope is completely visible from Highway 287. The trees that once lined the Madison River now stand gray and waterlogged at the bottom of Earthquake Lake, protruding from the surface as a memorial of the landscape that used to be.

 

Annie Jehle is the editor of This is Montana.

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