1959 – Hebgen Lake, MT – M 7.5

Intermountain Seismic Belt Historical Earthquake Project

August 17, 1959 – Hebgen Lake, MT – M 7.5

The Hebgen Lake earthquake—the largest and deadliest earthquake recorded in Montana and the Intermountain West—occurred at 11:37 p.m. (local time) on Monday, August 17, 1959. The epicenter of the magnitude 7.5 earthquake was approximately 15 miles north of West Yellowstone, Montana (later revised by the U.S. Geological Survey to magnitude 7.3 and located 6.5 miles northwest of West Yellowstone). The earthquake was reported felt as far north as Banff, Canada; as far south as Provo, Utah; as far east as Dickinson, North Dakota; and as far west as Seattle, Washington (Stover and Coffman, 1993). Seven significant aftershocks ranging in magnitude from 5½ to 6½ occurred in the three months following the mainshock.

The greatest number of reported injuries and deaths occurred in the Madison River Canyon where the earthquake triggered an 85-million-ton landslide on a mountain five miles west of Hebgen Lake. The landslide roared down over a popular recreation area where an estimated 200 people were camping. The earthquake also caused a northward tilt of the Hebgen Lake bed. This triggered a reported 20-foot wall of water that overtopped Hebgen Dam followed by several 3-4 foot surges. Eyewitnesses reported seeing camping trailers swept down into the Madison River, cars and their occupants buried in dirt and rock, and trees flying through the air. There were reports of screams and cries for help. Twenty-eight individuals died from their injuries or were presumed buried in the slide.

The landslide dammed the Madison River, creating what became known as “Quake Lake.” Montana Highway 287, the primary route through the Madison River Canyon, was rendered impassable due to slide debris, fault scarps (as high as 18 feet) and sections of the highway that fell into Hebgen Lake.

Emergency responders parachuted into the area to establish communication and to provide first-aid. The injured were evacuated by helicopter to an aid station in West Yellowstone and then on to nearby hospitals by airplane. Deceased were airlifted to a morgue in the town of Ennis, Montana. Remaining survivors were able to evacuate later on roads that had been cleared or newly constructed.

According to one report, the ground shaking produced sixteen cracks in the Hebgen Dam. In spite of the damage it was determined the dam would hold. However, precautions were taken to evacuate the town of Ennis 45 miles away and to warn residents in the Madison Valley. The Army Corps of Engineers moved quickly to construct a spillway at Quake Lake before the rising waters topped the landslide dam. Additional earthquake tremors slowed work on roads and dams as well as search and rescue efforts.

When it was determined that no other victims would be recovered from the landslide, a brief memorial service was held near the mouth of the Madison River Canyon. Officiators from several denominations led the group of approximately 50 attendees in prayer. They also consecrated the slide as the final resting place for those who had perished.

The West entrance to Yellowstone National Park was closed with no travel possible along the park’s west side due to landslides, rockfalls and bridge damage. One individual in West Yellowstone at the time of the earthquake reported hearing an awful roar, felt his cabin shaking and lost electrical power. No buildings collapsed but many were severely cracked or damaged. Thousands of frightened tourists left the park, while curious onlookers arrived to survey the damage.

In Billings, Montana, the earthquake awakened hundreds of residents who reported swinging light fixtures, rattling dishes, rolling beds, swinging doors and shaking houses. One person reported that his swimming pool completely overflowed onto the patio.

In Bozeman, Montana, damage included downed chimney tops and store merchandise shaken from shelves.

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1925 – Clarkston Valley, MT – M 6¾

Intermountain Seismic Belt Historical Earthquake Project

June 27, 1925 – Clarkston Valley, MT – 

The Clarkston Valley, Montana earthquake occurred at 6:21 p.m. local time on June 27, 1925. The epicenter was located approximately 8 miles north of Three Forks, MT just north of Yellowstone Park. It was reported felt over nearly two-thirds of the state (approximately 1,000,000 square kilometers) – as far west as Seattle, WA to the eastern Montana/South Dakota border, as far north as Thermopolis and Casper, WY and south to Spokane, WA.

Some buildings in areas near the epicenter were badly damaged. Buildings and pavement were cracked. Chimneys toppled. Windows shattered in some locations. Plaster was shaken from walls and merchandise fell from store shelves.

The heaviest damage in terms of quantity and severity was reported in Three Forks, Manhattan and White Sulphur Springs with some buildings being reduced to rubble. There were also reports of extensive damage to the town of Willow Creek, including reports that the town was in flames. Broken wire connections prevented communication to confirm these reports. It was later learned that damage in Willow Creek was slight.

Some individuals rushed into the streets, fainted or were knocked to the ground from the shaking, but no loss of life was reported. A woman sustained a broken leg (also reported as a broken hip) as she fell while rushing out of her home. Additional reported injuries were limited to bruises and cuts due to broken glass and falling materials. Many individuals were too nervous to sleep and some preferred to sleep out of doors.

The earthquake triggered several landslides and rockslides. Three passenger trains were stranded when rockslides blocked rail lines. There were also reports of rail tunnels caving in. And some concern was reported about the safety of area bridges. A number of ground cracks and fissures were reported in areas closest to the epicenter. There were also reports of increased flow at some springs in the area.

It was reported that the day following the earthquake, thousands of visitors from nearby towns and cities flooded into Manhattan and Three Forks to survey the damage.

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1935 – Helena, MT (series) – M 6¼

Intermountain Seismic Belt Historical Earthquake Project

October 18, 1935 – Helena, MT (series) – M 6¼

October 12, 1935 – Foreshock (M 5.9)

This early morning earthquake (12:50 a.m. local time) caused many frightened residents to run from their homes. It was reported that despite the alarm people felt, many maintained a sense of humor about the event as they gathered in the streets and swapped stories of their experiences. No deaths resulting from the foreshock were reported.

Reports described damage as severe and widespread throughout the city. Windows were broken, stock was shaken from store shelves, pipes and wires were broken, chimneys toppled, furniture overturned, walls were cracked and plaster was shaken from walls and ceilings. It was reported that City Engineer Oscar Baarson estimated total damages between $50,000 and $75,000.

Following the foreshock, two officials advised taking measures to make buildings more earthquake resistant. Suggested measures included bracing chimneys, deeper foundations especially on loose soils, fastening brick veneers to walls, discontinuing the use of veneers altogether. Other suggestions included revising the building codes to make structures more earthquake resistant.

The earthquake was reported felt in Great Falls, Butte and Dillon, MT. Additional smaller earthquakes continued to be felt. In a news article published on October 17 it was reported that the Helena Weather Bureau had recorded a total of 52 earthquakes as of October 16 with the latest two quakes being 12 hours and 45 minutes apart. The article concluded that, “The fact that the quivers are so far apart indicates that the ‘earthquake season’ is drawing to a conclusion.”

October 18, 1935 – Main Shock (M 6¼)

At 9:48 p.m. (local time) the city was rocked by the magnitude 6¼ main shock. Some individuals screamed and ran from buildings. One person was reported killed when he was crushed under a brick wall that fell into the street. Another died from injuries sustained from a building collapse. A score or more individuals were seriously injured, most from being struck by falling debris as they ran out of buildings. As terrified people fled the city by car, a number of automobile accidents occurred resulting in additional injuries.

The earthquake knocked out lights and power for approximately an hour causing further terror, and difficulty for doctors attempting to treat the injured.

Significant damage occurred to many buildings with some entirely destroyed. Approximately 300 homes were damaged so badly as to be uninhabitable. One report described the streets being strewn with debris. Telephone service was interrupted for more than two hours.

City Engineer Oscar Baarson estimated damages from the earthquake at a minimum of $2,500,000. A report on October 21 indicated that Mr. Baarson requested patience as he and a crew of seven worked their way through several hundred requests for damage inspections.

The American Red Cross, Federal Emergency Relief Administration (FERA) and National Guard, assisted in providing first aid stations, sleeping quarters and kitchens for the hundreds of people rendered homeless by the earthquake. The local Y.M.C.A. invited homeless individuals to shower at their facilities for no cost. Authorities estimated it would be a week before people were allowed to resume normal affairs in the city.

The Red Cross reported 100 requests (representing approximately 400 individuals) for emergency food and medical care. The Red Cross also prepared to assist with a home rebuilding program for families in need. Local banks pledged resources for making home repair loans as approved by the Federal Housing Administration.

Surface cracks 150 feet long, three feet deep and several inches wide were reported at one location in the Helena Valley.

The earthquake was reported felt over a wide area of western Montana, but no damage outside the city of Helena was reported. Additional felt reports were received from Washington and Idaho.

October 31, 1935 – Aftershock (M 6)

At 11:37 a.m. (local time) a significant aftershock occurred near East Helena, MT. One report noted that the shock surprised Helena residents, who had believed the worst of the shaking had occurred earlier in the month. The report also noted that aside from some fainting spells, little panic was observed. However, some individuals evacuated the city by car.

Cracked plaster and broken windows were reported. Two school buildings suffered significant damage. On the west side of the city, there were reports of fallen chimneys. However, on Helena’s east side, some buildings that had been only partly damaged by the main shock were completely destroyed when the aftershock occurred. It appeared that most of the damage was to structures already weakened by the main shock. Damage to buildings that had been unaffected by the main shock consisted mostly of cracks in plaster and exterior walls and damaged chimneys.

Two brick masons, part of a crew from Salt Lake City, were killed from falling bricks as they were removing a smokestack at the local brewery. There were at least nine individuals who suffered serious injuries during the aftershock.

The north wing of the new Helena High School, already badly damaged from the main shock, completely collapsed during the October 31 aftershock. It was reported that 25-30 men who were working in the building escaped without injury thanks in part, to their foreman who shouted reminders for them not to run out of the structure.

Plans to open city schools following the main shock were cancelled when the aftershock occurred. It was later decided that schools would not open until after the new year.

November 28, 1935 – Aftershock (M 5.5)

Less than a month later, the city experienced another significant aftershock that struck at 7:41 a.m. (local time). The earthquake did not cause significant new damage in the city of Helena. It was, however, reported to be among the strongest of the series felt outside the area in locations such as Great Falls, Butte, Missoula, Kalispell and Deer Lodge among others. Bozeman reported only light shaking.

Following the earthquake, City Engineer Oscar Baarson revised his estimate of total damages from the earthquake series to $5,000,000.00 or more.

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1928 – Helena, MT – M 5½ ±

Intermountain Seismic Belt Historical Earthquake Project

February 29, 1928 – Helena, MT – M 5½ ±

The 1928 Helena, Montana earthquake had no reported injuries or damage. The shaking startled people throughout the city of Helena and was more noticeable on upper floors of buildings with two or more stories above ground. The shaking was severe enough to disrupt a trial in one city courthouse. Without taking time to formally adjourn the proceedings, the judge and others fled the courtroom as the shaking began.

The earthquake was reported felt in areas southeast of Helena including: Trident, Three Forks, Manhattan, Logan, Lombard, and Sixteen-Mile Canyon. White Sulphur Springs, to the east of Helena, also reported earthquake shaking.

There were reports of shaken buildings, windows rattling, furniture moving, and goods being shaken from shelves.


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1947 – Virginia City, MT – M 6¼

Intermountain Seismic Belt Historical Earthquake Project

November 23, 1947 – Virginia City, MT – M 6¼

The Virginia City earthquake was reported felt in several communities in Montana, including: Billings, Missoula, Lewistown, Livingston, Helena, Harlowton, Malta, Havre, Glasgow, Kalispell, and Bozeman; and as far south as Idaho Falls, Idaho.

In most areas, the earthquake rocked buildings with, what was described in Helena as, a “long and easy” motion. There were widespread reports of swaying light fixtures, stopped clocks, dishes rattling, and window blinds and curtains moving back and forth. Cracks in plaster were observed and a plaster ceiling fell in a café in Hamilton.

Near the epicenter, in Virginia City, bricks and plaster were shaken loose from buildings, windowpanes were shattered, walls were cracked, and chimneys damaged. There were also reports of pictures being shaken off walls and dishes falling from cupboards.

In some locations sleeping residents were awakened as the shaking dislodged icicles from rooftops. Strange noises were reportedly heard during the shaking, and some residents fled their homes in fear. However, there were no reports of injuries or significant damage resulting from the earthquake.


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