Teton Dam Collapses Summary

  • Last updated on November 10, 2022

Despite opposition from environmentalists and concerns from the U.S. Geological Survey, the Teton Dam in Idaho was constructed. Its collapse resulted in eleven deaths and more than $1 billion in damage.

Summary of Event

On June 5, 1976, the Teton Dam near Rexburg, Idaho, partially collapsed, releasing eighty billion gallons of water. The resulting floodwaters killed eleven people, injured more than one thousand, flooded 400,000 acres of land, and resulted in more than $1 billion in damage. The dam was newly constructed, and the reservoir behind it was near capacity for the first time. The Teton Dam was an “earth-fill” type, consisting of some ten million cubic yards of earth materials dug from the bed of the reservoir. The dam rose more than three hundred feet above its base and extended across Teton Valley for more than one-half mile. The reservoir behind the dam backed up water for seventeen miles. Dams;Teton Disasters;dam collapses Teton Dam collapse Engineering;dams [kw]Teton Dam Collapses (June 5, 1976) [kw]Dam Collapses, Teton (June 5, 1976) Dams;Teton Disasters;dam collapses Teton Dam collapse Engineering;dams [g]North America;June 5, 1976: Teton Dam Collapses[02380] [g]United States;June 5, 1976: Teton Dam Collapses[02380] [c]Disasters;June 5, 1976: Teton Dam Collapses[02380] [c]Engineering;June 5, 1976: Teton Dam Collapses[02380] [c]Environmental issues;June 5, 1976: Teton Dam Collapses[02380] Curry, Robert Corbett, Marshall Eikenberry, F. William

The events leading to the collapse of the dam began on June 3. Two leaks were discovered about fifteen hundred feet downstream from the dam. On June 4, a third leak appeared three hundred feet from the foot of the dam. At 8:30 a.m. on June 5, two more leaks were discovered, one on the dam embankment face, and the other at the base of the dam. At around 10:00 a.m., the final leak appeared about 130 feet below the top of the dam near the junction of the dam embankment and the right abutment. The leak grew rapidly, eroding material from the embankment. A whirlpool had developed on the reservoir side of the dam, confirming embankment breach. Bulldozer crews had been called to move fill material into the hole on the downstream side of the dam and into the whirlpool. The efforts proved futile and were abandoned by 11:30 a.m., with the loss of two of the bulldozers. The hole continued to grow until daylight could be seen through it, and the right side of the dam took on the appearance of a natural bridge. At 11:57 a.m., the right side of the dam collapsed, releasing the reservoir water.

The Teton Dam collapsed in 1976, flooding parts of Idaho and killing eleven people.

(AP/Wide World Photos)

The water struck a power plant below the dam, and according to an observer, Dale Howard, “it just disintegrated. The water picked up a huge oil tank like a cork and away it went. There was a beautiful grove of cottonwood trees down below, and they were snapped off like matchsticks. Later I could see the water out on the plain. It was almost like a surrealist picture; as the water hit some of the farm fields, you could see an eerie cloud of dust and mist rise up three to five miles away.”

Dam failures can often be related to complications from unusual weather conditions, but weather was not a factor in the Teton Dam failure. Attention has thus focused on the dam and its location. The material on which the Teton Dam was founded was not ideal for such a structure. The material was basically weak and porous, with large fractures in it. The approach to preparing a dam site in such a situation is to fill any such openings with grout, a mixture of sand, water, bentonite clay, and calcium chloride. When forced into drill holes or natural openings in rock, this mixture is supposed to form a water barrier. Three times as much grout as is normally used to prepare a dam site was used at Teton Dam. Grout reached down three hundred feet or more and extended as much as one thousand feet into the dam abutments.

Other geologic concerns arose about the location of the Teton Dam. In 1972, the U.S. Geological Survey Geological Survey, U.S. (USGS) pointed out that the site for the proposed dam was in an area with seismic activity, an important factor for consideration in the evaluation of potential dam sites. The USGS also pointed out that the ground on one side of the dam was softer than the ground on the other. The structural implications of this difference were not carefully evaluated. Geologist Robert Curry of the University of Montana suggested that this situation would lead to compaction of the softer material, which would in turn cause leakage and eventually could lead to failure.

Court testimony was taken from geologist Shirley Pytlak Pytlak, Shirley in 1973 as part of a suit brought by environmentalists against the proposed dam. Pytlak was part of a team that was drilling holes in the future reservoir floor to determine how well it would hold water. Water fed into drill holes vanished, suggesting that the reservoir would leak. This finding, however, did not lead to suggestions that the future dam might have problems, even though the dam would be founded on similar materials.

Proposed dams frequently generate controversy because of their environmental impact. The Teton Dam was no exception; it was opposed by a number of environmental groups. Environmental activism The projected reservoir would eliminate a wild river, a trout fishery, and a wintering habitat for deer and elk. Indigenous wildlife, including bobcat, otter, and grouse populations, would be displaced. The environmentalists also suggested that the project was not economically feasible. Their calculations suggested a forty-cent return on each tax dollar spent on the project. An earlier assessment of the Teton Dam site by the Bureau of Reclamation Bureau of Reclamation, U.S. was in agreement that the Teton Dam was economically unjustifiable. As a result of pressure from politicians, however, the proposal was reevaluated and was found to be economically sound.

Federal courts made a final ruling on the environmentalists’ lawsuits in December, 1974, and ruled in favor of the Bureau of Reclamation. Construction at the dam site began early the next year.


The Teton Dam failure resulted in congressional hearings and an investigation of the cause of dam failure. The latter investigation led to a report on the failure of the Teton Dam by a panel called the Teton Dam Failure Review Group.

The cause of the failure of the Teton Dam was not well understood. Although the USGS had pointed out that the Teton Dam site was in a seismically active area, seismic monitors in the area did not detect any earthquake activity at the time of dam failure. Moreover, since weather was not a contributing factor, failure is believed to have been related to the dam site, structure, or material. These elements were the focus of both the ensuing congressional hearings and studies conducted by the Teton Dam Failure Review Group.

Leakage detected from the dam immediately before the dam failure could have been the result of a number of factors. The final report from the Teton Dam Failure Review Group concluded that failure resulted from inadequate protection of material in the dam from erosion by water seepage. The exact source of seepage could not be determined, however, because much of the evidence had been swept away in the ensuing floodwaters. Some evidence from observers pointed to percolation of water through the extensively grouted right embankment; other theories about the cause of the dam failure were also proposed. The report, however, concluded that whatever the water seepage source, dam failure could have been averted through proper defensive design.

The review group’s conclusions suggest that a safe dam could have been built at the Teton site. Some experts would disagree, however, and blame the choice of site. Geologist Marshall Corbett of Idaho State University, who served as an expert witness at congressional hearings on the dam collapse, pointed out that the valley of the Teton River was a fill valley, with bedrock buried well below relatively weak sediment. As a reservoir fills with water, the water seeps into the sediment, which may soak it up like a sponge. This weakens the material on which the dam is founded and may lead to failure.

The large amount of grout used in sealing rock and preparing the dam site was an indication of a rather weak and unstable foundation material. During excavation, large fissures were detected. According to the resident engineer in charge of the construction of the Teton Dam, “one fissure was a foot and a half wide, twenty feet long and of undetermined depth.”

The exact cause of the Teton Dam collapse may never be known. Some observers are as troubled by the process by which decisions are made to locate and build dams as by dam failures. An important flaw in the decision-making process, it has been argued, is a lack of independent review of site choices. Corbett argued that outside experts should have veto powers on the site selection of dam projects, claiming that “government geologists have a self-interest in such projects that could be an impediment to objectivity.” The role of Congress in final approval of the Teton Dam site was also criticized. The influence Congress has with respect to the locations of dams is part of what is referred to as “pork barrel” politics and has frequently been decisive in the choices of dam sites, overriding all other considerations, including scientific and engineering data. Such influence applied to the Teton Dam case. The Bureau of Reclamation had decided to scrap the Teton Dam project in 1971, but pressure from politicians caused the bureau to reevaluate its decision.

Many of these issues were considered in hearings conducted by a congressional committee on the Teton Dam disaster. Among the conclusions reached by the Committee on Government Operations were that the “Bureau of Reclamation . . . was deficient in the geologic examination of the site of the Teton Dam. It was deficient in resolving satisfactorily the warnings of safety hazards concerning the dam site it received before and during the course of construction of the dam.” Another conclusion stated that “once physical construction has commenced . . . safety problems . . . are generally met with unquestioned reliance on the Bureau’s ability to ’engineer’ workable solutions.”

Several recommendations of this committee incorporated suggestions made to improve the decision-making process on site selection for dams. For example, the secretary of the interior, the director of the U.S. Geological Survey, and the commissioner of the Bureau of Reclamation were advised to ensure that the Geological Survey perform “a complete and thorough geologic examination of each site chosen by the Bureau of Reclamation” and to prohibit the Bureau of Reclamation from proceeding with construction on any site that the Geological Survey determined presented a substantial risk. Moreover, the president was advised to establish an independent panel of experts “to ascertain the suitability of a site for the construction of a dam.” Acceptance of these recommendations would suggest a considerable improvement in the process of selecting dam sites, which would minimize not only the risk of dam failure but also the potential hazard to the public and associated damage to the environment. Dams;Teton Disasters;dam collapses Teton Dam collapse Engineering;dams

Further Reading
  • citation-type="booksimple"

    xlink:type="simple">Boffey, P. M. “Teton Dam Collapse: Was It a Predictable Disaster?” Science 193 (July 2, 1976): 30-32. Presents the events and circumstances surrounding the Teton Dam failure. Evaluates claims that the Teton Dam failure had been predicted before construction.
  • citation-type="booksimple"

    xlink:type="simple">Briggs, Peter. Rampage: The Story of Disastrous Floods, Broken Dams, and Human Fallibility. New York: Daniel McKay, 1973. Nontechnical volume on floods and dam failures, primarily in the United States. Gives step-by-step accounts of the disasters and features information from eyewitnesses.
  • citation-type="booksimple"

    xlink:type="simple">Floyd, Candace. America’s Great Disasters. New York: Mallard Press, 1990. Collection of photographs of U.S. disasters, with captions and limited text. Includes a section on floods and dam failures.
  • citation-type="booksimple"

    xlink:type="simple">McDonald, Dylan J. The Teton Dam Disaster. Mount Pleasant, S.C.: Arcadia, 2006. Documents the engineering disaster and the cleanup efforts. Includes photographs from newspapers, witnesses, and archives.
  • citation-type="booksimple"

    xlink:type="simple">U.S. Congress. House. Committee on Government Operations. The Teton Dam Disaster: Thirtieth Report. Washington, D.C.: U.S. Government Printing Office, 1976. Reports on an investigation into the process of construction of dams by federal agencies, with special reference to the process preceding the construction of the Teton Dam. Includes extensive testimony from eyewitnesses.
  • citation-type="booksimple"

    xlink:type="simple">U.S. Department of the Interior. Teton Dam Failure Review Group. Failure of Teton Dam: Final Report. Washington, D.C.: U.S. Government Printing Office, 1980. Technical review and compendium of data relating to the evaluation of the failure of the Teton Dam. Includes the results of tests conducted following failure of the dam. Especially informative with respect to the review group’s findings.

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