The Teton Dam (Yellowstone region)

Teton dam Rexburg Idaho flood break hazards
The biggest dam failure in history -- the Teton Dam.  (Rexburg Historical Society, photo by Mrs. Eunice Olson, 5 June 1976)



Why You Can’t Miss It
At 305 feet tall, the Teton Dam ranks as the tallest dam ever to fail.  EVER!  It also has the advantages of a museum not far away in Rexburg, Idaho, and accessibility to Yellowstone and Grand Teton National Parks about an hour away.
Time:  1-2 hours, a bit more if you visit the museum in Rexburg.  Fits nicely with a visit to Yellowstone or Grand Teton national parks.
Difficulty:  Easy 
Vehicle:  Any.  Off-road capability can be used down in the canyon, but is not necessary. 
What Matters
The Teton Dam failed just before noon on June 5, 1976, a sunny Saturday.  Word spread quickly, and evacuations saved countless lives.  Still, 11 people were killed directly, and two more died from heart attacks.  Over a billion dollars in damage was done in just a few hours.  The victims responded with the most remarkable recovery effort in American history.

The Route
The Teton Dam is conveniently located within an hour of both Yellowstone and Grand Teton national parks.  As such, it makes a memorable and unusual addition to any trip.   <coordinates> 43.909648, -111.53923


From Rexburg and U.S. highway 20, take state highway 33 east.  From Driggs and the west side of the Tetons, take highway 33 west.  The turn to the dam has a historical marker next to a power substation.  The dam is at the end of the road, about a mile north.  The road ends in a parking lot overlooking the dam.



The Teton Flood Museum is located at 51 North Center Street in Rexburg.
http://www.rexburghistoricalsociety.com/teton-flood-museum.html
Their summer hours are 10 a.m. to 5 p.m.  Admission is only $2.
(Rexburg Historical Society)

What you really want to see in the museum is the movie about the disaster.  Ask the staff for the next showing (they'll do it on demand).  The film was made shortly after the event, so it reeks of 70's fashions and music (kinda fun in their own way!), and it was made by the power company that rushed in resources to restore utilities, and so has a slight air of a propaganda film.  But it has spectacular scenes and first-hand interviews, and so is nearly as valuable as going to the dam itself.  The other thing to see is the collection of photographs just outside the film room, which are not available online.  The rest of the museum is typical of a small-town museum -- mostly stuff only long-time residents appreciate and all but the most inquisitive can't wait to skip.

What You'll See
Teton dam Rexburg Idaho flood break hazards
(Rexburg Historical Society)

This is the view you'll see.  The dam failed on the far side of the canyon.  The nearer side was excavated afterwards by the Bureau of Reclamation in their investigation into the causes of failure.  The remaining part of the dam looks like a big pyramid in the middle of the canyon.  It's hard to get a sense of scale unless a vehicle or people are in the canyon (usually there's no one), but the dam is 305 feet tall from the river to the top.  That's like a 30-story building!  The top of the dam used to extend 3200 feet from the top of the concrete spillway on the far side to the concrete structure visible to your right on the near side.  You'll know when you get the sense of scale because you'll not be able to help breathing in and saying, "Wow!"

Look at the cliffs on the far side.  The bedrock is called the Huckleberry Tuff, which was put here 2.1 million years ago during Yellowstone's biggest eruption.  The tuff is a pyroclastic flow, which was 1000 feet thick when laid down here.  Imagine a hot avalanche of crushed rock and toxic gases rushing all the way from Yellowstone (visible on the skyline to the NE) at 70-120 miles per hour! It blanketed all the landscape in the region, and places down-wind like Kansas were buried in 3 feet of heavy, sandy ash.  

Look for the abundant fractures, most of which are nearly vertical.  Most of those cracks are wide-open, which you can see when the sun angle is right.  Those are called cooling joints, and they formed when the pyroclastic flow cooled and hardened.  The fractures form a 3-D, interconnected network that extends through the entire volume of the rock -- an endless honeycomb of open passageways.


Teton dam Rexburg Idaho flood break hazards USGS
(U.S. Geological Survey)

These fractures are a primary reason the dam failed.  While building the dam, engineers were not able to seal the fractures, no matter how much concrete they pumped in (they call it grout).  And as the reservoir filled, water went around the side of the dam through the fractures, eventually tunneling its way right into the core of the dam.

Which brings us to the other primary cause of failure -- the core.  Look at the excavated side of the dam (the cut on the near side).  The soft, light-colored material in the center is a material called loess -- a unique type of wind-blown soil known for letting water slowly flow through instead of puddling.  Loess formed when ice ages ended and former lakebeds and wetlands dried up and their soils and sands blew away.  This happened world-wide, and gave us many of the world's most important agricultural areas, including the famous potato-growing areas of Idaho (like the area around the Teton dam).  It just happens to make a lousy dam core.

To save money, the dam builders scraped the loess off the farms on the other side of the canyon instead of hauling in clay -- which you're supposed to use in a dam core -- a long distance from the Henry's Fork river (visible off in the distance).  In short, they built the core out of a permeable soil.  Water from the fractures was able to easily tunnel its way into the dam, causing it to fail.


                       The light-colored core.  Gray is the gravel cover.

The dam failed almost instantly, creating a 280-foot waterfall.  80 billion gallons of water rushed down this canyon and out onto the flat lands below, picking up anything and everything and tumbling it all in a dusty jumble pushed by an 8 to 20 foot wall of muddy water.  Witnesses say it looked like a dust storm approaching.  A D-9 Caterpillar, weighing 250,000 pounds, that had been working on the dam was later found 5 miles down the canyon. The towns of Sugar City and Rexburg were hardest hit, but the flood also affected Idaho Falls and Blackfoot downstream.


Teton dam Rexburg Idaho flood break hazards fail
    Rexburg, flooded  (Rexburg Historical Society)


The Really Remarkable Parts of the Story
The dam failed near noon on a sunny Saturday.  Warning got out and only a few were killed by the raging flood.  Imagine if it had failed 12 hours earlier or later when the leak could not have been seen and warning could not have gotten out.  Think how many families would have lain asleep in the path of the flood, and how many children sleep in basements in an area like this.  Though a huge disaster, the timing itself was a blessing.

The response of the people in this area to the disaster is one of America's greatest disaster stories.  The communities banded together, organized by the Mormon church, to marshal resources, house the homeless, feed the hungry, and do the hard work of digging out basements and cleaning homes.  Ricks College (now called BYU-Idaho) on the hill in Rexburg became the refugee center for the rest of the summer.  Even more remarkably, busload after busload of volunteers came from throughout the region to help with the cleanup.  Thousands of volunteers swarmed the area, including contractors with their heavy equipment.  When the Federal agency (forerunner to FEMA) showed up, everyone pointed them to the local church leader in charge of the clean-up.  When the Fed said he was here to help, the church leader replied, "We've got it covered."  I heard this story from a man who was standing right there and heard it first-hand.  Amazing!

You can see photos of the relief effort and damage here: Snail Hollow Gazette

To this day, the affected communities have personalities, ethics, and attitudes that developed in the weeks and months after the Teton flood.  I guarantee, if your car were to break down in these towns, you wouldn't have to call the auto club to get help (I know this from personal experience!).


Teton Flood Summary
Date: June 5, 1976, noon (Saturday; clear and warm)
Deaths: 14 (11 directly)
Damages: estimated between $400 million and $1 billion (1976 dollars). Over      200 families left homeless.
Claims Paid: 7,563 claims for a total amount of $322 million
Water: 2 million gallons per second. 80 billion gallons (XX acre-feet). Reservoir    10 miles long, 280 feet deep.
Built By: U.S. Bureau of Reclamation; contract to team of Morrison-Knudsen-  Kiewit. $39 million.
Site Investigations: 1961 to 1970, U.S. Geological Survey.
Construction began in February, 1972. Began filling reservoir October 3, 1975, 3  feet per day.
Dam structure: This is the largest dam to fail in world history. 305 ft. tall, 3100  ft long. 1) 70 foot deep, steep-sided key trenches on the abutments above the  elevation of 5,100 feet; 2) a cutoff trench to rock below the elevation of 5,100  feet; 3) a continuous, single grout curtain along the entire foundation; and 4)  excavation of rock under the abutments.
Bedrock: Rhyolite pyroclastic flow, the Huckleberry Ridge Tuff, 2.1 million years  old. Largest eruption from Yellowstone, 2500 km3. Pervasively jointed (“cooling  joints” are ubiquitous in volcanic rocks).
Investigative Panel Findings:
1) Built without sufficient attention to the varied and unusual geological conditions of the site.
2) The volcanic rocks of the site are “highly permeable and moderately to intensely jointed.”
3) The fill soils used, “wind-deposited nonplastic to slightly plastic clayey silts,” (called “loess”) are highly erodible.
4) The rapid rate of filling of the dam did not contribute to the failure. If the dam had been filled more slowly, “a similar failure would have occurred at some later date.”
5) Considerable effort was used to construct a grout curtain of high quality, but the rock under the grout cap was not adequately sealed. The curtain was nevertheless subject to piping – “too much was expected of the grout curtain, and … the design should have provided measures to render the inevitable leakage harmless.” Should have had 3 grout curtains.
6) The dam’s geometry caused arching that reduces stresses in some areas and increased them in others and “favored the development of cracks that would open channels through the erodible fill.”
7) The Panel had quickly identified piping as the most probable cause of the failure, then focused its efforts on determining how the piping started. Two mechanisms were possible. The first was the flow of water under highly erodible and unprotected fill, through joints in unsealed rock beneath the grout cap, and development of an erosion tunnel. The second was “cracking caused by differential strains or hydraulic fracturing of the core material.” The Panel was unable to determine whether one or the other mechanism occurred, or a combination. 
8) “The fundamental cause of failure may be regarded as a combination of geological factors and design decisions that, taken together, permitted the failure to develop.” The design decisions were “complete dependence for seepage control on a combination of deep key trenches filled with windblown soils and a grout curtain,” a geometry of the key trench that “encouraged arching, cracking, and hydraulic fracturing” in the backfill, using compaction of the fill as the only protection against piping and erosion, and failure to provide for the inevitable seepage.
Lessons Learned: The Teton flood is used in Federal program training as an example of how not to run a program. The dam’s failure is attributed to “bureaucratic inertia.”

Relief: The Mormon church organization sprung into action, providing nearly all the personal aid needed. Pres. Henry Eyring opened Ricks College to anyone needing food and shelter. Volunteers from the region came by the busload into the autumn, including heavy equipment operators, builders, etc. It stands as perhaps the best private relief effort in history.

M.S. -- More Science   Report
Back to Top