Approximately 17,400 years ago, a wall of water more than 120 meters or 400 feet in
height raced across a section of southeast Idaho.
As this flood quickly overflowed the natural boundaries of river channels, it began depositing
house sized boulders on cliffs, and emplaced hundreds of millions of tons of sediment,
changing regional topography.
As this flood progressed along the Snake River near the town of American Falls in Idaho,
it caused a second lake to fail which measured 40 miles in length.
At its peak, this flood had a flow rate which was more than three times the combined output
of every single river on the planet.
What had just occurred was the Great Bonneville Flood, which had a dramatic impact in the
landscapes of both Utah and Idaho.
In total, more than 5,000 cubic kilometers of water was released in this catastrophic
event, exceeding the total volume of Lake Michigan.
So, how did this flood occur?
Where did all of this water originate from, as Utah is today a state with little water?
This video will answer these two questions, and discuss this ice age era natural disaster.
34,000 years ago, the latest glacial period was still ongoing as a thick glacial ice sheet
stretched across all of Canada and covered the northern half of Washington State.
The planet as a whole was much cooler, and as a result, the biomes and rainfall rates
of typically dry areas were far higher than they are at the present.
While the southern third of Utah was still a dry semi arid desert, it received a greatly
increased level of rainfall and snowfall.
On the other hand, mid elevations contained thick forests resembling those seen in eastern
California.
And, high elevations contained thick taiga, which is a biome today largely found in Alaska.
Because of the increased precipitation, large rivers and streams developed.
In areas and basins where there was little or no outlet, enormous lakes developed.
One of these basins encompassed much of western Utah, and since the area received more precipitation
than the amount of water which would subsequently evaporate, a large lake began to grow.
By 32,000 years ago, the vast lake had grown to more than twice the size of the modern
Great Salt Lake.
As the climate continued to get colder, small glaciers developed on the state's highest
peaks, continuing to add water to the lake.
By 18,000 years ago the massive Lake Bonneville had reached its maximum depth and covered
just under 1/4th of the modern state of Utah.
This lake was just as large as the combined modern states of New Hampshire and Massachusetts.
In some locations, it was more than 1,000 feet deep.
Much of the top section of the lake was held up via a natural earthen dam.
This dam was a small debris fan that formed at Red Rock Pass in Idaho.
Over thousands of years, a trickle of water escaped through it, which soon generated a
small river.
Yet, the lake continued to maintain its overall size.
Then, 17,400 years ago, the lengthy Wasatch Fault produced a major earthquake.
The exact magnitude of this quake was unclear, but it was likely in the high magnitude 6
or low magnitude 7 range.
This quake rapidly uplifted a large section of water within the lake, and alongside numerous
landslides created a towering tsunami.
When this tsunami reached the far northern edge of the lake at Red Rock Pass, it caused
the earthen dam to completely collapse.
This released a 410 foot high wall of water which raced up tributaries of the Snake River.
Carrying with it billions of tons of sediment, large boulders became emplaced high on cliff
walls.
Reaching the several million year old lava dam near the city of American Falls, the wall
of water destroyed it, releasing much of the water built up from the 40 mile long American
Falls Lake.
Over the next several hours, this several hundred foot tall wall of water continued
until it reached the Pacific Ocean at the border of Washington and Oregon.
This flood primarily lasted for several weeks, although the flood stage continued for up
to a year.
After the flood ended, the great Lake Bonneville was now 351 feet shallower.
As continued climate change occurred, the lake slowly continued to drop lower and lower.
Today, a small sliver of this ancient ice age lake remains through the much smaller
and shallower Great Salt Lake.
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