The floor of Zion National Park was created due to the damming of the Virgin River that occurred through the collapse of a Utah mountainside approximately 4,800 years ago in what is referred to as a "rock avalanche."
The new findings stem from a University of Utah study - the first to date the landslide - that reveals its size and dynamics, estimating that its speed was up to 180 miles per hour.
"The ancient Zion landslide would cover New York City's Central Park with 275 feet of debris," said Jeff Moore of the University of Utah and senior author of the study. "And you would need 90 times the volume of concrete in Hoover Dam to recreate the mountainside that failed."
The team estimates that the massive landslide had a volume of 286 million cubic meters, trumping Utah's 2013 Bingham Canyon copper mine landslide, which is one of the largest non-volcanic landslides in North America.
The volume was determined by using a computer to recreate what the canyon likely looked liked before the landslide. In addition, the team reconstructed what the top surface of the landslide looked like before erosion began.
Using computer simulations, the University of Utah team also revealed that the huge slide made its way across Zion Canyon in approximately 20 seconds, making its average speed 112 miles per hour, with a peak of 180 to 200 miles per hour.
"It was certainly moving more than 150 miles per hour when the huge wall and peak crashed down," Moore said. "By a minute it was pretty much done."
"This catastrophic landslide of massive proportions had two effects," he continued. "One was constructive - creating paradise through cataclysm. More than 3.6 million people last year enjoyed the flat and tranquil valley floor of Zion Canyon, which owes its existence to this landslide. The other aspect is the extreme hazard that a similar event would pose if it happened today."
Although such a massive landslide would be devastating, the frequency of similar events is infrequent, and Moore says that there is "no evidence that something like this is imminent."
However, the 4,800-year old landslide deposit is still the source of smaller slides, including one that took place in 1995 and damaged a road in Zion National Park.
The findings were published May 30 in GSA Today.
