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Cataclysmic Ancient Landslide Shaped Zion National Park: Study

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A massive landslide of rocks that occurred in Utah thousands of years ago blocked the flow of the nearby Virgin River, creating a lake that would eventually become Zion National Park, a new study says.

Researchers at the University of Utah examined the formation of Zion National Park, which currently covers the state counties of Iron, Kane and Washington.

They discovered that the Sentinel, a sandstone formation located on the west wall of Zion Canyon, suffered a cataclysmic event known as a rock avalanche about 4,800 years ago. This caused as much as 10 billion cubic feet of Kayenta and Navajo sandstone debris to block the Virgin River and form a 2-mile-long lake that lasted for 700 years.

The resulting sedimentation allowed the valley floor to be leveled, which is why it doesn't feature any rugged banks that are typically seen in riversides. The massive landslide and the subsequent transformation of the valley led to the creation of what is now Zion National Park.

Jeff Moore, geology professor from the University of Utah and one of the authors of the study, explained that the rock avalanche that formed Zion was so massive that it could bury the entirety of Central Park in New York under 275 feet of ruble.

He added that the amount of earth that collapsed from the mountainside was equivalent to 90 times the volume of concrete that was used to build Hoover Dam.

According to the researchers' estimates, the ancient landslide involved the displacement of as much as 10.1 billion cubic feet of earth, which is 4.4 times more than what was measured during the landslide of the Bingham Canyon copper mine in Utah in 2013. The copper mine's collapse had a volume of 2.3 billion cubic feet.

Moore and his colleagues said the Sentinel, which currently stands at 7,157 feet high, was significantly larger before the rock avalanche occurred thousands of years ago.

Computer simulations of the event showed that the massive landslide rushed toward the southeast side of the canyon in 20 seconds at an average speed of about 112 miles per hour and a peak speed of about 180 to 200 miles per hour.

Moore said the landslide was occurring at 150 miles per hour when the majority of the wall suddenly came crashing down. It took another 30 seconds for the debris to spread across the Zion Canyon. The entire rock avalanche was done in just a minute.

The researchers believe the massive landslide event produced two effects. The first one is constructive, as it shows how a paradise can be brought about following a cataclysm. The flat and serene valley floor of the Zion National Park came as a result of the ancient rock avalanche. The second effect of the landslide is to show just how dangerous such an event could be especially if it were to happen again today.

However, the researchers said that severe landslides, such as the one that helped create the Zion National Park, is extremely rare, and that they have found no evidence that would suggest a similar event could happen any time soon.

The findings of the University of Utah study are featured in the journal of Geological Society of America, GSA Today.

Photo: Les Haines | Flickr 

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