Massive, Violent Landslide Created Zion National Park, Study Says | The Weather Channel – The Weather Channel

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Every year, millions of people travel to Utah to take in the beautiful and peaceful scenery in Zion National Park. According to a new study, however, the geographic stunner was formed by a massive prehistoric landslide that was far from tranquil.

The study, published Thursday in the Geological Society of America, said the park’s flat valley floor owes its creation to the collapse of a wall of Navajo Sandstone that was almost 900 miles high. Weak layers in the underlying Kayenta Formation sent debris shooting across the canyon at speeds that likely reached 90 miles per second. It’s believed that the event took place around 4,800 years ago.

“The ancient Zion landslide would cover New York City’s Central Park with 275 feet of debris,” Jeff Moore, senior author of the study, told “And you would need 90 times the volume of concrete in Hoover Dam to recreate the mountainside that failed.”

He added that the avalanche “would bury Salt Lake City’s Liberty Park 2,340 feet deep, which is almost half a mile.”

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The massive slide blocked Zion Canyon over a distance of about two miles, damming what is now the Virgin River and forming Sentinel Lake, which lasted for 700 years before dissipating, according to the study. Remaining clay beds and fossil mollusks preserved throughout the canyon provide evidence of a time when the lake occupied the area before it became filled with sediment.

The landslide was first documented in a scientific paper in 1945, but this new study gives more details about when it took place, as well as insight into its characteristics.

According to the study, the researchers took samples from 12 boulders across the rock avalanche deposit to test using surface exposure dating. They found that boulders across the surface of the slide had deposited simultaneously, which indicates the slide was a single, massive event. However, there is no evidence of another seismic event in the area that could have triggered the avalanche.

This catastrophic landslide of massive proportions had two effects,” Moore told the Deseret News. “One was constructive – creating paradigm 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.”

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Deposits from the landslide still create smaller slides. In 1995, a main road in the canyon was damaged during the Virgin River slide and required extensive repairs, according to the study. Before that, in 1990, the Middle Fork Taylor Creek slide dammed a canyon, which drained three years later and created a flow of debris that impacted vehicles on a nearby interstate.

“From a long-term perspective, this is a part of a cycle,” Moore told the Deseret News. “The rivers dig deeper into the bedrock, the canyon walls grow higher. Ultimately they cannot sustain these heights and they respond by failing in small and big landslides alike.”

The large rock avalanches represent a hazard that is rare but has an extreme magnitude.

“All that sediment on the flat floor is also on its way out,” said Moore. “When that goes, Zion Canyon will look a lot different and feel a lot different.”

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Massive, Violent Landslide Created Zion National Park, Study Says | The Weather Channel – The Weather Channel