A New Crack Has Appeared In Yosemite, And It's Huge

By Abdul Rafay in Nature On 9th September 2023
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Last week, climbers in Yosemite discovered a fresh crack close to the Royal Arches wall. A subsequent examination, according to park officials, revealed that cracking was actively taking place, and as a safety measure, they have taken action to close specific areas of the park.

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A sizable pillar of granite close to the climbing route known as Super Slide has been partially dislodged by the new crack. The National Park Service is blocking off trails while their investigations are ongoing to lessen the risk of rockfall. 

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The restrictions went into effect on August 30 and will continue until further notice.

“The following week a climbing ranger and a geologist observed it firsthand and they could hear it cracking like a frozen lake that wasn’t consolidated,” Jesse McGahey, a Supervisory Park Ranger at Yosemite National Park, told Climbing. 

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“And there were pieces of rock rattling down the crack without touching it. The park geologist said they’d never seen anything like this. He’s never been able to observe that in his 15 years in Yosemite.”

Over the course of seven days, the crack is said to have shifted around an inch, but it's unclear what that implies for the future.

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Yosemite Valley's sheer cliffs, which a glacier carved out, are prone to rockfalls. It means that the landscape is always changing, which adds to the beauty of the national park, but rockfalls are something you probably don't want to watch up close.

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“Triggering mechanisms like water, ice, earthquakes, and vegetation growth are among the final forces that cause unstable rocks to fall,” writes the National Park Service. “If water enters fractures in the bedrock, it can build up pressure behind unstable rocks. Water also may seep into cracks in the rock and freeze, causing those cracks to grow. This process is called ‘frost wedging’ or ‘freeze-thaw’ and can incrementally lever loose rocks away from cliff faces.”

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The unusual topography of Bryce Canyon National Park in Utah, where a record-breaking amount of hoodoos may be discovered, is also a result of frost wedging.

The recent discovery of a dangerous crack in Yosemite National Park serves as a stark reminder of the ever-changing and powerful forces that shape our natural world. 

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Two tourists were struck by a rockfall in 2022 after some rubble became loose just below Union Point and fell to the valley floor. The biggest occurrence of the year was when a 1,344 cubic meter piece of rock came loose and fell on Middle Brother.

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The experts at Yosemite frequently examine the risk of rockfall inside the park's limits using high-definition imagery and laser mapping. 

McGahey reminds visitors that: “It’s an evolving and ongoing situation and we will continue to monitor it. It’ll remain closed due to the fact that it’s an active crack, and we are observing further propagation or growth of the crack. And also keep in mind that climbers can encounter rockfall on any route in any area of Yosemite.”