One dead, one injured after large rock breaks off El Capitan at Yosemite National Park

 The rock was released near "Waterfall Route", a popular climbing route on the East Buttress of the 914m-tall El Capitan.
The rock was released near "Waterfall Route", a popular climbing route on the East Buttress of the 914m-tall El Capitan. PHOTO: TWITTER/YOSEMITE NATIONAL PK

WASHINGTON (WASHINGTON POST) - One person was killed and another injured after a large rock broke off the popular El Capitan rock formation at Yosemite National Park in the United States on Wednesday (Sept 27), officials said.

The rock fell from one of the world's most famously scaled granite monoliths around 1.55pm local time on Wednesday. The rock was dislodged near "Waterfall Route", a popular climbing route on the East Buttress of the 914m-tall El Capitan, said park ranger and Yosemite spokesman Danielle Bonnici. The size of the rockfall has not yet been determined, she said.

She said officials could not provide an update on the status of the injured person, who was transported from the park, located about 241km east of San Francisco, to a hospital. Officials are using a helicopter to search the area for any other people injured in the rockfall, which occurred on a day with clear blue skies at the height of climbing season.

Multiple calls to rescue services were made just before 2pm, she said. Park officials are investigating why the rock fell.

Mr John DeGrazio, a wilderness guide in Yosemite, said the hiking group he was leading had stopped to take pictures on the summit of Half Dome, another famous monolith in Yosemite, when they saw a "huge plume of smoke" coming from El Capitan.

"At first, we thought it could have been a fire," he said. "Once we saw how quickly it dissipated, we knew it wasn't a fire. When someone said it was a rockfall, I immediately thought of the climbers and knew it could be potentially bad." On the way down, a park ranger told Mr DeGrazio that there had been a fatality.

He said there was "definite surprise and obvious remorse" among members of the hiking group for the victims and their families. The hikers were also concerned for their own safety. "They're thinking, 'We're on big rocks, too,'" he said. "There is always risk."

An ABC30 reporter said a Yosemite climber sent her a photograph of the rockfall, during which he said "a piece of granite the size of an apartment building came crashing down the Waterfall Route". El Capitan is considered the "Mount Everest of rock climbing", with thousands ascending it each year.

There were 58 rockfalls in Yosemite in 2016, slightly lower than in previous years, according to the National Park Service.

Sometimes, rockfalls have obvious causes, including storms or earthquakes, while others occur on clear, sunny days.

"We have a lot of rockfalls in Yosemite because the cliffs are so big and steep," Mr Greg Stock, Yosemite's park geologist, told the Smithsonian Magazine.

The rocks peel off in giant slabs because they are destabilised by small contractions that come with changes in season and temperature. Usually, the trigger is something recognisable, but the heat of the day can also be enough to cause a slab to break away, he said.

Mr Stock said that in the past 150 years, about 15 people have died as a result of rockfalls.

He has tried to reduce the hazard of rockfalls by moving buildings and places where hikers congregate away from cliffs from which rocks might tumble, according to the Smithsonian.