By Steve Gorman
LOS ANGELES (Reuters) - A 2,400-ton chunk of granite broke loose last week from the towering Half Dome formation in Yosemite National Park, altering one of North America's most popular rock-climbing routes, but no one was hurt and casual visitors will probably never notice.
The fallen slab, estimated to have measured about 800 cubic meters in volume, is believed to have crumbled from the middle the northwest face of Half Dome some time very late on July 2 or early July 3, park spokeswoman Jodi Bailey said on Wednesday.
No one saw the giant hunk of rock plunge to the valley floor in the park in California's Sierra Nevada mountains, and no climbers were affected when it fell.
Word has it a gap from the missing slab was discovered a day or two later by a group of mountaineers making their way up the northwest face of the iconic 4,700-foot-tall (1,432-meter) granite dome, Bailey said.
"This is probably one of the 50 classic climbs in North America," she said, adding that the northwest route remains open with signs warning climbers they must navigate their way around the altered section due to loose remaining rock.
Hiking trails around Half Dome and the famed cable route up the back side were not affected, and the general public is unlikely to detect any difference due to the immense scale of the granite formation as seen from the ground.
"There's already a boulder field at the base of it. You couldn't pick out the pieces that came from this slab," she said.
The uneven-shaped hunk of granite that broke away was about 2- to 3-feet (60 to 90 cm) thick and measured about 100 feet (30 meters) in length on one side and 200 feet (60 meters) along the other.
Rock falls due to constant weathering are common in Yosemite Valley year-round, with events of this size occurring about once a year. But this one stood out because it sloughed off the face of Half Dome, Bailey said.
Heavy rains that swept Yosemite Valley on Thursday and Friday may have contributed to the latest fall, she said.
(Editing by Eric Walsh)