[californiadisasters] Investigating The El Capitan Rock Avalanche

At 2:25 on the morning of March 26, 1872, one of the largest earthquakes recorded in California history struck along the Owens Valley fault near the town of Lone Pine just east of the Sierra Nevada. The earthquake leveled most buildings in Lone Pine and surrounding settlements, and killed 23 people. Although seismographs weren't yet available, the earthquake is estimated to have been about a magnitude 7.5. Shock waves from the tembler radiated out across the Sierra Nevada.

On that fateful morning, John Muir was sleeping in a cabin near Black's Hotel on the south side of Yosemite Valley, near present-day Swinging Bridge. The earthquake shook the naturalist out of bed. Realizing what was happening, Muir bolted outside, feeling "both glad and frightened" and shouting "A noble earthquake!" He recalled the experience in his 1912 book The Yosemite:

"I feared that the sheer-fronted Sentinel Rock, towering above my cabin, would be shaken down… The Eagle Rock on the south wall, about half a mile up the Valley, gave way and I saw it falling in thousands of the great boulders I had so long been studying… pouring to the Valley floor… After the ground began to calm I ran  across the meadow to the river to see in what direction it was flowing and was glad to find that down the valley was still down."

The earthquake and rockfall profoundly affected Muir, causing him to view earthquakes as the primary mechanism of rock debris, or talus, formation in Yosemite Valley. Noting the huge volumes of talus in Yosemite Valley, he went on to write:

"Judging by its effects, this earthquake was gentle as compared with the one that gave rise to the grand talus system of the Range and did so much for the cañon scenery."

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View entire article here: http://www.nps.gov/yose/naturescience/upload/rock-fall-ya-article.pdf

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