Massive rockfall - Waterfall route

Prepare yourselves, the San Joaquin Valley is moving east into the crumbling Sierra.

What's interesting about Werner's graph is that those are ambient temps. It has been my experience in taking surface temp readings that those ranges are even greater on the surface of an object.

Finally, our results offer a potential explanation for rockfalls that have no recognized trigger despite sometimes detailed observation at the time of failure. These include records of spontaneous summertime rockfalls in Japan, France, Brazil, Switzerland and Yosemite. In Yosemite, a disproportionate number (15%) of rockfalls with either an identified thermal stress trigger or an unrecognized trigger occur during the hottest summer months (July through September) and at the hottest times of the day (12:00 through 18:00 PST) compared to what would be expected under a random distribution (6%). We suggest that cyclic thermal stresses might be the trigger for these rockfalls and potentially many others around the world, highlighting the role of temperature in eroding steep landscapes.

I am wondering about how much piton pounding still goes on with these El Cap routes. Most everyone is doing most everything clean, but evidently not all?

Catastrophic rock avalanche 3600 years BP from El Capitan, Yosemite Valley, California

June 2010 
DOI: 10.1002/esp.1982

Greg M Stock and Robert A Uhrhammer
Abstract
Large rock slope failures from near-vertical cliffs are an important geomorphic process driving the evolution of mountainous landscapes, particularly glacially steepened cliffs. The morphology and age of a 2·19 × 106 m3 rock avalanche deposit beneath El Capitan in Yosemite Valley indicates a massive prehistoric failure of a large expanse of the southeast face. Geologic mapping of the deposit and the cliff face constrains the rock avalanche source to an area near the summit of ∼8·5 × 104 m2. The rock mass free fell ∼650 m, reaching a maximum velocity of 100 m s−1, impacted the talus slope and spread across the valley floor, extending 670 m from the base of the cliff. Cosmogenic beryllium-10 exposure ages from boulders in the deposit yield a mean age of 3·6 ± 0·2 ka. The ∼13 kyr time lag between deglaciation and failure suggests that the rock avalanche did not occur as a direct result of glacial debuttressing. The ∼3·6 ka age for the rock avalanche does coincide with estimated late Holocene rupture of the Owens Valley fault and/or White Mountain fault between 3·3 and 3·8 ka. The coincidence of ages, combined with the fact that the most recent (AD 1872) Owens Valley fault rupture triggered numerous large rock falls in Yosemite Valley, suggest that a large magnitude earthquake (≥M7.0) centered in the south-eastern Sierra Nevada may have triggered the rock avalanche. If correct, the extreme hazard posed by rock avalanches in Yosemite Valley remains present and depends on local earthquake recurrence intervals. Published in 2010 by John Wiley & Sons, Ltd.

Catastrophic rock avalanche 3600 years BP from El Capitan, Yosemite Valley, California. Available from: https://www.researchgate.net/publication/227781417_Catastrophic_rock_avalanche_3600_years_BP_from_El_Capitan_Yosemite_Valley_California [accessed Sep 30, 2017].

there are several errors on Sloan's lines in that pic. Weird that he made so many mistakes but hey it is Sloan after all.