Left panel shows the seasonality of documented rockfalls throughout Yosemite Valley for which the timing is known (1857-2011), right panel shows the seasonality of just those rockfalls from Half Dome over that same time period.
Yes, that is certainly a possibility, and no doubt there are many smaller rockfalls that are either not observed or not reported. However, I do think that certain cliffs really are more seasonal than others with respect to rockfalls.
We have documented >1 cm of daily movement of exfoliation slabs due to thermal stresses (heating and cooling of the rock). An interesting correlation for Half Dome is that more rockfalls occur from the NW face during the months that it gets more direct sun.
27 July 2006 rockfall from the NW face of Half Dome.
There is a very large flake, that one climbs on/past, roughly half way up Tis-sa-ack... (it is about 25 feet high and maybe 10 feet wide) You get to stand on the crusty broken-toothed top edge to place a wee pin up under a thin flake, and I swear it vibrated with the wind... I don't remember breathing very much...
Does any one know if it's still there?
It is/was a serious candidate for terminal velosity.