Slide 9 of 35
Notes:
Once the barely stable condition near equilibrium is reached, through thousands of years of weathering, changes in environmental conditions can provide triggering mechanisms capable of pushing the rock mass beyond equilibrium leading to rockslides and rockfalls. The areas of weakened rock, from which a portion of the June 10, 1996 rockslide originated, are clearly now exposed diagonally across the center of the photo above.
Well known triggering mechanisms for rockslides and rockfalls around the world include: excessive vibration; freeze-thaw; and, changes in groundwater flow patterns which create excess water pressure. It is rare for rocks to fall without a triggering mechanism although the mechanisms are sometimes unrecognized by those present at the time.
Vibrations from an earthquake are documented to have triggered at least one Yosemite rockslide. And, although construction-related blasting has occurred near Glacier Point, seismic records indicate that those vibrations are small. There is no evidence relating rockslides or rockfalls near Glacier Point to blast vibrations.
Freeze-thaw is not likely to have played a role in triggering Glacier Point rockslides and rockfalls. Only one event occurred at a time when air temperatures reached below zero and it was early enough in the season that rock temperatures were probably still above freezing.
