Slide 8 of 35
Notes:
It is VERY important to understand the difference between the causes of rockslides (and rockfalls) and the triggering mechanisms for those events.
The basic geologic setting that causes rockslides to occur from the Glacier Point cliffs include:
- Glacially steepened valley walls & stream erosion. The greatest occurrences of rockslides and rockfalls probably occurred immediately after glaciation as the landscape began its long adjustment to the newly shaped and oversteepened valley walls.
- Tectonically generated joints, which occur in nearly parallel sets, resulting in numerous obvious planar features within the Glacier Point landform. These planar features show up well in the photo above as well as in other photos throughout this report.
- Joints generated by stress relief resulting in exfoliation sheeting.
Over time, the normal processes of weathering and erosion weaken the geologic structures (naturally occurring faults, joints, and fractures) bringing those having unfavorable orientations closer and closer to failure. Eventually, the rock mass reaches a point close to equilibrium where the driving forces (gravity) are just barely balanced by the resisting forces (rock friction and cohesion).
