Slide 14 of 35
Notes:
Geologic Structures -- discontinuities
The wastewater management systems at Glacier Point are generating more than sufficient volume to trigger the slides that are being observed. The question therefore is, “Do subsurface pathways exist to conduct the water to the rockfall sites?”
Not only do the water pathways exist, but they are clearly visible in the cliffs of Glacier Point.
Discontinuities are geologic structures that represent any type of break in the continuity of a rock mass. Common types of discontinuities include joints, fractures, and faults. All result from natural geologic processes. Joints occur in sets. Different joint sets have different orientations but the members of a set are parallel or nearly parallel to each other. Discontinuities shape landscapes during erosion because rock masses separate along them, predetermining the trends of valleys and the appearances of valley walls. Some discontinuities are obvious as diagonal planes in pictures of Glacier Point.
Discontinuities affect rockslide potential in two ways. First, they provide release surfaces from which rock blocks detach and along which they can slide. Second, they can provide direct links to water sources capable of triggering slides.
The sloping surfaces visible in the picture above results from discontinuities.
