Blocky mass Failures

In the situation depicted in the above figure we have an
example of blocky mass failure. When the rocks were
covered by the glaciers some thousand years ago there
was not risk of failure, since there was a constant
temperature and the ice was permanent. However,
presently, rock joints are increasing when the water
freezes and expands. Because of that, most of the
blocky mass failures take place during the winter.
Failures also are caused in spring because of daily
alternation of freeze and heat. Of great importance in
that type of stability are also trees. The roots of trees
can fracture the rocks or increase the width of the
existing joints. In the figure, the arrow indicates the
direction of movement of the block. The A-shape of the
joint can be also seen. This type of joint indicates
movement.

References:

Information collected during the field trip in the Sierra
Nevada, as part of the "Engineering Geology" course
curriculum, instructed by Professor N. Sitar, Department
of Civil & Environmental Engineering, University of
California at Berkeley.

Blocky Mass Failures: An example from Echo Lake, California