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. 

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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.