Geology Reference
In-Depth Information
(b)
Figure 11.3.
(b) Near Chazeirollettes, southern Massif Central, France.
Figure 11.4.
Boulder with secondary fracture, unexploited by weathering or gravity, Hyden Rock, southern
Yilgarn, Western Australia.
Subsidiary fractures are penetrated by moisture and so widened, either as a result of freeze-thaw
activity or ice-wedging (as in the Pyrenees and the Snowy Mountains of New South Wales, for
example), or in consequence of alteration of the rock immediately adjacent to the parting.
Weathering along the secondary fracture weakens cohesion between the two adjacent masses, and,
unless the blocks and boulders have flat bases and rest on an even platform, the weight of the two
parts of the mass separated by the latent fracture causes them to fall apart (
Fig. 11.5).
Seismic
shaking may have assisted the process.
