![]() ![]() ![]() Figure 12.3.3 A depiction of joints developed in a rock that is under stress.įinally joints can also develop when rock is under compression as shown on Figure 12.3.3, where there is differential stress on the rock, and joint sets develop at angles to the compression directions. Figure 12.3.2 A depiction of joints developed in the hinge area of folded rocks. Note that in this situation some rock types are more likely to fracture than others.Ī fracture in a rock is also called a joint. There is no side-to-side movement of the rock on either side of a joint. Most joints form where a body of rock is expanding because of reduced pressure, as shown by the two examples in Figure 12.3.1, or where the rock itself is contracting but the body of rock remains the same size (the cooling volcanic rock in Figure 12.1.3a). In all of these cases, the pressure regime is one of tension as opposed to compression. Joints can also develop where rock is being folded because, while folding typically happens during compression, there may be some parts of the fold that are in tension (Figure 12.3.2). (right), both showing fracturing that has resulted from expansion due to removal of overlying rock. Figure 12.3.1 Granite in the Coquihalla Creek area, B.C. Fracturingįracturing is common in rocks near the surface, either in volcanic rocks that have shrunk on cooling (Figure 12.1.3a), or in other rocks that have been exposed by erosion and have expanded (Figure 12.3.1). A body of rock that is brittle-either because it is cold or because of its composition, or both- is likely to break rather than fold when subjected to stress, and the result is fracturing or faulting. ![]()
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