Tectonic Forces
Rocks are under stress when they are subjected to a force at depth. When the rocks are exposed at the surface after uplift and erosion, the effects of the stress can be studied. Stressed rocks show varying degrees of strain—the change in the volume and/or shape of the rock because of that stress. For example, a volcanic agglomerate may be compacted and its pyroclastic fragments stretched (strained) in response to a tectonic stress, such as compression.
