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Where plates are diverging the stress is extensive—rocks are being pulled apart. Here is a picture of a structure known as boudinage named after the French word for blood sausage - note the sausage-like structure. Lesson Review Questions Recall 1. Oxford Academic. Rocks have highly varying strain responses to stress because of their different compositions and physical properties, and because temperature is a big factor and rock temperatures within the crust can vary greatly. Other explanations are the same as for Fig. IF you can imagine this, you can think of tension almost like pulling apart silly putty, or gum.
Tension is the opposite of compression. While compression forces the rocks and crust to collide and move together, tension forces the rocks to pull apart. Tension can happen in two ways. Two separate plates can move farther away from each other, or the ends of one plate can move in different directions.
Some scientists think tension stress caused the ancient, massive continent Pangaea to break off into the seven continents we have today. When shear stress occurs, the force of the stress pushes some of the crust in different directions. When this happens, a large part of the crust can break off, which makes the plate size smaller.
Shear stress usually happens when two plates rub against each other as they move in opposite directions. The friction of a shear stress at the edges of the plate can cause earthquakes. Crust fills the developing gaps in the form of basalt, which can flood the surface to form a basaltic sill. In the mid-oceanic ridges in the Atlantic and Pacific oceans, molten basalt released under the water hardens into pillow-like blobs, creating new oceanic crust. Hydrothermal vents release hot, mineral-laden water, which resembles black smoke.
In some cases, the edges of the plates slide past each other, neither significantly pressing together, nor pulling apart. Here the movement causes a lateral shear.
Where movement causes horizontal displacement, it is called a "strike-slip" fault. The movement isn't smooth; the plates build up stress which eventually releases in a sudden movement, causing earthquakes like the San Fransisco event.
At the Earth's surface, rocks usually break quite quickly once stress is applied. But deeper in the crust, where temperatures and pressures are higher, rocks are . Is it more likely to break deep within Earth's crust or at the surface? What if the stress applied is sharp rather than gradual? At the Earth's surface, rocks usually.
The San Fransisco earthquake provides a vivid example of dangers arising from crustal movement.