Page 304 - Laboratory Manual in Physical Geology

ACTIVITY 10.2 Visualizing How Stresses Deform Rocks

Name: ______________________________________ Course/Section: ______________________ Date: ___________

Recall that Earth materials can deform when stress (amount of force acting on a unit surface area) exerts pressure on them.
Confining pressure occurs when stress is equal in all directions. Directed pressure occurs when the stress is greater in one direction
than another—described as compression, tension, or shear .
A. Stress in everyday objects and actions. Place checks in all of the boxes that describe the stress involved in each object and
action described below.

Confining Directed
Object or Action Compression Tension Shear
Pressure Pressure
1. A cardboard box collapses when you sit on it.
2. An unopened bottle of soft drink (soda, pop).

3. You stretch out a rubber band by pulling its ends apart.
4. You rub your hands together, and back and forth, to
keep warm.
B. Stress in the Geosphere . Think about how tectonic plates deform along convergent, divergent, and transform plate
boundaries. Draw arrows on each of the bottom six illustrations of plate deformation to show the directions of directed stress
(directed pressure) that are causing the deformation, then identify the stresses as compression, tension, or shear .

Undeformed lithospheric plate

C. REFLECT & DISCUSS The examples of deformation above (part B) are primarily caused by directed stresses that are

pressing on rocks in the horizontal dimension. What kinds of stress can you think of that are pushing or pulling on rocks in
the vertical dimension, and what kind of deformation do they cause or aid?

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