Forces in the Earth's Crust

Learn about Earth's crustal forces and plate boundaries: stress, compression, tension, shear, and convergent, divergent, transform boundaries.

Introduction The movements of the Earth's plates result in great forces that squeeze or pull the rocks in the crust. A force of this type is an example of stress. Stress acts on an area of rock changing its size, shape, or volume. Rock deformations due to stress are called strain. Because stress is a force, it adds energy to the rock. The energy is stored in the rock until the rock changes in shape or breaks. Types of Stress 1. Compression It happens when rocks on the Earth's crust are squeezed or compressed together. Compression stress decreases the volume of rocks. It also pushes the rocks either higher up or deeper down the Earth's crust. 2. Tension Stress Tension stress is the stress that tends to pull something apart. It is the stress component perpendicular to a given surface, such as a fault plane, that results from forces applied perpendicular to the surface or from remote forces transmitted through the surrounding rock. 3. Shear Stress Shear stress, force tending to cause deformation of a material by slippage along a plane or planes parallel to the imposed stress. The resultant shear is of great importance in nature, being intimately related to the downslope movement of earth materials and to earthquakes. Shear stress may occur in solids or liquids. Matching Type Match column A to column B Tension Stress It is the stress that tends to pull something apart. Shear Stress A force tending to cause deformation of a material by slippage along a plane or planes parallel to the imposed stress. Compression Stress It happens when rocks on the Earth's crust are squeezed or compressed together. Three Types of Plate BoundariesConvergent Plate Boundary Convergent Plate Boundaries are regions where two plates move toward each other and collide. Collisions involving two continental plates often cause the pair to fold in one direction, resulting in mountains or mountain ridges. Collisions involving a continental plate and an oceanic plate, however, undergo a process called subduction. This occurs when an oceanic plate goes under a continental plate. This may result in volcanoes and mountain ranges. Island arcs, which are chains of active volcanoes, may also form from subduction. Divergent Plate Boundary Divergent Plate Boundaries are regions where two plates move apart. This occurs when magma from the mantle rises toward the Earth's crust and pushes the two plates apart. Small mountains will then form along the rift, the area where the divergence occurred, resulting in rift valleys. The cooled magma will then become part of the crust and widen the ocean floor or the landmass. Transform Plate Boundary Transform Plate Boundaries are where two plates slide past each other. These cause devastating earthquakes and create fault lines, which are fractures on the plate. Earthquakes are most likely to occur again in fault lines because of the continuous sliding of the two plates.. 1. This occur when an oceanic plate goes under a continental plate. convergent boundary transform boundary divergent boundary subduction 2. It is a region where two plates move toward each other and collide. convergent boundary transform boundary divergent boundary subduction 3. It is a region where two plates move apart. convergent boundary transform boundary divergent boundary subduction 4. What kind of boundaries are two plates slide past each other? convergent transform divergent subduction