Forces in Earths Crust Can Earth be stressed

Forces in Earth’s Crust Can Earth be stressed?

How does stress change Earth’s crust? Rocks in Earth’s crust are hard and difficult to bend but with enough force, or stress, these rocks can bend and break Stress: a force that acts on rock to change its shape and/or volume Because stress increases as force increases, stress adds energy to the rock which is stored in the rock until the rock changes shape or breaks REMEMBER: Energy is the ability to do work or cause change = More energy means bigger change Three Types of Stress Tension Compression

Tension Rocks in the crust can be stretched so that it becomes thinner in the middle. This type of stress is called tension Occurs when two plates pull apart or diverge This causes rock to increase in volume but decrease in density

Compression Plates pushing against other plates can squeeze the plates together, compacting them Converging plates are caused by compression, when two plates come together Makes the rock smaller and denser Rocks are pushed up and deeper down

Shearing Stress that pushes a mass of rock in two opposite directions is called shearing Occurs at Transform Boundaries

Faults Fault: a break or crack along which rocks move Hanging Wall: the block of rock above the fault plane Foot Wall: the block or rock below the fault plane

Normal Fault Tension causes normal faults to form Normal faults: the fault cuts through rock at an angle so that the hanging wall slips down and the footwall is pushed up

Reverse Fault A reverse fault is caused by compression In a reverse fault, the hanging wall moves upwards and the foot wall sinks below

Strike-Slip Fault Shearing causes strike-slip faults at transform boundaries The rocks on either side slip past each other with little up or down motion

Folding in Earth’s Crust Have you ever skidded on a rug that wrinkled up as your feet pushed it across the floor? Earth’s crust can move the same way in certain circumstances Folds: bends in rock that form when compression shortens and thickens Earth’s crust. Folds can be a few centimeters or hundreds of kilometers wide.

Anticlines and Synclines Geologists use the terms anticline and syncline to describe upward and downward folds in rock. Anticline: An upward fold or bend in rock Syncline: A downward fold or bend in ● rock Most mountain ranges a are that creates “U” shape formed when compression causes land to fold along a large area of land

Fault-Block Mountains Tension in Earth’s crust causes Fault-Block Mountains to form Forms when tension causes several normal faults in an area.

Discussion Questions How does stress change Earth’s crust? How do faults form? How does plate movement create new landforms?