NSSS2.1

toc =2.1 Earth's Crust in Motion=


 * Earthquake:** The shaking of plate tectonics
 * Stress:** The force that changes rock and its shape and volume.
 * Shearing:** Stress that pushes rock in opposite directions.
 * Tension:** Stress that pulls on rock making it thinner in the middle.
 * Compression:** Stress that squeezes rock until it folds or breaks.
 * Deformation:** The change in the Earth's crust such as volume or shape is called deformation.
 * Fault:** A break in the Earth's crust where rocks have slipped past each other.
 * Strike-Slip Fault:** The rocks on both sides of the fault move past each other sideways or with up-or-down motion.
 * Normal Fault:** During a normal fault the fault is at an angle where one block of rock lies above the fault and the other block lies beneath the fault.
 * Hanging Wall:** The block of rock that lies above the fault is called the hanging wall.
 * Footwall:** The block of rock that lies beneath the fault is called the footwall.
 * Reverse Fault:** A reverse fault has the same structure as a normal fault but instead of the block going underneath the other, in a reverse fault the blocks of rock move in opposite directions.
 * Fault-block Mountain:** These mountains form when a normal fault uplifts a block of rock.
 * Folds:** Folds are bends in rock that form when compression thickens part of the Earth's crust and shortens it as well.
 * Anticline:** Anticlines form when a fold in rock bends upward forming an arch.
 * Syncline:** Synclines form when a fold in rock bends downward forming a bowl.
 * Plateau:** This area is a large area of flat land that is situated high above sea level.

Introduction

 * As you are sitting somewhere in your house, suddenly everthing starts to shake and fall.
 * After the shaking ends you turn on the news and you here that an earthquake just struck your area.
 * Earthquakes can be very destructive as they can destroy homes and wreck other things as well.

Stress in the Crust

 * For many years people have been wondering what earthquakes are and what causes them.
 * An earthquake is actually the shaking and trembling of plate tectonics and it is caused by stress.
 * There are three types of stresses. They are shearing, tension, and compression.
 * **Shearing**
 * Shearing is the stress force that pushes rock in opposite directions.
 * Shearing can cause rock to break or change its shape
 * **Tension**
 * Tension is the stress force that pulls on rock making it thinner in the middle.
 * Tension is like pulling on a warm piece of gum.
 * **Compression**
 * Compression is the stress force that squeezes rock until it folds or breaks.
 * Compression is like compressing rock like a giant compactor.[[image:torreavenue-1.jpg]]

Kinds of Faults

 * There are three different types of faults.
 * They are strike-slip faults, normal faults, and reverse faults.
 * **Strike-Slip Faults**
 * These faults make rocks on both sides to move past each other sideways or with up-or-down motion.
 * These faults form boundaries between plates ( transform boundaries ).
 * **Normal Faults**
 * During a normal fault the fault is at an angle where one block of rock lies above the fault and the other block lies beneath the fault.
 * The stress force tension creates normal faults in the places where plates diverge creating a divergent boundary.
 * **Reverse Faults**
 * A reverse fault has the same structure as a normal fault but instead of the block going underneath the other, in a reverse fault the blocks of rock move in opposite directions.
 * Compression creates a reverse fault.

Friction Along Faults

 * The movement of rocks along a fault depends on the amount of friction there is between the opposite sides of the fault.
 * A place along the fault where the friction is low, both sides of the fault go by each other without much sticking.
 * A place along the fault where the friction is moderate, the sides of the fault collide together.
 * A place along the fault where the friction is high, the rocks combine together and they stay put.
 * In some of these cases, the stress increases until it is powerful enough to overcome the friction force.

Mountain Building

 * There are two ways by which mountains can form.
 * They are by faulting and also by folding.
 * **Mountains formed by faulting**
 * Mountains formed by faulting are called fault-block mountains.
 * These mountains form when a normal fault uplifts a block of rock.
 * An example of fault-block mountain range is the Sierra Nevada of California.
 * **Mountains formed by folding**
 * Mountains formed by folding are actually mountains that have formed when compression thickens part of the Earth's crust and shortens it as well.
 * `An example of mountains formed by folding are the Himalayas in Asia and the Alps in Europe.

Anticlines and Synclines

 * Anticlines
 * Anticlines form when a fold in rock bends upward forming an arch.
 * Anticlines are found in many places on the Earth's surface where the stress force compression have folded the surface.
 * One example of an anticline are the Black Hills of South Dakota.
 * Synclines
 * Synclines form when a fold in rock bends downward forming a bowl.
 * Synclines are also found in many places on the Earth's surface where the stress force compression have folded the surface.
 * One example of a syncline is the Illinois Basin.[[image:torreavenue-4.jpg]]

Plateaus

 * A plateau is an area is a large area of flat land that is situated high above sea level.
 * It consists of many flat layers, and it is wider than it is tall.
 * One example of a plateau is the " Four Corners " of Arizona, Utah, Colorado, and New Mexico.