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PICTURE: ANYMOUNTAIN

The earth is a dynamic and constantly-changing planet. Oceans surge, weather rages, and land forms shift, uplift, and change with time.

It is the changing appearance of the land, as well as the formation of mountains and volcanoes that are the subjects of this lesson.

The earth's crust is composed of rocks that can change shape if they undergo enough stress. Compression, tension, and shearing all affect rock in different ways.

PICTURE: rockmor

PICTURE: rkstcm

Compression is the squeezing together of rocks. It results in rocks being pushed higher and deeper as the same amount of material tries to occupy less space.

The collision of a continental plate and an oceanic plate results in compression, volcanism, and mountain formation.

PICTURE: conocnpl

When rocks are compressed, they form folds by bending without breaking. If the fold curves up, an ANTICLINE is produced. If the fold curves down, a SYNCLINE is produced. Folds may be large or small.

PICTURE: antsycln

When tension pulls crustal plates apart, the plate thins. This is because the same amount of matter is occupying a greater space.

Shearing occurs when plates are pushed in opposite directions along a horizontal plane. Bending and breaking occurs because the same amount of matter is occupying the same amount of space, but in a different position.

These three types of tensions can change the appearance of rocks by altering its shape or volume.

Tension or pressure from deep inside the earth can cause rock to break or FRACTURE. If the two rock masses produced by the fracture were to move, a FAULT results.

One block moves up and the other moves down.

PICTURE: norfault

Similar to normal fault but with overhang produced.

PICTURE: revfault

One block slides over the other.

PICTURE: thrfault

Also called a lateral fault; movement is horizontal in opposite directions.

PICTURE: strfault

Folding and faults are important because they produce mountains. Mountains are landforms elevated high above sea level. The difference between hills and mountains is their height. To be classified a mountain, the landform must be at least 600 meters higher than the surrounding landscape.

A mountain can be a single peak, part of a chain, or a range of mountains. Mountains can form under the ocean or on land. On land, they influence the climate and water availability to a region and provide habitat for plants and animals.

Mountains on land are an important source of natural resources, including minerals and lumber.

Mountains pass through three stages in the process of developing.

YOUNG MOUNTAINS are characterized by steep sides with jagged peaks and narrow valleys.

MATURE MOUNTAINS have weathered, rounded peaks and gentle slopes.

OLD MOUNTAINS exhibit flattened, rolling peaks and wide valleys.

PICTURE

Groups of mountains form ranges, which are also known as chains. A group of ranges comprises a mountain system. A group of mountain systems make a mountain belt.

Individual Mountain

Mountain Range

Mountain System

Mountain Belt

MOUNT BLANC

WESTERN ALPS

ALPS

EURASIAN-MELANESIAN BELT

PICTURE: MT. ST HELENS

Mount St. Helens is a volcanic mountain located in the Cascade range in the state of Washington. This volcano erupted in 1980 causing tremendous property damage and several deaths. The cloud of ash it emitted exploded 12 miles into the air. It was the first volcanic eruption in the continental United States since 1921.

Mountains differ in many ways, including the way in which they were formed. There are various processes that can cause mountain formation. Each process results in a particular type of mountain.

FOLDED MOUNTAINS form when compression causes rock layers to bend and fold, but not break. This happens when crustal plates collide. Buckling occurs and folds result.

PICTURE: rockfold

FAULT-BLOCK MOUNTAINS form by vertical fault movement. Normal faults cause the formation of fault-block mountains. A block of crustal plate rises up, while blocks on either side of it slide down.

PICTURE: fltblkmn

A RIFT VALLEY is the reverse of a fault-block mountain. It forms when a wedge of coastal plate drops down between two blocks.

PICTURE: riftvall

DOME MOUNTAINS are formed from pools of magma that accumulate beneath the surface of the earth. They push up on the crustal plate and result in the formation of a domed mountain. This is not a volcano, because the magma does not reach the earth's surface.

Plateaus have been described as mountains with flat tops. They are elevated land forms that are flat rather than peaked.

Plateaus form when huge areas of the crust are pushed upward.

Plains are large flat areas of land. They are not elevated land forms, but are found fairly close to sea level. There are two type of plains: coastal and interior.

Coastal plains are found near coastal areas and interior plains are found in the interior of a land mass.

A coastal plain is a section of lowland that extends along a seacoast. The plain may have been below sea level at one time in history and been part of the continental shelf.

An interior plain is a flat stretch of land that extends for many miles without any noticeable changes in elevation. Interior plains may occur at any altitude.

Plains are usually composed of grasslands, which makes them good for farming. The soil is normally rich, and rainfall is usually adequate.

In the United States, the Great Plains area is called "The Breadbasket." This refers to the fact that most of the United States' grains and foods are produced in this region.

This area is also used for production of beef cattle, dairy cattle, hogs, and sheep. The grassland makes excellent grazing for these animals. Farms and ranches cover the Great Plains region.

Plains are located all across the globe. In South America, they are known as pampas and the cowboys who work on them are called gauchos.

In Africa, there is a huge plain called the savannah. It is well known as a home for much of Africa's wildlife. In southeast Europe and Asia, the plains region is known as the steppe.