Measuring Earth

Plains The three basic types of landforms are plains, plateaus, and mountains.

Plains Plains are large, flat areas, often found in the interior regions of continents. Plains often have thick, fertile soils and abundant, grassy meadows suitable for grazing animals.

Plains Plains also are home to a variety of wildlife, including foxes, ground squirrels, and snakes. When plains are found near the ocean, they’re called coastal plains.

Coastal Plains A coastal plain is often called a lowland because it is lower in elevation, or distance above sea level, than the land around it.

Coastal Plains The Atlantic Coastal Plain is a good example of this type of landform. This area has low rolling hills, swamps, and marshes.

Coastal Plains

Coastal Plains The Atlantic Coastal Plain began forming about 70 million years ago as sediment began accumulating on the ocean floor. Sea level eventually dropped, and the seafloor was exposed. As a result, the coastal plain was born.

Interior Plains The central portion of the United States is comprised largely of interior plains. A large part of the interior plains is known as the Great Plains. It is a flat, grassy, dry area with few trees. The Great Plains consist of nearly horizontal layers of sedimentary rocks.

Plateaus Plateaus are flat, raised areas of land made up of nearly horizontal rocks that have been uplifted by forces within Earth. They are different from plains in that their edges rise steeply from the land around them.

Mountains The world’s highest mountain peak is Mount Everest in the Himalaya—more than 8,800 m above sea level. The four main types of mountains are folded, unwrapped, fault-blocked, and volcanic.

Folded Mountains The Appalachian Mountains and the Rocky Mountains in Canada are comprised of folded rock layers. In folded mountains, the rock layers are folded like a rug that has been pushed up against a wall.

Folded Mountains To form folded mountains, tremendous forces inside Earth squeeze horizontal rock layers, causing them to fold.

Unwarped Mountains The southern Rocky Mountains in Colorado and New Mexico are unwarped mountains. High peaks and sharp ridges are common to this type of mountain.

Unwarped Mountains Unwarped mountains form when blocks of Earth’s crust are pushed up by forces inside Earth.

Fault-Block Mountains Fault-block mountains are made of huge, tilted blocks of rock that are separated from surrounding rock by faults.

Fault-Block Mountains These faults are large fractures in rock along which mostly vertical movement has occurred. When these mountains formed, one block was pushed up, while the adjacent block dropped down. This mountain-building process produces majestic peaks and steep slopes.

Volcanic Mountains Volcanic mountains begin to form when molten material reaches the surface through a weak area of the crust. The deposited materials pile up, layer upon layer, until a cone-shaped structure forms.

Question 1 ________ are flat, raised areas of land with horizontal rocks that were uplifted. A. Coastal plains B. Interior plains C. Mountains D. Plateaus

Answer The answer is D. Plateaus are found at higher elevations than plains.

Question 2 When molten material reaches Earth’s surface through a weak area, _______ mountains begin to form. A. fault-block B. folded C. upwarped D. volcanic

Answer The answer is D. Mount St. Helens and Mount Shasta are volcanic mountains.

Question 3 Describe the difference between the formation of folded mountains and fault-block mountains.

Answer Folded mountains form when rock layers are squeezed from opposite sides.

Answer Fault-block mountains form when some rock blocks move up along a fracture and an adjacent block moves down.