Download Landforms only

Earth’s Landforms
Lesson Objectives
• Differentiate between plains and plateaus.
• Compare and contrast folded, upwarped, fault-block, and volcanic
mountains.
• Be SURE TO COMPLETE the activities at the end of the chapter - some
are links — click on them……
PAGE !10
Vocabulary
• plain
• plateau
• folded mountain
• upwarped mountain
• fault-block mountain
• volcanic mountain
Introduction
Plains
There are a lot of interesting landforms around the world. A landform is a
feature that makes up the shape of the land at Earths surface. Figure 3-1
shows the three basic types of land. forms: plains, plateaus, and mountains.
We all know what mountains are. In our minds, we can see tall peaks
reaching towards the sky. But what do you think of when you hear the word
plains? You might think of endless flat fields of wheat or grass. That would be
accurate, because many plains are used to grow crops. Plains are large,
relatively flat areas. Plains found near the ocean are called coastal plains.
Flat, grassy areas used to grow crops or for grazing are also plains. Together,
these two types of plains make up one half of all the land in the United States.
Coastal Plains
Coastal plains are broad areas along the oceans shore. They are often called
lowlands because of their low elevations. Elevation refers to distance above
or below sea level. As you might guess, sea level has zero elevation. The
Atlantic Coastal Plain is a good example of this type of landform. It stretches
along the East Coast of the United States. This area is characterized by low
rolling hills, swamps, and marshes. A marsh grassy wetland, usually flooded
with water.
PAGE !11
Figure 3-1 - Three basic types of landforms are
plains, plateaus, and mountains.
If you hiked along the Atlantic Coastal Plain, you would realize it isn't
perfectly flat. Many low hills and valleys have been carved by rivers. What
do you suppose caused the Atlantic Coastal Plain to form? It actually began
forming under water about 70 million years ago from sediments composed of
marine organisms that fell to the ancient ocean floor. When sea level dropped,
the plain was exposed.
Another example of this landform is the Gulf Coastal Plain. It includes the
lowlands in the southern United States that surround the Gulf of Mexico.
Much of this plain was formed from sediments deposited by the Mississippi
River as it entered the Gulf of Mexico.
Interior Plains
A large portion of the center of the United States is called the interior plains.
The interior plains of the United States are shown in Figure 3-2. They extend
PAGE !12
Figure 3-2 The United States is made up of eight major
landforms.
from the Appalachian Mountains in the east to the Rocky Mountains in the
west, to the Gulf Coastal Plain in the south. They include the rolling hills of
the Great Lakes area and the Central Lowlands around the Missouri and
Mississippi Rivers.
A large portion of the interior plains is referred to as the Great Plains. They
lie between the Mississippi lowlands and the Rocky Mountains. They are
called high plains because of their elevation. They range from 350 meters
above sea level at their eastern border to 1500 meters above sea level at their
western boundary. The Great Plains are covered with nearly horizontal layers
of loose materials eroded from the Rocky Mountains. Streams deposited
these sediments over the course of the last 28 million years.
PAGE !13
Plateaus
If you would like to explore some higher regions, you might be interested in
going to the second basic type of landform---- a plateau. Plateaus are
relatively flat, raised areas of land. They are areas made up of nearly
horizontal rocks that have been uplifted by forces within Earth. Plateaus are
different from plains in that they rise steeply from the land around them. A
good example of a plateau in the United States is the Colorado Plateau, which
lies just west of the Rocky Mountains. As Figure 3-3 shows, the Colorado
River has cut deeply into the rock layers of the plateau, forming the Grand
Canyon. Because the Colorado Plateau is located in a very dry region, only a
few permanent rivers have developed on its surface. If you hiked around on
this plateau, you would see a
desert landscape.
Figure 3-3 Rivers cut deep into the Colorado Plateau
Mountains
Plains and plateaus are relatively flat. If you want to tackle a steep rock face,
you must go to the third basic type of landform a mountain. Mountains rise
PAGE !14
Figure 3-4 Folded mountains form when rock layers are squeezed from both sides
high above the surrounding land, often providing a spectacular view from the
top. The world's highest mountain peak is Mount Everest, in the Himalayan
Mountains. It is more than 8800 meters above sea level. By contrast,
mountain peaks in the United States reach over 6000 meters. Mountains vary
greatly in size and in how they are formed. The four main types of mountains
are folded, upwarped, fault-block, and volcanic.
Folded Mountains
The first mountains we will investigate are folded mountains. If you ever
travel through a road cut in the Appalachian Mountains, you'll see rock layers
PAGE !15
that are folded like the ones in Figure 3-4. Folded rock layers look like a rug
that has been pushed up against a wall. What do you think caused this to
happen?
Tremendous forces inside Earth force rock layers together. When rock layers
are squeezed from opposite sides, they buckle and fold into folded mountains.
You'll learn more about the forces that create mountains in later Chapters.
The Appalachian Mountains are folded mountains that formed in this way
300 to 250 million years ago. They are the oldest mountains in North
America and also one of the longest ranges, stretching from Newfoundland,
Canada, south to Alabama. At one time, the Appalachians were higher than
the Rocky Mountains, but weathering and erosion have worn them down to
less than 2000 meters above sea level.
Figure 3-5 Upwarped mountains form when crust is pushed up by forces inside the Earth.
PAGE !16
Upwarped Mountains
The southern Rocky Mountains in Colorado and New Mexico, the Black
Hills in South Dakota, and Adirondak Mountains in New York are upwarped
mountains. These mountains were formed when crust was pushed up by
forces inside Earth. Over time, the sedimentary rock on top of the crust
eroded, leaving behind the igneous and metamorphic rock underneath. These
igneous and metamorphic rocks then eroded to form sharp peaks and ridges,
as shown in Figure 3-5.
Fault-Block Mountains
The Grand Teton Mountains of Wyoming, the Sierra Nevada Mountains in
California, Steens and Hart Mountain in Oregon formed in yet another way.
Fault-block mountains are made of huge tilted blocks of rocks that are
separated from surrounding rock by faults. A fault is a large crack in rocks
along which there is movement. As Figure 3-6 shows, when these mountains
formed, One block was tilted and pushed up. The other block was pushed
own. If you decide to go to the Tetons or Steens Mountain you will see the
sharp, peaks characteristic
Figure 3-6 Fault-block mountains are created when faults
of fault-block mountains.
occur.some rock blocks move up, others move down.
PAGE !17
Volcanic Mountains
Mt. St. Helens in Washington and Mauna Loa in Hawaii are two of many
volcanic mountains in the United States. Volcanic mountains like the one
shown in Figure 5-7 begin when molten material reaches the surface through
a weak area of the crust. The materials pile up, one layer on top of other, until
a cone-shaped structure forms. The Hawaiian Islands are just the peaks of
huge volcanoes that stick out above the water.
Plains, plateaus, and mountains offer a wide variety of landforms to explore.
They range from low coastal plains
Figure 3-7 mountains formed when molten
and high desert plateaus to
material oozes from earth’s crust and forms a cone mountain ranges thousands of
shaped structure.
meters high.
PAGE !18