By Patti Hutchison /
1Have you ever made a snowball with your hands? You pick up some snow and press it together in you hands. It quickly freezes into ice. If you have done this, you have made a "mini" glacier.
2Real glaciers, of course, are much, much larger. But they are formed in the same way. Glaciers are mostly found in areas of high latitude or high elevation. These places have cold temperatures all year. Snow falls and never completely melts. The weight of the snow on top causes pressure on the layers of snow beneath. The snow underneath recrystallizes into ice.
3Glaciers cover about ten percent of the earth today. Even at the peak of the last ice age, only about thirty percent of the earth was covered. But glaciers made their mark in much of the northern hemisphere.
4There are two types of glaciers - continental glaciers and valley glaciers. Continental glaciers cover huge areas. As you can guess, they can be as big as continents. They are thickest in the middle. The pressure in the middle causes the glacier to spread out and cover large areas. Today these glaciers cover Antarctica and parts of Greenland and Canada.
5A valley glacier is much smaller than a continental glacier. They form in areas with high mountains. They form when a mass of ice becomes too thick. The weight causes it to start to move slowly down the valley. Deep cracks form in the ice.
6Glaciers are probably the most powerful force of erosion. Their mass allows them to move huge amounts of rock and land with them. As they melt and move back, the landscape is changed.
7The bedrock beneath a moving glacier is carved out. It is kind of like scooping ice cream out of the carton. U-shaped grooves are formed as the glacier moves down the slope.
8If there are glaciers on three sides of a mountain, they carve out a pyramid shape. This is called a horn.
9Glaciers also cause lakes to form. The Great Lakes were formed by glaciers. Large blocks of ice break off the glacier. They are covered with sediment. When the ice melts, a deep depression is formed in the bedrock. They fill with water and form a lake.
10The last ice age ended over 10,000 years ago. The massive glaciers drew back.
11They left scars in the bedrock. They have become some of the earth's most interesting geographic features.
Copyright © 2013 edHelper
By Patti Hutchison /
1You know that most mass movements are caused by gravity. Water is another powerful force that can cause the movement of large masses of earth. Movement of rocks and soil can be caused by too much water or too little.
2If there is too little water on a slope, particles have trouble holding together. It's sort of like trying to make a snowball out of dry, powdery snow. It just won't keep its shape. Wet snow stays together easily. The same is true of soil. Water helps hold the grains together. If the grains are dry they can be moved easily by wind or gravity.
3Sometimes there is too much water on a slope. The particles become loose. Water adds to the weight of the earth materials. It also reduces the friction of the surfaces. It is easier for gravity to pull the soil and rocks downhill.
4Mudslides are mixtures of mud and water. They move very quickly. They are common in areas with steep slopes that get short, severe rainstorms. California is an area that frequently has mudslides.
5Places that have mudslides receive little rainfall most of the time. The slopes have few plants and trees. Heavy rainfall occurs in short bursts. The water carries the soil quickly downhill.
6Volcanic eruptions can also cause mudslides. The eruption of Mount Saint Helens in 1980 caused destructive mudslides. The heat from the lava quickly melted the snow on the mountain. The rushing water moved soil and other particles down the slope. This caused major damage to homes at the bottom of the mountain.
7Mudslides are an example of how water can cause quick erosion. Water can also erode materials slowly. This process is called abrasion. Rivers and streams carry particles of sand and rock along with them. These materials rub up against the rock and soil on the bank. Slowly, over a long time, the bank wears away. The stream becomes wider or deeper.
8The Grand Canyon is an example of erosion by water. It was formed over thousands of years as the Colorado River abraded the rock it flowed through. This process is still going on there today.
9Water erosion can also be beneficial. Particles that are carried along are finally deposited in a larger body of water. Over time they build up. A delta is formed. Deltas are areas of very fertile soil.
10Moving water is a powerful force. It can change the landscape quickly or slowly. It can be helpful or harmful.
Copyright © 2013 edHelper
By Patti Hutchison /
1Have you ever seen a picture of a sand dune? If so, you have seen the effects of wind. Wind can transport earth materials the same way water does.
2There are some differences between wind and water movement, however. First, wind does not depend on gravity to help it. Water can only transport particles downhill. Wind can transport particles uphill. That is how a sand dune is made.
3Another difference between wind and water erosion is the size of the particles that can be transported. Unless there is a tornado or hurricane, wind can't carry large particles like water can. Because of this, wind is usually not a strong force of erosion.
4Winds can move particles in different ways. Sand dunes build up from sand being blown in a rolling motion. The sand blows up against a large rock or other object. Over time, more and more sand builds up forming a dune.
5Particles can also be transported in a dust storm. Strong winds keep the soil or sand in the air for long distances. This is called suspension.
6Wind erosion occurs in areas that get little rain. Particles of dirt and rock are not held strongly together in dry areas. Also, there are few plants to hold the soil in place. Wind easily picks up the particles and deposits them in another place.
7When the surface of the land is lowered because of wind erosion, it is called deflation. Usually small particles are whisked off, leaving pebbles and other larger pieces behind.
8During the Dust Bowl of the 1930's, a lot of deflation took place. A major drought covered much of the Midwest. The land dried out and was eroded by strong winds. Deflation blowouts were formed. These are areas of shallow depression on the surface. Many of these deflation blow outs still exist. Some are hundreds of meters in diameter.
9Wind can also cause a type of erosion called abrasion. If you file your fingernails, or rub sand paper against a piece of wood, you are causing abrasion. Wind can cause fine particles of sand and soil to rub against rocks and other surfaces. This causes them to wear down. Wind is an artist and can form rocks into unusual shapes.
10Wind erosion can change the shape of the land. Most of the time, this is a slow process. Usually the effects are simply a small bother. Wind might blow dust or sand in your eyes. However, wind can cause dust or sand storms that can be dangerous and destructive.
Copyright © 2013 edHelper
Earth Movers - Wind
1. / Like water, wind depends on gravity to help it move particles.False
True
/ 2. / What is a dust storm?
3. / Wind erosion takes place mostly in areas that ______.
Are covered with ice
Receive little rainfall
Receive a lot of rainfall
/ 4. / What is deflation?
5. / What caused the Dust Bowl?
A severe drought
A lot of snow and ice
Heavy rain
/ 6. / When wind causes sand and soil to rub against rocks and wear them down, it is called:
Abrasion
Dust storm
Deflation
Earth Movers - Water
1. / Mass movements can be caused by too little water on a surface.False
True
/ 2. / Explain two ways too much water can help gravity move materials.
3. / Why do most mudslides happen in areas where there is little rainfall?
Because the soil is very wet
Because the particles are packed tightly together
Because there are few plants to hold the soil in place
/ 4. / How can a volcano cause a mudslide?
5. / Water can erode earth materials slowly through a process called ______.
Deflation
Avalanche
Abrasion
/ 6. / What is formed when particles carried by a river are deposited in a larger body of water?
A delta
A mudslide
A canyon
Earth Movers - Glaciers
1. / Where are glaciers mostly found?/ 2. / What percent of the earth is covered with glaciers today?
20 percent
50 percent
10 percent
3. / Name the two kinds of glaciers.
/ 4. / Glaciers on three sides of a mountain form a pyramid shape called a ______.
Valley
Horn
Lake
5. / The Great Lakes were formed by glaciers.
False
True
/ 6. / How long ago did the last ice age end?
1000 years
1.5 million years
10,000 years