LAND FORMS

Unit Overview

This unit looks at the processes that build up and tear down landmasses on Earth. Both natural and manmade events have a direct impact on familiar landforms such as beaches, mountains, canyons, and valleys.

GLOSSARY OF KEY TERMS

Acidic rain (precipitation): acid rain is precipitation containing harmful amounts of nitric and sulfuric acids formed primarily by nitrogen oxides and sulfur oxides released into the atmosphere when fossil fuels are burned.

Chemical weathering: the wearing away or breaking down of various minerals in rocks and soils due to the chemical actions of natural physical and biological processes.

Continental crust: the Earth's crust that includes both the continents and the continental shelves.

Constructive process: a natural event in which a new land formation is created by deposits of old rock in a new location.

Depositional landform: where rock and mineral material has been transported from one location and deposited onto another such as a coastline or a beach.

Destructive process: a natural event in which new land formations are created by the wearing away of old land formations.

Erosional landforms: formed by slow break down of land formations by physical and chemical processes.

Fissure: a long narrow depression in the Earth’s crust.

Frost wedging: is the alternating freezing and thawing of moisture in the openings or cracks of rocks resulting in a breakdown of the rock.

Glacier: a large, slowly moving mass of ice.

Mantle: middle layer of Earth, made of solid and semi-solid hot rock with temperatures from 900 to 3000 degrees Celsius.

Molten rock: rock that has melted under the Earth’s crust. This melted or molten rock is called magma.

Physical weathering: breakdown of rock and minerals into small sized particles through mechanical stress.

Plate tectonics: A theory supported by a wide range of evidence that considers the earth's crust and upper mantle to be composed of several large, thin, relatively rigid plates that move relative to one another.

Root intrusion: invasion of plant roots into rock, soil, or other solid matter that causes breaking or separating of the solid matter.

Sediment: matter deposited by some natural process.

Structural landform: landforms caused by crustal plate movement and deformation of plates.

Weathering landform: landforms caused by the disintegration and breakdown of rock near the earth’s surface.

Study Suggestion: Make vocabulary flash cards to match the definition with the word. Practice a matching game with your cards.

Landforms

Our Earth has many land formations that are caused by a variety of natural events. Some landforms that you are familiar with are valleys, mountains, canyons, and rock formations. Scientists group these formations into four major categories: weathering, erosional, depositional, and structural landforms. The landforms are categorized by the events which caused their formation.

Some landforms are created when the natural event wears away the original rock. These are known as destructive processes. Other landforms are created by adding to the rock formations already present or by creating brand new rock formations. These processes are referred to as constructive.

Destructive Land Formation

· Weathering Landforms: These are landforms that were created by physical and chemical weathering. Natural events such as wind, acidic rain, and freezing and thawing can cause rock to break down into smaller rocks and sediment.

· Erosional Landforms: These landforms were created by natural events that remove the eroded surface rock. The Grand Canyon is a good example of this type of landform. The Colorado River is constantly carrying away rock material and deepening the canyon.

Constructive Land Formation

· Depositional Landforms: These landforms are created by the deposits of eroded rock material. Beaches and flood plains are formed in this way. The rocks are carried by streams and rivers. As the rocks are tumbled along, they break into smaller pieces until some of them are as small as the grains of sand that you see on our beaches. Sometimes these deposits are subjected to pressure, heat, and/or chemicals and will form sedimentary rocks.

Science proclaims that the Rocky Mountains we see today are not the original mountains that once occupied the land space of the western United States.  That’s right. Geologists say that at least two or three previous mountain ranges have built up and eroded away during the life span of the earth. Beaches were formed from rocks originally in the Rocky Mountains. The rocks were tumbled and broken up in the streams until they were tiny grains of sand.

· Structural Landforms: These landforms are created by plate tectonics. These large crustal plates are in constant motion. As they move, they can push up large masses of rock and form mountain ranges. This movement can also allow some of the molten mantle to work its way to the surface through volcanic activity.

Destructive Processes

· Weathering

Physical Weathering (mechanical) can occur in many ways:

Frost wedging: water seeps into cracks in the rocks and then freezes. The expanding ice cracks the rocks and breaks them apart. This is the single most abundant form of physical weathering.

Root intrusions: plant roots will work their way into rock cracks and push the rock apart.

Erosion: There has been a lot of talk over recent years of the weathering of the sphinx on the Giza plateau. Other monuments on the Giza plateau are also suffering from erosion as the wind combined with the desert sands has the effect of an industrial strength sand blaster.

Erosion: wind and rain continuously pound at the face of the rock, breaking it into small pieces that are washed away. The leftover rock is often left in very strange shapes like the rock formations above.

Chemical Weathering can occur in two ways:

Gunung Mulu National Park Headquarters (Sarawak, Malaysia)
Wind Cave: fantastic stalagmites and stalactites

Naturally: Common elements in nature will react with each other to form new compounds. As water mixes these elements together, the original rock formation can react with the elements traveling in the water causing the rock to break down. Elements such as oxygen and compounds like silicates are big contributors of natural chemical weathering. A common example of this is when carbon dioxide from the air dissolves in rainwater. This forms carbonic acid, which will react with some minerals in the ground. This process produces the many beautiful rock formations in underground caves.

Pollution: Many chemicals released by man through industry and waste products will also react with land formations. Even man-made structures such as building and statues made of rock can erode from chemical weathering.

Acidic rain can react with many rock types to cause erosion. Acid rain or more specifically, acid precipitation is a chemical reaction between sulfur dioxide and water or nitrogen oxide and water. When we burn fossil fuels (gas, coal, oil), the sulfur dioxide and nitrogen dioxide is released into the air and mixes with water in the air and clouds. This produces sulfuric acid and nitrous acid and then returns to the Earth through rain, snow and other forms of precipitation.

Poor visibility in Montana is caused by fine particles that scatter and absorb light. In Montana, the biggest sources of impaired visibility include wildfires, prescribed burning, power plants, motor vehicles, and certain industrial and chemical facilities.

Constructive Processes

· Depositional Landforms

Rock materials can be deposited in many ways, but water and glacial movements are the two ways most responsible for many of the landforms we see today.

Water breaks small pieces of rock from existing land forms and then carries them to other areas and drops or deposits the little pieces of rock into a new location. Beaches are formed by this process.

Glaciers are huge masses of ice that slowly move over the face of our planet. Many of the land formations we see today were created by glacial movement hundreds or even thousands of years ago. As these ice mountains move across the ground, they dig into the ground and pick up pieces of earth and rock. Eventually, the glaciers break into pieces or begin to melt and then leave the collected rock materials in new locations. Glacial sediment is made up of a great many types of rock and dirt. Glaciers carve out land formations such as valleys and plains.

· Structural Landforms

Displacement of rock can be caused by tectonic plate movement, and volcanic activity.

Tectonic Plate Movement: As the crustal plates move, they deform and push rocks into new formations. The illustration below shows the Mid-Atlantic Ridge. This is a region of great plate movement activity located under the Atlantic Ocean.

The next illustration shows how continental crust is pushed upward to form mountain ranges.

Volcanic Activity is caused by a fissure in the earth's crust (or in the surface of some other planet) through which molten lava and gases erupt.

Mountain ranges can form from volcanic activity.

Unit Review:

1. All land formations can fit into two categories. Name and explain each category.

2. What are the four main processes that create new land forms?

3. Describe how a tree growing near a rock wall can cause weathering of the wall.

4. Mechanical weathering is also referred to as ____________ weathering.

5. _______________ weathering occurs when elements and compounds in nature or man-made react with rock to break it down.

6. What are two ways that rocks can be deposited into a new location to create a new landform?

7. What natural events can create mountain ranges?

Answers to Review PDF File

Weathering Activity

CHEMICAL WEATHERING ACTIVITY

Materials Needed

· Plastic coffee can lid or Frisbee

· Two pieces of sandstone and two pieces of limestone

To print a copy of this activity, click on the Weathering PDF File

These rock types can most likely be found in your neighborhood. Here is a picture of each:

· Small bottle of vinegar with dropper

· Dirt and small rocks

· An assortment of leaves, rocks, shells, twigs

· Small plastic containers with holes punched in the bottom (to form a “rain cloud”). Note: Containers from frozen lunches or small plastic margarine containers make excellent clouds.

· Water

· Paper and pencil

Procedure:
1. As a demonstration of chemical weathering:

· Place several drops of vinegar on the sandstone and observe the action of acid on the rock. Record your observations.

· Place several drops of vinegar on the limestone and observe the action of the acid on the rock. Record your observations.

Which type of rock is most affected by chemical weathering by an acid like vinegar?

Which type of rock produced the most new soil?

Which type of rock took longer to erode?

· Place one cup of dirt into the middle of your container. This will represent the amount of dirt it would take to grow a plant. Estimate the amount of time that it would take you to erode a full cup of each rock type.

· Write down your theory on how long it takes nature to produce one cup of soil.

· What is the difference between your procedure to make soil and nature's processes to make soil?

· Now take your leaves, twigs, and small rocks and stabilize your land form that you have in your container. This means to make the formation stronger by pressing the materials into the dirt.

· Place a small amount of water into the container with holes. Then slowly pass the container over your land formation. Record your results and answer the following questions:

§ Did any erosion occur?

§ Which type of matter (rocks, twigs, leaves) did the best in preventing erosion?

If you were to do this again, would you change the arrangement of the matter that you added to your landform?

Why/Why not?

Was there a relationship between the amount of rain water poured on your landform and the amount of erosion that took place? Describe your results.