Weathering and Erosion

Elise Olivieri

Curtis High School, Staten Island

Summer Research Program for Science Teachers

August 2008

Aim:  How do we Explain Weathering and Erosion?

IO:  Students will be able to identify 3 characteristics of weathering and 3 characteristics of erosion.

Do Now:  Look at the picture.  What is happening here?

I  Physical Weathering

Weathering is the process that produces change in the surface of rocks exposed to the atmosphere and/or hydrosphere.

Physical weathering is breaking rock by force.

Example: hitting, scratching, cracking

Frost action (AKA ice wedging)-

Water seeps into small cracks in rocks.

When the water freezes it expands creating great pressure.

The crack widens and allows water to seep deeper into the rock.

Plant action

Tiny root hairs seek out small cracks and pits in rock.

Once the root hairs find a place they grow and expand.

The expansion causes great pressure and cracks the rock.

II Chemical Weathering

Chemical weathering is where the rock material is changed into another substance by reacting with a chemical.

Oxidation

• Oxygen in the atmosphere chemically reacts with minerals.
• ex.: rusting of a nail

Water (hydrolysis)

• Minerals are dissolved in water.
• ex.: Halite, calcite

Acid

·         Carbonic acid:

o    C02 dissolves in rain water forming a weak acid (seltzer).

·         Acid Rain: Sulfur Dioxide in the atmosphere dissolves in rain water forming a strong acid (sulfuric acid).

Rates of weathering will be influenced by...

Surface area exposed - weathering occurs on the surface. More surface exposed, the faster the weathering will occur.

Mineral composition- some minerals are more resistant than others.
ex.: Quartz is resistant to chemical and physical weathering.

In the diagram above the different layers of the rock are weathered at different rates depending on the minerals within the rock. The layers sticking up most are the most resistant.

 Climatic Conditions:

• Cold and/or dry climates favor physical weathering.
• Warm and wet climates favor chemical weathering.
• Frost action works best in areas where the temperature fluctuates wildly.

Soil - The product of weathering

Soil is made from rocks, minerals (mainly sand and clay), and organic material (regolith and organic matter)

III Erosion

Erosion- the process of moving sediment from one location to another.

The most important FORCE of erosion is GRAVITY. The most important AGENT of erosion is WATER.

The amount of erosion by a stream depends on the velocity and volume of water flow.

Velocity is influenced by the slope & volume of a stream.
As the velocity increases the size of the particles transported will get bigger.

Volume (amount of water flowing) is influenced by rainfall.
The shape of a stream will determine where erosion will occur. The fastest water goes to the outside of the curve. The outside curve gets eroded away.
In a straight run of water, the fastest water runs above center of the stream.
The rate of erosion increases where the velocity increases. (Direct Relationship)

Erosion Reading

If you've ever had the privilege of traveling to foreign countries or even across the United States, you've certainly observed the many different landforms that make up the fascinating surface of our Planet Earth! But there's something about these landforms that is impossible to notice with just a casual glance. From the vast plains and plateaus to the rolling hills, towering mountains, and deep valleys; the Earth's surface is very gradually, but very constantly, being molded and worn down by a process called erosion.
 
Erosion happens when running water, sea waves, wind, or glaciers pick up materials from the Earth's surface and carry them to other locations. The actions of erosion and deposition work together to alter existing landforms and create new ones. Deposition occurs when silt, sand and other materials are carried by flowing water and deposited at other places on the Earth's surface.
 
Moving waters, such as rivers and streams, are the most important natural agents of erosion. Whenever it rains, water washes over the land, picks up loose soil, and carries it away. Water also washes weathered rocks (rocks altered through a process called weathering) into rivers and streams. We'll learn more about how weathering impacts the erosion process in Part 2 of "The Ever-changing Surface of the Earth."
 
Gravitational pull plays a major role in the process of erosion and can cause huge amounts of soil or rock debris to be carried down a slope, such as in the case of a mudslide. This occurrence is referred to as a mass movement. Another type of mass movement is when certain areas of the Earth's surface are pulled by gravity and sink below ground level.

Erosion by Rivers

Here is a V-shaped valley?  In this picture, where is the water moving at the fastest rate? ______________________________________________

In the meandering stream, label the locations where erosion is taking place.

This is how water erodes land. 

Another example of how rivers erode land. 

The NYC Science Performance Standards

Standard 6 Key Idea 1.  Through systems thinking people can recognize the commonalities that exist among all systems and how parts of a system interrelate and combine to perform specific functions.