Tuesday, February 4, 2014

Unit 5 Geology Day 4: Mechanical and Chemical Weathering and Erosion

Big Idea

·         Weathering_________ and erosion________ are geological processes that act together to shape the surface of the Earth.
·         Erosion_______ is the movement of soil, mud, rock and other particles which is caused by wind, water, or ice.
·         Weathering_________ is the breakdown of rocks, soils and their minerals into smaller pieces by the effects of weather. There are two types of weathering!
·         Mechanical weathering________ takes place when rocks are broken down without any change in the chemical nature of the rocks. The rocks are essentially torn apart by physical force. The primary process in mechanical weathering is abrasion____ - the process by which rocks and other particles are reduced in size
·         Chemical weathering__________ involves the change in the chemical s structure __________________ of rocks, often leading to a 'break down' in its form and something new being created. This type of weathering happens over a period of time.


1.      Read annotate the article “Erosion and Weathering”.
2.      Read and annotate the section erosion with your shoulder buddy.  

3. Read and annotate the sections mechanical weathering and chemical weathering on your own.

4.      Complete the 3-Circle Venn diagram on your own.
5.      Complete the Exit Ticket.

Try as a Class….Then On Your Own
Erosion and Weathering
National Geographic Education
Erosion is the act in which earth is worn away, often by water, wind, or ice. A similar process, weathering, breaks down or dissolves rock, weakening it or turning it into tiny fragments. No rock is hard enough to resist the forces of weathering and erosion. Together, they shaped the sharp peaks of the Himalaya Mountains in Asia and sculpted the spectacular forest of rock towers of Bryce Canyon, in the U.S. state of Utah.

The process of erosion moves bits of rock or soil from one place to another. Most erosion is performed by water, wind, or ice (usually in the form of a glacier). These forces carry the rocks and soil from the places where they were weathered. If water is muddy, it is a sign that erosion is taking place. The brown color indicates that bits of rock and soil are suspended in the water and being transported from one place to another. This transported material is called sediment.

Many of the changes to the Earth’s surface come about through the process of weathering, erosion, and deposition. The surface of the Earth is constantly exposed to water, wind, ice, and growing plants. Each of these can break down rocks into smaller and smaller pieces. This breaking down of the rocks is called weathering. Water can cause some rocks and minerals to dissolve. When this happens underground, huge caverns can be formed. Water rushing through these underground caves pushes the smaller bits of rock and sand away and smooths down rough edges of larger rocks. Strong winds can also break down large rocks into smaller pieces and smooth out rough parts of large rocks. The wind can carry away very small pieces of rocks and dirt to other places. Ice can cause rocks to break as well. When water seeps into small cracks of rocks and freezes, the ice expands and breaks the rock. Plants can also break some rocks as their roots grow underground. The roots spread inside cracks and cause the rocks to break apart.

Weathering is the chemical and physical processes that change the characteristics of rocks on the Earth’s surface. It is also known as the preparation for erosion. In order for weathering to occur, the environment of a rock sample must change and the rock needs to be exposed to some form of water and the air. Human processes such as pollution, which can be a large factor in acid rain, along with the acts of other living organisms, can cause chemical weathering to occur at faster rates.

The weathering process occurs when rocks are exposed to the hydrosphere (water) and atmosphere (air). These weathering agents can change the physical and chemical characteristics of rocks. As rocks are broken down (weathered) they can be classified as different types of sediments, which are: boulders, cobbles, pebbles, sand, silt, clay, and colloids.

Mechanical Weathering (also called Physical Weathering)
Physical weathering occurs when rocks are broken in to smaller pieces without changing the chemical composition of the rock. Think of a physical change (e.g., ripping a piece of paper) where the sample will change in size but all its other characteristics will remain the same. There are a few types of physical weathering such as:
Frost action/ice wedging is the breakup of rock caused by the freezing and thawing (contracting and expansion) of water. Water can seep into the cracks of a rock and as the climate cools the water freezes and expands breaking the rock apart. A very similar process occurs on roads, which causes potholes.
Abrasion is the physical wearing down of rocks as they rub or bounce against each other. This process is most common in windy areas, under glaciers, or in stream channels.
Exfoliation is the peeling away of large sheets of loosened materials at the surface of a rock.

Chemical Weathering
Chemical weathering occurs when a rock is broken down by chemical action resulting in a change in the composition of a rock. Such as the change a piece of paper would go through after being burned. The main agents of chemical weathering are oxygen, rainwater, carbon dioxide, and acids produced by decaying plants and animals that leads to the formation of soil. There are a few types of chemical weathering such as:

Oxidation occurs when oxygen interacts chemically with minerals. For example, when a nail rusts oxygen combines with the iron in the nail to form iron oxide.
Hydration occurs when water interacts chemically with minerals. For example, when hornblende and feldspar unite with water they eventually form into clay.
Carbonation occurs when carbon dioxide interacts chemically with minerals. When carbon dioxide is dissolved in water, it forms weak carbonic acid. Carbonic acid when it comes in contact with the surface of the earth dissolves large masses of limestone, creating caves and caverns. Other common terms associated with carbonation are sink holes, karst topography, stalactites and stalagmites.

Unit 5 Geology Day 4 Exit Ticket: Weathering and Erosion

1)     True or False: Chemical Weathering causes the breakdown of rocks without changing the physical properties.

2)     What are the two processes that shape the surface of earth?

a.       Mechanical weathering and Chemical weathering
b.      Weathering and Erosion
c.       Erosion and Decomposition

3)     Erosion is the ______________.
a.       Movement of solids such as soil and rock
b.      Breakdown of rock and soils
c.       Change in structure of rocks and minerals

4)     What are two similarities between chemical weathering and mechanical weathering?

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