Tear it downBuild it up

Constructive and Destructive Processes

Chapter 1 Lessons 2 and 3Textbook Pages 22-41

Let’s focus on Destructive Processes first…

Words to know Weathering Erosion Sediment Organisms Earthquake Volcano

Destructive ProcessesDestructive Processes are when things happen to the earth that destroy or break down part of it. One example of a destructive process is a river wearing away the rocks and dirt to form a canyon.

In the story, an example of a destructive process was the erosion that carried the dirt and the minerals from rocks down into the cave.

WeatheringWeathering is the process that breaks rocks down into pieces called sediment. There are two types of weathering.

Mechanical Breaks larger rock into smaller pieces called sediment

Water trickling in between cracks in rocks, freezing, and breaking the rocks apart

Blown sand or rushing water Plant roots Burrowing animals

Chemical Minerals that make up rocks are dissolved

Weak acids from water and chemicals in the air or soil Dissolve limestone and marble easily The minerals are not necessarily dissolved completely.

Erosion

Weathering breaks rock into sediment. Erosion is the process of that sediment being carried away by moving water, wind, or moving ice.

Some examples of causes for erosion are

Water moving down a river

Glaciers moving Ocean waves and

currents Wind

Erosion, cont.As they transport sediment from one place to another, erosion can cause

Wider and deeper rivers Valleys Canyons Transformation from V-

shaped river valley to U-shaped river valley

Why do you think this is? Lakes Sea caves

Grand Canyon

Earthquakes

Volcanoes

Mount St. Helens

Top: August 1979

Bottom: May 1980

OK… What about constructive processes?

Words to know Deposition Earthquakes Volcanoes Faults

Constructive ProcessesConstructive processes are processes that happen to the earth that build it up. One example of a constructive process is when sand is deposited on a river bank by the running water. The sand gathers, and builds the river bank up, making it higher.

In the story, an example of a constructive process was the stalactites that grew from the deposition of the minerals.

Deposition

Think back for a second… Weathering Erosion

You have learned how rocks are broken apart by weathering into sediment. Then the sediment is carried away by erosion. The sediment doesn’t just disappear, though. It is deposited in a new place. That’s called deposition.

Deposition, cont.

Where can you see evidence of deposition?

At the mouth of a river

On flood plains (from the flooding of rivers)

Curves of a river (p. 35)

Alluvial fans (p. 35) Deltas

delta

Earthquakes

Volcanoes

Mauna Loa – A Hawaiian island formed by shield volcanoes.

Did I make a mistake?Wait a minute… Did you notice that I listed earthquakes and volcanoes twice? Some processes can be a combination of constructive and destructive. They build the earth up in some ways, and destroy it in others.

Volcanoes Earthquakes

How are volcanoes constructive processes?How are they destructive processes?

Links for more information

Forces of Naturehttp://www.nationalgeographic.com/forcesofnature/