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Weathering Unit 4: Lesson 2

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1 Weathering Unit 4: Lesson 2
Mechanical and Chemical

2 TEKS: Analyze the effects of weathering, erosion, and deposition on the environment in Texas’ Eco-regions.

3 What Caused This?

4 What is Weathering? First step to forming soil and sedimentary rock
Breakdown of rock into smaller pieces The smaller pieces do not move to a new location until erosion carries them away. Many types of weathering

5 What is Mechanical Weathering?
Breakdown of rock into smaller pieces without any change in the composition of its minerals Sometimes called “physical” weathering Rock is torn apart by physical force Smaller pieces do not move to a new location until erosion carries them away.

6 Mechanical - Ice Wedging
Water fills joints of rocks and freezes. Water expands 10% when it freezes, pushing rock apart. Repeated freeze and thaw cycles over the years cause rock to break along the joint.

7 Mechanical - Exfoliation
Exfoliation or Unloading -Rock breaks off into sheets along joints which are parallel to the surface -Caused by expansion of rock due to uplift and removal of surface material that originally buried the rock

8 Mechanical - Thermal Thermal Expansion
Repeated daily heating and cooling of rock Heat causes expansion; cooling causes contraction. Different minerals expand and contract at different rates causing the rock to split.

9 Mechanical - Biotic Biotic – means life
Weathering caused by living organisms Plant roots act as a wedge and widen cracks. Other causes of biotic weathering: burrowing animals microscopic plants animals algae fungi

10 What is Chemical Weathering?
Chemical reactions break down the bonds holding the rocks together, causing them to fall apart. Occurs in all types of rock. Rock reacts with water, gases, and solutions.

11 Chemical - Oxidation Oxidation - oxygen combines with other elements in rocks to form new types of rock New substances due to oxidation: rock becomes softer easier to break apart “rusting” of the rock color change in the rock

12 Chemical - Carbonation
Carbonation – carbon dioxide (CO2) is dissolved in water making carbonic acid Acid rain forms with it mixes with air. Acid is too weak to harm plants and animals but slowly causes feldspars and limestone to decompose.


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