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Weathering

Weathering. Lets break it down!. Physical Weathering. The process of rocks being broken down into smaller pieces by external conditions. Types of Physical weathering Frost heaving and Frost wedging Plant roots Friction and impact Burrowing of animals. Frost Wedging.

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Weathering

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  1. Weathering Lets break it down!

  2. Physical Weathering • The process of rocks being broken down into smaller pieces by external conditions. • Types of Physical weathering • Frost heaving and Frost wedging • Plant roots • Friction and impact • Burrowing of animals

  3. Frost Wedging Frost wedging is caused by the repeated freeze-thaw cycle of water. Most rocks have small cracks or joints in them. When it rains, water seeps into these joints. As the day cools and temperatures at night drop below freezing, the water inside the cracks freezes. As water freezes into ice, it expands. The expanding ice places pressure on the cracks in the rock. Finally, when the pressure is too much, the crack expands. In some cases, the rock will split, though this usually happens after repeated freeze and thaws. As new water is added during the warmer days, more ice is created at night, make the crack larger and larger.

  4. Plant Roots Plant roots work their way into rock crevices called joints. As the plants grow, roots create pressure on the sides of the crack making it bigger until the rock breaks apart.

  5. Friction and Repeated Impact Rocks are also broken up by friction and repeated impact with other rock fragments during transportation. For example, a rock fragment carried along in a river's current continuously bounces against other rocks in the river bottom and eventually is broken into smaller pieces. This process also occurs during transportation by wind and glacial ice.

  6. Burrowing of Animals Animals burrowing or moving through cracks can break apart the rock.

  7. Chemical Weathering • The process that breaks down rocks through chemical change. • The agents of chemical weathering are: • water • oxygen • carbon dioxide • living organisms • acid rain

  8. Water Water is the essential agent in chemical weathering, either reacting with the minerals directly or carrying dissolved materials to a place where they react with the minerals. 

  9. Oxygen • Iron combines with oxygen in the presence of water in a process called oxidation • The product of oxidation is rust Oxidation is the bonding of oxygen, in dissolved surface water, to the metallic elements like potassium, calcium, magnesium, and iron of primary minerals.  A common example is the formation of the rusty brown and orange oxides of iron on the surface of rocks. 

  10. Carbon Dioxide • CO2 dissolves in rain water and creates carbonic acid • Carbonic acid easily weathers limestone and marble • Carbonation is the reaction with carbonic acid, which forms when carbon dioxide from the atmosphere dissolves in rain water:    CO2        +        H2O      ------->       H2CO3 (Carbon dioxide gas + rain water ------>  carbonic acid)

  11. Carbonic Acid- As the rain water soaks into the upper layers of the soil, it passes through a layer of decaying plants and animal material that are rich in carbon dioxide. (Smaller amounts of CO2 are also collected from the air and snow.) This carbon dioxide combines with the water to form a weak acid called carbonic acid. This acidic water (carbonic acid) flows down through the cracks in the limestone, dissolving the rock along the way. That’s how the opening of the cave was created. The hole was then possibly enlarged by other factors such as geothermal waters rising from below or groundwater running inside of the cave. While the water is coming through the rock, it is also dissolving and picking up a mineral called calcite (calcium carbonate). It carries this calcite until it finds a space large enough to leave it behind. As it comes into the hole, with each drip of water, it leaves traces of calcite behind which then create the different cave formations.

  12. Living Organisms Lichens that grow on rocks produce weak acids that chemically weather the rock

  13. Acid Rain • Compounds from burning coal, oil and gas react chemically with rain water forming acids. • Acid rain causes very rapid chemical weathering

  14. Test it out!! • Experiment #1 • Build your own cave • Experiment #2 • Disappearing Rocks • Experiment #3 • Weather or Not?

  15. Build Your Own Cave! Build your own Cave! Objective • Create a cave using the process of deposition which allows the calcite to build up to form crystalline structures. Materials • Cardboard box(a shoe box will be great!) • Yarn • Cup • Epsom Salt • Water • Scissors Steps • Lie the box on its side so you can look into it. Cut a hole in the side of the box (which is now the top). • Stir the Epsom salt into the cup of water. Add salt until it will not dissolve anymore. • Put the cup on top of the box next to the hole. • Let the yarn hang from the cup into the hole. Conclusion • What do you think will happen? • Pay attention to how much time it takes and what starts to form.

  16. Disappearing Rocks Objective • You will see how rocks can change through physical and chemical weathering creating passageways and caves. Materials • White table vinegar • Squeeze droppers or straws • Sample of rocks, including one limestone • Containers Steps • Chart and describe the characteristics of the rocks (appearance, hardness, color, texture, solubility). Solubility is like adding jello mix to hot water and dissolving into a solution. • Most caves are formed in limestone areas. Limestone is unique because its mineral grains can be dissolved in nature by a very mild carbonic acid. The weak acid forms from a mixture of water from rain and carbon dioxide from air and the soil. When the carbonic acid comes in contact with calcite, it dissolves small amounts of the calcite and carries it away in a solution through cracks and pores in the rock, leaving behind a bigger opening. Over a very long time, these holes can create caves. • One of the samples is limestone. How can we determine which one it is? • The Bubble Test! • The samples with calcite will bubble! • Apply drops of vinegar on the samples . • Which rock is limestone- how do you know? Conclusion • THINK ABOUT THIS! What would happen if a limestone layer of rock is sandwiched between harder rock layers that don’t dissolve? • How does chemical weathering break down rock? • How does a cave form in limestone?

  17. Weather or Not? Objective • Experiment the effects of weathering. Materials • Tin cans • Sedimentary rocks • Other rocks • Water • Chart paper Steps • Place one sedimentary rock in the can and shake. Empty the can. • Record the results on the chart. • Put the sedimentary rock back in the can with other rocks. Shake. Empty the can. • Record the results on the chart. • Put the sedimentary rock back in the can with a little bit of water. Shake. Empty the can. • Record the results on the chart. Conclusion • What test causes more weathering? • Why do sedimentary rocks weather so easily?

  18. Interactive Extras • Interactive Tutor- Geology Crossword

  19. Sources • http://library.thinkquest.org • Timpanogos Cave National Monument • http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/mass_movement_weathering/outline.html • Bryce Shelley, Lehi Junior High School • Project Underground, A Natural Resource Education Guide, Second Edition. 1993

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