Weathering - PowerPoint Presentation

Slide1

Weathering

Lets break it down!Slide2

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 animalsSlide3

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.Slide4

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.

Plant RootsSlide5

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.

Friction and Repeated ImpactSlide6

Burrowing of Animals

Animals burrowing or moving through cracks can break apart the rock.Slide7

Chemical Weathering

The process that breaks down rocks through chemical change.

The agents of chemical weathering are:

water

oxygen

carbon dioxideliving organismsacid rainSlide8

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. Slide9

Oxygen

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. 

Iron combines with oxygen in the presence of water in a process called oxidation

The product of oxidation is rustSlide10
Slide11

Carbon Dioxide

CO

2

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      ------->       H

2CO3

(Carbon dioxide gas + rain water ------>  carbonic acid) Slide12

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.Slide13

Living Organisms

Lichens that grow on rocks produce weak acids that chemically weather the rockSlide14

Acid Rain

Compounds from burning coal, oil and gas react chemically with rain water forming acids.

Acid rain causes very rapid chemical weatheringSlide15

Test it out!!

Experiment #1

Build your own cave

Experiment #2

Disappearing Rocks

Experiment #3Weather or Not?Slide16

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.

MaterialsCardboard box(a shoe box will be great!)

YarnCupEpsom SaltWaterScissors

StepsLie 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.ConclusionWhat do you think will happen?Pay attention to how much time it takes and what starts to form.Slide17

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 strawsSample of rocks, including one limestone

ContainersStepsChart 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?

 Slide18

Weather or Not?

Objective

Experiment the effects of weathering.

Materials

Tin cans

Sedimentary rocksOther rocksWater

Chart paperStepsPlace 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.

ConclusionWhat test causes more weathering?Why do sedimentary rocks weather so easily?Slide19

Interactive Extras

Interactive Tutor

- Geology CrosswordSlide20

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 SchoolProject Underground, A Natural Resource Education Guide, Second Edition. 1993