WeatheringLets break it down!

Physical WeatheringThe process of rocks being broken down into

smaller pieces by external conditions.Types of Physical weathering

Frost heaving and Frost wedgingPlant rootsFriction and impactBurrowing of animals

Frost WedgingFrost 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.

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 Roots

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 Impact

Burrowing of Animals

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

Chemical WeatheringThe process that breaks down rocks

through chemical change.The agents of chemical weathering

are:wateroxygencarbon dioxideliving organismsacid rain

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. 

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 rust

Carbon DioxideCO2 dissolves in rain water

and creates carbonic acidCarbonic 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)

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 acidcalled 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.

Living OrganismsLichens that grow on

rocks produce weak acids that chemically weather the rock

Acid RainCompounds from

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

Acid rain causes very rapid chemical weathering

Test it out!!Experiment #1

Build your own caveExperiment #2

Disappearing RocksExperiment #3

Weather or Not?

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 ScissorsSteps1. 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).2. Stir the Epsom salt into the cup of water. Add salt until it will not dissolve

anymore.3. Put the cup on top of the box next to the hole.4. 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.

Disappearing RocksObjective 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 ContainersSteps 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?

 

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?

Interactive Extras Interactive Tutor- Geology Crossword

Sourceshttp://library.thinkquest.orgTimpanogos Cave National Monumenthttp://www.uwsp.edu/geo/faculty/ritter/geog10

1/textbook/mass_movement_weathering/outline.html

Bryce Shelley, Lehi Junior High SchoolProject Underground, A Natural Resource

Education Guide, Second Edition. 1993