WEATHERING

BYMS. HOUSTON

ARMS 6TH GRADE EARTH SCIENCE

Weathering Natural process

that breaks down rock into sediment (sand, silt, clay)

Begins the process of forming soil from rock and sediment.

Affects sediment particle size and soil texture.

Mechanical Weathering

Burrowing AnimalsIce WedgingPlant RootsWindWater

Physical process that breaks down rock but does not change the composition of rock.

Mechanical Weathering Ice wedging is

the process that occurs when water freezes, expands and thaws in the cracks of a rock

Overtime the cracks will get wider and deeper and the rock will break

Plant growth causes rock to break by roots exerting pressure on the rock

Plant roots can seek their way into rock cracks and continue to grow creating pressure in the cracks of rock.

Mechanical Weathering Burrowing

animals dig tunnels in the ground loosening small rocks and sediment and eventually pushing them to the surface

Wind carries other sediment and potentially beat on the surface of other rock loosening or breaking other rock

Water can exert pressure on sediment and small rock thereby further breaking the rock.

Chemical Weathering

Chemical process that breaks down rock by chemical reactions that dissolve minerals or change them into different minerals.

Rock composition will change!

Carbonic acid Natural plant acids Oxidation Acid rain

Chemical Weathering-Natural Acids

Carbonic acid forms when water reacts w/ carbon dioxide gas in the air.

Carbonic acid is a weak acid that can dissolve some minerals found in rock.

Carbonic acid dissolves calcite a mineral found in limestone

Ex: cave formation Other natural acids

can dissolve the mineral feldspar which is found in granite, some types of sandstone and other rocks.

Kaolinite is a clay mineral found in some soil and is formed from dissolved (broken down) feldspar.

Chemical Weathering-Plant Acids and Oxidation

Plant roots give off acids

These acids can dissolve some minerals found in rock making the rock weak and causing the rock to break into smaller pieces

Oxidation occurs when oxygen gas and moisture react with certain materials to form a new material

This new material looks like rust.

Oxidation of minerals gives some rock a red or rust color

Effects of Climate and Rock Type

Climate affects the rate (how fast) weathering occurs

Cold, polar climates increases MECHANCAL weathering

Warm, wet climates increases CHEMICAL weathering

Desert climate slows CHEMICAL weathering

Cold, polar climates slows CHEMICAL weathering

For Additional Information:See the Glencoe textbook. You may access the textbook online via the ARMS website. • Click on Academics• Click on Science

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