Weathering means the process of

breaking down rocks and other

substances at Earth’s surface.

Two Types OF Weathering:

Mechanical (Physical) Weathering is

When rock is physically broken into

smaller pieces (but still

have the same chemical composition).

Chemical weathering is

Breaking down rocks through chemical changes (different

composition -what its made of and physical makeup- how it

looks).

There are 5 Types of Mechanical

Weathering

Change in Temperature

Environmental, Frost Wedging

Changes in Pressure

Actions of Plants and Animals

Abrasion (wind, water, gravity)

1- Freezing and thawing of water.

(Ice/ Frost Wedging)-

The repeated freezing and

thawing of water found in

cracks of rocks.

As water flows into the cracks in

rocks it freezes and expands.

Common in mountainous regions.

2- Change in environmental temperature –

Thermal Stress

As temperatures rise a rock will expand or get

larger. As temperatures cool, a rock will contract

or get smaller. These changes in temperature weakens and cracks rock.

Release of pressure

As erosion carries away

rocks from the top of a

mountain it reduces

pressure on the rocks

below. This causes the

outer layer of rocks to

crack and flake off like

layers of an onion.

Plant action-

Plant roots grow in

cracks of rocks and pry

rocks apart.

Actions of Animals

Animals burrow in the ground and break apart

rocks.

Abrasion- rubbing by other

rocks.

Sand and other rock particles

carried by wind, water, ice, or gravity wear away rocks.

Abrasion

Water: moving water causes

rocks to tumble.

Rocks are usually

round and smooth.

Wind: Wind lifts small

particles – think sand blasting.

Gravity: Ex- Landslides

Can also occur with rocks in

glaciers – how??

Reactions with Oxygen (Rust)

Reactions with Acids (Acid precipitation

Reactions with Water

Reactions with Organism

Types of Chemical Weathering

Reaction with oxygen –AKA Oxidation-

Oxygen combines with water

to make rust. (Oxidation)

ex.: rusty bicycle

Acid precipitationBurning fossil fuels causes

sulfur, carbon, and nitrogen to

mix with water vapor in clouds

to form acid precipitation.

CO2

Carbon dioxide dissolves in rainwater to make

carbonic acid (weathers marble and limestone).

Water (ground water)Minerals are dissolved in water.

(minerals come from rocks that the

water is coming into contact wirh.

ex.: Halite, calcite

Living Organisms

Plants produce weak acids that dissolve rocks. Lichens

grow on rocks and make weak acids.

Rates of Weathering will depend on:

Surface area exposed - More surface exposed,

the faster the weathering will occur.

A full, solid block has the least surface area. The interior is safe from exposure.

A smashed piece has greatest surface area exposed. The interior can now be attacked.

Type of Rock - some rocks and minerals are

more resistant than others. – ex.:Quartz is resistant to chemical and physical

weathering. Slate tombstones weather slower than

marble tombstones.

Rates of Weathering will depend on:

Climate:

Cold and/or dry climates favor physical

weathering.

Warm and wet climates favor chemical

weathering.

Rates of Weathering will depend on: