Lets break it down!Lets break it down!

The process of rocks being broken down into

smaller pieces by outside conditions. Types of Physical/mechanical weathering (PRIAA)

Plant roots

Release of pressure

Ice wedging

Abrasion

Actions of animals (burrowing, digging, clawing, etc.)

Physical (Mechanical) Weathering

Ice WedgingIce 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 RootsPlant 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.

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.

Burrowing of Animals

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

The process that breaks down rocks through chemical change.

The agents of chemical weathering are (WALCO):

Water

Acid rain

Living organisms

Carbon dioxide

Oxygen

Chemical Weathering

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 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. 

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)

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 Organisms

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

Acid Rain

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

Acid rain causes very rapid chemical weathering