Weathering - the break down of rocks on the Earth’s surface.

Two Types 1.Mechanical weathering – rocks are physically broken into smaller pieces, but there is no chemical change in the rock. 2.Chemical weathering – the chemical composition of rocks is altered.

Types of Mechanical Weathering 1.Frost Wedging – occurs when water is trapped inside the cracks of a rock and then freezes. The ice expands and exerts a force strong enough to fracture the rock.

Types of Mechanical Weathering… 2. Crystal Growth (salt cracking) occurs when saltwater enters a crack in a rock and then evaporates. It leaves behind salt crystals which can exert force and enlarge the cracks.

Types of Mechanical Weathering 3.Thermal Expansion – occurs when rocks are exposed to severe heat. The crystal structure of the minerals in the rock expand, causing the outer layers of the rock to “peel” off.

4. Root Penetration – occurs when plants and trees take root in the crevices of rocks. The growing root can expand the crevice.

Root Penetration

Types of Mechanical Weathering 5.Mechanical Exfoliation – occurs after an intrusive igneous rock has been exposed at the surface. The overlying rock no longer exerts pressure on the igneous rock and so it expands outward, fracturing into sheets parallel to its exposed surface.

6. Abrasion – occurs when rocks collide and grind each other.

Types of Chemical Weathering 1.Dissolution water removes chemicals from a rock and carries them away. Chemicals such as: Halite (rock salt), Limestone is dissolved when water (H 2 O) and carbon dioxide (CO 2 ) in the atmosphere combine to form carbonic acid (H 2 CO 3 ).Can also dissolve in the presence of Sulfuric acid (H 2 SO 4 )

Dissolution of Limestone Water + carbon dioxide = carbonic acid (in atmosphere) (dissolves limestone)

Chemical Formula to form calcium carbonate – agent to dissolve limestone H2O + CO2 + CaCO3 --> Ca+2 + 2HCO3- water + carbon dioxide + calcite dissolve into calcium ion and bicarbonate ion

Types of Chemical Weathering 2.Oxidation – this is another word for rust. The surfaces of iron-rich rocks will rust when they come in contact with water (oxygen in water).

Oxidation – example

Types of Chemical Weathering 3.Hydrolysis –chemical bonding of water with a mineral creates a new mineral.  Aluminum-rich rocks are weathered through hydrolysis to form clay.

Hydrolysis: Seven Colored Earth, Chamarel Village, Mauritius

Factors That Affect Chemical Weathering Climate – warm, moist climates (tropics) have the highest rates of chemical weathering. Living Organisms – burrowing animals (earthworms, groundhogs, ant colonies, etc.) transport unweathered rocks from below ground to the surface where they can be exposed to weathering agents.

Factors That Affect Chemical Weathering Time – the longer a rock is exposed to weathering agents, the more it will decompose. Mineral composition – rocks composed of silica strongly resist weathering, while those containing iron, halite, limestone, etc. are more susceptible to weathering.

Erosion The movement of weathered materials via water, ice, air, gravity.