Weathering & Erosion

Weathering the process that produces

change in the surface of rocks exposed to the atmosphere

and/or hydrosphere.

Two Types OF Weathering:•Physical weathering is breaking rock by force.

•ex: hitting, scratching, cracking

•Chemical weathering is where the rock material is changed into another substance by reacting with a chemical.

•Frost action •(ice wedging)-

1.Water seeps into small cracks in rocks. 2.When the water freezes it expands creating great pressure. 3.The crack widens and allows water to seep deeper into the rock.

TYPE OF PHYSICAL WEATHERING?

•Plant action- 1.Tiny root hairs seek out small cracks and pits in rock. 2.Once the root hairs find a place they grow and expand. 3.The expansion causes great pressure and cracks the rock.

TYPE OF PHYSICAL WEATHERING?

•Exfoliation 1.Rocks formed

deep in the Earth are made under high pressure.

2.When the pressure is released the rocks expand & crack.

3.May also be caused by alternate heating and cooling of rocks by weather conditions.

•Abrasion- rubbing by other rocks.

CHEMICAL WEATHERINGRock reacts with water, gases and solutions (may be

acidic); will add or remove elements from minerals. 1. Dissolution (or solution)

- also includes leaching2. Oxidation 3. Hydrolysis 4. Biological Action5. Spheroidal

•Oxidation- •Oxygen in the atmosphere chemically reacts with minerals. •ex.: rusting of a nail

•Water (hydrolysis)•Minerals are dissolved in water. •ex.: Halite, calcite

BIOLOGICAL ACTION•Lichens, fungi, and other micro-organisms •Chemically and physically change rock

•Acid- Carbonic acid:

•C02 dissolves in rain water forming a weak acid. •Sulfuric Acid also

ACID LEACHING

SPHEROIDAL WEATHERING

•chemical weathering of jointed rocks. •weather to form spherical shapes

FACTORS AFFECTING WEATHERING•Type of material – both are from 1780’s; one is slate, the other is marble. Which is which? Why is there a difference?

RATES OF WEATHERING WILL BE INFLUENCED BY:

Surface area exposed - weathering occurs on the surface. 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.

EROSION•Movement / transportation

•Wind, water, glacier

•Mast Wasting - Movement of large amounts of material downhill under gravity

•Creep •Mudflows •Slump •Rockfalls •Landfalls

•Avalanches

4 TRIGGERS OF MASS MOVEMENTS:•Water—saturates surface materials by heavy rain or

rapid snow melt; lubricates particles so they move easier•Oversteepened slopes—a slope remains stable only up to 25-40° based on particle type & size•Removal of vegetation—plants stabilize slopes because roots bind soil & regolith together; w/o plants soil moves easily•Earthquakes—can dislodge huge amounts of rock and unconsolidated material

• Types of Mass Movements are based on the kind of material that moved, how it moved, and the speed of movement

Types of Mass Movements:•Rockfall—rocks freefall through air •Rockslide—a block of rock and

loose material moves suddenly along a flat, inclined surface; common in high mountain areas; fastest moving mass movement (200 km/hr)

Types of Mass Movements:• Slump—downward movement of

material on a curved surface; does not move fast or far

• Flow—movement of material containing a large amount of water; moves like a thick liquid (think cake mix)

• Earthflow—moves slowlyMudflow—moves quickly

Types of Mass Movements:• Creep—caused by alternating

expansion & contraction of the ground (freeze/thaw); slowest mass movement (1mm-3cm/yr); cannot be directly observed