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.

T YPE 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.

T YPE 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. Abrasion-

C HEMICAL W EATHERING Rock reacts with water, gases and solutions (may be acidic); will add or remove elements from minerals. 1. Dissolution (or solution) - also includes leaching 2. Oxidation 3. Hydrolysis 4. Biological Action 5. 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

B IOLOGICAL A CTION Lichens, fungi, and other micro-organisms Chemically and physically change rock

Acid- Carbonic acid: C0 2 dissolves in rain water forming a weak acid. Sulfuric Acid also

A CID L EACHING

S PHEROIDAL W EATHERING chemical weathering of jointed rocks. weather to form spherical shapes

F ACTORS A FFECTING W EATHERING Type of material – both are from 1780’s; one is slate, the other is marble. Which is which? Why is there a difference?

R ATES 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.

E ROSION Movement / transportation Wind, water, glacier Mast Wasting - Movement of large amounts of material downhill under gravity Creep Mudflows Slump Rockfalls Landfalls Avalanches

4 T RIGGERS OF M ASS M OVEMENTS : 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 slowly Mudflow—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