Weathering The process by which materials on or near the Earth’s surface break down and change.

1. Mechanical / Physical Weathering Refers only to the physical breakdown of matter (as opposed to chemical breakdown) Frost Wedging: Water expands in volume by 9%. As water infiltrates cracks in rock causes additional cracking due to freeze-thaw cycles Pressure: pressure on underlying rock is consistent until erosion, or another process, removes matter. The reduction in pressure can cause elastic energy within underlying rock to be released. This looks likes widening cracks or fractures

1. Mechanical / Physical Weathering Refers only to the physical breakdown of matter (as opposed to chemical breakdown) Exfoliation: As pressure cycles and freeze-thaw cycles proceed, outer layers of rock can be stripped away in succession (like an onion)

1. Mechanical Weathering The rate of physical weathering is relatively high in cool climates. Frost wedging / freeze-thaw cycles Cool climates are not ideal for chemical reactions / dissolution

Pylon of Ramses II, Egypt Cleopatra’s Needle, New York

Surface Area versus Volume As rocks break down into fragments, they maintain the same volume, but increase their surface area. Side Length Volume Surface Area 1 cm 1 cm3 6 cm2 2 cm 8 cm3 24 cm2 3 cm 27 cm3 54 cm2

2. Chemical Weathering Process by which rocks and minerals undergo changes in their composition and is dependent on a mineral’s chemical composition and temperature Oxidation: reaction with oxygen. EX Iron and Oxygen = Iron Oxide (Hematite) Water: able to dissolve minerals and rocks. Water may also act as a medium in which reactions can occur.

2. Chemical Weathering Carbon Dioxide: when CO2 (from living and decaying organic matter) reacts with water in the atmosphere it produces carbonic acid that falls to Earth as acid precipitation which then cuts through mineral and rock. Acid Precipitation: Usually at pH 5.6 or below Carbon dioxide, Sulfur dioxide

2. Chemical Weathering Rate of chemical weathering is relatively high in climates with warm temperatures, abundant rainfall and lush vegetation. Chemical weathering has the greatest effect at, and around the equator.

Transportation of Weathered Materials Erosion: The removal of weathered rock and soil from its original location. Running water, glacier, wind, ocean currents, and waves. When material ‘drops’ after being eroded it experiences deposition.

Erosion by Water Rill erosion: Running water cuts small channels into the side of a slope. Gully erosion: Rill erosion eventually becomes gully erosion as the channel widens.

Glacial Erosion Glaciers account for < 10% of Earth’s water, yet cover about 30% of Earth’s surface (due to expansion) Scrape out large sections of Earth’s landscape

Erosion by Wind and by Living Things ???

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