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

1. Mechanical / Physical 1. Mechanical / Physical WeatheringWeatheringRefers 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 1. Mechanical / Physical WeatheringWeatheringRefers 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 Weathering1. Mechanical WeatheringThe 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, EgyptPylon of Ramses II, Egypt

Cleopatra’s Needle, New YorkCleopatra’s Needle, New York

Surface Area versus Surface Area versus VolumeVolumeAs rocks break down into

fragments, they maintain the same volume, but increase their surface area.Side

LengthVolume Surface

Area

1 cm 1 cm3 6 cm2

2 cm 8 cm3 24 cm2

3 cm 27 cm3 54 cm2

2. Chemical Weathering2. Chemical WeatheringProcess 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 Weathering2. 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 Weathering2. Chemical WeatheringRate 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 Transportation of Weathered MaterialsMaterialsErosion:

◦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 WaterErosion by WaterRill 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 ErosionGlacial ErosionGlaciers 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 Erosion by Wind and by Living ThingsLiving Things

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