WEATHERING Breaking down of rock in Earth’s surface

Mechanical Weathering Breaking down of rock into smaller pieces Works slowly

Examples of Mechanical Weathering Water Wind Heat Ice Pressure

Water Abrasion Water crashes into rocks and causes rocks to hit each other. Rocks become smaller, smoother, and rounder

Be A Wave Right side of the room: breath in loudly Left side of the room: breath out loudly Keep doing this until the rocks are all broken down.

Frost Wedging Water enter cracks in the rocks, expands and breaks rock apart. – Ice expands when it freezes

Wind Abrasion Particles of sand, pebbles, and dust are carries by wind and cause abrasion which slowly breaks down rock.

Cliff Dwellers / Ancient Peoples lived in areas carved by wind weathering. – Mesa Verde National Park Copyright © 2010 Ryan P. Murphy

Thermal Expansion Repeated daily heating and cooling of rock – Heat causes expansion – Cooling causes contraction

Root Wedging Roots enter cracks in rock and force the cracks farther apart.

Animal Activity Animals mechanically wear away rock

Human Activity

Exfoliation Rock breaks off into sheets Caused by expansion of rock due to uplift and erosion Removal of pressure

Chemical Weathering Breaks down rock through chemical changes Chemical weathering weakens rock which facilitates entry of water and further mechanical weathering

Causes of Chemical Weathering Chemicals Biological chemicals Water – most important chemical weathering agent

Chemical Weathering Depends On: Temperature Amount of surface area Availability of water or natural acid

Hydrolysis Chemical reaction between the minerals in the rock and hydrogen in rain water Water weathers rock by dissolving it Limestone and marble contain minerals (calcite) that are soluble in acidic water.

Carbonation Water and carbon dioxide create carbonic acid which wears down rock Carbon dioxide becomes dissolved in rainwater and produces carbonic acid. Dissolves marble and limestone Water + pollution = chemical weathering Egyptian Obelisks: 3 removed from Egypt (dry) and brought to London, Paris, and New York

Central Park 1881 Central Park Present

Oxidation Process by which oxygen combines with water and minerals in the rock to weaken it Iron combines with oxygen in the presence of water Rust is the product of oxidation Rust makes the rock soft and crumbly Georgia red clay comes from the oxidation of iron

Sulfuric Acid Acid rain Produced from the burning of fossil fuels Sulfur combines with water vapor in the air to produce acid rain

Plant Acids Roots of plants produce weak acids that dissolves rock. Lichens also produce weak acids – Lichens are an algae and fungus living symbiotically together

Solution Process by which mineral sin rock dissolve directly in water Limestone caves: as water reacts with soil, absorbs carbon dioxide, and becomes acidic and then wears away rock

Factors That Affect Rates of Weathering

Surface Area As rock breaks down into smaller pieces, more surface area is exposed and the rock weathers faster Cracks and ores allow water to penetrate and increase the rate of weathering

Rock Type Different minerals weather at different rates. – Marble and limestone dissolve easily in weak acids. – Quartz is most resistant to weathering. – Sedimentary rock weathers faster than igneous or metamorphic

Climate Warm temperatures and abundant moisture lead to rapid weathering.

Slope Angle On a steep slope, weathered particles move away quickly, exposing fresh bedrock to more weathering On a gentle slope, weathered particles are not easily washed away

Burrowing Animals Large and small burrowing animals bring rock particles to the surface Create tunnels which gives water access to deep underground