Weathering, Erosion & Deposition

ESS 2015-16

Weathering•The breaking up of rock into smaller pieces

Chemical Weathering•Chemical weathering breaks down bonds holding the rocks together, thus they fall apart, forming smaller and smaller pieces.

Chemical Weathering•More common where there is a lot of water.

•Water is important to many of the chemical reactions that can take place.

•More common where temperatures are warmer.

Chemical WeatheringMost common types of chemical weathering•Oxidation•Hydrolysis •Dissolution •Plant acid •Hydration

Oxidation•Rocks containing metals are combined with oxygen to form “rusts”. •The areas in these rocks that are oxidized are weaker & thus more susceptible to physical weathering.

Hydrolysis•A reaction with water in which a molecule is cleaved into two parts by the addition of a molecule of water •Affects silicate and carbonate minerals. •Pure water ionizes & reacts with silicate minerals.

HydrolysisExample

Mg2SiO4 + 4H+ + 4OH- ⇌ 2Mg2+ + 4OH- + H4SiO4

Olivine (forsterite) + 4 ionized H2O molecules ⇌ ions in solution + silicic acid in solution

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Dissolution•Slightly acidic water dissolves rock.•Carbonic acid •Sulfuric Acid

DissolutionWhen carbonic acid is combined with a mineral like calcite (CaCO3), calcium and bicarbonate ions are released and carried off by groundwater. 

CaCO3 + H2CO3  Ca+2  +  2 HCO-3

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Marble & Limeston

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Dissolution•Sulfurous gas (volcanoes & factories) can dissolve in water to form sulfuric acid.

Acid Rain •SO2 + H2O H2SO4

Plant Acid•Mosses and lichens produce weak acids that dissolve the minerals that hold rocks together.

Hydration•H+ and OH- ions attach to the atoms & molecules of a mineral.• Increases volume within rock, creates stress & breaks rock down

Rates of weathering Factors :

•Amount of surface area exposed to chemical weathering•Type of mineral•Climate•Especially warm & wet