Module 13: Weathering, Soil, And Mass Wasting

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weather is influenced by

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the character of the bedrock and the climate

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physical weathering predominates in

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dry, cool, climates

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chemiacal weathering predoniates in

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warm wet climates

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Mechanical weathering

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breaks rock into smaller and smaller pieces thereby increasing the surface available for chemical weathering

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crystallization

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occurs when water evaporates from the surfacce of rocks and salt crystals form from the dissolved mineral salts; the crystals grow and begin breaking apart the rock

Front 6

weather is influenced by

Back 6

the character of the bedrock and the climate

Front 7

physical weathering predominates in

Back 7

dry, cool, climates

Front 8

chemiacal weathering predoniates in

Back 8

warm wet climates

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Mechanical weathering

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breaks rock into smaller and smaller pieces thereby increasing the surface available for chemical weathering

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crystallization

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occurs when water evaporates from the surfacce of rocks and salt crystals form from the dissolved mineral salts; the crystals grow and begin breaking apart the rock

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hydration

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occurs when water is added to a mineral, which swells and stresses the rock mechanically forcing mineral grains apart

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frost wedging

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the freeze thaw action of water that breaks rock segments apart; joint block separtation can occur along preexisting joints and fractures and produce discrete blocks of rock

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pressure release jointing

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unloading; takes place as deeply buried plutons expeience uplift, the pressure of deep burial is lessened, and the granite body responds by shedding layers of rock; curved plates of rock are peeled off

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exofoliation

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creating dome shaped features

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thermal expanison

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the daily cycle of temperature that weakens rocks, especially ind eserts due to large diurnal temperature changes

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biological activity

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weathering due to activities of plants, animals, and humans

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the internal structure of the rock is

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altered by the addition and/or remval of elements

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the original rock decomposes into substances that are

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stable in the surface environment; substances will remain in th3e surfacew environment unchanged as long as the surface environment remains unchanged

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what is the most important agent of chemical weathering

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water

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pure water is

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nonreactive

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water is reactive when

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a material is dissolved in the water

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carbon dioxide dissolved in water will produce

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carbonic acid

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carbonic acid

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ionizes to form reactive hydrogen ions and bicarbonate ions

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carbon dioxide is dissolved into the water as

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rain falls through the atmosphere

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dissolution

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the process by which the rock forms a solution in a solvent, usually water

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oxidation

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occurs when the oxygen dissolved in water oxidizes combines with mettalic elements in rock to form oxidizes; the oxide is weaker than the original minerall constituents

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carbonation

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weathering by a weak carbonic acid that reacts with many minerals; the acid readily decomposes these rocks, and produces products that are water soluable; from this process large quantities of rock are dissolved and carried away by groundwater

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hydrolisis

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occurs when materials in the rock chemically combine with water to produce different compounds and minerals; the primary process by which the silicates are decomposed; the felsic minerals are more resistant tot his form of weathering than the mafic minerals; when the weaker minerals are dissolved by hydrolosis the interlocking crystalline structure is compromised and granualr decomposition takes place

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how does granite weather

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when attacked by carbonic acid the hydrogen ions attack and replace pottassium ions thereby disrupting the crystalline structure of the mineral...the pottasium then is available as a nutrient plants or becomes potassium bicarbonate a soluable salt that can be incorporated into other minerals or transported in dissolved form to the ocean by streams and rivers

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clay minerals

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are important produccts of weathering of feldspar; they are very stable under surface conditions

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clay minerals

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comprise a high percentage of the inorganic material in soils

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clay minerals

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are the major constituent of the most abundant sedimentary rock...shale

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clay minerals

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the silica in the felldspar is removed from the feldspar structure as well and is carried away by the ground water

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clay minerals

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the silica can precipitate to form nodules of chert or flint or be used by microscopic animals in the ocean to build silica shells

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clay minerals

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the quartz in granite is very resistant to chemical weathering and will be released from the structure of the rock once the feldspar has been broken down

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clay minerals

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it is often carried tothe ocean where it forms beeches and sand dunes or sandstone

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spheroidal weathering

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a chemical weathering process in which the sharp edges and corners of boulders and rocks are weathered in thin plates that creates a rounded, spherioidal form

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differential weathering

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chemical breakdown>with>temps and precipitation; the felsic minerals are more resistant to chemical weathering than the mafic minerals; differential weathering is affected by mineral makeup, degree of jointing, and exposure to the environment

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soil

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a dynamic natural body made up of fine materials covering the earth's surface

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the mineral compnent of soils

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is ultimately derivedfrom the physicla and chemical weathering of bedrock