Chapeter 2 Flashcards
(41 cards)
Weathering
In-situ breakdown and alteration of earth forming materials (physical or chemical)
Why does weathering happen
Rocks are formed within the crust: higher P,T
Unstable under surface conditions
Products of weathering are more stable
Controls on weathering rate
Mineralogy
Petrology
Climate
Vegetation
Main control on weathering
Climate
Most active part of the weathering zone
soils
Active process on soil weathering
Organic accumulation and decay Oxidation Reduction Ground water movement Bioturbation Microbial activity
Soil O
Organics
Soil A
Surface soil layer (top soil)
Soil E
Zone of eluvation
Soil B
Zone of Accumulation
Soil C
Realtively unalterd parent material
Types of Physical weathering
Unloading Thermal expansion Frost action Wetting and drying Salt crystal growth Root action
Unloading
(pressure release)
Erosion removes overburden–> rocks expand
Rocks split into sheets parallel to the topography
Thermal expansion
Rocks and minerals expand/ contract in respoince to heating and cooling
Need frequent, extreme fluctuations
Frost action
Repeated formation and melting of ice in pore
Water expands 9% upon freezinf
Wetting and drying
Materials swell when wet and shrink. crack when dry
Most effective in clay-rich rocks and sediment
Salt crystal growth
Precipitation of salt crystals in rock pores/ cracks
Typical of dry climate and coasts
Root action
Plant roots grow into joints, force rock apart
Chemical weathering
AKA Decomposition
Secondary minerals are produced (clays)
Types of Chemical Weathering
Hydrolysis
Oxidation
Solution
Carbonation
Hydrolysis
Breakdown of water into H+ and OH- ions H ions replace metal cations in rock Freed cations form soluble oxides Accelerated if there is CO2 in the water Dominant process in igneous rocks
Oxidation
Addition of oxygen to minerals- forms oxides
Most effective in aerated zone: presence of air and water
Solution
Dissociation of minerals in water Ions lost to ground water Most effective in acidic water Forms karst like features Salts, gypsum, carbonate are especially prone
Carbonation
So;ution of minerals in carbonic acid
CO2 from atmosphere, decaying organic matter
Prevalent in limestone bedrock, dolomite and marble
