chapter 16 weathering, erosion & mass wasting

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what does climate affect?

weathering rates, temperature and rainfall.

What modifies weathering

CO2 uptake

cycle of climate

Reduced Weathering rate-> leads to increase in atmosphere CO2->climate warming which increases weathering->weathering reduces CO2 in atmosphere as Co2 changes to HCO3- --> lower CO2 leads to climate cooling -> lower temperatures and decreases in atmospheric CO2 reduce weathering

weathering

refers to any process that eventually breaks apart rocks

erosion

refers to transport of weathering products after they have been broken a part

average igneous rocks weather by

mechanical fragmentation, chemical alteration, solution (dissolved rocks)

two types of weathering

chemical and physical (mechanical) weathering

What are all rocks exposed to

water or air with rate/degree controlled by - rock properties, rainfall and temperature, presence or absence of soil (vegetation) length of exposure (t)

how does time affect weathering

more weathing over time less weathering erosion and soil formation

mineral stability affect weathering

more mineral stability means less weathering for quartz less mineral stability means more weathering for feldspar

how does temperature affect weathering

less physical weathering , more chemical weathering when temperature increases, less chemical weathering more physical weatheirng (thermal expansion and contradiction frost wedging)

increasing amount of rainfall on weathering

more physical and chemical weathering when rainfall increases, fragmentation and erosion and dissolution of minerals less rainfall means less physical and chemical weathering less fragmentation erosion, and dissolution of minerals

rainfall acidity on weathering

more chemical weathering when acidity increases, more chemical weatheirng more dissolutions of minerals, less chemical and physical weathering less dissolution of minerals

increasing slope steepness on climate

the more slope increases more erosion, less chemical weathering, less erosion more chemical weathering

chemical weathering principle agent

water

why does chemical weathering occur

because minerals formed deep in Earth's interior are not stable at the surface of earth

What is Stability the reverse of?

bowen's reaction series (quartz which forms late in bowen series is very stable whereas olivine which forms early weathers easily)

thermodynamics

consider the stability of any phase or group of phases under specified conditions temperature,pressure, oxygen levels aqueous solutions, etc.

kinetics

consider the rates at which reactions will proceed

minerals stable under the conditions of their formattion are

often not stable at the earth's surface - persistence due to slow reaction kinetics

chemical weather dissolution

it involves dissolution or transformation of minerals, product solutes are carried away as dissolved load - ground coffee with water, turns to liquid coffee containing caffeine and other substances

primary reactions of chemical weathering

dissociation: NaCl = Na +Cl
hydration K-feldspar + H -> Ca2+ +HCO3-
Acid Base Reaction: CaCO3 +H+ -> Ca2+ HCO3-
oxidation: Iron (fe2+) o2 -> hematite and silica

Feldspar chemical weathering

an abundant mineral in many rocks , 2KalSi3O8 (feldspar) + 2H+ + 9H2O -> Al2Si2O5(OH)4 (Kaolinite) 2K+ 4H4Sio4

H+ can come from

carbonic, sulfuric, nitric acids

carbonic Acid forms when

CO2 and H2O molecules combine, carbonic acid ionizes to form hydrogen and bicarbonate ions, bicarbonate ions react with feldspar, to form Kaolinite clay

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