week 6- weathering and soils Flashcards
what are the differences between solid rock and the critical zone
- colour due to different minerals
- disaggregated
- less dense
- plants on top of the CZ as there is pore space for roots and nutrients can be provided
- more water due to pore space, leading to more hydrated minerals
how is the critical zone formed
- through chemical physical and biological weathering
how does physical weathering occur
- rocks and minerals go to smaller fragments
- through temperature, abrasion and plants and animals
how does temperature cause physical weathering
- driven by the diurnal cycle
- contraction and expansion causing differential stress which can form cracks
- exfoliation temp influenced peeling away of rock layers due to stress induced by outer layers being warmer/colder than inner
- frost wedging, breaking rock when water expands as ice inside pore space
how does abrasion by water ice and wind cause physical weathering
WATER
- freeze thaw where flow can dislodge loose bits of rock
- debris in water abrade which can cause rounding of rocks in rivers
WIND
debri in wind abrades rocks
ICE
- freeze/thaw
- debris in ice
- ice also transports lots of ground up rock material
how do plants and animals cause physical weathering
- plant roots pry cracks apart
- burrowing organisms very minor
why is a larger surface area significant
- increases exposure to chemical weathering
why does chemical weathering occur
- as most rock forming minerals are not thermodynamically stable at earths surface temp/pressure
what factors effect chemical weathering
- temperature
- water and its flow (reactants = acids and/or oxygen and products= if conc of dissolved products is too high then reaction will stop)
what are the net results of chemical weathering
- primary to secondary minerals
- deliver nutrients from rocks to biosphere in soluble forms
types of chem weathering reactions
- dissolution
- direct transformation of minerals
- precipitation of secondary minerals
how does dissolution occur
- acid attack
- h+ from water and other acids
- these ions dissolve minerals thru hydrolysis
what compound is on of the main influencers of chem weathering
- carbonic acid which occurs in rainwater and from microbial respiration
what is congruent
- dissolution where the whole mineral dissolves
reactions for direct mineral transformation
- hydration
- redox
- cation exchange
