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
what minerals are secondary precipitated
- soluble
- oxides and hydroxides
- clays
how do lichens enhance chem and phys weathering
- penetrate cracks
- secrete organic acids
name of soil formation
pedogenesis
what is a soil profile
- vertical cross section of soil horizons revealed by digging a pit
what factors affect soil formation
CLORPTS
what is residual material
- inorganic parent material, developed in place from weathering of underlying rock
warm climate- oxidation
cool climate- closely resembles original rock
such as: saprolite derived from granite in a dry, cold region
organic deposit name and explanation
- peat
-moss,woody, herbaceous, sedimentary
what does a water deficiency do
- promotes formation of salts
- promotes accumulation of carbonates
- limited chem weathering
high effective rain leads too…..
- increasing clay and organic matter contents
- higher soil acidity
- lower si/Al ratio
how does nutrient upcycling by tress operate
- conifers take up and store very small amounts of ca,mg, and K
- conifers retain needles and debris released are very acidic and resinous
- conifer debris accumulate as thick O horizon
- soils have low PH and highly leached
what helps to identify time-dependancies
- chronosequences
stages of soil profile development
- no layering/OM just accumulating/ weathering start/ OM allows nutrient accum so faster plant growth
a activity of organism and plant decay- cm of OM rich soil/ soluble ions move down to form clays
- deeper OM- distinctive A
- b is deeper and differentiation into sub horizons
