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regolith
loose material that covers bedrock (soil)
sediment
loose fragments of rock/minerals from bedrock, precipitated crystals for water, shells
weathering
physical + chemical breakdown of rock
physical weathering
breaks intact rock into unconnected clasts
jointing
rocks heat w/ burial, as they coll they contract + form cracks
frost wedging
water freezes in cracks + pushes rock apart
salt wedging
salt crystals grow in open pore spaces + push grains apart
root wedging
roots grow in joints + push them apart
abrasion
water, wind, glacial ice scratch at rock
temp-induced exfolitation
peeling away of rock layers b/c of stresses induced by outer layers being a diff T
weathering is climate dependent
↑ precip. ↑ chem. weathering
↓ temp. ↑ phys. weathering
chem. weathering
chem rxns. alter rocks + minerals @ surface conditions
b/c most primary minerals not thermodynamically stable at surface conditions
deliver nutrients from rocks to biosphere in soluble forms
mineral susceptibility to chem weathering
less complicated mineral structures less susceptible to chem. weathering
↑ complexity of structure ↑ chem. weathering
reverse of Bowen’s rxn series
dissolution
water, especially when acidic, can chemically attack and break down the bonds within minerals, causing them to dissolve and move
soluble product flows away from rxn site → mass loss
carbonates + salts
hydrolysis
water reacts w/ minerals to form secondary ones
breaks down silicate minerals
oxidation
Fe-bearing minerals weakened by the addition of O2
breaks down mafic minerals
hydration
introduction of water causes minerals to expand
produces many secondary minerals (clay)
cation exchange
common in clays in phylosillicates
interlayer cations swap
how to form CZ
break down of rock via weathering w/ biological enhancement
in situ CZ
evolves from weathering + organismal colonization
deposited CZ
weathered products transported + deposited before local CZ evolves
critical zone (CZ)
near surface enviro. from tree tops to groundwater
soil
containing living matter + capable of supporting plants
pedogenesis
soil formation
soil horizons
O, A, E, B, C, R
O horizon
humus + organic matter
A horizon
topsoil
E horizon
eluviated layer → minerals + organics exit
B horizon
subsoil → minerals stop leaching
C horizon
parent material
soil profile
vertical cross-section of soil formation
inceptisols
barely developed soils
spodosols
formed under coniferous forests
histosols
high in organic matter (peat bogs)
morlisols
grassland soils
soil formation
CLORPT
climate
organisms
relief
parent material
time
residual material
inorganic parent material developed from weatheirng
if climate is cool + dry residual material closely resembles parent material
laterite
Fe oxide/clay layer rich in acid leached elements
saprolite
retains most original rock texture but is oxidized in warm/humid enviros.
peat-organic deposit
most extensive in cool climates where precip. > evap. + drainage is poor
colluvial
gravity weathered
poorly sorted
well drained
alluvial
water sorted
nutrient-rich deposits of eroded minerals
glacial
till
poorly sorted
aeolian
wind
well sorted
relief
soils at bottom of slopes have better developed horizons
climate
precip. + T
precipitation (climate)
essential for chem. weathering
water promotes differentiation of diff soil horizons
water fuels percolation + leaching
increase weathering, increase CZ depth
effective precip.
portion of total precip. available for plants
temp. (climate)
increases rate of rxn
soil biota + formation
macro + micro organisms enhance soil health
veg. cover reduces erosion rates
organic acids released from plants + decay of plant litter promotes accumulation of secondary minerals in B horizon
development of a soil profile
positive feedback w/ accumulation
development of a soil profile (phase 1)
no layering
early colonization by pioneers
organics begin to accumulate
development of a soil profile (phase 2)
activity of small soil organisms
soluble ions move down → clay formation
development of a soil profile (phase 3)
more/deeper organic matter → distinctive A horizon
B horizon deeper + differentiation into sub-horizons