Chapter 16 Flashcards
what four key factors control rates of weathering?
- properties of parent rock
- climate - rainfall and temperature
- presence or absence of soil
- length of exposure
rind
external layer of weathred material
is the weathering rate for a mineral with high solubility fast or slow?
fast
does a massive rock structure have a fast or slow weathering rate?
slow
does more rainfall speed up or slow down the weathering rate?
speed up
does a high temperature speed up or slow down the weathering rate?
speed up
as the thickness of the soil layer in a rock increases, does the weathering rate increase or decrease?
increase
- constantly exposed to groundwater
- carbonic acid
does high organic content in soil speed up or slow down the weathering rate?
speed up
three types of weathering
- biological
- physical
- chemical
- silicate
- carbonate
true or false: the more stable a rock is, the slower it weathers (two examples)
true
halite - unstable - weathers rapidly
granite - stable - weathers slowly
three main processes of chemical weathering
- solubility
- acids
- oxidation
how does solubility affect chemical weathering?
minerals with weak ionic bonds are more soluble therefor they chemically erode faster
how do acids affect chemical weathering?
- H+ attacks surfaces
- natural acids erode rock
what are three types of natural acids involved in chemical weathering?
- sulfuric
- hydrochloric
- carbonic
which type of natural acid has the biggest effect on chemical weathering?
carbonic - weak acid but it is the most abundant
when did oxygen become a part of the chemical weathering process?
2.2 billion years ago as a result of photosynthesis
is silicate weathering slower or faster than carbonic weathering?
slower
products of chemical weathering
- clay minerals - kaolonite, smectite
- oxides
- salts - halite, calcite
main processes of physical weathering
- water/ice
- thermal expansion
- organic activity
- salt
- exfoliation
how does water/ice physically weather rocks?
water gets inside cracks and expands 9% when it freezes, causing further fracturing in the rock
what is thermal expansion?
rocks are a bad conductor of heat so the surface gets hot and expands while the inner rock stays cool
what type of organic activity physically weathers rock?
- tree roots growing through rocks
- organisms get in cracks
how does salt physically weather rocks?
it expands with warming and when it absorbs water
exfoliation
large, flat or curved sheets of rock detach from the outcrop
soil
mineral and organic residue from weathering
soil composition
45% minerals
20-30% water
20-30% air
5% organic
what are horizons?
zones of alteration, addition, and translocation
order of horizons
O A E B C
O horizon
- surface
- consists of organic materials
A horizon
- darkest - most humus
- addition of organics
- loss of material
E horizon
leeched zone - clay
B horizon
addition of weathering products (clay and salt)
C horizon
- parent material
- slightly altered
5 factors of soil formation
- parent material
- climate
- topography
- organisms
- time
4 types of soil
- oxisol
- alfisol
- aridisol
- mollisol
oxisol
- deeply weathered
- very red
- very little organic matter
- Australia
alfisol
- woodland soil
- Ohio soil
- decent organic matter
aridisol
- desert soil
- very little organic matter
- accumulates salt
mollisol
- grassland soil
- great for agriculture
what are the most important formation factors of oxisol?
climate and time
what are the most important formation factors for alfisol?
climate and organisms
what are the most important formation factors for aridisol?
climate
what are the most important formation factors for mollisol?
climate and organisms
what does CLORPT stand for? (Midwest example)
CLimate - semi-arid Organisms - prarie, grassland Relief/Topography - minimal, open-prarie Parent material - glacial loess Time - 18,000
main causes of soil erosion
- overgrazing 35%
- agricultural practices (bad) 28%
- deforestation 30%
- fuel wood 7%
how can we slow down soil erosion?
- crop rotation
- contour plowing
- terracing (levels)
how much less soil does the U.S. have each year?
24 billion metric tons
how rapid are the rates of soil production?
extremely low - soil is non-renewable
How much total prim topsoil is gone in the U.S.?
1/3
