Weathering Flashcards
tallis slope
slope of highly angular rock fragments
4 main factors on weathering
water, chemical enviro., pressure, temp.
equifinality
different processes leading to the same rock type or formation
4 key components in the weathering system
process, materials, form and environment
4 important effects of rock breakdown
soil formation, landscape and landform evolution, prepares rock for erosion and transportation, dissolved nutrients
4 products of weathering systems
physical particles, chemicals dissolved in water in form of ions, oxides, clay minerals from chemical trans of minerals
explain weathering feedback
landforms produced by weathering will influence further weathering-> increased surface area makes rock break down more quickly
3 types of weathering
physical, chemical, biological
explain dilation weathering
removal of overlying material over an igneous dome leads to pressure release, joints and fractures, top layer breaks up-> more uplift
two features formed from dilation
exfoliation dome, exfoliation sheet
explain thermoclasty
driven by sun, forest fires, lightning strikes. thermal shock when temp. changes so rapidly that rock cracks.
fatigue failure, repeated app. of stress
granular disintegration- grain by grain weathering
how much does water expand by when frozen
9%
what temp is needed for effective ice expansion in freeze-thaw
-22C
difference between macro and microgélivation
macrogélivation: large blocks get broken off, microgélivation: granular disintegration and flaking
explain salt crystal weathering
water evaporates to leave salt behind, grows, wedges rock apart
micropores allow movement of saline solution into pores
causes flaking, alveoli
what are tafoni
larger alveoli (cavernous weathering)
where does salt weathering mostly occur
desert and coastal environments
explain hydration weathering
water into rock, water molecules attach to crystalline structure of mineral, expansion when hydrated, mineral grains flake off
which out of the two main controls is most influential on weathering
climate but can be overtaken by material factors
substance that increases the proton conc. of water
acidic/proton donor
substance that decreases the proton conc. of water
proton acceptor/base
what is the most common proton donor in nature
carbonic acid
redox potential (Eh)
ability of a chemical species to bring about an oxidation or reduction reaction
what is solubility in natural environments dependent on
pH and Eh, both of which are influenced by temp.
give characteristics of water that allows it to weather physically
high cohesiveness, high surface tension, high capillarity, freely changes from solid to liquid to gas
slaking
alternate wetting and drying that causes materials to disintegrate and crumble
explain hydrolysis
chemical reaction between mineral and slightly acidic water to break bonds of a partic. substance. congruent dissolution: metal cations selectively replaced in the crystal lattice and minerals altered into clay minerals
what minerals are especially affected by hydrolysis
feldspars
what minerals can carbonation weather
carbonate, silicate and ferro-magnesium minerals
why is limestone dissolved more quickly beneath soil
soil carries a higher conc. of dissolved CO2
how does temp affect carbonation
partial pressure of CO2 falls with a rise in temperature so colder temps may lead to more weathering. (but other factors at play)
how do oxidation and reduction transform substances
addition and removal of oxygen
what is chelation
metal ions are kept in solution and prevented from precipitating within plant roots-> causes the removal of these cations by ion exchange, replaced by hydrogen ions which acidify soils
give example of bacteria that weathers rock
cyanobacteria cause locally concentrated weathering and erosion
function of lichens
communities of fungi and algae, bioprotectors, can promote weathering by excreting organic acids or prevent it by producing oxalic acid (quite insoluble coating on limestone)
resistates
unaltered primary materials basically immune to a specific process that survive while surrounding rocks are weathered away
what are secondary materials
weathering products of primary materials
what determines the composition of clay material in secondary materials
the initial material and the intensity/duration of weathering
how are sandy regoliths formed
minerals less susceptible to weathering continue to break down into smaller fragments
what causes thermal shock (type of thermoclasty)
sudden temp change doesnt allow time to expand/contract quickly enough. adjacent crystals heat and expand at diff rates
give factors that can prevent or slow down freeze-thaw
increased pressure during ice formation can lower freezing point and slow further freezing, impurities slow down freezing, rocks not at near saturation
does salt weathering occur through shock or fatigue
fatigue
what are the three main processes at work in salt weathering
crystallisation, hydration, differential thermal expansion
what is granular disaggregation
salt weathering of some rocks results in larger grains formed
what is efflorescence
the near-surface accumulation of salt
contour scaling
the accumulation of salt in the subsurface zone leads to surface layer blistering and falling away
cavernous weathering
salt weathering creates hollows where salts are retained, microclimates= moister and cooler, deeper absorption of salt = further weathering
how can fungi and lichens weathering through hydration
turgor pressure
5 methods of physical weathering
- unloading, dilation, pressure release
- thermal expansion and contraction (thermoclasty)
- freeze-thaw
- salt crystal growth
- hydration
grus
accumulation of angular, coarse-grained fragments resulting from granular disintegration (usually in arid regions)
why is salt weathering more common in coastal and desert enviros
great temp range and moisture containing salt exists
