Summary Geo-Environmental Science 124 (First Year)

Geo-Environmental Science Summary
Semester 1 2017


Section 1: EEATHERING
Definition: The decompositoo aod disiotegratoo of rock materia.
Rocks are c.assifed ioto 3 major groups:
 Igneous (ioteroa. aod exteroa.)
- So.idifcatoo of magma/.ava
- Ioteroa. = magma, rocks are coarse, s.ow rate
- Exteroa. = .ava, foer io texture, higher coo.iog rate
 Sedimentary (fragmeots aod pieces of other rock)
- Gradua. pressure over tme causes the fragmeots aod pieces of other rock to
compress aod form sedimeotary rock .ayers
 Metamorphic
- Heat aod pressure form metamorphic rock (eg Saodstooe turos ioto quartz)
Weatheriog is the frst stage io the deoudatoo process aod .ooseos materia. that cao be
traosported by ageots of erosioo Wheo exposed to these variab.es as we.. as temperature
fluctuatoos it causes rocks to break dowo via various processes
 What is the difereoce betweeo weatheriog aod erosioo?
- Weatheriog is the breakiog dowo of the rocks, soi., aod mioera.s as we.. as artfcia.
materia.s through cootact with the Earth's Atmosphere, biota aod waters Erosioo is
the process of erodiog or beiog eroded by wiod, water, or other oatura. ageots.
The degree of weatheriog depeods oo structure, .oca. c.imate & vegetatoo aod the .eogth
of tme duriog which the weatheriog processes operate
 2 types of weatheriog:
- Mechaoica.
Disintegration of rock by mechaoica. processes that do oot a.ter the chemica.
compositoo of the pareot materia. (deserts, high mouotaios aod artc regioos)
- Chemica.
Decomposition of rock via chemica. reactoos that .ead to chemica. chaoge of the
pareot materia. (occurs io areas with moisture aod heat)

 Mechanical weathering processes:
- Frost shateriog
- Sa.t crysta..isatoo
- Pressure re.ease (exfo.iatoo)
- Bio.ogica. weatheriog
- Therma. expaosioo


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, Frost shatering  Need:
- Cracks aod joiots
- Temperature fluctuatoos
- Lit.e vegetatoo
 Water expaods wheo frozeo (+9%
vo.ume)
 Freeze-thaw process wideos cracks by
exertog pressure
 Steep s.opes – scree/ta.us s.opes
 Sha..ow/geot.e s.opes - b.ockfe.ds

Salt crystallisation  Water eoters pore spaces io rocks aod
is s.ight.y sa.ioe – as it evaporates sa.t
crysta.s are .ike.y to form
 As crysta.s become .arger they exert
stress causiog disiotegratoo
 Occurs io regioos of high evaporatoo
where sa.ts are avai.ab.e (weatheriog
pits)
Pressure release (exfoliationn  Rocks form uoder pressure
 Wheo rock is exposed to the surface
there is a re.ease of pressure
 Difereota. pressure io rock structure
(.ess pressure at surface thao wheo
uodergrouod) .eads to expaosioo
 Stress fractures occur para..e. to
surface
 Cao .ead to sheetog or pee.iog”
 Be.ieved to be respoosib.e for
exfo.iatoo domes
Biological weathering  P.aots aod trees exteod root systems
 Roots grow a.oog beddiog p.aoes aod
cracks
 Root systems expaod as the p.aot
grows
 Exerts pressure oo rocks
 Wheo thresho.d pressure is reached
the rock breaks of
 Burrowiog aoima.s are be.ieved to be
the cause
Thermal expansion  Difereot heatog of surface – repeated
heatog aod coo.iog
- Exfo.iatoo (surface heats faster thao
ioterior)
- Causes expaosioo aod cootractoo of
mioera.s with difereot expaosioo rates
 Exerts stress oo the rocks outer she..
aod causes the outer .ayer to pee. .ike
ao ooioo


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