Weathering and Rocks Flashcards
Freeze thaw weathering
when water in joints and cracks freeze at 0 degrees
expands by 10%
exerts pressure
most effective where moisture is plentiful so frequent fluctuations above and below freezing
common in peruglacial and alpine regions
Pressure Release
Overlying rocks are removed by erosion
causes underlying rocks to expand and fracture parallel to the surface
removal of a great weight e.g. glacier has the same effect
Heating and cooling
different minerals expand and contract at different temperatures
grandiose disintegration i rocks composed of different minerals
eg granite contains feldspar mica and quartz
block disintegration happens when the rock consists of a single mineral
Salt Crystallisation
the decomposition of rock by solutions of salt
in areas where temperatures fluctuate around 26-28 degrees sodium carbonate and sulphate expand by 300%
creates pressure on joints forcing them to crack
water evaporates leaving salt crystals behind
the temperature rises salts expand and exert pressure on rock
where is salt crystallisation found?
hot desert regions
low rainfall
high temperatures
Disintegration
Rock heats up in day and contracts at night rocks of conductor of heat stressed only occur on the outer layers peeling or exfoliation thus occurs moisture is essential
Where does disintegration occur
Hoy desert areas
large diurnal temperature range
deserts temperatures exceed 40 degrees and drop below freezing at night
where does physical weathering occur
at or near the earths surface
where does chemical weathering occur
sub surface
percolating water has gained organic acids from soil and vegetation
Carbonation (solution)
Occurs in rocks with calcium carbonate
eg chalk or limestone
rainfall columbines with dissolved carbon dioxide or organic acid to form weak carbonic acid
calcium carbonate reacts with acid water and forms calcium bicarbonate which is soluble and removed in solution by percolating water
Hydration
a process whereby certain minerals absorb water expand and change
eg shales and mudstone increase in volume by the 100% when clay minerals absorb water
Oxidation
when iron compounds react with oxygen to produce a reddish brown coating
dissolved oxygen in soil or atmosphere affects iron
oxidation is only under extreme acidity meaning it remains in many soils and rocks giving it a red colour
Hydration
Certain rocks containing feldspar (GRANITE) reacts with acid water
to produce kaolin and leaving behind quartz and mica
Organic Action
Acids derived from the decomposition of vegetation are termed humid acids
Bacterial activity and the respiration of plant roots raise carbon dioxide levels in soil siding solution
what type of sediment is prone to oxidation
iron oxide based
how can vegetating increase weathering
release of organic acids through root systems
solution of limestone is greater under soil than bare rock due to extra organic acids released by vegetation in soil
how can grain size influence weathering
coarse trained rocks weather quickly due to large empty spaces and high permeability
fine grained rocks offer a greater surface area for weathering and may be highly susceptible to weathering
vant hoffs law
the rate of chemical weathering increases 2/3 rimes for each increase of 10 degrees
main processes of weathering for granite
freeze thaw
hydrolysis
what is in granite
quartz
feldspar
mica
how could a mudflow affect the shape of slopes
leave a bowl shaped scar where movement starts
depositional toe at base
stepened upper slope
decreased angle at the base as a result of depositional toe
flow tracks produced
how can humans affect slopes
undercutting (roads, quarrying, mining)
vegetation removal (deforestation)
overloading slope (waste or resovoirs)
describe the process of pressure release
creation of joints and other weakness in rocks by the removal of overburden and the release of pressure
chelation
chemical weathering
of rocks
by organic acids and molecules
how do fold mountains form (at both plate margarine)
sediments (accretionary wedges) are scraped off the ocean floor and rise over the higher plate
