7 WEATHERING The Hoodoos near to Drumheller Alberta What weathering processes likely contributed to the development of these remarkable rock formations Weathering Weathering is the result of a series of physical biological and chemical processes ID: 277691
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Slide1
CHAPTER
7:
WEATHERINGSlide2
The
Hoodoos
near to Drumheller, Alberta
What weathering processes likely contributed to the development of these remarkable rock formations?Slide3
Weathering
Weathering is the result of a series of physical, biological, and chemical processes.
Modifies rocks and the minerals within themProduces sediment which is subsequently removed by erosion and transported
elsewhereEnables growth of new minerals through crystallizationContributes to the production of soilSlide4
Weathering Mechanisms
Physical and biological weathering causes rock to fracture and fragment
Chemical weathering attacks exposed surfaces and weakens the rock
Explain how physical (a.k.a. mechanical) and chemical weathering complement each other in breaking rock into smaller fragments.Slide5
Physical
Weathering
Physical Weathering causes Fragmentation of Rock
Pressure release, abrasion, freeze-thaw, hydraulic action, growth of salt crystals, and other physical meansPhysical weathering is aided by bedding, rock joints and other types of
fracturesSlide6
Pressure release jointing -
Exfoliation
Exfoliation contributed to jointing of granitic rock adjacent to the Coquihalla Highway, north of Hope,
BC
What other mechanical weathering processes may also be important in this area?Slide7
Wind abrasion forming
Ventifacts
The photo to the left was taken on Earth. Which other planet has similar weathering features? Can you explain the connection with the area shown here?Slide8
Growth of Salt Crystals
Saline water seeps into permeable rock and then evaporates, causing interstitial growth of salt crystals, which pry the rock grains or crystals apart
.
Honeycomb weathering of sandstone on a rocky ocean shore, Gabriola Island, BCSlide9
FREEZE-THAW
Hydraulic
ActionOn rocky shorelines, the powerful force of breaking waves forces water into cracks
and fractures in the rockWind ErosionGrowth of Salt CrystalsOther physical meansInsolation – daily temperature changes cause expansion and contraction of rocks.
Slaking – interstitial water (due to alternate wetting and drying of rocks) creates tension.
FREEZE-THAW
Talus slope created by ice-wedgingSlide10
Hydrolysis, Oxidation and Dissolution are chemical weathering processes
Water
molecule is polarized (H is positive, O is negative)The negative O ions attract
cationsWater is known as the “Universal Solvent” because so many substances are water soluble.Slide11
Hydrolysis
Hydrolysis is the chemical reaction (
cation exchange) of a compound with acidic water.Example: Feldspar
(either orthoclase or plagioclase) is converted to the clay mineral kaolinite
Carbonic acidSlide12
Oxidation
Oxidation
is the loss of electrons by cations and their use by free oxygen.
The red coloration here is the result of oxidation. Which element, that turns red in its oxidized state, is responsible for this
colour? Slide13
Dissolution
Dissolution occurs when carbonic acid (produced when atmospheric CO2 dissolves in water) dissolves the mineral calcite, which is the main constituent of limestone
.Widespread dissolution of carbonate rock leads to the development
of: Karst TopographySlide14
Biological
Weathering
Biological Weathering involves both chemical and physical processes
Moving, mixing, decomposition and CO2 production (resulting in carbonic acid)
Growing plants exert pressure on the rockSlide15
Sedimentary products result from all three types of weatheringSlide16
Rocks and minerals can be ranked by their vulnerability to weathering
Weathered granite outcrop
Which mineral in granite is most susceptible to chemical weathering? Slide17
Natural bridges are
products of weatheringSlide18Slide19
Clay minerals
are phyllosilicates
… They have sheet structures composed of silica tetrahedra and aluminum
octahedra
Aluminum
octahedron
Kaolinite under a scanning electron microscopeSlide20
Weathering can contribute to climate change
When the feldspar in a rock like this gneiss is weathered to clay minerals, carbon dioxide from the atmosphere is consumed and ends up as dissolved bicarbonate which is transported to and stored in the
oceans.
What type of sedimentary rock forms from the dissolved bicarbonate? Slide21
The Uplift - Weathering hypothesis
The global rate of chemical weathering is dependent on availability of fresh
rockMountain chains (formed during orogenesis
resulting from continental collisions) lead to significantly enhanced weatheringAs new silicate-rich crust is exposed to weathering, atmospheric carbon dioxide is consumed and the climate cools.The formation of the Himalayan Mountains and the Tibetan Plateau took place over the past 40 million years, and contributed to the cooling that resulted in the Pleistocene glaciations
.Slide22
Weathering produces soil
SOIL FORMATION
influenced by:
biological processes nature of parent rock climate topography timeSlide23
Climate is critical in soil formation
Physical Weathering dominates
in regions of low temperature and
low rainfall. Chemical Weathering dominates in regions of high temperature and high rainfall.
Why are cold humid climates not common? Slide24
Environments
HOT, ARID
ENVIRONMENTSSalts accumulate at the surface due to evaporation.Frost, abrasion, and slaking break the rocky surface into sand or gravel.Wind blows smaller particles away – creating a desert pavement of cobbles and boulders
.COLD ENVIRONMENTSMechanical breakdown (by ice wedging)
is the major weathering process. Slide25
Hot and humid environments
Hot
and humid environments lead to the formation of insoluble residues with crusts of iron oxides (laterite) and aluminum oxides (bauxite) Slide26
Soil surface becomes rich in organic plant debris, known as the
humus
L
ayer
Soil Horizons Animation
Seasonal freezing allows vegetation debris to accumulate in the soil. Slide27
Soil erosion is a significant problem
Fluvial
Erosion – particles of sediment removed by flowing water in a channel:Suspension
Bed LoadSaltationMass Wasting – sediment moved by gravityDebris flowsMudflows
Eolian Erosion – sediment moved by windSlide28
Fluvial erosion involves several different processesSlide29
The power of wind –
eolian erosion!
Which parts of Canada are susceptible to wind erosion? Slide30
There
are 10 orders in
the Canadian soil classification systemSlide31
What is the main soil type in your region of Canada?Slide32
Which climate, weathering processes and soil profiles
are likely in each of these five settings?Slide33
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