wk 5 weathering - school of ocean and earth science and ... · the effects of weathering can...
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WEATHERINGCHAPTER 7CHAPTER 7
Monument Valley, Utah. What weathering processes contributed to the development of these remarkable rock formations?
Weathering Includes Physical, Chemical, Biological processes
Weathering is a Series of Physical, Biological, and Chemical processes.
• Modifies rocks, minerals, and sediments.
• Produces sediment transported by Erosion.
• Enables growth of new minerals (called sedimentary minerals) through crystallization.
• Produces Soil.
Weathering Mechanisms
• Physical and biological weathering causes rock to fracture and fragment
• Chemical weathering attacks exposed surfaces
Physical Weathering causes Fragmentation of Rock.
Pressure Release, Abrasion, Freeze‐Thaw, Hydraulic Action, Growth of Salt Crystals, other Physical Means
Physical weathering is aided by rock joints and other types of fractures
Pressure release jointing ‐Exfoliation
Wind abrasion forming Ventifacts
Desert pavement
FREEZE‐THAWTalus slope
created by Ice‐Wedging
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FREEZE‐THAWTalus slope created by
Ice‐Wedging
Soil, Spheroidal Weathering …
…and Natural Bridges are products of weathering
Hydrolysis, Oxidation, and Dissolution Are Chemical Weathering Processes.
• Water molecule is polarized.• Attracts cations.• “Universal Solvent”• Hydrogen bond ‐ polar
Hydrolysis is the chemical reaction (cation exchange) of a compound
with acidic water.
Orthoclase feldspar becomes Kaolinite
2KAlSi3O8+2H+H2CO3+H2O Al2Si2O5(OH)4+2K+2HCO3+4SiO2
feldspar + rainwater react to form clay + dissolved salts + silicic acid
Oxidation = O bonds with cation (K, Ca, Fe, Mg) by electron sharing (covalent)
Fe2O3 ‐ Hematite
Dissolution occurs when carbonic acid dissolves
the mineral calcite (found in limestone).
(a) CO2 + H2O H2CO3carbon dioxide gas + water carbonic acid
Widespread dissolution
causes: Karst Topography
(b) CaCO3 + H2CO3 Ca2+ + 2HCO3‐calcite + carbonic acid dissolved calcium +
dissolved bicarbonate
Forms of Limestone – CaCO3
Travertine or FlowstoneChalk
Coquina
SkeletalLimestoneMicrite
Biological Weathering Involves Both Chemical and Physical Processes
1. Simple breaking2. Movement and
mixing3. Carbon dioxide
d d bproduced byrespiration forms carbonic acid
4. Organisms influence moisture in soil
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Sedimentary Products Result from All Three Types of Weathering Rocks and Minerals Can Be Ranked by Their Vulnerability to Weathering
weathered granite outcrop
Clays arephyllosilicates…
sheet structures composed of silica tetrahedra.
The Effects of Weathering Can Produce Climate Change.
Volcanic outgassing of Greenhouse Gas ‐ part of Carbon Cycle
The Uplift Weathering Hypothesis:
• Global rate of chemical weathering dependent on availability of fresh rock.
• Atmospheric carbon dioxide decreases as new silicate‐rich crust is exposed to hydrolysis during orogenesis (i.e., raising the Himalayas)
Global Cooling or Global Warming?BOTH – it depends on the time span under consideration.
Weathering Produces Soil
SOIL FORMATIONinfluenced by:
• biological processes, • nature of parent rock,• climate,• topography,• and time.
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HOT, ARID ENVIRONMENTS
Salts accumulate at the surface due to evaporation.
Frost, abrasion, and slaking break the rocky surface into sand or gravel.
Wind blows larger particles away – creating desert
tpavement.
COLD ENVIRONMENTS
Mechanical breakdown (by ice wedging) is the major weathering process.
CLIMATE CRITICALin SOIL FORMATION
• Physical Weathering
dominates in regions
of low temperature
and low rainfall.
• Chemical Weathering
dominates in regions
of high temperature
and high rainfall.
HOT, HUMID ENVIRONMENTS INSOLUBLE RESIDUES with crusts of iron oxides (LATERITE) and
aluminum oxides (BAUXITE)
Seasonal freezing allowsvegetation debris toaccumulate in the soil.
Soil surface becomesextremely rich in
Soil Horizons Animation
HUMID, MIDLATITUDE ENVIRONMENTS
extremely rich inorganic plant debris,known as the HUMUSLAYER
Soil Erosion Is a Significant Problem.
• Fluvial Erosion – particles of sediment removed by flowingwater in a channel:
SuspensionBed LoadSaltation
• Mass Wasting – sediment moved by gravity:Landslides Mudflows
• Eolian Erosion – sediment moved by wind.
Raindrops to Sheets to Rills to Gullies!
The Power of Wind – Eolian Erosion!
There Are 12 Orders in the Soil
Classification System.
Mollisols Alfisols Entisols
Inceptisols Ultisols GelisolsU.S. SOIL MAP
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Which climate, weathering processes and soil profiles are likely in each of these five settings?
Residual soils contain accumulations of stableelements and compounds – Al, Fe bauxite, gibbsite
Oxisols
Sedimentary Minerals
Microcrystalline quartz(chert, agate, quartz)SiO2
Clay ‐ kaolinite
Calcite – CaCO3
Hematite/limoniteFe2O3
Granite – quartz, feldspar,biotite, amphibole
Saprolite – quartz, clay,hematite, Al‐oxide
BauxiteAl2O3 H2O
Erosion