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Introduction Definition Weathering vs. erosion

Types of weathering Mechanical weathering Agents of Mechanical weathering

Frost Action Pressure Release (Exfoliation) Insulation Some minor Agents of Mechanical weathering

Chemical weathering Main process of Chemical Weathering

Hydrolysis Oxidation Carbonation Acidic Rain Solution

Biological weathering Mechanical weathering vs. chemical weathering Factors af fecting weathering Signif icance of weathering

“Weathering is the process of disintegration and decomposition of rocks of the earth’s surface”.

Weathering Vs. Erosion

Mechanical weathering Disintegration by physical agents Composition of rock does not change

Frost Action Weathering process by ice Water increases in volume by about 9% when it freezes Produces about 1890 metric tons pressure for every 1 ft2

Common in high altitude zones

Pressure Release (Exfoliation) Metamorphic and intrusive igneous rocks are under

pressure Upper layer is removed by erosion Due to pressure release the cracks are formed

Insolation Common in arid and desert regions Temperature is high in day time and low in night Disintegration due to expansion and contraction

Block Disintegration Granular disintegration

Rainfall Gravity Salt wedging

Weathering process by chemical agents Composition of rocks is changed

These weathered tombstones are from a burying ground in Boston, Massachusetts. The marker on the left, carved in marble, has been strongly weathered, weakening the lettering. The marker on the right, made of slate, is much more resistant to erosion.

Hydrolysis Addition of water When minerals are moistened, hydrolysis occurs.

H2O + CO2 + CaCO3 --> Ca+2 + 2HCO3-

water + carbon dioxide + calcite dissolve into calcium ion and bicarbonate ion

Feldspars to clay

+ H2CO3 (acid)

Oxidation Iron combines with oxygen in the presence of water in a

processes called oxidation The product of oxidation is rust

Carbonation Mostly in humid areas CO2 dissolves in rain water and creates carbonic acid Carbonic acid easily weathers limestone and marble

CaCo3+H2CO3 Ca2+ + 2HCO3

Acidic Rain Compounds from burning coal, oil and gas react chemically with

water forming acids. Acid rain causes very rapid chemical weathering

Solution Rock salt and gypsum may be dissolved by water and

then removed in solution

Can be both chemical and mechanical in nature.

• roots split rocks apart

• roots produce acidsthat dissolve rocks.

• Animal And Insects

• Vegetation• Human

Activities

MECHANICAL WEATHERING CHEMICAL WEATHERING Rocks are disintegrated by

physical force There is no chemical change

Prominent in dry and cool areas Rocks are broken into great

depth Hard rocks are weathered too

Rocks are decomposed by chemical action

Rocks undergo chemical change Prominent in hot and humid

areas Only surface rocks are affected Hard rock like quartz resist

chemical weathering

Nature of rock Slope of land Joints Vegetation cover Climate

Landforms Formation of sedimentary rocks Mass wasting Regolith formation

Niche habitation of native Americans wall of canyon de chelly Arizona

This granite outcrop in Yosemite National Park, California, displays sheetlike joints, giving a stepped appearance to the mountain slope.

Monolith Buttes Mesas

Mesa

Butte

Monolith

Bajwa.A.S, “Modern Physical Geography” publishers emporium Urdu Bazar Lahore

Strahler.A “Physical Geography” 2nd 2005 http://www.soils.wisc.edu/courses/SS325/weathering.htm http://www.physicalgeography.net/fundamentals/10s.html

http://russiatrek.org/blog/nature/the-weathering-pillars-of-komi-republic-photos/

http://www.allrussiantours.com/natural-attractions/pillars-of-weathering.html