Eastern Desert, by A Abdelhalim
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Geomorphology210
Geology Dep. Cairo Univ.
Content
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
Weathering and Erosion

Physical weathering

Chemical wathering

Bilogical weathering

Erosion

Soil
Geomorphology210
Geology Dep. Cairo Univ.
Weathering and Erosion
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Geomorphology210
Geology Dep. Cairo Univ.
Weathering: The processes that decompose rocks and
convert them to loose gravel, sand, clay, and soil are called
weathering (Breakdown).
 Physical weathering (without chemical composition changes)
 Chemical weathering (with chemical composition changes)
 Biological weathering (effects of organisms)
Erosion: The processes that pick up and carry off weathered
rocks and minerals are called erosion (Transport).
Rain, running water, wind, glaciers, and gravity are the most
common agents of erosion (Transporter).
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Geomorphology210
Geology Dep. Cairo Univ.
Physcial weathering
• Weathering Processes
Pressure release (uploading)
Frost wedging and salt weathering
Abrasion
Thermal Expansion
• Associated Weathering Landforms
Exfoliation Domes, Joint Sheets,….
Shattered Rocks (Fragmentation)
Talus Slopes
Crystal Growth Wedging (Wideing Fractures)
Pressure release, by A Abdelhalim
Frost wedging, by A Abdelhalim
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Geomorphology210
Geology Dep. Cairo Univ.
• Pressure release
Exfoliation domes, onion skin
and sheet joints
Exfoliation doms, by A Abdelhalim
Sheet joints, by A Abdelhalim
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Geomorphology210
Geology Dep. Cairo Univ.
• Frost wedging
Rock breakdown caused by
expansion of ice in cracks
and joints produced Talus
cone
Frost wedging, by A Abdelhalim
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Geomorphology210
Geology Dep. Cairo Univ.
• abrasion
Wind action is near to surface that
is causing eroded to the lower part.
• Thermal expansion
Shattered rock:
Extreme range of temperatures in
desert environments
Repeated swelling and shrinking of
minerals
Frost wedging, by A Abdelhalim
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Geomorphology210
Geology Dep. Cairo Univ.
Consequences of physical weathering
Reduces rock material to
smaller fragments that
are easier to transport
(more later)
Increases exposed
surface area of rock,
making it more
vulnerable to further
physical (and chemical)
weathering
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Geology Dep. Cairo Univ.
Cemical weathering
Chemical Weathering Factors influencing rate of chemical
weathering are: Particle size :Smaller the particle size the
greater the surface area and hence the more rapid the
weathering.
•Composition
•Climate
•Temperature
•Water Type
•Amount of vegetation
The three common chemical reactions are:
•Dissolution,
•Hydrolysis, and
•Oxidation.
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Geomorphology210
Geology Dep. Cairo Univ.
Dissolution: rock is completely dissolved (Produces
caves)
Soluble compounds, such as limestone, are dissolved
Oxidation: reaction with oxygen (rock rusts)
Minerals ions combine with oxygen to form an oxide (common
with iron)
Hydrolysis: reaction with water (new minerals form mostly
are clay minerals)
H+ ions displace other ions to form a different mineral
(common with feldspars)
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Geomorphology210
Geology Dep. Cairo Univ.
Dissolution
•Many ionic and organic compounds dissolve in water Silica,
K, Na, Mg, Ca, Cl, CO3, SO4
Acid Reactions
•Water + carbon dioxide <---> carbonic acid
•Water + sulfur <---> sulfuric acid
•H+ effective at breaking down minerals
Chemical Weathering
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Geomorphology210
Geology Dep. Cairo Univ.
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Wadi Sanur Cave
Geomorphology210
Geology Dep. Cairo Univ.
Oxidation
Oxidation can affect any iron
bearing
mineral,
for
example,
ferromagnesian
silicates which react to form
hematite and limonite
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Geomorphology210
Geology Dep. Cairo Univ.
Oxidation
Oxidation of pyrite and other sulfide minerals forms sulfuric
acid which acidifies surface water and rain
Pyrite + oxygen + water = sulfuric acid + goethite
(iron sulfide)
(iron oxide)
Fawakheir gold mine, by A Abdelhalim
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Geomorphology210
http://www.soes.soton.ac.uk/resources/collection/minerals/pages/M07-Goethite.htm
Geology Dep. Cairo Univ.
Hydrolysis
Hydration: attachment of water molecules to crystalline
structure of a rock, causing expansion and weakness
Hydrolysis: combination of hydrogen and oxygen in water
with rock to form new substances
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Geomorphology210
Geology Dep. Cairo Univ.
Hydrolysis
Feldspar + carbonic acid +H2O
= kaolinite (clay)
+ dissolved K (potassium) ion
+ dissolved bicarbonate ion
+ dissolved silica
Clay is a soft, platy mineral, so
the rock disintegrates
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Geomorphology210
Geology Dep. Cairo Univ.
Biological weathering
Can be both chemical and
mechanical in nature.
• roots split rocks apart
•
–
•
•
•
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roots produce acids
that dissolve rocks.
tree throw
burrowing animals
makes H+ ions available
(acid)
Geomorphology210
Geology Dep. Cairo Univ.
Spherical weathering
Diffusion of weathering into lattice creates corestones…
Egyptian basalt, by A Abdelhalim
Corestones result from differential
weathering
fractures.
Sixth October,
Egypt, by Aalong
Abdelhalim
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Geomorphology210
Geology Dep. Cairo Univ.
Course materials
Text
books:
Environmental
Remote
Sensing,
By
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
(from geology department library)
{The Earth Science and the Environment (Unit 3) (PDF online),
By GRAHAM R.THOMPSON, and JONATHAN TURK University of
Montana.
Guide presentation: find a pdf copy online at the Cairo University Scholar
website
http://scholar.cu.edu.eg/?q=ahmedabdelhalim
Classes-210
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Geomorphology210
Geology Dep. Cairo Univ.
21
Geomorphology210
Geology Dep. Cairo Univ.