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Weathering, Erosion Weathering, Erosion & Deposition& Deposition
THINK!!!!THINK!!!!
Imagine the tiniest rock you have ever found. How did it get so small? It didn’t start out that way! What forces created this rock?
Weathering is the breaking down of rocks and other materials on the earth’s surface
What is the What is the difference difference between between
weathering and weathering and erosion?erosion?
• Weathering - processes at or near Earth’s surface that cause rocks and minerals to break down by air, water, plants and animals
• Erosion - process of removing Earth materials from their original sites through weathering and transport by water, wind or gravity
What are the What are the twotwo types of weathering?
2 Types of WeatheringMechanical/Physical
Weathering processes that break a rock or mineral into
smaller pieces without altering its
composition
Chemical Weathering processes that
change the chemical composition of rocks
and minerals
What is Mechanical/Physical What is Mechanical/Physical Weathering?Weathering?
A rock is physically changed without a change in chemical composition
Processes include:• Frost Action / Ice Wedging• Abrasion by wind and water• Plant and Animal Action• Thermal Expansion and contraction • Pressure Unloading / Exfoliation
Frost Action / Ice WedgingFrost Action / Ice WedgingAlternating freezing and thawing of water
causes material to break up• Example – Pot holes, Ice cubes in an
ice tray• Water expands between 4 and 0
degrees Celsius
Volume increases by 9%!!!!
The Bigger the crack gets, the more water it lets in……causing a snowball effect
Frost Action / Ice Wedging
AbrasionAbrasionWearing down or smoothing of a
material due to constant collisions• Example – Beach glass, sandblasting• Breakdown caused by friction• Rocks become rounded• Waterfalls may result
Abrasions
Plant and Animal ActionPlant and Animal Action• Plant root growth and uplift
fracture rocks• Animals burrowing also cause
breakdown of rocks• Actions also increase the
exposure of rocks to air and water
Plant Action
Lichen (moss) on a rock or growth of tree out of the rock
Animal Action
Thermal Expansion and Thermal Expansion and ContractionContractionExtreme changes in
temperature may cause cracking
Pressure Unloading / Pressure Unloading / ExfoliationExfoliation
Cracking at weak joints due to a release of pressure
Cause and effect of Exfoliation• Rock breaks off into leaves or sheets along
joints which parallel the ground surface• Expansion of rock due to uplift and erosion• removal of pressure of deep burial• Occurs often in bedrock when glaciers
recede
Exfoliation• Peeling away of surface layers, caused by changes
in temperature, pressure or vegetation (trees, grass, vegetation growing on rocks.)
• Roots wedge into pores and cracks, splitting the rock
Dome Exfoliation
What is Chemical What is Chemical Weathering?Weathering?
The Chemical composition of the rock is altered causing a change
in properties
Processes include:•Hydrolysis•Oxidation•Acid Reactions / Carbonation
HydrolysisHydrolysisReaction of water with other
substancesChange is a very slow process
Examples are:
Feldspar Kaolinite
Anhydrite Gypsum
Kaolin mine in Central Georgia
OxidationOxidationWhere Oxygen combines with
other substances to produce rust
Oxidation in the presence
of water takes on a
reddish- yellow brown
color
Oxidation of basalt
Acid Reactions / Acid Reactions / CarbonationCarbonation
Carbon reacts with other substances to alter the chemical makeup of
rocksExample: Carbonic acids (water + carbon dioxide) dissolve limestone
which can results in the formation of underground caves
Nitric acids produced by the decay of organic material can alter soil composition
Caves are formed when Carbonic Acid dissolves
limestone
Stalactites (from the top) and Stalagmites (from the bottom) are formed in a limestone cave as a result of Chemical Weathering
Acid Rain has a drastic effect on rocks!
Nitric Acids in Soil
When organisms or plants decay Nitric Acid is produced. This is absorbed into the soil and the chemical make-up of the soil has been changed.
Differential WeatheringDifferential WeatheringThe variable rate of which rocks weather is called differential weathering
Factors affecting the rate of weathering include:
•Composition (granite vs. limestone) •Climate (hot, wet, cold, dry) •Rock size (surface area)
Rocks weather at different rates due to differences in mineral composition. The harder the rock, the slower the rate of weathering is.
Some minerals are more Stable at the earth’s surface than others! These take longer to weather. Composition dictates hardness which determines resistance to weathering.
The climateclimate that a rock is in is a factor in the rate of weathering.
Warm, wet climates – chemical weathering breaks down rocks rapidly
Cold Climates– mechanical weathering breaks down rocks rapidly
In which shape will weathering occur
faster?
How much exposed area of the rock will How much exposed area of the rock will
also effect weatheringalso effect weathering
EROSION/DEPOSITIONEROSION/DEPOSITIONThe process of removing Earth
materials from their original sites through weathering and transport agents or forces
Transport Agents or Forces include:• Water (Rain, streams, rivers, oceans, and
ice/glaciers)• Wind• Gravity
Stream Erosion and Deposition
Streams
Glaciers
Wind Transport of Dust
Wind Transport of Dust
GravitGravityy
Deposition Formations
Delta Formation from Deposition
Alluvial Fan from Deposition
REVIEWREVIEWWhat is the difference between
Weathering and Erosion?Weathering - processes at or near Earth’s
surface that cause rocks and minerals to break down by air, water, plants and animals
Erosion - process of removing Earth materials from their original sites through weathering and transport by water, wind or gravity
REVIEW- 2 Types of REVIEW- 2 Types of WeatheringWeathering
Mechanical/Physical Weathering - A rock is physically changed without a change in chemical composition
• Frost Action / Ice Wedging Alternating freezing and thawing of water causes material to break up
• Abrasion by wind and water Wearing down or smoothing of a material due to constant collisions
• Plant and Animal Action Plant root growth and animals burrowing increase the exposure of rocks to the air and water and causes breakdown
• Thermal Expansion and contraction Extreme changes in temperature causes cracking
• Pressure Unloading / Exfoliation Earth’s forces can push rock that formed deep underground up to the surface. The pressure causes the rock to expand and crack. This leads to exfoliation.
REVIEW -2 Types of REVIEW -2 Types of WeatheringWeathering
Chemical Weathering - Processes that change the chemical composition of rocks and minerals
• Hydrolysis Water is very slow reaction and the main cause of chemical weathering.
• Oxidation Where Oxygen combines with other substances to produce rust
• Acid Reactions / Carbonation Carbon reacts with other substances to dissolve and alter the chemical makeup of rocks forming caves. Nitric acid produced by the decay of organic material can alter soil composition
REVIEW (Continued)REVIEW (Continued)Differential Weathering - The variable rate of
which rocks weather is called differential weathering. Most weathering occurs over long periods of time- hundreds, thousands, or even millions of years.
Factors affecting the rate of weathering include:• Composition (granite vs. limestone) What
minerals a rock is made from • Climate (hot, wet, cold, dry) hot, wet regions
weather rocks faster than cold, dry ones • Rock size (surface area) How large or small a
rock’s surface is