Download Weathering

Weathering, Erosion
& Deposition
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
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
What are the two types of
weathering?
2 Types of Weathering
Mechanical/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
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 Wedging
Alternating 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
Abrasion
Wearing 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 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 Contraction
Extreme changes in temperature may
cause cracking
Pressure Unloading / Exfoliation
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 Weathering?
The Chemical composition of
the rock is altered causing a change
in properties
Processes include:
• Hydrolysis
• Oxidation
• Acid Reactions / Carbonation
Hydrolysis
Reaction of water with other substances
Change is a very slow process
Examples are:
Feldspar  Kaolinite
Anhydrite  Gypsum
Kaolin mine in Central Georgia
Oxidation
Where 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 / Carbonation
Carbon reacts with other substances to
alter the chemical makeup of rocks
Example: 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 Weathering
The 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 climate that a rock is in is a
factor in the rate of weathering.
Cold Climates–
mechanical
weathering
breaks down
rocks rapidly
Warm, wet
climates –
chemical
weathering breaks
down rocks rapidly
How much exposed area of the rock will
also effect weathering
In which shape will weathering occur faster?
EROSION/DEPOSITION
The 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
Gravity
Deposition Formations
Delta Formation from
Deposition
Alluvial Fan from Deposition
REVIEW
What 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 Weathering
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 Weathering
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)
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