Download Weathering - Madison Public Schools

Weathering and Erosion
Earth Processes
Hill Science 6
Weathering


Weathering is the wearing or breaking of
rocks into smaller pieces by water,
temperature changes, wind, living things,
or chemical changes.
The fragments of rock stay in place.
Weathering



There are two types of weathering:
Mechanical weathering
and
Chemical weathering
Mechanical Weathering

The physical breakdown of rocks into
smaller pieces, gradually reducing them to
the tiny particles that make up soil.
Agents of Mechanical Weathering





Wind, water, gravity, glaciers - Abrasion
Ice – ice wedging
Pressure change – inside earth to surface
of earth - exfoliation
Temperature change – alternating hot to
cold - exfoliation
Plants and animals – organic activity –
root pry, animal burrowing
Wind
Arches National Park, Utah, USA
These rocks
have been
blasted by
wind and
sand causing
them to
become
rounded.
Type of Weathering?
WIND ABRASION
Water
The Grand Canyon created by the Colorado River
Water
Friction and
Repeated
Impact
Type of weathering?
Abrasion
Glacial Action
Glacial ice will scour and
abrade the surface it slowly
scraps over. Glaciers form
broad U-shaped valleys in
their wake.
What type of weathering?
Abrasion
Exfoliation
On Half Dome, the rock
is peeling away from the
mountain in layers just
like an onion. This is
called exfoliation which
is caused by the change
in pressure when a rock
that was formed
underground is thrust to
the surface.
Pressure Changes
Peeling of the surface
of a rock due to
pressure change.
What type of
weathering?
Exfoliation
Temperature Changes

Warm to cold and back again

Splits rocks or peels off layers
Temperature Change
Repetition of cooling
and heating over
and over again.
When might that
happen?
What type of
weathering?
Exfoliation
Temperature Changes

Water to Ice



Ice Wedging
Heaving
Glaciers
Ice Wedging
Water fills a crack, freezes and
expands making a larger crack.
This process repeats over and
over.
Ice wedging slowly breaks up this sedimentary
rock into unusual shapes.
Frost Heaving
Repetitious freezing and
thawing of water under the
patio causes the surface to
heave when the ice expands
under the patio and contracts
when ice melts.
Organic Activity
Plants
What do you
see happening
here?
Root Pry
Plant Roots
The action of plant roots is called
root pry
Animal Activity- how does this
cause weathering?
Pictures of Mechanical Weathering

Link to pictures

Link to places
Mechanical Weathering


1. Abrasion – the wearing away of solid
particles; caused by wind, water, glacier
ice, and gravity
2. Ice wedging - when water in a crack
or hole in a rock freezes it expands
making the opening larger. Melting moves
it deeper into the opening and the process
repeats; Caused by the repeated thawing
and freezing of water.
Mechanical Weathering



3. Organic activity – people, animals, or plants
break up rock by digging or burrowing. Root
pry the splitting of rock caused by the
expanding root growing deeper.
4. Exfoliation – flaking off of the surface of the
rock; caused by change in pressure from inside
earth where formed to lower surface pressure or
temperature change.
5. Heaving – rocks shift and crack; caused by
repeated freezing and thawing
Chemical Weathering

Chemical weathering is the breaking down
of rocks by changing their chemical
composition.
Agents of Chemical Weathering



Acid precipitation - carbonation
Acid from plants – humic acids
Oxygen - oxidation
Water

Carbonation
- Water
weathers rock
by dissolving
it
Carbon Dioxide
CO2 dissolves in rain water and creates
carbonic acid
 Carbonic acid easily weathers limestone and
marble (CaCO3)
 A cave may
result
Type of weathering?

carbonation
 Chemical
Weathering
 Carbonation
Sinkhole
Karst terrain
Stalactites
and
Stalagmites
Result of Rainwater Weathering
Type of Weathering?
carbonation
Humic Acids
Acid from Lichens Weathering Rock
Living Organisms

Lichens that grow on rocks produce weak
acids that chemically weather rock
Type of weathering?
Humic acids
Oxygen


Iron combines with
oxygen in the
presence of water in
a process called
oxidation
The product of
oxidation is rust
Oxygen Caused Chemical
Weathering
Type of weathering?
oxidation
Chemical Weathering



Carbonation-Acid precipitation - CO2 dissolves
in rain water and creates carbonic acid which
easily changes the chemical composition of
certain rocks (limestone and marble)
Humic Acids – lichens and moss produce acids
that break down the minerals found in rocks
they are growing on
Oxidation – when oxygen combines with
another substance to create an entirely new
substance Fe + O produces iron oxide (rust)
Weathering and Erosion



Weathering and erosion are called
external processes because they occur at
or near Earth’s surface.
Weathering and erosion are part of the
rock cycle because they are responsible
for transforming solid rock into sediment.
So how do they differ?
Weathering or Erosion?



Weathering is the breaking of rocks into
smaller pieces.
Erosion is the moving of weathered
sediments from one place to another.
Erosion is the transportation of
weathered material by the mobile agents
of wind, water and glacial action (ice).
Video Links

Formation of the Grand Canyon

Grand Canyon Lava Flows

Ireland: Glaciated Landscape
Principal of Uniformity

Belief that the processes that changed our
world in the past are still in existence
today and continue to change the earth.
Chemical Weathering

Chemical weathering is the breaking down
of rocks by changing their chemical
composition.
Chapter 10
Rates of Weathering
Differential Weathering
• What Is Differential Weathering?
Differential weathering is a process by
which softer, less weather resistant
rock wear away and leave harder, more
weather resistant rock. The image
below is an example of differential
weathering.
Devil’s Tower,
Wyoming
Rates of Weathering

What determines how quickly a rock will
weather?




Type of Rock (differential weathering) – some
rocks weather more quickly than others, due to
composition or condition
Pollution – causes acid precipitation which will
weather rocks more quickly
Climate – tropical fastest due to more moisture and
plant action, deserts slowest due to lack of humidity
Size – smaller rock has more surface area to volume
than a larger rock. More surface is exposed to
weathering, so it will weather more quickly.
Chapter 10
Rates of Weathering
Chapter 10
Rates of Weathering
Weathering and Elevation
• High Elevations Rocks at higher elevations, as
on a mountain, are exposed to more wind,
rain, and ice than rocks at lower elevations.
• Steep Slopes The steepness of mountain
slopes increases the effects of mechanical
and chemical weathering. Steep slopes cause
water and sediments to quickly run down the
side of the mountain.
Weathering Website

Weathering animation click here

http://www.uky.edu/AS/Geology/howell/goodies/elearning/module07swf.swf