69
Weathering and Erosion Notes
10/20/14
Starter: Warm Up:
Weathering and Erosion Notes
10/20/14
Application/Connection/: Notes
Paste Notes here
when done.
Practice:
Architects change the
landscape around us all the
time, what are natures 4
architects?
Exit: Explain how the
landscape is changed by the 4
architects.
70
October 20, 2014
AGENDA
Objective 7.8B Review
and Analyze the
effects of
weathering, erosion,
and deposition on the
environment in
ecoregions of Texas
by analyzing and
completing notes.
1 Starter
2. Notes
3. Exit
Table of Contents
Date
Lecture/ Activity/ Lab
10/16
Unit 5 vocabulary
10/17 Quiz/Writing
10/20 Weathering Notes
Page
65-66
67-68
69-70
She can plant trees and
other vegetation.
She could reduce the
slope of the land;
The
deposit of
sediment
where a
river flows
into an
ocean or
lake
Weathering
Mechanical
and
Chemical
What Caused This?
What is Weathering?
• First step to forming soil and
sedimentary rock
– Breakdown of rock into smaller pieces
– The smaller pieces do not move to a new
location until erosion carries them away
– Many types of weathering
What is Mechanical Weathering?
• Breakdown of rock into smaller pieces
without any change in the chemical
composition of its minerals
– Sometimes called “physical” weathering
– Rock is torn apart by physical force, rather
than by chemical breakdown
– Smaller pieces do not move to a new
location until erosion carries them away
Mechanical - Ice Wedging
 Ice Wedging
– Water fills joints of rocks and freezes
– Water expands 10% when it freezes, pushes
rock apart
– Repeated freeze and thaw cycles over the
years causes rock to break along joint
Mechanical - Exfoliation
• Exfoliation or unloading
– Rock breaks off into sheets along joints which
are parallel to the surface
– Caused by expansion of rock due to uplift and
removal of surface material that originally
buried the rock
Mechanical - Thermal
• Thermal expansion
– Repeated daily heating and cooling of rock
which causes rock to expand and contract
then break
– Different minerals expand and contract at
different rates causing the rock to split
Mechanical - Biotic
• Biotic – means life
– Weathering caused by living organisms
– Plant roots act as a wedge and widen cracks
– Other causes of biotic weathering are digging
animals, microscopic plants and animals,
algae and fungi.
What is Chemical Weathering?
• Breakdown of rock into smaller pieces because
of change in the chemical composition of its
minerals
– Chemical reactions break down the bonds holding
the rocks together, causing them to fall apart
– Chemical weathering occurs in all types of rock
– Rock reacts with water, gases and solutions
Chemical - Oxidation
• Oxidation - oxygen combines with other
elements in rocks to form new types of
rock
– New substances are usually much softer than
original, easier for other forces to break rock
apart
– Causes a “rusting” of the rock, often causes a
color change in the rock
Chemical - Carbonation
• Carbonation – Carbon dioxide (CO2) is
dissolved in water making carbonic acid
– Weak acid is formed when CO2 in the air
mixes with rain. This is the same acid found in
soft drinks.
– Acid is too weak to harm plants and animals
but slowly causes feldspars and limestone to
decompose
Erosion and Deposition
Agents, Forces, and Results
What Caused This?
What is Erosion?
• Erosion - moving of rock material from
one place to a new location
– For erosion to occur three processes must
take place: detachment of particles, lifting
them, and transporting them
– Many agents of erosion - flowing water,
moving ice, waves, gravity, or wind
– Sand consists of small pieces of rock that
have been weathered from a parent rock,
eroded, and deposited somewhere else
What Is Wind Erosion?
• Wind - responsible for wearing away rocks and
creating great deserts like the Sahara Desert
and Gobi
– Most effective in moving loose material
– Two main effects: (1) Wind causes small
particles to be lifted and moved away. (2)
Suspended particles may impact on solid
objects causing erosion by abrasion (rubbing).
– Occurs in areas where there is not enough
rainfall to support vegetation
What Is Water Erosion?
• Water - most influential force in erosion
– Ability to move materials from one location to
another over long distances
– The faster water moves in streams the larger
objects it can pick up and transport
– Responsible for wearing away of rocks in
rivers, lakes, and the oceans
What Is Wave Erosion?
• Waves - relentless pounding
– Erodes the softer, weaker parts of the rock
first, leaving harder, more resistant rock
behind
– Can take over 100 years to erode a rock to
sand
– Energy of waves along with the chemical
content of the water erodes the rock off the
coastline
What Is Gravitational Erosion?
• Mass movement - downward movement of
rock and sediments, mainly due to the force of
gravity.
– Moves material from higher elevations to
lower elevations where streams and glaciers
can pick up the material and move it to lower
elevations
– Process is occurring continuously on all
slopes, some act very slowly while others
occur very suddenly until equilibrium is
reached
What Is Glacial Erosion?
• Ice
- moves and carries rocks, grinding the
rocks beneath the glacier
– Glaciers pluck and abrade to cause erosion
– Plucking occurs when water enters cracks
under the glacier, freezing, and breaking off
pieces of rock that are then carried by the
glacier.
– Abrasion cuts into the rock under the glacier,
smoothing and polishing the rock surface
What is Deposition?
• Deposition - laying down of sediment that has
been transported by a medium such as wind,
water, or ice
– Process of erosion stops when the moving
particles fall out of the transporting medium
and settle on a surface. This settling is
deposition.
– If the speed of the medium slows or the
resistance of the particles increases, the
balance changes and causes deposition.
– Speed can be reduced by large rocks, hills,
vegetation, etc.
Deposition - Wind
• Wind speed can be related to variations in
heating and cooling
– Wind can transport fine particles in suspension
hundreds of km from its original source in the desert.
– Heavier material may be blown along the ground.
– Material is eventually deposited when the wind
changes direction or loses its strength.
– Obstacles, whether natural of man-made, will often
decide where the deposition occurs and the nature of
the feature formed.
Deposition - Water
• Running water enters a large, fairly still body of
water and its speed decreases.
– As speed decreases, water's ability to carry
sediments decreases
– Sediments carried by running water are deposited
where the slowing water can no longer move them.
Largest particles are deposited near the shore.
Increasingly smaller particles settle out farther from
the shore where the water is calmer
– Occurs in streams, rivers, oceans, etc.
Deposition - Ice
• Glacial flows of ice - become slower when the ice
begins melting
– Deposits left by glaciers are called moraines and
outwashes
– Moraines are large chunks of broken rock left at the base
and sides of the glacier as it melts and recedes
– Finer material is carried in the rivers that form when the
glacial ice melts. The deposits of these rivers look similar
to normal river deposits and are called outwashes
What’s the Difference?
• WEATHERING - think weather wearing
rock down
• EROSION - think of a road and traveling
• DEPOSITION – think of depositing money
in a bank
69
Weathering and Erosion Notes
10/20/14
Starter: Warm Up:
Weathering and Erosion Notes
10/20/14
Application/Connection/: Notes
Paste Notes here
when done.
Practice:
Architects change the
landscape around us all the
time, what are natures 4
architects?
Exit: Explain how the
landscape is changed by the 4
architects.
70