Download Weathering, Erosion and Deposition

Weathering, Erosion
and Deposition
Ms. Sauer
Weathering, Erosion, and Deposition
Weathering – the breakdown of rocks into smaller
pieces, called sediments.
Erosion – the process where the sediments are
transported by wind, gravity, glaciers, man, and running
water.
Deposition – the process whereby these sediments are
released by their transporting agents (dropped).
Weathering breaks down the rocks, erosion
moves the particles, and deposition drops the
sediments in another location.
What is Weathering?
• The Chemical and Physical Breakdown of
rocks on or at Earth’s Surface into smaller
fragments
• Weathering Occurs when rocks are exposed
to the hydrosphere or atmosphere.
http://www.youtube.com/watch?v=LS0GDLP8oIo&feature=related
What are atleast three
examples of
weathering?
Weathering
• Physical /
Mechanical
–
–
–
–
Frost Action
Abrasion
Exfoliation
Plant & Animal
• Chemical
– Oxidation
– Hydration
– Carbonation
(including Sink
Holes, Karst
Topography,
Stalactites, &
Stalagmites)
– Organic Decay
Mechanical/ Physical Weathering
• When rocks are physically cracked, split, or
broken into smaller pieces known as
SEDIMENTS.
• Rock’s chemical makeup stays the same.
• Physical Weathering is Common in Mid-Latitude
Climates where freezing and thawing occurs
• COLD & MOIST climates produce more
mechanical weathering
Types of Mechanical Weathering
• 1) Frost Action- breakup of rocks caused by
alternating freezing and thawing of water.
• Very common in Cold, Wet Climates
Physical Weathering:
Ice/Frost Wedging/Action
Frost action is the breakup of rocks caused by alternate
freezing and thawing of water. Water condenses or seeps
into the smallest cracks or spaces in rock as well as larger
openings. When the water freezes, it expands, forcing the
rock grains apart. When ice melts, the rock is more porous
than before.
Repeated freezing and expanding of water in these spaces
will cause the rock to crumble into smaller pieces.
Physical Weathering:
Frost Wedging
Frost Action
Frost Wedging
nd
2
Type
• 2) Abrasion- physical wearing down of
rocks as they rub or bounce against one
another.
• Dry, Windy Areas
• Common under glaciers, and in stream
channels
Physical Weathering:
Abrasion
The physical wearing down of
rocks as they rub or bounce
against each other.
Abrasion is most important in
dry windy areas, under
glaciers, or in stream channels.
Physical Weathering:
Abrasion
ABRASION - A physical erosion process, the wearing down of
rock particles by friction due to constant scratching. Where solid
particles are moved across a solid surface with the help of wind or
water.
Mojave Desert, CA
Valley of Fire, Nevada
Glacial Abrasion in Bedrock
Source: Tom Bean
Physical Weathering:
Abrasion
rd
3
Type
• Exfoliation- the peeling away of large
sheets of loosened material at the surface of
a rock
Physical Weathering:
Exfoliation
The peeling away of large sheets of loosened
material at the surface of a rock.
Exfoliation
th
4
Type
• Plants/ Animals- plant roots growing
through the rocks and breaking them up.
• Ants, earthworms, and other small animals
burrowing into cracks breaking rocks down
further.
Physical Weathering:
Root/Plant Wedging/Action
•Large shrubs and trees growing through cracks in boulders
may break the rocks apart.
•Smaller plants that grow on rocks, such as lichens and mosses,
wedge their tiny roots into pores and cracks, splitting the rock
as they grow.
•Ants, earthworms and other burrowing animals digging holes
in the soil break it down further.
Physical Weathering:
PLANT ROOTS
Physical Weathering:
Animal Action (Burrowing)
What type of mechanical
weathering?
Abrasion
What type of Mechanical
Weathering?
Exfoliation
What type of Mechanical
Weathering
Frost Action
How did this rock get this way?
Abrasion
What happened to this road?
Frost Action
How did this happen?
Plant & Animal
Chemical Weathering
• Rock is broken down by chemical action, which
results in a change in the composition of the
rock.
• Intense in warm, moist climates
• Minerals in the rock change
• New minerals created by chemical
reaction
• WARM & MOIST climates produce more
chemical weathering
http://www.youtube.com/watch?v=Sw58a4yjFtc
2. Chemical Weathering – the breakdown of rocks and minerals
into smaller pieces by chemical action. The rocks breaks down at
the same time as it changes chemical composition. The end result
is different from the original rock. There are 4 types of chemical
weathering:
Chemical Weathering:
1. Oxidation – oxygen combines with the elements in the rock and it
reacts. This the scientific name for rust.
2. Hydration – water can dissolve away many earth
materials, including certain rocks.
3. Carbonation – carbon dioxide dissolves in water to form
carbonic acid. This makes acid rain which chemically weathers
(dissolves) rocks. Other acids also combine with water to make
acid rain.
4. Organic Decay – occurs when acids, which are formed when
plants and animals decay, dissolve in water. The acid solutions
dissolve rock minerals much the same way as in carbonation.
Types of Chemical Weathering
• 1) Oxidation- Oxygen uniting chemically
with minerals.
• Oxygen and Iron (Fe)- Create Rust
Chemical Weathering:
• Iron combines
with oxygen in
the presence of
water in a
processes called
oxidation.
• The product of
oxidation is
rust.
Oxygen
Chemical Weathering:
Oxidation
nd
2
Type of Chemical Weathering
• 2) Water / Hydration
• Water weathers rock by dissolving it.
rd
3
Type of Chemical Weathering
• 3) Carbonation- CO2 unites chemically with
minerals
• When CO2 is dissolved in water it forms
weak carbonic acid. Carbonic Acid
dissolves large masses of limestone. This
creates caves, caverns, and other structures
in bedrock.
• Sinkholes- CO2 Acid dissolves limestone
creating Karst Topography
Chemical Weathering:
Carbon Dioxide
• CO2 dissolves in
rain water and
creates carbonic
acid.
• Carbonic acid
easily weathers
limestone and
marble.
Chemical Weathering:
Acid Rain
• Compounds from burning coal, oil and gas
react chemically with water forming acids.
• Acid rain causes very rapid chemical
weathering.
Chemical Weathering:
Carbonation
• Sink Holes – saucer-shaped holes on the surface of the
land are left when carbonic acid dissolves limestone in
the ground.
• A limestone area pitted with sink holes is called Karst
Topography.
• In caves, the carbonic acid solution containing the
dissolved limestone drips from the roof of the cave.
Evaporation leaves limestone deposits on the ceiling and
floor. The icicle-like deposits that “grow down” from the
ceiling are called stalactites. Those deposits which
“grow up” from the ground are called stalagmites.
Chemical Weathering:
Sink Holes
Chemical Weathering:
Devil’s Throat, Nevada
Sink Holes
Chemical Weathering:
Sink Holes
Carbonation causing a sink hole
Guatemala City, June 2010
More than 100 deaths, approx 200ft deep
Chemical Weathering:
Karst Topography
• A type of landscape created by chemical
weathering of limestone
• Located in rainy regions where there is
limestone near the surface, characterized by
sinkholes and caves.
Karst Topography
Chemical Weathering:
Stalactites
“grow down”
Chemical Weathering:
Stalagmites
“grow up”
th
4
Type of Chemical Weathering
• Organic Decay- acids from dead plants and
animals dissolve rock.
Chemical Weathering:
Living Organisms
• Lichens that grow on rocks produce weak
acids that chemically weather rock.
There are 4 factors that effect the rate of weathering:
1. Surface Area (exposure) - Exposing more surface area will
increase the rate of weathering.
2. Particle Size – Larger particles weather slower and smaller
particles weather at a faster rate.
3. Chemical Composition (what a rock is made of) – Certain rocks
and minerals are naturally weaker than others, while others are more
resistant (stronger).
4. Climate – Warmer, moister climates have the most weathering.
Heat & Water speed up all chemical reactions. This is the most
important factor in weathering.
1 & 2) Particle Size and Surface Area
•The weathering rate of rock material
varies inversely with particle size. In
equal quantities of the same rock,
the smaller the particles, the greater
the weathering rate – the faster the
particles weather.
•This rate difference occurs because the
total surface area of the smaller
particles is greater than the total
surface area of the larger particles.
•Larger, solid pieces of rock weather
more slowly than do smaller, loose
pieces of the same rock.
1 & 2) Particle Size and Surface Area
Particle Size- Smaller the Particle Size the faster the weathering.
Smaller particles have a greater surface area.
1) Surface Area
3) Mineral Composition & Amount of Weathering:
•Rock particles weather at different rates depending on
their mineral composition. Because the hardness of
minerals differs, different minerals have different
resistances to weathering.
•Hard rocks weather more slowly than soft rocks.
3) Mineral Composition & Amount of Weathering:
Mineral Composition- Hardness of minerals differ,
minerals have different resistances to weathering. Harder
the rock the slower it weathers
4) Climate
•Weathering of rocks occurs at a faster rate
in humid climates than it does in dry
climates.
•This is explained by the fact that most
weathering agents – frost action,
carbonation, organic decay, etc. – require, or
are more effective in the presence of
moisture.
Climate and Weathering
Climate Conditions and Types of Weathering:
•Physical weathering is more
pronounced in moist climates,
where the wide range of
temperatures cause alternate
freezing and thawing.
•Chemical weathering is more
intense in warm, moist climates.
•The amount of moisture
available is the key factor in
weathering.
•Usually, the more moisture
available, the more weathering
occurs.
What type of weathering occurs in an area that has an average of 165 cm of rain each
year and an average temperature of 18°C? strong chemical
What type of weathering occurs in an area that has about 140 cm of precipitation each
year and an average temperature of 5°C?
moderate chemical with frost action
Disappearing Lake
• http://www.youtube.com/watch?v=dHol4IC
eDoo
What is Erosion?
• Erosion – Movement of weathered
material from one place to another.
What are the major causes
of erosion?
Factors of Erosion & Characteristics
of Transported Sediment:
1. Gravity – moves small & large particles;
unsorted.
2. Wind – moves small particles; sorted.
3. Running Water – moves small & large
particles; sorted; smooth & round.
4. Glaciers - moves small & large particles;
unsorted.
5. Waves / Beaches - moves small particles;
sorted.
st
1
Factor of Erosion:
• Gravity – moves small & large particles.
- unsorted deposition.
- pulls rocks down slopes.
- causes particles to be angular.
GRAVITY
Gravity:
• Gravity is the primary driving force behind
all transporting (erosional) systems.
• Gravity provides each agent (running water,
glaciers, or winds) with enough kinetic
energy to transport sediments.
Avalanche
Mudslides
Landslides
Videos:
• Avalanche video:
http://www.youtube.com/watch?v=B0RWLxOFG
LY
• Mudslide Video:
http://www.youtube.com/watch?v=51C7vEAVbx
k
• Landslide Video:
http://www.youtube.com/watch?v=mknStAMia0Q
Mount Rushmore
It will not be there forever!!
There is a pile of weathered
material at the bottom. It is
slowly being eroded down hill
by gravity.
***However, maintenance is done to maintain it***
You can identify which agent of erosion transported each sediment by looking at
a few characteristics:
Gravity – sediments that are transported by gravity are found in
piles at the bottom of cliffs or steep slopes. They appear angular
and unsorted.
nd
2
Factor of Erosion:
• Wind – moves small particles.
- stronger the wind, bigger the sediment
(FAST= carries more).
- sorted deposition of sediment.
- Carries loose rocks through air & scrapes
at other rocks
- Causes particles to be frosted or angular.
Wind Erosion
Wind Erosion
Wind Erosion
Wind Erosion
Wind:
• The greater the velocity of wind, the larger
the particles it can carry.
• Although erosion by wind is generally
thought of as occurring in deserts or along
beaches, dust storms can occur inland
following long periods of drought.
You can identify which agent of erosion transported each sediment by looking at
a few characteristics:
Wind - sediments that have been transported by wind appear
pitted (random holes) and frosted (glazed look) and are deposited
in sorted piles. Only very small particles can be transported by
wind.
rd
3
Factor of Erosion:
• Glaciers – A moving mass of ice
- unsorted
- moves small & large particles.
– Picks up and drags rock- grinds across other
rocks
– Digs into land, widens valleys
Glaciers
New Zealand
You can identify which agent of erosion transported each sediment by looking at
a few characteristics:
Glaciers – sediments that have been transported by glaciers appear
scratched, grooved, and are deposited in completely unsorted
piles, because they were dropped during melting. Also, boulders
can only be transported by glaciers.
th
4
Factor of Erosion:
• Running Water – moves small & large
particles
- faster water moves, bigger the sediment
(FASTER= carries more)
- smooth & round
- sorted
Three Ways Rivers Carry Sediment:
1. Rolling or Bouncing Along the Bottom
2. Suspension – floating
3. Solution - dissolved
Running Water
Running Water
Running Water:
• Running water is the primary agent of
erosion on Earth. Most running water is
found in rivers or streams.
You can identify which agent of erosion transported each sediment by looking at
a few characteristics:
Running Water – sediments that have been transported through
running water appear rounded and smooth and are deposited in
sorted piles.
th
5
Factor of Erosion:
• Waves / Beaches - moves small particles
- sorted deposition
– Crashing waves chip away at rocks
– Abrasion forms cliffs, arches and caves
Wave Erosion
Wave Erosion
Video:
• Smith’s Point Beach Erosion Video:
http://www.youtube.com/watch?v=B24JIhi
7Nlc
Effects of Humans on Erosion:
• Humans add to the erosion of the land through
individual and societal activities.
• The natural processes of erosion can take a very
long time; human activities can erode the land
almost overnight (earth moved for roadways /
railroad; surface exposed to erosion by wind or
running water).
• Human activities contribute more than ever before
to the erosion of Earth’s surface.
There are 5 ways that man can cause erosion:
1. Forestry – all vegetation of removed,
and without roots, the soil will erode
away.
2. Strip Mining – removing rock cover to
get to the resources below, which causes
the loose sediments to erode away.
3. Construction – the clearing of land to
build buildings/houses also causes all
loose soil to erode away.
4. Improper Farming – not plowing the
land at right angles to slopes causes soil
to erode away.
5. Salting Highways – the salt is washed
off the road to the sides, where it
prevents vegetative growth along the
sides.
What is Deposition?
• Deposition – Eroded rock particles are
dumped off or deposited in a new location
http://www.youtube.com/watch?v=AE771AdF5dM
DEPOSITION
DEPOSITION - When
the carrying power of
an erosional agent
(wind, water, gravity,
glaciers) decreases.
Particles being carried
will be dropped or
deposited in a process
called sedimentation.
Mississippi Delta
DEPOSITION
Dissolved minerals fall out of the solution when water evaporates.
This depositional process is called precipitation.
Salt Farming
4 Factors that affect Deposition
Rate
• 1. Particle Size – all other factors being
equal, larger particles settle more quickly
than smaller particles.
• The smaller the particle (clay, silt) the slower it
will settle out. Larger sediments (cobbles,
boulders) will settle quickly.
2nd Factor that affects
Deposition Rate
• 2. Particle Shape - All other factors being
equal, smooth, spherical particles settle
faster than angular, flatter particles.
Why is this?
Answer
• Friction is decreased when a particle is rounded
and therefore it settles faster. It’s like it’s more
aerodynamic - like a sports car. But in this case,
it’s hydro-dynamic.
3rd Factor that affects
Deposition Rate
• 3. Density - If two particles have the same
basic size and shape, the denser particle will
settle faster.
Which will settle faster – a glass marble or a
lead marble? (they are both the SAME
SIZE)
4th Factor that affects
Deposition Rate
• 4. As the stream
slows down, the
larger particles
settle first
Silt particles are very small, slow moving water can
carry it.
Sorting of Deposited Particles
Horizontal Sorting
• Final deposition of particles (sediments) at
the mouth of a stream. This is due to the
faster flowing stream emptying into a
slower larger body of water.
The sediments that were once carried down
the stream are arranged from largest to
smallest.
Horizontal Sorting – a situation where moving water enters a
larger, still body of water slowly, and causes the larger particles to
be deposited closer to the shoreline. Particle size decreases as you
move away from the shore.
Delta – a fan shaped deposit that forms at the mouth of a
river/stream when it enters a larger body of water. This is seen
under the water. The particles are horizontally sorted.
Horizontal Sorting
Nile River Delta, Egypt
Vertical Sorting
• Happens in QUIET WATER (still – lake, pond)
• Particles sort out from bottom to top in layers
• On bottom – largest, roundest, densest
particles
• On top – smallest, flattest, least dense particles
• Can occur when a depositional event, like a
landslide, dumps a large volume of unsorted
sediments into a still body of water like a lake
• It creates “graded beds” of sediments
http://www.youtube.com/watch?v=3CavQ1o-CSc (0:33)
Graded Bedding/Vertical Sorting – a situation where larger
particles settle on the bottom and smaller particles settle towards the
top. This happens naturally when a fast moving river/stream meets a
large standing body of water. This happens because the velocity of
the water decreases very quickly. (A waterfall emptying into a lake)
Graded Bedding
One
depositional
event
One
depositional
event
Alluvial Fan - a fan shaped deposit of sediments that forms
when a stream/river flows out of a mountain on to flat, dry plains.
These are not under water and are very visible. This only
happens on the land. You can call it a “land delta”.
Graded Bedding
One
depositional
event
One
depositional
event
CROSS BEDDING
• Layers of sediments deposited at angles. The angle
shows the direction of movement. (wind and water
erosion is responsible for most cross bedding)
Cross-Bedding – a situation where
layers of sediments are deposited
at angles to one another as a result
of a change of direction of the
erosional agent.
These are usually found in sand
dunes, deltas, and alluvial fans.
(3) Deposition
(3) Glacial deposits are unsorted, and river deposits are sorted.
(4) Bigger particles are generally deposited first.
(2) The rate of deposition is greater than the rate of erosion.
(1) 50 cm/sec
(4) Running
Water
(a) The velocity decreases
(b) Clay
Erosion and Deposition
• Erosion
• Movement of weathered
material from one place to
another.
• Deposition
• Eroded rock particles are
dumped off or deposited in a
new location
Erosion and Deposition
• Wind
• How does it erode?
– Carries loose rocks through airscrapes at other rocks
– FAST= carries more
• How does it deposit?
– When it slows down, dumps off
rocks to form dunes/piles
Erosion and Deposition
• Gravity
• How does it erode?
– Pulls rocks down slopes
• How does it deposit?
– Materials pile up at lower
elevations
Erosion and Deposition
• Glaciers
• How does it erode?
– Moving mass of ice
– Picks up and drags rock- grinds
across other rocks
– Digs into land, widens valleys
• How does it deposit?
– Rocks dump when glacier melts
– Makes moraines and drumlins
Erosion and Deposition
• Running
Water
• How does it erode?
– Drags rocks along in water
– Bumping of rocks widens and
deepens waterways
– FASTER= carries more
• How does it deposit?
– Where water slows down, rocks are
dumped off
– Form deltas/fans or plains
Erosion and Deposition
• Waves
• How does it erode?
– Crashing waves chip away at
rocks
– Abrasion forms cliffs, arches
and caves
• How does it deposit?
– Carried particles are dumped on
shore
– Form beaches, sand bars, spits
Soils
Soil forms from the weathering of the rock below it. The solid rock below is
called Bedrock. The rock is exposed to wind, rain etc… The rock breaks down
over time to form soil. Soil has different layers called Soil Horizons.
O- Horizon = the very thin surface covering (not really a layer)
A – Horizon (TOPSOIL) = dark surface soil that contains a lot of
living material and dead plant/animal remains (humus). This is the
layer with all of the nutrients needed to grow plants.
B-Horizon (SUBSOIL) = lighter colored soil with less nutrients and
more clay
C-Horizon (REGOLITH) = larger rock fragments that sit on top of
the unweathered bedrock
Soils
There are 2 types of soil:
1. Transported
2. Residual
Transported soils are the most
common throughout New York
State!!!!!!!!
Transported Soils – soils that formed in one place and were
transported to their present location by glaciers. You can tell
when the soil does not chemically match the bedrock below it.
Residual Soils – soils that are located above the rocks that they
formed from. In other words, the soil chemically matches the
bedrock below it, because it is a product of that rock’s weathering
over time.
Soil Conservation:
Depletion occurs when too many
nutrients are removed from the
soil for a crop to grow.
• Crop Rotation is a type of
farming used to prevent
depletion, crops must be
alternated on the same soil
each year.
• Contour Plowing - crops are
planted in rows parallel to the
contours of the land.
• Strip Cropping - involves
planting strips of low cover
crops between strips of other
crops.
Soil Conservation:
Sometimes topsoil is carried down the slopes
of a hill by water. To prevent this the land
can be terraced or wind breaks can be set
up.
• Terraced – the hill is terraced into a series
of level steps.
Soil Conservation:
• Wind Breaks (belts of trees along the edge
of farming areas) are set up to prevent the
winds from carrying topsoil away.
If overgrazing occurs, the land can dry out and the area become
a desert. This process is known as desertification.