Transcript Weathering, Erosion, Deposition, and Landscapes

Weathering, Erosion,
Deposition, and Landscapes
forces at work
© Lisa Michalek
Weathering
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The
breakdown
of rocks
due to
physical or
chemical
changes
Physical Weathering
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Changes the size and/or shape of a rock without changing
the chemical composition
In frost action, water seeps into cracks in rocks. The
water expands as
it freezes and makes
cracks in the rock a
little larger
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When the
ice melts and the liquid
evaporates, the rock
is left more porous
Over time, the freezing
and melting in the cracks
will cause the rock to
crumble
Physical Weathering
 Plant
roots grow in rock
crevices and gradually push
the rock apart
 Animals that burrow beneath
the ground will expose new
rock surfaces to weathering
 Abrasion occurs when rock
particles are carried
in water, they
bump and rub
against other rocks
Chemical Weathering
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When rocks are exposed to the atmosphere
and hydrosphere, they often undergo
changes in the chemical composition of
rock, forming new substances
Usually requires heat and water to bring
about chemical changes
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Therefore, it takes place more rapidly in warm,
moist climates
Observe an animation of cave formation.
Soil Formation
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Soil is a mixture of weathered
rock and organic remains the
usually covers bedrock
The weathering of soil produces
horizon layers
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The top layer is usually the best
for growing crops because it is
rich in organic remains called
humus
The next layer is usually mineral
enriched from groundwater
transporting minerals
The lowest layer is composed of
broken-up bedrock
Soil Formation
Erosion of Sediments
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Sediments are rocks that have been
broken into fragments
Erosion is the transporting of sediments
away from their
place of origin and
depositing them
elsewhere
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Gravity, water,
wind, and ice
erode sediments
Forces of Erosion and
Deposition
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The 1st type of Erosion and
Deposition is: Gravity
-Causes the downward movement
of sediments called mass
movement
a.
A sign of gravity erosion: Landslide –
soil, rocks, & boulders move down a
slope or off a cliff
Landslide (slow loading)
LANDSLIDE
Another sign of Gravity causing
Erosion: :
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b. Mudflow – water mixes with rock and soil
and moves down a slope. Usually happens
after rain and water content can be as high
as 60%.
A sign of gravity erosion: Slump
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Slump – loose,
water-filled earth
(permeable) sits on
top of a water
proof
(impermeable)
layer. The loose
earth changes
position.
Slump animation
Slump
Another sign of gravity erosion:
Creep
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is a very, very slow form of mass
movement. It's just a slow adjustment of
soil and rocks. Gravity always causes the
rocks and soil to settle just a little farther
down slope than where they started from.
Creep
Erosion by Water
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The smallest particles are carried in solution
The largest and most dense particles are
rolled or bounced along the streambed
Particles of low density, such as organic
remains, are carried along the surface by
flotation
Deposition
waterfall
Velocity of Streams
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The velocity of a stream is controlled by the
slope and the amount of water flowing in the
stream (discharge). As velocity increases the
kinetic energy also increases.
As the stream gradient
increases, so does the
velocity of the water
flowing in the stream
Velocity is also increased
by an increase in the
quantity of water
in the stream
Velocity of Streams
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There is a direct
relationship
between the
velocity of a
stream and the
size of the
particles it can
transport
Large grains of
sediment can only
be eroded by
fast-moving water
Velocity of Streams
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Streams with broad, flat valleys often develop Sshaped curves called meanders
At the bends in the stream, the fastest-flowing
water swings to the outside of the bends, causing
erosion along the outer bank
The slowest moving water stays to the inside of the
bends, causing deposition
Meander oxbow lake
waterfall
Erosion by Wind
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Wind can pick up loose rock materials, such
as sand, silt, and clay, and carry them away
Wind erosion occurs mostly in dry areas,
such as deserts and beaches
Sand blown by
the wind can
erode down
material on
a rock’s surface
dune formation
Erosion by Wind
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Wind erosion happens when the soil is left
unprotected from the strong winds. The
loss of topsoil lowers the quality of the
soil. This makes it more expensive and
harder to grow good crops.
formation of an arch
Erosion by Ice
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If more snow accumulates in the winter
than melts in the summer, the snow on the
bottom turns to ice glacial retreat
If it becomes thick enough, its weight will
cause it to move under the pull of gravity
A glacier is a large
mass of moving ice
As a glacier moves,
it carries, pushes,
and drags loose
rock material
Erosion by Ice
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The glacier, with pieces
of rock, smoothes,
striates (scratches),
and grooves bedrock
As a glacier moves
through a valley, it will
make a U-shape instead
of a V-shape caused by
water
When the ice melts,
unsorted rocks and
boulders are left
scattered around on
hilltops and sides of
valleys
Plucking
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Plucking occurs
when ice flows into or
refreezes in fractures
in the bedrock. The
ice wedges and
removes blocks of
bedrock and
incorporates it into
the glacier. This process is
most rapid in areas where
water is refreezing near the
bed.
Plucking animation
Formed by a glacier
Formed by a glacier
HORN
Glacial Lake-formed by a glacier
Deposition
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When an agent of erosion deposits, or lays
down particles and fragments of earth
materials (sediments)
Also called sedimentation
Most deposition takes place in water
Deposition Factors
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Particle Size
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Smaller particles (clay and silt) settle more
slowly than cobbles and boulders
Particle Shape
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Friction between water and the surfaces of
particles slows down settling
Smooth, rounded
particles settle
more slowly
Deposition Factors
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Particle Density
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Denser particles settle faster, less dense
particles take more time to settle
Settling Rate and Time
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Sediments that settle at a
faster rate require less time
As the rate of settling
increases, the settling
time decreases
Sorting of Sediments
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Horizontal sorting
occurs at the end of
streams
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The smaller sediments
can be carried a greater
distance from shore
Vertical sorting occurs when a
landscape dumps a variety of
particle sizes in to still water
Deposition by Wind
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Usually sorts sediments by size
Cross bedding layers meet a different angles
Deposition by Gravity
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At the base of a cliff,
where pieces of
weathered rock have
fallen, you will find
pieces of many
different sizes
The sediments are
not sorted
Deposition by Glaciers
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Occurs when a glacier
melts and sediments are
released
Glacial erratics are large
rocks that have been
transported by glacial ice
without being broken into
small particles
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They are often found high
above stream valleys
Rounding and striations
(scratches) indicate
transport by glaciers
Alpine Glaciers
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Also known as
valley
glaciers, occur
in mountain
regions, and
may carve out
U-shaped
valleys with
their moving ice
Continental Glaciers
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Also known as ice
sheets causes
sculpting of the
land as rocks are
carried within the
glacier or dragged
under the flowing
ice
Glacial Features
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Glacial Polish –
when glaciers act like
sandpaper, grinding the
jagged edges from the
mountains and
smoothing hard
bedrock surfaces
Striation – parallel
grooves and scratches
in the bedrock left by
the rocks in the glacier
Glacial Features
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Drumlins – accumulation of rock and soil that
builds up in front of the flowing ice
Moraines – where the ice front stops its
southward advance, piles of
unsorted soil and rock remain
Glacial Features
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Kettles – Low spots in the glacial
deposits and places where large, buried
ice blocks melt leave these dry
depressions
and ponds
called
Kettle Lakes
North American
Continental Glaciation
The Oceans and Coasts
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Seawater covers almost 71%
of our planet
The average depth is about 4 km
(3 mi)
One Liter of seawater
contains about 3.5% of
dissolved solids
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Sodium chloride (table
salt) is the most common
When evaporation of ocean
water causes the salts to
become too concentrated to
stay in solution, they are
precipitated as sediment
The Oceans and Coasts
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The edges of the oceans are places of
change caused by the action of waves and
long shore currents long shore drift
Beach sediments are rounded and reduced
in size by abrasion as the energy in the
breaking waves causes the particles to rub
against one another
The Oceans and Coasts
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Sand is often transported along the beach
and just outside the breaking waves in the
zone of longshore transport
This movement of sand builds the
features of the
ocean shorelines
including sand bars,
barrier islands,
and sand spits
beach processes
Landscapes
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A region on Earth’s surface with physical
features, such as hills, valleys, and streams
The shape (topography) and composition
of the landscape is determined by the
climate, bedrock, geologic structures, and
human activities
Topographic relief is
the change in elevation
between the highest
and the lowest places
Landscape Regions
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Mountain landscapes have the greatest relief
between the highest peaks and the deepest valleys
A great variety of rock types are common
Mountains are common where converging tectonic
plates collide
Stream gradients are
high, and the fast
moving streams quickly
erode deep valleys
between the
mountain peaks
Landscape Regions
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Plateau landscapes are relatively flat or
rolling uplands where streams have cut deep
valleys
Commonly underlain by flat layers of
sedimentary rock
Less topographic
relief than mountains
but more relief than
the plains
Landscape Regions
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Plains have the least topographic relief
They may contain a few small hills, but
are generally flat and at low elevation
Commonly underlain by flat layers of
sedimentary rock
Climate Influence on Regions
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Moist, Humid climates usually have rounded
landscapes
Slopes are not as steep because moist
climates promote a protective cover of
vegetation
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Plants cover protects the soil
from rapid runoff and erosion
Climate Influence on Regions
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Arid (dry) climates usually produce thin
soils with little humus
With little plant cover to protect the soil,
sediment is carried away during rainfall
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Large areas of exposed bedrock and steep rock
faces are the result
Landscape Regions of the US
Landscape Regions of NY
Drainage Patterns
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Harder rocks will form hills and ridges
Erosion of the weaker rock will make the
major valleys
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Streams will tend to follow zones of weaker
rock and flow downhill
Drainage Patterns
Human Activities
Can Affect Landscapes
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Farming and construction projects can
accelerate erosion and effect landscape
development
Farmers and engineers must be guided in
planning their projects by appropriate
conservation practices