Erosion and Soil
Depostion
Chapter 8
Section One:
Changing Earth’s Surface
Erosion
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“Erosion” moves
sediment from one place
to another
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While “deposition” lays
down sediment in new
locations.
What are the forces
which cause erosion?
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The force of gravity.
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The force of running
water.
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The force of glaciers.
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The force of waves.
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And the force of wind.
What Do You Remember?
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What does erosion do?
moves sediment from one place to another
What does deposition do?
lays down sediment in new locations.
What are the forces which cause erosion?
Gravity, water, glaciers, waves, and wind.
Section 2: Water Erosion
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Moving water is the
major cause of erosion
on Earth’s surface.
Runoff and Erosion
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Runoff is water
which moves
over the land,
carrying soil
particles with it.
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The amount of
erosion caused by
runoff can depend on
how much plant life is
there to hold the soil.
With very little plant
life, a desert can have
high runoff and
erosion.
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Because of
gravity,
runoff and
the soil in it
carve little
grooves
called rills.
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As rills flow
into one
another,
they grow
larger and
form
gullies.
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Gullies join
together to
form streams.
While gullies
only flow
when it rains,
streams flow
all the time.
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A stream
grows into a
larger stream
by receiving
water from
tributaries.
Together, all these streams, from
tiny rills to great rivers, form a
system that drains the land. A
drainage basin is a land area where
all this water collects.
What Do You Remember?
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What is the major cause of erosion on Earth’s surface?
Moving water.
What is water which moves over the land, carrying soil
particles with it?
Runoff
Describe the system by which water is moved from
small to large.
Rills to Gullies to Streams which are Tributaries to
Larger Streams, which run to a Drainage Basin.
Rivers have features which are
caused by erosion.
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Near its source, a
river flows
quickly and
follows a straight,
narrow course.
The steep slopes
along the river
erode rapidly and
we see a deep,
V-shaped valley
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Waterfalls occur where a
river meets an area of
rock that is very hard,
followed by softer rock.
The soft rock wears away
more quickly, creating a
waterfall.
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Lower down on its
course, a river
usually flows over
more gently sloping
land. It spreads out
and erodes the land,
forming a wide river
valley.
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A wide, flat
area of land
along a river
is called a
flood plain.
A river can
cover the
flood plain
during
floods.
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A river can have
meanders, which
are looplike
bends in the
river caused by
uneven erosion.
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Sometimes a
meandering river
forms an oxbow
lake. This is a
meander that has
been cut off
from the river
when the water
level drops.
Complete River System
What Features Do You Remember?
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High in the mountains near the river’s source are…
deep, V-shaped valleys.
When the river runs over hard rock, then soft rock?
Waterfalls
When it flows over gently sloping land?
Wide river valleys
When it comes to a wide, flat area of land?
Flood plains
Looplike bends in the river caused by uneven erosion?
Meanders
River Deposits
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As water moves, it
carries sediments
with it. Any time
moving water slows
down, it drops
some of the
sediment.
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Soil deposition
creates new
landforms, such as
alluvial fans, which is
a wide, sloping
deposit of sediment.
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Sediment
deposited where a
river flows into an
ocean or lake
builds up a
landform called a
delta, which can
take a variety of
shapes, like this
“birds foot” delta.
What Do You Remember?
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What happens when water flow slows down?
The water drops its sediment.
What are wide, sloping deposits of sediment?
Alluvial fans
When a river flows into an ocean or lake,
sediment builds up at the mouth. What is this
landform called?
A delta
Groundwater Erosion and
Deposition
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Not all rainwater goes to
runoff or evaporates.
Some of it soaks into the
ground. This
underground water is
called groundwater.
Underground water combines with carbon dioxide to
form a weak acid, which can dissolve limestone.
These hollowed out pockets in the underground
stone become caves.
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Inside the caves,
water containing
dissolved limestone
drips from the roof,
forming stalactites
(which hang down)
and stalagmites
(which grow up
from the cave
floor).
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Sometimes the
ground above a
cave can
collapse,
creating a
depression
called a
sinkhole.
What Do You Remember?
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What is water that soaks into the ground?
Groundwater
How do caves form?
Water combines with carbon dioxide to form a weak
acid, which dissolves limestone.
What are the deposits of dissolved limestone in caves
called?
Stalactites (ceiling) and Stalagmites (floor).
What is the name for a collapsed cave?
Sinkhole
Section 3: The Force of Moving
Water
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A river’s
moving water
has energy, and
we can use this
energy to create
power.
There are two kinds of
energy:
Potential Energy and
Kinetic Energy.
.
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As water moves down
from a higher slope, its
potential energy is
released into kinetic
energy.
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This released
energy picks
up sediment,
pebbles, and
even rocks,
which wear the
riverbed away
with a grinding
action. This is
called abrasion.
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The power of
a river
depends on
how steep it is
(slope), how
much water is
flowing
(volume) and
the shape of
its streambed.
A streambed can be full of boulders and other
obstacles. All these rough surfaces can increase
friction, which causes the water to move every which
way. This is called turbulence.
What Do You Remember?
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What are the two kinds of energy?
Potential and Kinetic
Water at a high place has which kind of energy?
Potential
Water flowing downhill has which kind of energy?
Kinetic
Moving water can be used to create…
Power
The grinding action of pebbles and rocks on the riverbed is called…
Abrasion
What are the three features which determine the power of a river?
Slope, volume, and shape
River obstcles like boulders create more friction, which increases…
Turbulence
Section 4: Glaciers
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A glacier is
any large
mass of ice
that moves
slowly over
land.
There are two kinds of glaciers:
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Valley Glaciers,
which are long,
narrow glaciers
which forms
when snow and
ice build up
high in a
mountain
valley.
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Continental
Glaciers,
which cover
much of a
continent or
large island.
They cover
10% of the
earth today.
Many times in the past, continental glaciers
have covered large parts of Earth’s surface.
These times are known as the ice ages.
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Although glaciers move
slowly, they are a major
force of erosion.
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The glacier flows over
the land and picks up
rocks. This is called
“plucking”. As the
rocks are dragged
across the land they
gouge and scrape the
bedrock. This is called
“abrasion”.
When the glacier melts, it deposits the sediments,
which are called “till”. The till at the edge of a
glacier forms a ridge, which is called a “moraine” A
“terminal moraine” is the farthest point reached by a
glacier.
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Continental
glaciers can
scoop out
huge basins.
The Great
Lakes were
formed by
glaciers of
the past.
What Do You Remember?
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What is a glacier?
A large mass of ice which moves over the land.
What are the two kinds of glaciers?
Valley glaciers and Continental glaciers.
What is an ice age?
A time when glaciers covered huge amounts of Earth.
What are the two things glaciers do to change the surface of earth?
Plucking and Abrasion
What are sediments left by glaciers called?
Till
What is the ridge of sediment at the edge of a glacier?
Moraine
What is the farthest point of sediment left by a retreating glacier?
Terminal Moraine.
Section 5: Waves
The energy in waves comes from wind that
blows across the water’s surface.
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The energy from waves
can break apart rocks.
Over time, waves can
make the small cracks in
the rocks larger.
Eventually, pieces of the
rock break off.
Waves also erode land by abrasion. When a wave hits land, the
sediment in it is carried forward by the wave and wears away
rock like sandpaper wearing away wood.
Waves not only erode the land, but
they also deposit sediment.
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As waves reach the shore, they drop
the sediment they carry, forming a
beach
What Do You Remember?
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What causes waves?
The pressure of wind across the surface of water.
What causes waves to break on the beach?
The friction of the land slows down the bottom water,
but the top water keeps moving forward.
What are the two ways that waves erode land?
They hit rocks and cause cracks, and they abrade the
rocks with their sediment like sandpaper.
What deposits do waves leave?
Sandy beaches.
Section 6: Wind
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Wind is actually the
weakest force of erosion.
Water, ice, and waves are
much stronger agents.
But wind can be a
powerful shaping force if
there are no plants to
hold the soil in place.
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Wind picks up the
smallest particles
of sediment. The
stronger the wind,
the larger the
particles it can pick
up. This sweeping
away of earth is
called “deflation”.
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When the wind
slows down, or
some obstacle
traps the
windblown
material, sand
dunes form.
These are
formed by the
coarser particles
blown by the
wind.
The finer particles in the wind are carried very far away from
their source. These are particles of clay and silt and can
create rich farmland. This windblown material is called
“loess”.
What Do You Remember?
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When can wind be a powerful force for shaping earth?
When there are few or no plants to hold the soil.
What is the sweeping away of particles by wind?
Deflation
How are sand dunes formed?
The wind-carried particles are trapped by obstacles or
the wind slows down and drops the particles.
What are the finer particles which can be carried long
distances before they fall?
Loess