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Erosion and Deposition
Chapter 9
Chapter 9 – Erosion and Deposition
• Weathering, erosion, and
deposition act together in a cycle
that wears down and builds up
Earth’s surface.
Chapter 9 – Erosion and Deposition
• Erosion is the movement of
pieces of rock and other materials
(sediment) on Earth’s surface.
– Can be caused by gravity, running
water, glaciers, waves or wind.
Chapter 9 – Erosion and Deposition
• Most sediment comes from
weathering.
• Weathering is the breakdown of rock
and other materials at Earth’s
surface.
Chapter 9 – Erosion and Deposition
• Deposition happens when sediment is
dropped.
• Dropped sediment can build up over
time and make new landforms.
Chapter 9 – Erosion and Deposition
• Mass movement is any process that
moves sediment downhill.
–Caused by gravity.
• Different types of mass movement
include landslides, mudflows, slump
and creep.
Chapter 9 – Erosion and Deposition
• Landslides happen when rocks and
soil quickly slide down a steep slope.
• Mudflows happen when rocks and
mud quickly slide down a steep slope.
Chapter 9 – Erosion and Deposition
• Slump happens when a mass of rocks and
soil suddenly slides down a steep slope.
– Slump is different than a landslide.
– The material in slump moves down the
slope in one large mass.
Chapter 9 – Erosion and Deposition
• Creep happens when rocks and soil move
very slowly down a hill.
– Creep can happen even on gentle
slopes.
Chapter 9 – Erosion and Deposition
• Moving water is the major cause of the
erosion that has shaped Earth’s land
surface.
• Runoff (rainfall that does not soak in but
runs over the ground) forms tiny grooves
in the soil called rills, which flow together
to form bigger grooves called gullies which
join together to form streams which join
together to form rivers.
– A tributary is a stream or river that flows
into a bigger river.
Chapter 9 – Erosion and Deposition
Chapter 9 – Erosion and Deposition
• A river on a steep slope flows straight &
fast. This is usually at the origin or
beginning of the river. Forms a V-shaped
valley as it flows.
• A river toward the end flows slow on a
gentle slope with more curves (meanders).
Forms a wide, flat valley.
Chapter 9 – Erosion and Deposition
• When a river flows from hard rock to soft
rock, the soft rock wears away faster than
the hard rock, this forms a waterfall.
Chapter 9 – Erosion and Deposition
• A meander is a big bend in a river which
forms in a flood plain.
• An oxbow lake is a meander that has been
cut off from a river and is curved like a
meander.
Chapter 9 – Erosion and Deposition
• When rivers slow down as they leave
mountains, flow into lakes or oceans, or
flood their banks, they drop sediment,
called a deposit.
– An alluvial fan is a deposit that forms where a
river leaves a mountain range.
Chapter 9 – Erosion and Deposition
–A delta is a deposit that forms
where a river flows into a lake or
ocean.
Chapter 9 – Erosion and Deposition
–When a river floods, it drops
sediment on its flood plain which
results in flood plain soil being thick
and fertile.
Chapter 9 – Erosion and Deposition
• Groundwater (water that sinks into the ground)
can cause erosion when it mixes with carbon
dioxide to become a weak acid and can
dissolve limestone and make holes in the rock.
– Big holes in limestone are called caves.
– If the roof of a cave wears away, the land over it
can sink in making a hole in the ground called a
sink hole.
Chapter 9 – Erosion and Deposition
• Groundwater can drip from the roof of a
cave and form deposits that look like
icicles.
– Deposits that hang down from the roof of a
cave are stalactites, while deposits that stick
up from the floor are called stalagmites.
Chapter 9 – Erosion and Deposition
• Moving water has energy.
• As water goes down a slope, potential
energy changes into kinetic energy.
• A river erodes Earth’s surface by picking
up and moving sediment.
• Most sediment washes or falls into a river
as a result of mass movement (landslides
for example) and runoff.
Chapter 9 – Erosion and Deposition
• A river can get sediment through the
process of abrasion.
– Abrasion occurs when sediment in the water
scrapes against the bottom and sides of the
river and chips away bits of rock.
• Sediment moves downstream with the
water.
Chapter 9 – Erosion and Deposition
• A river’s slope, volume of flow, and the
shape of its streambed all affect how fast
the river flows and how much sediment it
can erode.
• High volume = fast speed
• Narrow, deep channel = fast speed
• Steep slope = fast speed
Chapter 9 – Erosion and Deposition
• A big river with a lot of water can carry
more sediment and larger pieces than a
small river.
• Big rocks in a streambed can make water
rough which wears away the streambed
faster than smooth water.
Chapter 9 – Erosion and Deposition
• Where a river curves, water moves faster
along the outside of the curve and slower
on the inside of the curve.
• Faster water wears away the outside bank
and slower water drops sediment along
the inside bank.
Chapter 9 – Erosion and Deposition
• A glacier is a huge chunk of ice that
moves over the land and forms when
snow and ice build up year after year
because more snow falls than melts.
Chapter 9 – Erosion and Deposition
• A continental glacier covers all or most of a
continent, it moves very slowly in all directions.
– When continental glaciers cover much of Earth’s
surface, it is called an ice age.
• A valley glacier is a long, narrow glacier in a
mountain valley which moves only down the
valley and can move faster than a continental
glacier.
Chapter 9 – Erosion and Deposition
• As a glacier moves, it erodes
the land under it.
• Two processes by which
glaciers erode the land are
plucking and abrasion.
• Plucking: as a glacier flows
over land it picks up rocks.
Chapter 9 – Erosion and Deposition
• Abrasion: As the glacier moves, the
sediment on the bottom scrapes the
land.
–Abrasion can make valleys wider and
can scrape away mountainsides
leaving a small mountain peak called
a horn.
Chapter 9 – Erosion and Deposition
• When a glacier melts, it deposits the sediment it
eroded from the land, called till.
• A moraine is a ridge or mound that forms where
till is dropped along the edge of a glacier.
• Sometimes a glacier drops a big chunk of ice
instead of rock or soil, when the ice melts, it
leaves a low spot in the ground called a kettle.
Glacial Landforms
Chapter 9 – Erosion and Deposition
• When ocean wind touches ocean water,
energy passes from the wind to the water
which causes waves, which in turn carry
energy across the ocean.
Chapter 9 – Erosion and Deposition
• Waves shape the coast through erosion by
breaking down rock and transporting sand and
other sediment which can wear away rock by
abrasion when it hits the shore.
– Some rock on shore is harder than the rock
around it and wears away slower. This forms a
headland which is part of a shore that sticks out
into the ocean.
– Waves can wear away the bottoms of cliffs along
the shore
– Waves can wear away holes in cliffs and form
caves.
Chapter 9 – Erosion and Deposition
• Waves shape a coast when they deposit
sediment, forming coastal features such as
beaches, spits, and barrier beaches.
– These form when waves slow down at a coast
and drop sediment which can build up to
make different landforms.
• A beach is an area of sediment at the edge of
the water, usually sand.
Chapter 9 – Erosion and Deposition
• A longshore drift occurs when waves hit a
beach at an angle and carry sand down
the beach.
Chapter 9 – Erosion and Deposition
• A spit is a beach that sticks out into the
water like a finger and forms when a
headland stops longshore drift, and the
sand piles up.
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Chapter 9 – Erosion and Deposition
• When waves drop sand in a long ridge
parallel to shore, a sandbar is formed.
• If the sand builds up above the surface of
the water it forms a narrow island called a
barrier beach.
Chapter 9 – Erosion and Deposition
• Wind causes erosion by deflation and
abrasion.
– Deflation is the process by which wind
removes surface materials (sediment)
• The stronger the wind, the bigger the
pieces of sediment the wind can pick
up.
– The blowing sediment scrubs and
polishes rock in a process called
abrasion.
Chapter 9 – Erosion and Deposition
Chapter 9 – Erosion and Deposition
• Wind erosion and deposition may
form sand dunes and loess deposits.
• Wind drops the sediment it is carrying
when a wall or other barrier slows the
wind.
Chapter 9 – Erosion and Deposition
• Sand dunes are ridges
or mounds that form
when the wind drops
sand. Sand dunes can
be small or large.
Chapter 9 – Erosion and Deposition
• Loess is tiny pieces of sediment that are
dropped by the wind. Loess helps make
soil fertile.
– There are big loess deposits in states
such as Nebraska and Iowa.