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Erosion and Deposition
Vocab to know…
• Erosion – the process by which
weathered rock and soil particles are
moved from one place to another. Can
be caused by gravity, wind, running
water, glaciers, and waves.
• Deposition – the process by which
sediments are laid down in new locations.
• Gravity – pulls rocks and soil down
slopes. This is called mass wasting. Can
be fast or slow. The sediments come to
rest at the bottom forming a talus.
Erosion Causes
• 1. gravity
• 2. wind
• 3. running water
• 4. glaciers
• 5. waves
Each of these will be discussed, you need to
know all five of them………….
1. Gravity
• This is called mass wasting
• Sediments that come to rest are called
talus
• Rapid mass wasting is landslides,
mudflows, and slumps
• Slow mass wasting can be earth flows and
soil creep
Mass wasting type 1.
• Landslide – rapid,
caused by an
earthquake, a
volcanic eruption, or
the weakening of
rocks due to heavy
rain. Has the ability
to move millions of
tons at once.
Mass Wasting type 2
• Mudflow – rapid,
caused by heavy rain,
the mud moves
downhill picking up
more soil and
becomes thicker.
Can move anything
in its path.
Mudflow pic
Mass Wasting type 3
• Slump – when a
block of rock or soil
on the face of a slope
slips down so that its
upper surface is
tilted backwards.
Mass Wasting type 4
• Earth flow –
slow, caused
by heavy
rains, where a
mass of soil
and plant life
slowly slides
down a slope.
Mass Wasting type 5
• Soil creep –
slowest, caused by
alternating
periods of freezing
and thawing,
animal activity, or
water movement.
Particles move
slowly downhill.
Soil Creep pic
2. Wind
• Wind – the most active
agent of erosion in
deserts, in plowed fields,
and on beaches.
• Types of wind erosion
– Deflation – fine particles
are carried high up into
the air.
– Abrasion – larger
particles roll or bounce
along the ground.
Wind continued…
• The amount of erosion is
dependent on size of the
particles, the speed of the
wind, the length of time the
wind blows, and the
resistance of the rocks.
• An oasis forms when the
wind erodes the desert
until it reaches the depth
where water is present
allowing grass and trees to
grow.
• Sand dunes – a mound of
sand deposited by wind.
They protect the area on the
side of the dune away from
the ocean from further
erosion. Small plants often
grow here. Can vary in size
and shape: the side facing the
wind has a gentle slope
(windward side), the top
(crest), and the other side
(slip face) and is very steep.
Dune Formation
Wind continued
• Loess is very fine
particles of sand and
silt not deposited in
dunes, instead it is
blown away from
where it originates
• Loess deposits are very
fertile
All we are is dust in the wind.
Now, let us continue………….
3. Running Water
• Running water – the major cause of erosion.
• Rain can:
– Evaporate
– Sink into the ground
– Flow over the land as runoff
As runoff, it carries particles of clay, sand, and
gravel, Gravity pulls it downhill: water and
sediment cut into soil forming tiny grooves
called rills.
• As erosion
continues, rills grow
wider and deeper.
Eventually tiny
stream valleys called
gullies form, which
act as channels for
runoff.
• Example: on the
side of many roads
in southern Virginia
Beach.
3 factors affecting runoff
amount
• 1. Amount of
rainfall
• 2. Amount of plant
growth in an area
• 3. The shape of the
land: steep slopes =
more runoff because
it moves too fast to
soak into the ground.
Streams and Erosion
• When several gullies come together, a
large stream form. The particles and
rocks being carried form a load.
• Large – rolls along bottom.
• Small- flows with water.
• Salt – some is dissolved and some is
carried.
River System develops
• The network of rills, gullies, streams, and
rivers in an area is called a drainage
system.
• Large streams are called tributaries,
which flow into the main river.
• The area drained by a main river and its
channels is called a drainage basin.
Life Cycle of a River
• Immature river is Vshaped, its waters flow
very quickly, waterfalls
are common
Mature River
• One that has been forming for thousands
of years, erosion has changed the valley
to more of a U-shape, river has slowed
down, waterfalls are mostly gone.
• River’s course is
curvy and winding,
forming meanders
River Formations
• Oxbow lakes are
formed when the
water supply to a
meander is cut off
• Alluvial fans occur
when the sediments
that a river carries
are dropped forming
a fan shape
• Deltas are formed at
the mouth of a river
when sediments are
dropped
Flood Plains and Levees
Flood plains are the sediments that the
river has deposited through time, they
are very fertile
Levees are the build up of the larger
particles of sediment along the sides of
the river’s flood plain
• The land that separates
basins is called a divide.
• The Continental Divide
is 80 km west of Denver,
CO. Runs north and
south the length of N.
America.
• West of divide flows into
Pacific Ocean.
• East of divide flows into
Atlantic Ocean.
• Divides get narrower
with time and can cut
through and share
water from basins.
The Divide
Continental Divide
More great erosion pics!!!
Cave Humor!
Karst topography
• Cavern – used to describe a very
large cave.
• Speleology – the study of caves.
• Spelunking – the hobby of
exploring caves.
• Caves and sinkholes are formed
by the dissolving action of
running water mixed with
carbonic acid in rocks such as
limestone, gypsum, and
travertine.
Sinkhole Pictures
SINKHOLES COMMONLY
HAVE PONDS IN THE MIDDLE
WHEN IT REACHES GROUND
WATER.
Cave terminology
• Speleothems are the mineral
formations and deposits in
caves.
• Stalactites – icicle like, from the
ceiling down, calcite deposits.
• Stalagmites – calcite deposits,
built up pillars from the floor.
• If the two join a column is
formed.
Cave life
• Permanent cave dwellers include fish,
salamanders, crayfish, insects, spiders,
and bats.
• Animals like bears, lions, foxes, and
wildcats use caves for hibernation or
shelters.
• Animals that live there permanently are
usually partially or completely blind.
Have a keen sense of smell and touch.
Usually pale in color. Most of these
animals are modified for cave life.
Cave Life
Erosion humor…
4. Glaciers
Glaciers
• Glacier – a large mass of moving ice and snow.
Forms where there are many large snowfalls
and the temp remains very cold.
• Glacial ice erodes by abrasion and by plucking
away at the rock beneath it. One of the most
powerful agents of erosion.
• May carry large boulders as well as smaller
particles of rock.
Deposits by Glaciers
• Till – rocks and soil
deposited directly by a
glacier. Particles vary in
size from large boulders to
fine clay. Not sorted at all.
• Moraines – formed with a
glacier melts and retreats
leaving a ridge of till.
– Terminal moraine – deposited
at the front end of a glacier.
– Lateral moraine – till
deposited along the sides of a
glacier.
Terminal and Lateral
Moraines
Glacier deposits continued…
• Drumlins – an ovalshaped mound of till.
Its tip points in the
direction the glacier was
moving.
• Meltwater – streams
formed by melting ice.
• Outwash plains –
sediments deposited by
rivers of meltwater; fanshaped; usually in front
of terminal moraines,
fertile land.
Uses for glacier deposits
Still more…
• Iceberg deposits – when parts of the
glaciers break off and drift into the sea.
• Glacial lakes – when the holes left by
glaciers fill with water. Examples: The
Great Lakes of Michigan, The Finger
Lakes in New York.
• Kettle lakes – when a huge block of
glacial ice is left behind and melts to form
a deep round hole that fills with the water
from melting.
The Great Lakes
LAKE HURON
Iceberg pics
Icebergs
Beach
Property?
5. Wave Erosion
• The powerful force of
waves constantly
erodes and shapes the
shoreline.
• Under normal
conditions, waves erode
about 1 to 1.5 meters
per year. During
storms it is increased
and can erode up to 25
meters per day.
Wave Erosion cont.
• Sea cliffs- a steep face of rock .
• Terrace – when a sea cliff is erodes and a
buildup or rocks and sand form a flat
platform.
• Sea stack – a column of resistant rock left
standing.
• Sea cave – when wave action erodes rock
and forms a cave.
Sand bar and a Spit
Sand bar
WHAT IS THE NAME OF THE
LOCAL SPIT?
Spit
Shape of the Shoreline
• Shape of the shoreline - often results
from changes in the sea level. If it
suddenly drops then there will be many
sea cliffs and terraces; if it rises then
there will be many bays and harbors.
Had enough yet?