Download - Deposition
Deposition
Deposition is the process whereby sediments are
“released” or “fall out” of an erosional system.
River Delta
Glacial Moraine
Sand Dune
Barrier Island
Factors that Impact Deposition -- Velocity
The primary factor that impacts the
deposition of sediments is the velocity of the
erosional system.
The slower the erosional system, the more likely sediments
will deposit.
In addition, the slower the erosional system the more diverse the types of sediments to
be deposited.
Velo
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Deposition
High Deposition Rate = Low Velocity
Low Deposition Rate = High Velocity
Factors that Impact Deposition -- Velocity
RT = Pg. 6
The velocity of stream has changed from 100 cm/s to 0.1 cm/s. What
type of sediments would deposit in the stream?
A stream that is moving at a rate of 100 cm/s can carry small pebbles,
sand, silt, and clay.
A stream that is moving at a rate of 0.1 cm/s can carry small silt and
clay.
This means that as the stream decreases in velocity, the small
pebbles and sand cannot be carried and will be deposited.
Factors that Impact Deposition – Characteristics of Sediments
Sediment Size
Depo
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rate
Depo
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Depo
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Sediment DensitySediment Shape (round – flat)
Large sediments deposit more quickly
than small sediments.
Round sediments deposit more quickly than flat sediments.
Sediments with a high density deposit more quickly than
sediments with a low density
Deposition of Dissolved Substances.
Some sediments are dissolved in water.
Dissolved sediments are commonly found in stream and tidal erosion systems.
In order for dissolved sediments to be be deposited, the water in solution needs to be evaporated. The remaining sediments would then deposit out of the
system.
As this lake evaporates, the salt is deposited. Minerals which precipitate as a result of the evaporation of water in solution are known
as evaporites.
Minerals are deposited from solution of water that drip into
underground caverns.
Deposition by Gravity (Mass Movement) Sediments that are deposited
from a mass movement event (Ex: avalanche,
mudflow, rockfall) tend to deposit quickly.
The sediments deposited are usually found in a pile at the base of the erosional system.
The sediments tend to be varied in shape and size and are unsorted and unlayered.
Deposition by Streams
HORIZONTAL SORTING: As the stream empties in to the ocean (mouth), the velocity decreases. Sediments will settle out of the stream as they enter into the ocean. (Larger sediments closer to the mouth of the stream – smaller sediments further out into the
ocean.
Deposition of sediments in a stream will take place when the
velocity of the stream decreases.
The deposition of sediments can take place in many areas of the
stream.
Mouth of the Stream
Deposition by Streams
Meanders
Stream velocity changes as water moves through the meanders of a stream.
The stream velocity (kinetic energy) of the stream is high on the outer edges of the stream.
HIGH EROSION
The stream velocity (kinetic energy) of the stream is low on the inner edges of the stream.
HIGH DEPOSITION
AREAS OF DEPOSITION
Deposition by Streams
Levees and Floodplain
Levee
Floodplain
Stream discharge: The amount of water (volume) that passes through
a given point in a stream.
At times, the discharge of a stream increases. This may happen during
heavy precipitation or sudden, significant snowmelt. This will lead
to flooding.
When flooding occurs, water flows over the banks of the stream. The
sediments carried by the water also flow over the stream banks.
These sediments can deposit quickly into mounds found on the
edges of the stream bank (levee) or throughout the land surrounding
the stream (floodplain).
Deposition by Streams
Graded Bedding – Stream to Lake Deposit
Sudden stream flow into a lake creates turbidity currents.
Flooding events may also create a sudden increase in discharge from a stream into a
lake.
The increased discharge creates turbidity currents (a swirling mixture of various size
sediments).
Sediments will deposit at the lake bottom in graded beds. Graded bedding is the sorting
of sediments by size. Larger sediments settle out first followed by smaller
sediments.
Larger sediments settle out by size from largest (bottom) to smallest (top).
Series of graded beds can provide scientists with clues as to the number of flooding events that have occurred in the
lake.
Deposition by Wind Sediments are deposited out of the
wind as the wind velocity decreases.
Most sediments deposited out of the
wind are sand-sized or smaller.
The wind can deposit small sediments over a
large area.
Sand is deposited in windy environments in the form of sand dunes.
Wind direction
Windward side of the dune =
GENTLE SLOPE
Leeward side of the dune =
STEEP SLOPE
Deposition by Glaciers Sediments are deposited out of a
glacier as the glacier moves
across a landscape and/or as the glacier
melts.
Most sediments deposited out of glaciers are of
assorted sizes and origins. Sediments
deposited by glaciers are most usually angular,
sub-rounded, polished and unsorted.
Glacial deposits = Unsorted, angular, sub-rounded, polished
Drumlin= A collection of unsorted sediments released by a glacier. The steep end of the drumlin points towards the direction the glacier came from.
Deposition by Glaciers As a glacier moves across a landscape it is continually depositing sediments. Assorted sediments that are
deposited underneath a glacier as it moves
becomes part of the ground moraine.
The pile of sediments found in front of a
glacier -- pushed by the glacier will become a
terminal moraine.
Ground moraines can be found throughout much of upstate New York.
Terminal moraines make up the composition of
Long Island.Terminal Moraine
Ground Moraine (under glacier)
Long Island MorainesThe last major Ice
Age led to the advance and retreat of large continental glaciers the covered
much of the northern US
(between 60,000 to 40,000 yrs ago).
The retreat and melt of the glacier created two
terminal moraines that make up of the topography of Long
Island.
Deposition by Tides The waves drag
along the bottom of the sea as they
approach the shoreline.
This action will pull sediment
from the sea floor.
This sediment may then deposit
along the shoreline in the form of a beach.
Deposition by Tides
A projection from the shoreline into the ocean, such as a pier, groin or jetty can impact how sediments are deposited on a beach.
As the current moves towards the groin, its velocity slows down causing sediments to deposit more rapidly. High deposition rates are found on the side of the groin
facing the current.
The opposite side of the groin encounters unusually high erosion rates because the sand is not there to protect the beach from the currents.
Movement of
longshore current
Deposition by Tides Barrier Islands
Strong storms can cause heavy erosion to occur along a beach. Much of the sediment on a beach may be carried
back out to sea during a strong storm. The extra sediment carried out to sea can deposit as a sandbar. If this sandbar rises
above the sea, a layer of soil may develop
along with vegetation and create a barrier
island.
Barrier islands help to protect coastlines from strong storm surges,