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Deposition

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  1. Deposition Sand Dune River Delta Glacial Moraine Deposition is the process whereby sediments are “released” or “fall out” of an erosional system. Barrier Island

  2. 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. Velocity of Erosional System Deposition High Deposition Rate = Low Velocity Low Deposition Rate = High Velocity

  3. Factors that Impact Deposition -- Velocity 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. RT = Pg. 6

  4. Factors that Impact Deposition – Characteristics of Sediments Deposition rate Deposition rate Deposition rate Sediment Size Sediment Shape (round – flat) Sediment Density 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

  5. Deposition of Dissolved Substances. 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. 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.

  6. 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.

  7. Deposition by Streams 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 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.

  8. Deposition by Streams 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 Meanders AREAS OF DEPOSITION

  9. Deposition by Streams 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). Levees and Floodplain Levee Floodplain

  10. 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.

  11. 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

  12. 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.

  13. 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. Ground Moraine (under glacier) Terminal Moraine

  14. Long Island Moraines The last majorIce 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.

  15. 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.

  16. 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

  17. 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,