Deposition

Factors causing Deposition Deposition occurs when the velocity, or speed of the stream, wind, or other erosional system decreases or just stops moving.

Factors causing Deposition The amount of time it takes for a sediment to get deposited is called the rate of deposition. The faster the rate of deposition, the less time it takes to deposit the sediment. The slower the rate of deposition, the more time the deposition takes.

Factors causing Deposition Two major factors affect deposition: Velocity of the erosional system How fast the stream, wind, glacier is moving Characteristic of sediment Physical characteristics of the rock/soil

Velocity of the Erosional System & Rate of Deposition The faster the stream moves, the larger pieces of sediments the stream can carry. Use the “Relationship of Transported Particle Size to Water Velocity” in the ESRT.

Characteristic of Sediments & Rate of Deposition Many factors affect how fast the sediments will be deposited in the air or water. Size Shape Density Saturation of Dissolved Minerals

*Disclaimer* These factors are discussed as if all the other factors are the same. So when discussing size, we are talking about two rocks made of the exact same material, density, shape, and saturation of minerals.

Size Larger objects are deposited (settled/dropped off) first. Generally larger objects are heavier and sink faster. Clay sized particles may ‘float’ in the water forever. Clay floating in water is muddy/cloudy water.

Shape A round sediment will settle faster than a flat sediment. A flat sediment has greater resistance, due to friction, to be deposited.

Density The higher the density the faster it will be deposited. A more dense object of the same size and shape will have a larger mass.

Saturation of Dissolved Minerals Evaporation, temperature changes, or increases in amount of dissolved minerals in a water body such as a lake, sea, or ocean may result in a saturated condition. Saturated condition is when no more minerals can be dissolved into the water. (Saturated=Full) When the water is saturated, extra minerals precipitate out forming rocks such as rock salt and dolostone.

Sorting of Sediments and Deposition Sorted Sediments: Layers of sediments that are similar in size. Unsorted Sediments: Mixed in size, density, and shape. Graded: Based on density.

Unsorted Glacial and Mass Movement Deposits In a landslide (mass movement) or with a glacier, the deposited sediments are very random. There is no pattern to the deposition of the sediments.

Erosion and Deposition in Relation to Energy Changes When the amount of energy is large, erosion is dominant. When the amount of energy is low, deposition is dominant Velocity Kinetic Energy Erosion High Deposition Low

Erosion and Deposition in Relation to Energy Changes Slope Steep Gentle Curve Outside Inside Discharge High Low Location Source Mouth

Slope Erosion Deposition Steep Gentle

Meanders/Curves Erosion Deposition

Discharge Erosion Deposition High Low

Discharge If more streams or tributaries enter the stream, it increases the discharge. This would cause the velocity to increase. Causing erosion to increase and deposition of solid sediments to decrease.

Location Deposition

Erosional-Depositional Interfaces Meanders Source and Mouth Changes in slope

Dynamic Equilibrium of an Erosional System Dynamic Equilibrium means moving balance. The amount of sediments eroded will be the same amount of sediments deposited.

Characteristic Features of the Chief Depositional Agents

Deposition by Streams In the stream itself, the sediments are deposited on the inside of the meander, where the stream velocity is slow. When a stream floods and overflows, some sediments are deposited on the edge of the river called a levee.

Depositions by Streams The high velocity of a flooding stream will cut a straight path through a meander. Separating the meander, forming a curved lake. The deposition at the end of a stream is called a delta.

Deposition by Glaciers At the end of a glacier, the unsorted piles of debris are called moraines. If a glacier mounds up the ground into a streamlined oval shape, this is called a drumlin. Drumlins look like an upside down spoon. Drumlin tails indicate the direction of former movement, pointing in the direction the glacier came from.

Deposition by Glaciers Glaciers leave behind depressions called kettle holes or kettles. If the kettle is deep enough it will be filled with water and is called a kettle lake.

Deposition by Glaciers When glaciers melt, the allow sediments to get deposited by particle size. This feature is called an outwash plain. Long Island is made of an outwash plain.

Deposition on Coastlines by Water Waves and Currents Wind-generated ocean or lake waves slow down when they approach the shore. This creates a beach. A beach can be made of any sediment that is deposited, but usually it is sand. When a shoreline has a natural or man-made pier or peninsula, sediments are deposited facing an oncoming longshore current.

Deposition on Coastlines by Water Waves and Currents The waves drag sediments away from the shore, depositing them parallel to the shore line. This creates a sand bar. If the sandbar break the surface of the water and vegetation grows, it is called a barrier island.

Deposition by Wind When wind slows down or stops, the sediments its carrying are dropped. Wind usually carries sand size sediments and smaller, called dust. Dust is usually carried by wind over a long distance from a volcanic eruption.

Deposition by Wind Sand deposited by wind in layers or mounds are called sand dunes. Sand dunes usually have a steep slope on the side the wind is blowing towards.

Deposition by Mass Movement When an avalanche or other mass movement hits the ground and stops moving, the sediments are deposited as a landform on the earth’s surface. It is usually composed of unsorted and unlayered sediments.