Aim: Unit 8 Review • Do Now:

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– H.W. Finish your unit 8 test corrections.

Sorting of Sediments and Deposition

Agents of Deposition

• The agents of erosion are also agents of deposition.

• Depositional rate depends on sediment size, shape and density.

• Depositional rate also depends on characteristics of the depositional agent.

Speed or velocity

Agents of Deposition

• Stream sediments and wind sediments get deposited when the speed or velocity of the eroding agent decreases enough so that the agent can no longer carry the sediment.

Settling Rate Vs. Velocity

• As the velocity (speed) of the wind or stream decreases, deposition begins – usually with the largest, heaviest, most dense, most rounded, particles settling out first.

Velocity

Sett

ling

Rate

Settling Rate Vs. Density

• Particle density affects settling rate. Particles with similar size and shape should settle at the same rate, but particles with a higher density will settle faster.

Density

Sett

ling

Rate

Settling Time Vs. Rate

• Be oh-so-careful when answering questions about which particles settle fastest. There is a HUGE difference between settling time and settling rate.

Settling Time

Sett

ling

Rate

Mountain side

Stream

Lake

As the stream enters the lake or an ocean, the stream velocity decreases

and sediments are deposited.

Stream velocity

decreases

Sediments are deposited in size order horizontally.

Horizontal Sorting

BouldersCobbles

PebblesSand Silt Clay

Region of maximum stream velocity changes when streams bend or turn. There is an interface between regions of erosion and deposition…

Stream

BouldersCobblesPebblesSand

Vertical SortingClay

Silt

Vertical Sorting

Vertical Sorting

•During vertical sorting the largest, roundest, most dense particles settle to the bottom with the smallest, flattest, least dense particles settling at the top.

Vertical Sorting

Latest layer

Earliest layerLater layer

•Vertical sorting can occur as a single depositional event in still water or a series of events as when a stream’s velocity decreases through the seasons allowing particles to settle in a graded bed.

Vertical Sorting

Where a stream or river enters a lake or ocean, deposition begins at the mouth forming a delta.

Named for the Greek letter

Stream

Ocean

Deltas

Mississippi Delta• Sediment-laden

river water mixes with cold, deep-sea currents, creating a nutrient rich zone where both salt and freshwater fish flourish.

• Wind-born particles are generally sorted by size, but are small. Cross bedding is common in sand dunes.

• Sediments eroded and deposited by gravity are unsorted.

Deposition by other agents of erosion

Crossbeds in a Sand Dune

Unsorted Sediments

• Unsorted till left behind by a Glacier.

• Unsorted sediments due to Mass Movement.

Final Question

• What are the factors that affect the settling rates of sediments?