DEPOSITION Deposition is the final step in the erosional-depositional system. AGENTS OF EROSION BECOME AGENTS OF DEPOSITION

Deposition by Gravity mass movement – unsorted - no distinct layering Ex. Rockfalls, mudflows, slump, soil creep

A. Deposition by Moving water: streams deposit sediment when they slow down or decrease in volume resulting in sand bar-build up of sand size sediments in a stream or ocean at a point where the water slows

- oxbow lakes form, floodplains: stream overflows its banks Mississippi delta as seen from space - oxbow lakes form, floodplains: stream overflows its banks - deltas: formed where river meets open water creating a fan shaped deposit alluvial fans: sediment deposited by a stream onto open flat land Delta

Beaches, sandbars, spits (connected to the mainland), and lagoons B. Deposition by Oceans - form new landforms Beaches, sandbars, spits (connected to the mainland), and lagoons Farewell Spit in New Zealand

C. Deposition by Wind: contains fine sediments Dunes: windward vs leeward side and cross-bedding Leeward side Windward side

Cross bedding – arrangement of strata (sedimentary rocks) inclined at an angle to the main layers.

D. Deposition by Glaciers: Indirect – fluvio-glacial –sorted (meltwater streams sort sediments. Sorted then deposited in layers) Direct – glacial drift/till –unsorted (glacial ice melts and sediments drop out in a jumble)

U-shaped valleys – erosion

What Factors Affect Deposition? a. Particle Size: smaller particles settle out more slowly 10 time taken in minutes Indirect Relationship small large

b. Particle Shape: flat particles resist settling more than round particles 10 time taken in minutes Direct Relationship round oval flat

c. Particle Density: Particles with greater density settle out faster 10 time taken in minutes Indirect Relationship Density

d. Velocity: stream slows down – carrying power decreases – sizes carried and deposited also decreases (and vice versa).

SORTING: When particles are deposited the load can be sorted in different ways. A: Horizontal

Horizontal sorting   - When deposition occurs at the mouth of a stream, a process called horizontal sorting takes place. - sediments that were once carried down the stream are arranged from largest to smallest. - smaller particles settle more slowly than larger particles – due to pull of gravity  smaller particles stay in suspension longer.

B. Vertical Bedding (aka graded bedding) decreasing grain size upward through the bed indicating deposition from a waning (lessening) current. One episode or layer of vertical bedding

Youthful stream-fast moving, steep gradient, rapids On the back of your notes read about Life of a Stream and add the notes. Take a look at the pictures to help you understand the concepts.: LIFE OF A STREAM Youthful stream-fast moving, steep gradient, rapids Mature stream-slows down, gradual decrease in gradient, flood plains begin to develop Old Stream- very slow, large, carries much sediment, oxbow lakes, meanders, big flood plains “Age” of Stream is due to landscapes it covers

Youthful Stream

Waterfalls-develop due to varying resistance in bedrock

Flood Plain-characterizes an old stream

Stream bed- notice varying sediment sizes