Delta (Fluvial Deposition) Flashcards
Why are deltas formed?
The velocity and sediment-carrying capacity of the river decreases on entering the lake or sea, and bedload and suspended materials are dumped.
What is flocculation?
It occurs when fresh water mixes with seawater and clay particles coagulate due to chemical reactions. The clay then settles on the river bed.
What conditions are likely to be met for delta formation?
- Large sediment load e.g. Mississippi river
- Coastal area has to have a small tidal range and weak currents (limited wave action and little transportation of sediment after it is deposited) e.g. Mediterranean Sea
What are the three types of deposits that deltas are usually composed of?
Topset, foreset and bottomset
What are topset beds?
Larger and heavier particles deposited first as the river loses its energy.
What are foreset beds?
Medium graded particles are deposited second and as steep-angled wedges of sediment.
What are bottomset beds?
The last material to be deposited, it is the finest material.
What is the most common delta shape?
Arcuate detla e.g. the Nile delta
What are arcuate deltas?
- curving shoreline
- dendritic pattern of drainage
- braided river
- smooth shape
What are bird’s foot deltas?
E.g. Mississippi delta
*fingers of deposition that branch out to sea
What is a cuspate delta?
- pointed like a tooth
* gentle but opposing sea currents or longshore drift shapes it
Where are deltas located?
At the mouth of a river as it enters a sea or lake.
