Deltas Flashcards
When the river meets a lake or…
sea(estuary), the discharge and the velocity drops.
According to Hjustrom curve…
larger sediment deposits first. The fine sediment is deposited further downstream, creating outwards fans(Alluvium fans)
The Alluvium fans create zones of…
accretion, which are above the water level.
The zones of accretion split…
the stream into distributaries and delta is formed.
Types of material deposited by deltas:
- bottomset beds
- forest beds
- topset beds
Turbidity currents are currents…
of water loaded with material.
Bottomset beds are…
the lower parts of the delta built outwards along the sea floor by turbidity currents. The beds are composed of very fine material.
Forest beds form over…
the bottomset beds, sloping layers of coarse material are deposited. Each bed is deposited above and in front of the previous one, so the delta is built a seaward.
Topset beds are composed of…
fine material, this is the main part of the continuation of the river’s floodplain. These beds are extended and by the work of numerous distributaries.
The character of a delta is influenced by:
- the rate of river deposition
- the rate of stabilisation by veg. growth
- tidal currents
- the presence of long-shore drift
- human activity
Main types of delta:
- Arcuate delta/fan-shaped
- Cuspate delta
- Bird’s-foot delta
Arcuate delta can be found…
in areas where long-shore drift or other currents keep the seaward edge of the delta trimmed and smooth shape. E.g. Nile.
Cuspate delta is pointed like…
a tooth or cusp. E.g. Tiber delta, shaped by regular but opposing gentle water movements.
Bird’s-foot delta is where the river…
brings down enormous amounts of fine silt, the deposition can occur in a still sea area, along the edges of distributaries for very long distance offshore. E.g. Mississippi delta
Lacustrine delta is formed…
when the river enters the lake, it will deposit some of its load. As the delta builds up, it can ultimately fill the lake basin.
