Deltas

Question 1

Distributary

Answer 1

A small channel that leaves the main river channel and doesn’t return. They occur when a river is overloaded with sediment, so the sediment is deposited, meaning that the river must split into two channels. These two channels will have a reduced energy level, so further deposition and dividing will occur

Question 2

Levée

Answer 2

Natural embankments that are formed when the rate of deposition is greater than the rate of erosion (coastal accretion)

Question 3

Crevasse splay

Answer 3

A sedimentary fluvial deposit which forms when a stream breaks its natural or artificial levees and deposits sediment on a floodplain

Question 4

Cuspate delta

Answer 4

Cuspate deltas are vaguely shaped like a V with curved sides. They form when a river flows into a sea with waves that hit it head on, spreading the deposited sediment out.

Question 5

Arcuate delta

Answer 5

Triangle-shaped deltas formed of sands and gravels

Question 6

Bird’s foot delta

Answer 6

Deposited material divides the river into smaller distributaries

Question 7

What is a delta?

Answer 7

Large areas of sediment found at the mouths of many rivers.

Question 8

Deltas typically form where…

Answer 8

• Rivers entering the sea are carrying large sediment loads
• A broad continental shelf margin exists at the river mouth to provide a platform for sediment accumulation
• Low-energy environments exist in the coastal area
• Tidal ranges are low

Question 9

The structure of deltas usually consists of three different components:

Answer 9

• The upper delta plain (furthest inland, beyond the reach of tides and composed entirely of river deposits)
• The lower delta plain (in the inter-tidal zone, regularly submerged and composed of both river and marine deposits)
• The submerged delta plain (lies below mean low water mark, is composed mainly of marine sediments and represents the seaward growth of the delta)