Depositional Coastal Landforms

Describe how a spit forms:

Sediment accumulates in a sea-ward arm due to longshore drift and deposition.

Describe how spit recurves form:

Recurves form when waves refract in the deep waters surrounding the distal end, or when there are two different main wave directions.  

What is the ecological importance of a spit?

They shelter the water behind, leading to mudflat/marsh development, providing important habitat.

Give an example of a spit and it’s ecological importance:

 

E.g. Dawlish Warren Spit is a Special Area of Conservation (SAC) as it hosts wading birds (e.g. plovers, oystercatchers, and black tailed godwits), rare petalworts, and 600 types of flowering plant, and 2000 species of invertebrate. 

Define a barrier island:

Linear wave-built islands form parallel to the coastline due to deposition. They can be 100m to many km wide and reach 10s of m high.

Give some key features of a barrier island:

• Ocean front beaches

• Inlets

• Interior with vegetated dunes and washover flats

• Sheltered lagoons behind, forming tidal flats and marshes

Describe how a barrier island inlet forms:

Formed by storm breaches, pushing the crest down so water can flow and exchange of sediment occurs. 

If tidal flow > littoral sediment drift, the inlet can become permanent, or grow. 

Give an example of inadvisable barrier island development:

Since 2020, 27 homes in Buxton and Rodanthe, NC, have collapsed into the sea, especially during storms. 

Define a tombolo:

Wave-built ridges of sediment that link islands together or to the mainland. They are usually swash-aligned, and form when wave refraction round the island slows the waves and leads to deposition in the "shadow". 

 

However they can form when long-shore drift reaches an island. E.g. Chesil Beach connects the Isle of Portland to the mainland.  

Define a swash-aligned beach:

Aligned perpendicular to the direction of prevailing waves.

Define a drift-aligned beach:

Aligned at an angle to the wave direction, leading to sediment flow through the beach.

Describe the impact of climate change on barriers:

• Barrier erosion (Bruun rule) 

• Barrier translation  - entire barrier moves without loss of material 

• Barrier overstepping – the barrier is drowned, leaving it as a relict feature (happens when the change is fast) 

This process is called transgression (e.g. during the early Holocene due to rapid sea level rise) 

Define a cuspate foreland and give an example:

These form when longshore drift currents in opposite directions converge.  

E.g. Dungeness in Kent is 11km long. It is thought to have formed from 2 opposing spits that connected, then infilled through succession and deposition.

Define a delta:

Depositional lowlands formed around river mouths. In some places (e.g. north coast of Java) these can become confluent with other deltas, creating deltaic plains.

Give an example of a river delta:

E.g. the Mississippi Delta, which has a 3.3m km^2 catchment and delivers 240bn kg of sediment each year. The delta itself is 28.5 thousand square km. It has 7 major lobes. 

What species does the Mississippi delta support?

There are 40% of NA migratory birds, 10m ducks and geese, bass, catfish, redfish, tuna, 100 black bears, beavers, armadillos, and much more. 

Describe the shape of washover deposits:

Usually lobe-shaped, with tree-like branches of sediment or water.