Depositional Landforms

Agents of deposition

Wind, Flowing Water, Glaciation, Flocculation, Gravity and Weight, Sea

Depositional landforms are what?

Temporary (constantly changing) stores of sediment

They form in lower energy environment where deposition > erosion

Parts of a beach

Backshore, Forsehore, Nearshore, Offshore

Ridges and Runnels

Sand allows for little percolation

Holds water

Swash and backwash retreat leads to peak and trough formation

Parallel to the coastline

Broken up by drainage channels

Ridges and runnels

Drainage system for the shallow beach

Example = Woolacombe Beach

Shingle beaches

Steep due to rapid percolation and therefore weak backwash

Sandy beaches

Shallow (5 degrees) due to lots of friction and backwash due to little percolation spreading material out

Top of beach (Backshore)

Storm beach

Largest bits of material deposited here above the high tide line

Moved by huge waves in storm conditions

Nearshore

Contains ridges called berms built up by strongest constructive waves

As a result of variation in the high tide mark

Due to change in spring and neap tides

Cusp

Semicircular formations where sandy beach meets single beach

Waves break directly onto this structure
Get reflected around the edge of the cusp, focus the backwash onto the centre

Leads to increased erosion in the centre

So cusp grows

Swash Alligned

Waves hit at approx 90 degrees

Minimal LSD effect

Material is deposited quickly

No transport takes place

Drift aligned beaches

Waves do not hit at 90 degrees

Longshore drift is dominant

Fine sediment can be moved easily

Culminate in depositional landforms other than beach e.g. spit bar

Overall transport in direction of prevailing wind

Spit

LSD causes beach to extend past headland / over landform

Extend out into sea lose energy and deposit

Change in direction forms a hook

Sheltered area behind spit can form salt marsh or mud flat

Spit example

West Wittering

Spits usually form on

A drift aligned beach

Curve / Hook in spit caused by

Change in prevailing wind or current

Change in dominant energy source

Simple vs compound spit

Simple: Straight or slight curve, no other landforms on the spit

Compound: More complex shape, Landforms on the spit e.g. minor spits as a result of previous spit termination

What can form on spits over time

Sand dunes

Spit joins land to island

Tombolo

Spit covers up a bay

Bar

Bar form when

INflow / outflow is reduced enough to allow deposition between the two headlands

Leads to the formation of a lagoon

Potential for a marsh to form in the lagoon

Bar can be

Offshore - does not need to form over a headland / bay

Submerged - it can be covered up at high tide

Bar formation

Beach material is eroded and carried offshore

Reduce in energy and deposit into the bar

Barrier island

Narrow island of sand or gravel that run parallel to the shore

Barrier island

Lies offshore and protects the coastline from wave energy

Sand dunes can develop on it

Sheltered area can become a lagoon or marsh

In tropical areas it could grow mangroves

Formed when a spit is breached

Barrier island formation

Need:

Good sediment supply

Shallow Coast

Low tidal range

Result of:

Eustatic sea level rise

Erosion of bar or other landform

Sand dunes

Mounds and ridges of sand piled up at the back of the beach as a result of Aeolian deposition

Pre requisites for sand dune formation

Large tidal range

Large sediment supply

Dominant onshore wind

(obstacle to form around)

Why is wind typically onshore

Due to localised differences in heating on and offshore

Typically lower pressure on land, heats faster

Wind transport sediment by

Saltation, Traction, Suspension

NOT Solution

Dune order

Dune start

Embryo dune

Fore dune

Yellow dune

Grey dune

Mature dune

Increases / decreases in order

pH increases as further back - more acidic in bigger dunes

Size increases as go back

Soil fertility increases as further back - leads to greyish dunes

Organic material in the dunes increases as further back

Organic material called?

Humus

Water table?

Increases as further back

Vegetation

Succesive vegetation, with more and larger plants the further back

First colonising species

Marram Grass

Vegetation role

Trap sediment and add root systems for structure to grow the dune

Plant adaptations

Halophyte: Adapted to live in high salinity

Xerophyte: Adapted to live in dry conditions

Halophyte example

Sea grass

Xerophyte example

Marram grass

Semif fixed vs fixed

Semi fixed - early stages, not fully fixed in place

Fixed - permanent features and landforms

What can form between Mature fixed dunes?

Dune Slack

Blowouts

Blowouts

Where people, wind or plant life has burrowed a channel into a dune system and removed material

Dune Slack

Wetland environment between dunes

How does dune slack form

Water table rises up above the trough of the dune, percolates up through the sand, usually brackish stagnant water, great wetland environment with high biodiversity

Mudflat vs Saltmarsh

Mudflat: Bare, collection of sediment with little structure or vegetation

Saltmarsh: More permanentt, stable landform of eastaurine deposition with an ecosystem and successive vegetation

Further differences

Mudflat is low lying and can be submerged at high tide

Mud flats or salt marshes form in?

Dune Slacks

Estuaries

Both of them form due to

Reduction in energy in the water and it drops sediment

Typically brackish water

Why does brackish water lead to deposition?

Flocculation

Floculation

Sediment carried in both the fresh and saltwater clumps together to form an aggregate when they meet.

Gain weight and water doesnt have enough energy to carry = deposition

Mudflat can have?

Small channels in which water is always present

Mud flat does not get?

Colonised, may be temporary or within early stages of development into a saltmarsh

Mud flat example

Morecambe Bay, Northwest England

Saltmarsh is when?

The mudflat gets colonised with a significant amount of successive plant species

Plant species lead to?

Stability within the marsh

Root systems

Trap more sediment and growth of the marsh

Once plants die

Humus added to the soil

Can bubt not always break down into organic material

This enocurages?

Further successive plat growth and the eventual creation of an ecosystem

Mudflat typically

Closer to the sea

Higher energy

Firs species there

Cordgrass, Marsh Grass, Spartina

Spartina has?

Specifically thick root systems, fine mat of roots

Makes it dominant over other pioneer species

Develop into?

Small trees, Slat Grass, Denser vegetation, adapted to the salinity

Halophytes

Vegetation succession known as

Halosere

Salt marsh when it is mature cnas have

Drainage channels

Steep banks

Thick vegetation

High saline conditions

Drainage Channels

Mud levels rise, water need to drain

Easy to erode a drainage channel

At this mature stage

Trees such as Oak and Ash trees can start to grow in the environment