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A Level Geography > 8.2. Depositional Landforms > Flashcards

8.2. Depositional Landforms Flashcards

1
Q

Depositional Landforms

A
  • produced by build up of sediment

- occurs where inputs > outputs (where rate of accumulation of sand and shingle exceeds the rate of its removal)

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2
Q

Beaches

A
  • most typical of all coastal landforms
  • usually made of sand and shingle
  • usually form between HWM (high water mark) and the LWM (low water mark) - in inter-tidal zone
  • sediment is moved longshore drift
  • a dynamic landform like a conveyer belt
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3
Q

Beach zones

A

1) backshore zone
2) foreshore zone
3) nearshore zone
4) offshore zone

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4
Q

Backshore Zone

A
  • part of the beach that is only underwater when there are storm waves or during the highest tides, so this zone is usually not under the influence of waves
  • lower energy than the foreshore and therefore there is less potential to remove sand
  • as a result, a greater amount of sand accumulates in the backshore environment
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5
Q

Foreshore Zone

A
  • part of coastal zone that is exposed at low tide and underwater at high tide
  • includes majority of wave action
  • higher energy removes sand
  • berm is the highest point on the beah and forms the foreshore-backshore boundary which changes seasonally
  • foreshore gives some protection to backshore against the effects of wave and tidal energy
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6
Q

Nearshore Zone

A
  • Seaward of the foreshore
  • permanently covered with water, except at extremely low tides
  • where waves break
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7
Q

Offshore Zone

A
  • further out to sea
  • beyond the influence of the waves
  • sediment can build-up in bars
  • if the bar grows enough to pierce the surface of the water, it can become a barrier island and a barrier beach
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8
Q

Role of Tides in the Formation of the beach profile

A
  • ebb and flow of the tides make the beach a transitional zone between land and sea
  • width and nature of foreshore and nearshore zones are determined by the tidal range as well as by the amount and type of beach sediment
  • spring tides shape the berms at the top of the beach
  • on beaches with a high tidal range, each falling tide reveals a new beach environment, washing clean of any sign of human activity
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9
Q

Role of waves in the Formation of the beach profile

A
  • waves have energy to change the beach
  • constructive waves move material up the beach, contributing to the berms and increasing gradient of the beach
  • destructive waves comb material down the beach, contributing the longshore bars and reducing the gradient of the beach
  • type of waves that break on any beach will change from day to day and season to season, depending on changing weather and climatic conditions like wind intensity and direction
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10
Q

The role of sediment in the formation of the beach profile

A
  • beach sediment is in constant motion and arrives on the beach from a range of sources: cliff collapse, rivers and sea bed
  • the larger the particle size, the steeper the beach
  • shingle is more permeable than sand so the backwash drains into it, rather than across it
  • shingle often makes up the upper part of the beach - thrown up by strong waves
  • sand is less permeable than single so there is more backwash
  • sand is smoother than shingle and causes less friction with the waves but the beach is gentler, so wider. This means the wave energy is dissipated over a wide area, not concentrated into a small area
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11
Q

Berm

A

terrace of a beach that has formed in the backshore, above the water level at high tide

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12
Q

Beach Cusps

A

semi-circular, scalloped depressions cut into the lower edge of the storm beach
- origins are controversial

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13
Q

Draw a Beach Diagram

A
  • dunes
  • backshore
  • foreshore
  • nearshore
  • offshore
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14
Q

Swash-aligned beaches

A
  • beaches where wave crests are parallel to the beach
  • waves come into the shore at 90 degrees, usually due to wave refraction. The waves wash up the beach and then swash back down the beach
  • there is therefore no longshore drift
  • located in bays
  • waves are parallel to the beach so the beach is swash aligned
  • rare
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15
Q

Drift-aligned beaches

A
  • formed by longshore drift (zig-zag migration of sediment along the beach)
  • wave crests approach the beach at an angle
  • hence, the beach will migrate laterally with the tide and the beaches are referred to as drift-aligned
  • beach may well continue parallel to the drift and detach from the coastline to form spits
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16
Q

Spit

A

an extension of sand and shingle extending from the mainland out into the sea.

17
Q

Spit Formation

A
  • The formation of a spit begins where the is a sudden change in the shape and direction of the coastline, for example at a headland.
  • Normally longshore drift carries sediment around the coast, however, when there is a substantial change in the shape longshore drift continues to deposit material in the same direction rather than following the coastline.
  • Overtime the ridge grows in size with material being deposited faster than it can be removed.
  • Deposition of sediment can be brought about earlier near estuaries as the flow of water into the sea is stronger than the drift, forcing the sediment to be dropped.
  • The shape of a spit can be changed by a couple of things:
  • Firstly wave refraction curves around the spit, forming a ‘hook’ on the end known as a recurved spit.
  • Change in the prevailing wind can also form the recurved end.
  • Sand dunes often form on spits as well as halophytic vegetation colonising the sheltered part of the sea behind the spit creating a salt marsh or mangrove swamp.
  • Spits are eroded by the sea and wind but as longshore drift continues along the coast, a constant supply of sediment ensures their continued existence.
18
Q

Features of a Spit

A
  • As spits grow, the water behind them is sheltered
    from wind and waves, and a salt marsh (temperate
    areas) or mangrove swamp (tropical areas) is likely to
    develop.
  • The end of a spit attached to land is called the
    proximal end, and the end extending out into water is
    called the distal end.
19
Q

Simple spit

A
  • A simple spit, either straight or recurved, occurs
    without the development of minor spits at its end or
    along its inner side.
  • One wind direction is dominant (prevailing wind), preventing the ‘hook’ at the end of the spit.
20
Q

Compound (recurved) spit

A

If the wave direction change is repeated more than once, hooked features may form along the length of the spit.
- This type of spit is called a compound recurved spit.

21
Q

Bars

A
  • formed as a spit grows across a bay, joining up 2 headlands
22
Q

Bars Formation

A
  • Bars are formed in similar ways to spits.
  • As longshore drift transports sediment down the coast, it deposits in low energy zones, such as a bay.
  • Bars are particularly noticeable at low tide where they can be exposed in relation to the rest of the beach.
  • During high tide, the bar can make the water shallow
    resulting in the waves breaking earlier before they reach
    the shore.
  • When a spit or a bar has enough sediment to continue to build up, it is possible that it may reach an island just off the coast. This is then known as a tombolo.
23
Q

Real world example of a spit

A

Laem Talumphuk in Thailand

  • long sandy spit with a hook is located along the coastline of Nakhon Si Thammarat province
  • the hook shape protects mangroves from strong waves and erosion of the mud flats
  • formed of sand deposited by the mainly northward current interacting with the outflow of the Pak Phanang River
24
Q

Real world example of a tombolo

A

Nang Yuan tombolo in Southern Thailand

25
Q

Tombolo

A

When a beach extends outwards to join an offshore island

26
Q

Barrier beaches

A

long, sandy beaches, detached from but parallel to the coastline

  • a tidal lagoon forms between the beach and original coastline
  • salt marshes and mangrove swamps often develop in this lagoon but sometimes strong currents are able to scour the lagoon clear of vegetation and loose sediment
27
Q

Barrier Islands

A
  • similar to bars, but they are detached from the beach and the processes operating on it
  • they take the form of a ridge of deposits parallel to the shoreline
28
Q

Theories of barrier island formation

A

1) Emergence Theory
2) Connected Spit Theory
3) Post-glacial Theory

29
Q

Emergence Theory (barrier island formation)

A
  • waves break over a submerged bar
  • bar emerges above sea level due to deposited sediment
  • bar develops into barrier island and lagoon
30
Q

Connected Spit Theory (barrier island formation)

A
  • spit starts to grow from point of land
  • spit is extended along the coast by longshore currents
  • spit is breached during a storm, forming a tidal inlet and barrier island
31
Q

Post-glacial Theory (barrier island formation)

A
  • dune ridge along the coast
  • rise in sea level starts to submerge dune and goes to other side of dune (trapping water on the other side)
  • barrier island and lagoon formed from the ridge

A Level Geography (30 decks)

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