ddCoastal landscapes and change - Coastal landforms and landscapes

Question 1

What are waves caused by?

Answer 1

Waves are caused by friction between wind and water.

Question 2

Why are waves extremely important along any stretch of the coast?

Answer 2

They are extremely important along any stretch of the coast as they directly influence the three marine processes of erosion, transport and deposition.

Question 3

What factors does wave size and strength depend on?

Answer 3

Wave size and strength depends on:

• the strength of the wind
• the length of time the wind blows for
• water depth
• wave fetch

Question 4

What is the fetch?

Answer 4

The uninterrupted distance across water over which the wind blows. It is the distance over which waves are able to grow in size.

Question 5

What is the difference between waves and tides?

Answer 5

Tides are formed by the gravitational pull of the Moon on water on the Earth’s surface. This causes sea level (the tide) to rise and fall twice a day. Tidal ranges vary from place to place. Waves are more localised disturbances of the sea caused mainly by wind.

Question 6

What is happening to the water particles within a wave?

Answer 6

They are moving in a circular rotation.

Question 7

What are the characteristics of constructive waves?

Answer 7

Constructive waves are of low height and long length. They are sometimes described as ‘spilling’ waves with a strong swash and a weak backwash. The strong swash pushes sediment up the beach and deposits it in a ridge at the top of the beach. The weak backwash means that the deposited material is not dragged back to the sea.

Question 8

What is swash?

Answer 8

The flow of seawater up a beach as a wave breaks.

Question 9

What is backwash?

Answer 9

The return flow of seawater back down the beach to meet the next incoming wave.

Question 10

What are the characteristics of destructive waves?

Answer 10

Destructive waves are relatively high with a short length. This makes them ‘plunging’ waves with a strong backwash that erodes and carries away beach material.

Question 11

What is beach morphology?

Answer 11

The shape of a beach, including its width and slope (the beach profile) and features such as berms, ridges and runnels. It also includes the type of sediment (shingle, sand, mud) forming the beach.

Question 12

What is beach morphology strongly conditioned by?

Answer 12

Beach morphology is strongly conditioned by the nature of the prevailing waves. But wave conditions can fluctuate over time and bring with them changes to beach morphology.

Question 13

What are the four diagnostic beach features of prevailing wave conditions?

Answer 13

There are four diagnostic beach features of prevailing wave conditions:

• storm beach: the result of constructive waves during stormy weather
• berms: small ridges built by constructive waves during relatively calm weather
• cusps: the product of gentle destructive waves eroding berms
• offshore bars: formed by persistent destructive waves.

Question 14

Identify the sources of beach material.

Answer 14

From the erosion of the coast from silt and sand brought down the coast by rivers. Some may also come directly from weathering and mass movement. Material can also be rolled towards the coast from offshore deposits.

Question 15

When does erosion mostly occur?

Answer 15

It mostly occurs during storms when:

• waves approach the coast at rights angles
• the tide is high
• heavy rainfall has weakened the rocks of the cliff
• debris at the foot of the cliff has been removed and no longer protects this critical point.

Question 16

Why does most erosion take place during storms?

Answer 16

That is when wave energy is at its strongest and waves strike the coast with great force. Wave activity at this time will predominantly destructive rather than constructive.

Question 17

What are the four main types of marine erosion?

Answer 17

There are four main types of marine erosion:

• hydraulic action: wave quarrying when air trapped in joints and cracks is compressed by the force of waves crashing against the cliff
• abrasion (corrasion): sediment being carried in the waves has a wearing-down effect
• attrition: the wearing down of sediment as it is moved around by the waves
• corrosion (solution): carbonate rocks such as limestone are dissolved by rainwater, sea spray and seawater.

Question 18

H

Answer 18

d

Question 19

d

Answer 19

d

Question 20

Attrition

Answer 20

d

Question 21

Corrosion (solution)

Answer 21

d

Question 22

How is a wave-cut notch formed?

Answer 22

Perhaps the most critical erosional feature is the wave-cut notch formed by the process of hydraulic action and abrasion. As the notch becomes deeper, the rocks overhanging it become unstable and eventually collapse. Repeated cycles of notch cutting and collapse cause cliffs to recede inland.

Question 23

Explain the sequence of erosional landforms that starts with a cave and finishes with a stack.

Answer 23

The cave is subjected to erosion, particularly hydraulic action. The cave is gradually enlarged until it reaches a cave being excavated on the other side of the headland. When they join, an arch is formed. This is gradually weakened until the point is reached when the cave roof collapses and the outer-limb of the each becomes a stack.

Question 24

What are the four different ways sediment is transported by the sea?

Answer 24

Sediment is transported by the sea in four different ways:

• traction: heavier sediment (pebbles, boulders) rolls along the sea floor, pushed by waves and currents
• saltation: sediment (mainly sand particles) bounces along the floor
• suspension: fine sediment (silt, clay) is carried within the body of water
• solution: dissolved sediment (calcium carbonate) is carried in the water as a solution.

Question 25

What are currents?

Answer 25

Flows of seawater in a particular direction driven by wind, tides and differences in density, salinity and temperature.

Question 26

What is longshore drift?

Answer 26

Much of the transport of sediment takes place along the coast rather than into and away from the shore. This is known as longshore drift. Such a movement is produced by waves approaching the coast at an angle. The swash pushes sediment obliquely up the beach and backwash returns it directly to the sea. The combination results in sediment slowly moving along the coast in the same general direction as the waves approach the shore.

Question 27

Is longshore drift a current? Give your reasons.

Answer 27

Yes, because it flows consistently in a given direction. But unlike ocean currents, it is not driven by differences in water salinity and temperature. It provides a means of transporting sediment along the coast.

Question 28

What are the main features produced by the deposition of transported sediment?

Answer 28

The main features produced by the deposition of transported sediment are:

• bayhead beach
• spit
• recurved hooked spit
• bar
• tombolo
• cuspate foreland.

Question 29

What is a bayhead beach?

Answer 29

An accumulation of sand at the head of a sheltered stretch of water between two headlands

Question 30

What is a spit?

Answer 30

A sand or shingle beach ridge extending beyond a turn in the coastline

Question 31

What is a recurved hooked spit?

Answer 31

A spit built out into a bay or across an estuary, the end of which curves landward into shallower water

Question 32

What is a bar?

Answer 32

A sand or shingle beach extending across a coastal indentation with a lagoon behind

Question 33

What is a tombolo?

Answer 33

A sand or shingle bar that attaches a former offshore island to the coast

Question 34

What is a cuspate foreland?

Answer 34

A triangular area of shingle extending out from a shoreline, possibly formed by longshore drifts from opposing directions.

Question 35

What are sediment cells?

Answer 35

Long stretches of coastline that operate as almost self-contained physical systems. In each sediment cell there are sources (inputs), where sediment is generated (e.g. eroding cliffs and beaches), transfer zones (flows), which are stretches where sediment is moving along the coast by longshore drift and currents, and sinks (outputs), locations where the dominant process is deposition (e.g. spits and offshore bars).

Question 36

What is weathering?

Answer 36

The disintegration and decomposition of rocks in situ by the combined actions of the weather, plants and animals.

Question 37

What is mass movement?

Answer 37

A collective term for the process responsible for the downslope movement of weathered material under the influence of gravity.

Question 38

What are the three types of weathering?

Answer 38

There are three types of weathering:

• mechanical: the breakdown of rock by some form of physical force
• chemical: involving a chemical reaction and decomposition
• biological: the actions of bacteria, plants and animals, which speed up mechanical or physical weathering.

Question 39

What are the processes of weathering at work in any location conditioned by?

Answer 39

The processes of weathering work in any location are controlled by climate (rather than the weather). Temperature and precipitation are the key climatic elements.

Question 40

What type of weathering prevails in the hot, humid parts of the world?

Answer 40

Strong chemical weathering

Question 41

Where in the world is mechanical weathering most effective, and why?

Answer 41

In cold, temperate or periglacial regions, where there is little precipitation but temperatures fluctuate around freezing point. Much freeze-thaw activity causes much mechanical weathering.

Question 42

What can mass movement be classified according to?

Answer 42

Mass movement can be classified in a number of ways, such as by the speed of movement and the type of material moving (solid rock, debris or soil).

Question 43

What are the common types of mass movement along cliffed coastlines?

Answer 43

• Rockfalls occur where the rock on a cliff being undercut by the sea is weakened by weathering. Falls can be sudden and spectacular.
• Rotational slides are slow downslope movements of a mass of rock or debris over a curved plane. They are particularly common where a permeable rock (e.g. sandstone) overlies an unstable impermeable rock (e.g. clay). Water passing through the permeable rock lubricates the junction with the underlying impermeable rock, thus facilitating the sliding.
• Landslides are sudden downslope surges occurring when weathered rock and soil become saturated and lubricated by water (meltwater, springs).

Question 44

When do rockfalls occur?

Answer 44

Rockfalls occur where the rock on a cliff being undercut by the sea is weakened by weathering. Falls can be sudden and spectacular.

Question 45

What are rotational slides and when are they particularly common?

Answer 45

Rotational slides are slow downslope movements of a mass of rock or debris over a curved plane. They are particularly common where a permeable rock (e.g. sandstone) overlies an unstable impermeable rock (e.g. clay). Water passing through the permeable rock lubricates the junction with the underlying impermeable rock, thus facilitating the sliding.

Question 46

What are landslides and when do they occur?

Answer 46

Landslides are sudden downslope surges occurring when weathered rock and soil become saturated and lubricated by water (meltwater, springs).

Question 47

What are the distinctive coastal landforms created by mass movement?

Answer 47

The distinctive coastal landforms created by mass movement include screes (the product of mechanical weathering of an exposed rock face), rotational scars (the outcome of slumping) and cliff terraces (the result of rotational sliding).

Question 48

What is the difference between a) rockfalls and rotational slides, b) screes and cliff terraces?

Answer 48

a) Rockfalls are a rapid form of mass movement (rocks often falling vertically) whereas rotational slides are the outcome of mass movement along curved failure surfaces.
b) Screes are masses of weathered, angular rock fragments collecting below a free face to create a talus. Cliff terraces are the result of rotational sliding.

Question 49

Why do sea levels change on a day-to-day basis?

Answer 49

Sea levels change on a day-to-day basis as a result of tides, changes in atmospheric air pressure and winds. Such changes are very short term.

Question 50

Why do sea levels change over long time scales?

Answer 50

Sea-level changes are more permanent and the outcome of complex factors. Part of the complexity is that a change in sea level can be brought about by a change in either land level (isostatic change) or in the volume of the sea (eustatic change).

Question 51

What does a marine regression result from?

Answer 51

A marine regression results from a eustatic fall in sea level (as during glacial periods when water becomes locked up in ice and snow) and an isostatic fall in sea level (when ice sheets melt and the land rises). Both movements expose the seabed and produce an emergent coast.

Question 52

What type of coast is produced by marine regression?

Answer 52

Both movements expose the seabed and produce an emergent coast.

Question 53

What does a marine transgression result from?

Answer 53

A marine transgression results from a eustatic rise in sea level (at the end of a glacial period) and an isostatic rise in sea level (when land sinks under the weight of accumulated snow and ice). In both cases, large areas of land are submerged beneath the sea, producing a submergent coast. The ria coastline is one of the best examples of such a coast.

Question 54

What type of coast is produced by marine transgression?

Answer 54

Large areas of land are submerged beneath the sea, producing a submergent coast. The ria coastline is one of the best examples of such a coast.