Coasts Part 2

Question 1

Rate the erosion rates of the 3 rock types from most to least?

Answer 1

Igneous very slow(less than 0.1cm per year) crystalline interlocking, and limited joints

Metamorphic slow(0.1-0.3cm per year)crystalline however foliation

Sedimentary moderate to fast(0.5-10cm per year) clastic young rocks are weak

Question 2

What are erosion and weathering influenced by?

Answer 2

How reactive minerals in the rock are

Whether rocks are clastic or crystalline

The degree to which rocks have crack, fractures and fissures

Question 3

What are waves caused by?

Answer 3

Waves are caused by friction between wind and water transferring energy from the wind into the water, the force of the wind blowing onto the water creates ripples which grow into waves when the wind is sustained.

Question 4

What does wave size depend on?

Answer 4

The strength of the wind

Water depth

The duration of the wind blowing

Wave fetch

Question 5

What are the erosional processes?

Answer 5

Hydraulic action
Air is trapped in cracks and fissures and the rock is forced apart

Abrasion:sediment picked up by breaking waves is thrown against the cliff face chiselling away at the surface

Attrition: numerous collisions between particles slowly chip fragments off the sediment as they are moved by the waves

Corrosion:carbonate rocks vulnerable to solution by rainwater spray from the sea and seawater.0

Question 6

Explain the cave arch stack stump?

Answer 6

First a wave cut notch is formed which is eroded at the base of a cliff by hydraulic action and abrasion

As the notch becomes deeper, the overhanging rock above becomes unstable and eventually collapses as a rockfall

Repeated cycles of notch cutting and collapse cause cliffs to recede inland

The former cliff position is shown by a horizontal rock platform visible at low tide, called a wave cut platform

Question 7

What is salt crystallisation and what type of weathering is it?

Answer 7

Mechanical weathering and it is the growth of salt crystals in cracks and pore spaces which can exert a breaking force, porous and fractured rocks are vulnerable

Question 8

What is rock boring and what type of weathering is it?

Answer 8

It is biological and it is when clams and molluscs that bore into rock and may also secrets chemicals that dissolve rocks

Question 9

What is mass movement?

Answer 9

The downslope movement of rock and soil. It includes landslide, rockfall and rotational slide

Question 10

What are the four different mass movement processes?

Answer 10

Rockfall:Blocks can be dislodged by mechanical weathering or by hydraulic action. Undercutting of cliffs by wave cut notches can also be a cause

Topple: geological structure influences topple, it is when cliff is undercut so there is instability and blocks of material fall seaward

Rotational slide/slumping: huge masses of material can slowly rotate downslope from days to years, water is an important role and rotational slides create a back scar and terraced cliff profile

Flow: they are common in weak rocks such as clay or unconsolidated sands, it’s when materials become saturated lose cohesion and flow downslope. High waves and heavy rain contribute to this

Question 11

What causes eustatic fall in sea level?

Answer 11

During glacial periods, ice sheets form on land in high latitudes, water evaporated from the sea is locked in land as ice so there is a fall in sea level

Question 12

When is there eustatic rise in sea level?

Answer 12

At the end of a glacial period, melting ice sheets return water to the sea causing global sea levels to rise. Global temperatures then increase and sea level increases due to thermal expansion

Question 13

When is there isostatic fall in sea level?

Answer 13

During the build up of land based ice sheets the weight office causes the crust to sag, when the ice sheets melt the land surface slowly rebounds upward over thousands of years

Question 14

When is there isostatic rise in sea level?

Answer 14

Land can sink at the coast because of the deposition of sediment, particularly in large river deltas where weight of sediment deposition leads to very slow ‘crustal sag’

Question 15

Why is sea level rise hard to predict?

Answer 15

Thermal expansion of the ocean depends on how much global temperatures increase

Melting of mountain glaciers in the Alps Himalayas and other mountain ranges will increase ocean water volume

Melting of major ice sheets could also cause a dramatic increase

Question 16

What physical features do rapidly eroding coastlines have in common?

Answer 16

Long wave fetch, large destructive waves

Soft geology

Cliffs with structural weaknesses

Cliffs which are vulnerable to mass movement and weathering, and marine erosion

Strong longshore drift, so eroded debris is quickly removed exposing the cliff base to further erosion

Question 17

The most common cause of coastal flooding is a storm surge what is it caused by?

Answer 17

A depression(low pressure weather system) in mid latitudes

A tropical cyclone(hurricane,typhoon ) in areas jus north and south of the equator

Question 18

Why is Bangladesh vulnerable to flooding?

Answer 18

Much of the country is a low lying river delta(only 1-3m above sea level)

There is intense rainfall

The Ganges

Much of the coastline is unconsolidated delta sediment

Deforestation of coastal mangroves which used to stabilise costal swamps and dissipate wave energy

Question 19

What are the economic costs of coastal recession?

Answer 19

Loss of property in the form of homes businesses and farmland. These are relatively easy to quantify.

Question 20

What are the social costs of coastal recession?

Answer 20

Costs of relocation and loss of livelihood/jobs which although can be quantified there may be an impact on healt(stress and worry) which is much harder to quantify