2B.8 Rapid Coastal Retreat

Question 1

how is rapid coastal erosion caused?

Answer 1

by physical factors when geological and marine characteristics combine to promote erosion

Question 2

geological factors

Answer 2

-lithology (hardness of rock, bonds, pores)
-structure (joints, dipping bends, faults)

Question 3

marine factors

Answer 3

-long wave fetch causing destructive waves
-strong longshore drift- removing sediment for erosion

Question 4

how can human activity increase rates of coastal recession?

Answer 4

by interrupting the operation of the sediment cell
e.g. constructing major dams of rivers, trapping sediment, starving sediment source

Question 5

example of dam construction

Answer 5

Aswan High Dam on the River Nile in 1964 reduced sediment volume from 130 million tonnes to about 15 million tonnes per year
- the delta was starved of sediment so erosion rates increased significantly

Question 6

coastal recession

Answer 6

the retreat of a coastline due to erosion, sea level rise or submergence

Question 7

dredging

Answer 7

the removal of sediment from a beach, sea or river

Question 8

how does dredging work?

Answer 8

-sands or gravels are scooped and sucked up for construction
-often done to maintain navigable channels in river mouths and estuaries for ship transport.

Question 9

how do sub-aerial processes work together to influence rates of coastal recession?

Answer 9

weathering
-weakens rocks above high tide mark, making mass movement easier by reducing internal cohesion of rock

mass movement
-repetitive actions lead to rapid coastal recession

Question 10

give examples of short term variations in coastal recession

Answer 10

-wind direction and fetch
-tides
-storms

Question 11

give examples of long term variations in coastal recession

Answer 11

-seasons
-weather systems

Question 12

wind direction and fetch influencing rates of recession

Answer 12

-winds change direction daily, when wind blows onshore, recession rates are higher
-dominant wind is the direction of the strongest wind/ prevailing wind is the direction of the most common wind

when wind blows from prevailing direction, strong winds produce large destructive waves

Question 13

tides influencing rates of recession

Answer 13

high tide has higher levels of recession
-this is because there is deeper water in the foreshore zone, so waves can maintain more energy when they reach the backshore
-greater energy of impact on backshore increases erosion and rates of recession

Question 14

storms influencing rates of recession

Answer 14

storm events are low pressure/ deep depressions
-they produce large, high energy destructive waves and fats rates of recessions

-global warming is predicted to increase intensity of storms and frequency

Question 15

seasons influencing rates of recession

Answer 15

-storm events occur more in winter, when the contrast in temp and pressure between tropical and polar air masses is the greatest
-in the UK, rates of recession are faster in the winter than summer

Question 16

weather systems influencing rates of recession

Answer 16

common interaction between the polar front (cold air) and tropical air (warm air from ferrel cell) produces high air pressure anticyclone and low air pressure depression weather systems

-anticyclones produce gentle winds and small waves (low rates of recession)
-depressions are areas of rising air- low pressure (produce strong winds and rapid rates of recession)