Coasts

Question 1

Why do cliffs retreat and how are wave cut notches & platforms created?

Answer 1

• Cliffs retreat due to erosion from the wave being continually smashed against the rock. This leads to abrasion, hydraulic action, and solution.
• Wave cut notches form by erosional marine processes when destructive waves smash against the base of a cliff, causing it to retreat and form undercut. The cliff eventually collapses as it cannot hold its own weight. The material is broken down and rounded by attrition processes.
• Wave cut platforms form after the process of wave cut notches happens over and over again, leaving behind lots of material as the cliffs retreat inland. They can be uneven due to rocks having differences in erodibility. This is called differential erosion.

Question 2

How are bays and headlands created?

Answer 2

• Headlands are formed when the sea attacks a section of coast with alternating bands of hard and soft rock. The bands of hard rock erode more slowly than the bands of soft rock and they leave scetions of land jutting out into the sea. This is the headland.
• Bays are formed where the soft rock has eroded away.

Question 3

• How is a sea stack & stump created?

Answer 3

• A sea stack starts with a small crack in the rock. Hydraulic action and other marine erosional processes make the crack bigger and it eventually forms a cave. As the caves get very big and erode all the way through, they form a sea arch. As time goes on, the arch gets wider and wider due to marine erosional processes. Once the arch becomes so wide that the roof cannot support its own weight, it collapses, and we are left with a sea stack.
• As time goes on, erosional marine processes cause wave cut notches in the sea stack. When it cannot hold its own weight anymore, it collapses, leaving a sea stump.

Question 4

How is a beach created?

Answer 4

• Beaches are made up of eroded material that has been transported from elsewhere and then deposited by the sea. For this to occur, the wave must have limited energy, so beaches often form in places like bays. Constructive waves build beaches because they have a strong swash and a weak backwash.

Question 4

How is a spit created?

Answer 4

• A spit is created when the coastline changes direction, and sediment that is being carried by longshore drift continues to extend the coastline in the original direction by deposition. Longshore drift is when swash and backwash carry sediment across a beach according to the direction of the prevailing wind. Over time salt marshes can form on a well established spit.

Question 5

What conditions are needed for a sand dune to be created? How is a sand dune created?

Answer 5

• A beach needs a few conditions for sand dunes to be created.
• Large sand beach.
• A strong onshore wind to dry and transport the sand via saltation.
• An obstruction to trap the sand.
• When the wind encounters the obstacle on the beach velocity falls and sediment / sand is deposited around it
• Over time plants such as marram grass take root on the dune - this helps to stabilise the sand and establish the dune.
• As the plants on the dune die off they build up a layer of nutrient rich humus which allows for other more diverse plants to grow

Question 6

Where are coral reefs and mangroves located?

Answer 6

• Coral reefs are mainly found in tropical environments between the tropics of Capricorn and Cancer. They are found close to shorelines in shallow, warm water.
• Mangroves are mainly found in tropical environments between the tropics of Capricorn and Cancer. They can live in fresh or saltwater. They live on the coast. Australia & SE Asia as well as the coast of sub-Saharan West Africa, the Caribbean, and the Brazilian coast.

Question 7

What are the 3 types of coral reefs and what are they like?

Answer 7

• Fringing reefs: Reefs which are attached to the mainland and grow out into the sea.
• Barrier reefs: Coral grows in shallow water just off the coast. Usually the largest reefs.
• Atoll: Develop around sunken islands - a ring of coral in the sea with a lagoon in the centre.

Question 8

State 3 ways mangroves have adapted to their environment.

Answer 8

• Waxy leaves to prevent salt intrusion
• Pneumatophores - ‘snorkel roots’ that stick out of the water for breathing
• Cable roots that spread out to stabilise the mangrove tree

Question 9

State 5 benefits of mangroves.

Answer 9

• Carbon sink
• Habitat for marine life
• Coastal protection
• Water filtering
• A source of medicine

Question 10

Describe the conditions required for developing coral reefs.

Answer 10

• Warm water (18-32C - not too warm!)
• Shallow water (no deeper than 25m)
• Seawater, but not high salinity
• No sediment blocking the light
• Wave action for freshly oxygenated water - but not too harsh waves

Question 11

Describe the conditions required for developing mangroves.

Answer 11

• Warm environment (>20C, but cannot vary too much - max of 5ishC/y)
• Murky, dark, & silty water
• Tropical environment
• Saline environment (but can also survive and thrive in freshwater)
• Tide fluctuation to reduce competition & wash away waste as well as distribute seeds & provide nutrients