Coasts

Key definitions

Swash — the rush of sea water up the beach after a wave is broken.

Backwash — the flow of sea water back down into the sea.

• Swash — the rush of sea water up the beach after a wave is broken
• Backwash — flow of sea water back down into the sea

Waves

There are 2 types of waves:

• Constructive waves — powerful swash, weak backwash
• Destructive waves — powerful backwash, weak swash

Longshore drift

1. The waves swash at the angle of the prevailing winds
2. The backwash is 90 degrees towards the sea
3. The continuous swash and backwash transports the sediment across the beach

Erosional landforms

Similar to features of rivers — use keywords and the names of fluvial processes.

Headlands and bays

1. A cliff is made of alternating layers of hard and soft rock
2. The soft rock erodes quicker than the hard rock due to hydraulic action
3. Hard rock is more resistant and erodes slower
4. This difference in erosion speeds causes headlands and bays
5. Headlands — hard rock
6. Bays — soft rock

Caves, arches, stacks and stumps

1. The headland is surrounded by waves on all sides, so energy is concentrated
2. A crack opens up due to hydraulic action
3. The crack grows due to erosion (hydraulic action and abrasion); the base of the cliff erodes, causing a wave-cut notch to form
4. Over time, a cave forms
5. The cave erodes on opposite sides of the headland, causing a natural arch to form
6. The arch collapses after erosion to form a stack
7. The stack erodes into a stump

Cliffs and wave-cut platforms

1. The sea attacks the base of the cliff
2. A wave-cut notch forms
3. The backwash of the waves carries the rubble back into the sea, forming a wave-cut platform
4. The notch increases in size, undercutting the cliff and causing it to collapse

Depositional landforms

Spit

1. Longshore drift carries/transports sediment in the direction of the prevailing wind
2. Material is curved due to the secondary winds as it meets the estuary — this is called a curved end
3. The coastline changes direction, but the material is still deposited in the direction of the prevailing wind
4. Behind the spit, a lagoon/marsh often forms

Beaches

1. Material is deposited in bays
2. Bays are more sheltered land with lower-energy waves that tend to be constructive
3. More sediment is deposited than eroded
4. Longshore drift transports this sediment along the coast, forming a beach

Sand dunes

1. Embryo dunes form around deposited material such as a piece of rock or wood
2. They develop and become stabilised by vegetation (marram grass)
3. As vegetation dies, nutrients are provided to the dune, making it more fertile for vegetation to grow
4. Wind may cause depressions in the sand called slack dunes, where ponds may form

Coral reefs

• Found in shallow waters less than 25 m
• Located in tropical water
• Thrive in saline water
• High biodiversity — home to over 25% of all marine species
• Temperatures of 23–25 degrees C
• The largest coral reef is the Great Barrier Reef

3 types of coral reefs

Benefits and threats to coral reefs

Mangroves

• Found in between the tropics in warmer water
• Found around the coasts of every continent except Antarctica and Europe
• Salt-tolerant trees adapted for coastal conditions
• Has salt-secreting leaves, aerial roots and stilt roots to breathe during different tidal levels

Benefits and threats to mangroves

Coastal management

Case study of a coast — Hawaii

• Tourism: $17 billion (2019) in visitor spending
• 10 million tourists in 2019
• 7,300 farm operations (2022)
• 60% of USA's coral reefs

Opportunities and hazards of living near a coast

Solutions

1. Hawaii Coastal Zone Management Program takes aerial pictures of the coast and discusses the next steps to stopping erosion and predicting future erosion.
2. Sea walls (but this could threaten nearby coastlines like Sunset Beach).
3. Sandbag gabions for citizens to use as a form of small-scale protection.

Coastal disaster case study — Typhoon Haiyan (Philippines)

• Wind speeds of 315 km/h
• 8th November 2013
• Category 5 tropical cyclone
• $2.98 billion in damage

Causes, impacts and response