Coastal Systems

What is a coastal system?

an area where the sea and land interact and energy and sediment are transferred between inputs, processes, and outputs

What are the main inputs in a coastal system?

• wave energy

• tidal currents

• sediment supply

• wind energy

What are the main outputs in a coastal system?

• sediment lost offshore

• deposition beyond the sediment cell

• sediment transported alongshore

What is a sediment cell?

a stretch of coastline where sediment movement is largely self-contained

Why are sediment cells important?

• manage sediment supply effectively

• prevent erosion elsewhere along the coast

What is longshore drift?

the movement of sediment along the coast in a zigzag pattern, caused by waves approaching at an angle

What factors affect wave energy?

• wind speed

• wind duration

• fetch

What is the difference between constructive and destructive waves?

• constructive waves have strong swash and weak backwash, leading to deposition

• destructive waves have weak swash and strong backwash, leading to erosion

What are the main types of coastal erosion?

• hydraulic action

• abrasion

• attrition

• solution

What is hydraulic action?

waves compress air in cracks, causing pressure that weakens rock

What is abrasion?

sediment in waves wears away cliffs like sandpaper

What is attrition?

rocks collide with each other becoming smaller and smoother

What is solution?

acidic water dissolves soluble rocks, such as limestone

What is differential erosion?

softer rock erodes faster than harder rock, creating varied landforms

How are headlands and bays formed?

• alternating bands of hard and soft rock

• soft rock erodes faster, forming bays

• hard rock erodes slower, forming headlands

Why do headlands experience more erosion?

wave refraction concentrates energy on headlands

Why do bays experience more deposition?

wave refraction reduces energy, allowing sediment to accumulate

How does a wave-cut platform eventually form?

1. waves erode the cliff base

2. a notch is formed

3. the cliff collapses, leaving a flat platform

How do caves, arches, stacks, and stumps form?

1. waves exploit weaknesses/cracks in the cliff to form caves

2. caves enlarge to arches

3. arches collapse to form stacks

4. stacks erode to stumps

What is a spit?

a narrow ridge of sand or shingle extending from the coast, formed by longshore drift

Why do spits often have a recurved end?

changes in wind and wave direction curve the end landward

What is a bar?

a spit that extends across a bay, trapping water behind to form a lagoon

What is a tombolo?

a ridge of sand connecting an island to the mainland, formed in the island’s wave shadow

What is a beach?

a depositional landform made of sand, shingle, or pebbles accumulated by waves

What factors influence beach formation?

• wave energy

• sediment supply

• tidal range

• geology

What are the main features of a beach profile?

• berm

• beach crest

• beach face

• offshore bars

What is a berm?

a ridge of sand or shingle deposited at the back of a beach by constructive waves

What are sand dunes?

mounds of wind-blown sand stabilised by vegetation behind beaches

What are the stages of sand dune succession?

1. embryo dunes

2. foredunes

3. grey dunes

4. dune slacks

What are salt marshes?

coastal wetlands formed where fine sediment accumulates and vegetation stabilises it

Why are salt marshes important?

• reduce wave energy

• trap sediment

• support biodiversity

• act as natural flood defences

What is negative feedback in coastal environments?

a change in the system that reduces the impact of the change, helping maintain equilibrium

What is positive feedback in coastal environments?

a change in the system that increases further change, pushing the system away from equilibrium