Coasts

Chapter Summary

• Waves come in two flavours — destructive (erode) and constructive (build beaches) — and their shape tells you which one you're dealing with.
• Erosion happens through four processes (hydraulic action, attrition, corrosion, abrasion) and carves cliffs, wave-cut platforms, headlands, bays, caves, arches, stacks and stumps.
• Transportation is mostly by longshore drift — a zig-zag conveyor belt that moves sand and shingle along the coast.
• Deposition builds beaches, spits, bars, tombolos, lagoons, barrier islands and sand dunes wherever the sea loses energy.
• Coastal ecosystems — coral reefs, salt marshes and mangroves — each thrive under very specific conditions and offer natural coastal protection.
• Coasts create opportunities (tourism, industry, fishing, farming, ports) but also hazards (storm surges, tsunamis, sea-level rise, tropical storms).
• Geology (hard vs soft rock) controls how fast and in what shape a coastline erodes.
• Coastal management uses soft engineering (works with nature) and hard engineering (fights nature) — chosen using Integrated Coastal Zone Management and Shoreline Management Plans (hold the line / advance the line / managed realignment / do nothing).
• Case study: Typhoon Haiyan (2013) shows how tropical storms form, how the Philippines prepared, and the social/economic/environmental impacts — both short and long-term.

1. Coastal Processes

Coastal regions — the vocabulary you need first

Before anything else, get these four terms straight — they get mixed up constantly in exams:

Tides happen roughly twice a day, and the tidal range determines how much of the shore gets exposed and attacked by waves.

How waves are made — and why size matters

Wind blowing across open sea creates waves. Three things decide how big a wave gets:

1. Wind speed — faster wind, bigger wave
2. Fetch — the distance the wind has travelled over open water. A longer fetch = more time for the wave to build energy
3. Duration — how long the wind has been blowing in the same direction

As a wave nears the coast, friction with the seabed slows its base down while the top keeps moving — this makes it rear up, crest, and crash onto the beach. Water rushing up the beach is the swash; water draining back down is the backwash.

Destructive vs Constructive waves

This is one of the most frequently tested comparisons in this whole chapter — memorise this table cold.

Marine erosion — the four processes

Destructive waves do most of the erosion, and they attack the coast in four distinct ways:

Marine transportation — how sediment moves

Sediment gets into the sea from cliff erosion, rivers, and longshore drift, then moves through the water via four methods:

• Traction — large boulders/pebbles rolled along the seabed
• Saltation — smaller stones bounced along the bed
• Suspension — fine sand/silt carried within the water
• Solution — dissolved minerals carried invisibly in the water

Longshore Drift (LSD) — the main transporter

This is arguably the single most important process in the whole coasts topic, because it explains why beaches shrink in one place and grow in another, and it supplies the raw material for almost every depositional landform you'll study.

Step by step: waves approach the beach at an angle (because of the prevailing wind direction). The swash carries sand/shingle up the beach at that same angle. But gravity pulls the backwash straight back down the beach, at 90° to the shore. Repeat this thousands of times and material slowly zig-zags its way along the coast in one direction.

Marine deposition

When constructive waves lose energy, they simply can't carry sediment any further, so they drop it. The largest material gets dropped first (at the top of the swash), and finer material settles further down/out, because the backwash loses energy as water drains into the porous sand.

During storms, large shingle gets thrown above the normal high-tide line, forming a ridge called a berm.

2. Coastal Landforms

A) Erosional Landforms

Cliffs & Wave-Cut Platforms

Waves attack the base of a cliff around the high-water mark, forming a wave-cut notch. Hydraulic action, abrasion and corrosion keep deepening this notch. Eventually the rock above the notch has nothing supporting it — so it collapses. The backwash carries the rubble away, leaving a flat, gently sloping rock platform at the cliff's base: the wave-cut platform. This process just keeps repeating, so the cliff face retreats further inland over time.

Headlands & Bays

These form on a discordant coastline — where bands of hard and soft rock run perpendicular (at right angles) to the waves. The soft rock (e.g. clay) erodes quickly, carving out a bay. The hard rock (e.g. limestone) resists erosion and is left sticking out as a headland.

Caves, Arches, Stacks & Stumps

This is a classic exam sequence — you need to be able to draw AND explain each stage.

1. Waves refract (bend) around a headland, concentrating their energy on all sides of it.
2. Hydraulic action, abrasion and corrosion exploit a weakness (a crack) in the headland → widens into a cave.
3. The cave is eroded from both sides until it breaks all the way through the headland → forms an arch.
4. Weathering from above + erosion below thins the arch's roof until it collapses → leaves an isolated pillar of rock called a stack.
5. The stack itself gets undercut at its base and eventually collapses into a low stump, mostly submerged at high tide → a stump.

B) Depositional Landforms

All of these landforms exist because longshore drift is bringing material somewhere and constructive waves are dropping it there.

Beach

Forms in sheltered places (like bays) where constructive waves dominate — swash > backwash, so material is deposited rather than removed.

Spit

A finger of sand/shingle that grows out from the coast into open water. It forms where the coastline suddenly changes direction (e.g. at a river mouth) — longshore drift keeps carrying material in the same direction, but there's no coastline left to deposit it against, so it just keeps building out into open water. If the wind direction shifts, the tip can curve into a "hook." Behind the spit, the water is sheltered, allowing fine silts to settle and form a salt marsh.

Real example: Spurn Point, stretching 3.5 miles across the Humber Estuary, England.

Bar, Lagoon, Tombolo & Barrier Island

Sand Dunes

Strong onshore winds pick up dried sand from the beach and carry it inland, where it gets trapped against obstacles (driftwood, rubbish, rocks) and starts to pile up. Over time, this becomes a dynamic process of succession — different plant species colonise the dune in a specific order as conditions improve.

The very first "pioneer species" have a brutal job — they must survive high salinity, almost no water retention (sand drains instantly), constant wind, being buried by fresh sand, and rising sea levels. As they die, they add organic matter, which lets less hardy plants move in behind them.

3. Coastal Ecosystems

Coral Reefs

Coral reefs are built by billions of tiny living animals called polyps. Only the outer/upper layer of a reef is alive — when a polyp dies, its hard calcareous (limestone-like) skeleton stays behind, and the next generation grows on top of it. Do this for thousands of years and you get a reef that grows both upward and outward.

Local factors also matter: reefs need well-oxygenated water from wave action, can't be exposed to air too long, and need clear water — sediment blocks light and clogs their feeding.

Three types of coral reef

Salt Marshes

Unlike coral, salt marshes aren't temperature-dependent — they're found worldwide, in sheltered, muddy inlets and estuaries where fine sediment can settle (also behind spits and sea defences). They start life as tidal mud flats. Pioneer plants called halophytes (salt-tolerant plants) colonise first; as they die, they add nutrients and trap more sediment, raising the land and letting new species move in — again, a process of succession.

Salt marshes act as a natural buffer, soaking up flood water and reducing coastal erosion — but human development (agriculture, construction) has destroyed many of them.

Mangrove Swamps

Mangroves are trees that literally grow standing in seawater (0.5–2.5m deep), ranging from small shrubs to giants over 60m tall. They're incredibly successful because — unlike sensitive coral — they've adapted to constantly changing, harsh conditions.

Where: warm tropical waters within 30°N/S of the equator (ideal ~27°C), needing high humidity (75–80%) and heavy rainfall (1,500–3,000mm/year).

Their secret weapon: root systems

• Prop roots / buttresses — anchor the tree upright in soft, shifting mud
• Snorkel roots — stick up out of the mud to grab air, since the soil is waterlogged and oxygen-poor
• These tangled roots trap mud, sand and silt — actually building up the intertidal zone into new land over time

Mangrove seeds/fruits can float and drift on ocean currents for many kilometres before lodging in mud and sprouting — that's how they colonise new coastlines.

4. Coastal Opportunities & Hazards

Opportunities

Coasts are hugely valuable to people — that's exactly why so many cities are built on them. Opportunities include: development (homes, shops, hotels, roads, schools), nature reserves, swimming/sports, industry, fishing and aquaculture, tourism, agriculture, and ports/harbours.

Hazards — Human-Induced

Every one of those opportunities above also creates consequences (what humans actually do) and impacts (the environmental result). This cause-and-effect pattern shows up again and again in exam questions:

Hazards — Natural

Several natural processes can combine to cause dangerous coastal flooding:

• Storm surges — extremely low-pressure storms (like tropical storms) cause the sea level to rise rapidly
• Storm tides — occur when a storm surge coincides with high tide, making the flooding much worse
• Tsunamis — huge waves triggered by underwater earthquakes; the closer to the coast, the bigger the impact
• King tides — unusually high natural tides
• Sea level rise — the long-term effect of global warming (melting ice + thermal expansion)
• High river discharge + spring tide — river water can't drain into a sea that's already high, causing backflow flooding upstream

Tropical Storms

Hurricanes, typhoons, and cyclones are literally the same phenomenon — they just get different names depending on where they form.

They form between 5–20°N and S of the equator (never right on the equator — there isn't enough Coriolis spin there). Northern hemisphere season: May–November. Southern hemisphere season: October–May.

How a tropical storm forms — step by step

1. Needs warm, deep ocean water (>27°C, depth >70m)
2. Warm water evaporates rapidly; the rising air cools, condenses, releases latent heat, and builds towering thunderclouds
3. This heat release fuels more uplift → an intense low-pressure cell develops
4. Winds get drawn into this low-pressure centre and the whole system starts to spin (thanks to the Coriolis force from Earth's rotation) and drift westward
5. Winds rotate around a calm central eye, where cold air actually descends
6. The eyewall surrounding the eye has the strongest winds of the whole storm

Changing Sea Levels & Geology

Rising sea levels drown existing valleys, producing submergent coastlines with features like rias (drowned river valleys) and fjords (drowned glacial valleys).

Falling sea levels expose old features, producing emergent coastlines with relic landforms like raised beaches and cliffs with old, dry caves/arches sitting well above the current waterline.

Pacific islands like Kiribati and Tuvalu are at real risk of total submersion from rising seas, while cities like New York and Miami — built essentially at sea level — are highly vulnerable too.

How geology (rock type) shapes the coast

5. Coastal Management

There's no single "correct" way to defend a coastline — it always comes down to weighing the cost of protection against the value of what's being protected. This is called Integrated Coastal Zone Management (ICZM) — using a mix of methods to satisfy all the different stakeholders involved.

Soft Engineering (works WITH nature)

Cheaper, more sustainable, less visually damaging — but generally less powerful than hard engineering.

Hard Engineering (fights against nature)

Expensive to build and maintain, but generally more reliable for protecting high-value land. Used when the economic value of what's protected (e.g. a power station, a city) outweighs the huge cost.

Predicting & Preventing Coastal Flooding

Prediction uses two approaches: past records (diaries, newspapers, council records) to identify high-risk zones and frequency, plus modern technology (GIS, satellites, weather stations) to actively track storms and earthquakes in real time.

Prevention reduces or removes the risk: flood defences on high-risk stretches, emergency centres on high ground, early warning systems, public education, and smart planning (raised buildings, dry/wet floodproofing, buffer zones that let land flood before it reaches settlements).

Shoreline Management Plans (SMPs)

Long coastlines are broken into manageable coastal cells to identify two key risks (erosion/land retreat and flooding), which makes cost-benefit decisions easier. Each cell is then assigned one of four strategies:

The choice between these depends on: economic value of what's protected, whether engineering is even feasible (you can't "hold the line" on a naturally shifting spit), cultural/ecological value, community pressure, and the social value of long-standing communities.

6. Case Study: Super Typhoon Haiyan (2013)

Background

Typhoon Haiyan (locally "Yolanda") was one of the strongest tropical storms ever to make landfall — a Category 5 storm hitting the Philippines on 8 November 2013 with sustained winds above 195 mph. The Philippines is a chain of islands in the South China Sea, regularly hit by southwest typhoons every storm season. Sea temperatures at the time were around 30°C — ideal fuel for a monster storm. Since 1900, global sea levels have risen ~20cm, contributing to stronger storm surges, and over-abstraction of groundwater has caused parts of the country to sink further. The city of Tacloban sits at the end of a funnel-shaped bay, which squeezed incoming water into an especially destructive storm surge.

Key statistics

Preparation

Despite being a developing country, the Philippines takes disaster preparedness extremely seriously — they're usually the first Pacific landmass any typhoon hits, so they've had decades of practice. Before Haiyan struck: risk maps were published, evacuation shelters were pre-designated, the military pre-deployed planes and helicopters to the areas expected to be worst hit, and the entire population of the island Tulang Diyot (1,000 residents) was evacuated in advance thanks to years of community education. One local mayor had even set up a "Purok system," where community members regularly pay into a shared fund for post-disaster recovery — rather than waiting on slow government relief.

Impacts

Immediate relief

Survivors immediately began searching flattened buildings for bodies, and looting broke out as government aid was slow. Debris-clogged roads and closed airports/harbours badly hampered the aid effort. International help arrived via charities (UK/USA sent diggers and heavy lifting gear), the European Commission ($4m), the UK Rapid Response Facility ($8m), and twelve IFRC Emergency Response Units worldwide. Recovery was made even harder because the Philippines had already been hit by a 7.3-magnitude earthquake just weeks earlier (Oct 2013) and Typhoon Bopha the year before — leaving national resources already stretched thin.

What to Memorise

Concepts Checklist

• I can define coast, shoreline, shore and tidal range correctly
• I can list and compare the features of destructive vs constructive waves
• I can name and explain all four processes of marine erosion
• I can describe and diagram how longshore drift works
• I can explain how a wave-cut platform and retreating cliff form
• I can explain how headlands and bays form on a discordant coastline
• I can sequence and explain cave → arch → stack → stump
• I can explain how a spit, bar, tombolo, lagoon and barrier island form
• I can describe sand dune succession from embryo to mature dune
• I know the four conditions coral reefs need and the three reef types
• I can explain how salt marshes and mangroves form and survive
• I can list coastal opportunities and match human activities to their consequences/impacts
• I can list natural coastal hazards and explain how tropical storms form
• I can explain submergent vs emergent coastlines
• I can compare hard vs soft rock coastlines and their landforms
• I can name soft engineering methods with one advantage/disadvantage each
• I can name hard engineering methods with one advantage/disadvantage each
• I understand the four SMP strategies (hold/advance/realign/do nothing)
• I can recall key facts, preparation measures and impacts from the Typhoon Haiyan case study

Exam Tips