Bar A mound of sand and pebbles that builds up offshore. It is formed by waves and currents moving sand from one place to another along the coastline.

Bay A wide, curving area of sea between two headlands. Bays form where soft rock has been worn away by the sea.

Beach An area of sand or pebbles on the seashore. Beaches are formed when waves wear cliffs down into sand and pebbles, which they then pile up on the wave-cut platform, the flat area between the cliff and the sea.

Blowhole A hole in the top of a sea cave. When waves pound at the cave, they push water and air up through the blowhole. It bursts out above the ground as a spray of water.

Cliff A steep, nearly vertical, wall of rock, often found along coastlines. Cliffs are shaped both by the waves and by rockfalls and landslides.

Coast The coast, or seashore, is the place where land meets sea. It can take the form of rocky cliffs, beaches or marshy wetlands. The shape and features of a coastline depend on its rocks, winds and currents. As powerful waves crash against cliffs, they gradually wear away the rocks, sometimes carving out caves, or stone arches. When pieces of rock fall into the sea, the waves grind them down into pebbles or sand and lay them down in sheltered places to form beaches.

Coastal erosion The gradual wearing down of the coastline by waves and the wind. Waves pick up rocks from the bottom of the sea and hurl them at the cliffs, knocking off fragments of rock. Sometimes air is trapped between a wave and a rock face. The force of the wave pushes the air into cracks in the rock, making the rock split open further.

Estuary The wide part of a river near its mouth where it meets the sea and fresh and salt water mix.

Fjord A deep, U-shaped valley that has been gouged out by a glacier and “drowned” by rising sea levels. There are many fjords on the coast of Norway and New Zealand.

Headland An area of land that projects out into the sea. It is sometimes called a promontory. A headland is formed from hard rock that resists coastal erosion.

Intertidal zone The part of the coast that is submerged by the sea during high tide and is exposed to the air during low tide.

Island An area of land that is completely surrounded by water.

Lagoon A shallow pool of seawater cut off from the sea by a spit or coral reef.

Longshore drift The sideways movement of sand and pebbles along the coast. Longshore drift is caused by waves hitting the shore at an angle instead of head-on.

Neap tide A tide with a very small difference between high tide and low tide. Neap tides occur when there is a quarter Moon. The Sun and Moon are at right angles to one another, pulling in different directions, so that the force of their pull on the tides is lessened.

Pebble A small, round rock. Pebbles are formed when rocks that fall into the sea are worn down and smoothed by waves.

Peninsula An area of land that extends into the sea with water on three of its sides.

Ria A coastal inlet formed by the partial submergence of a lowland river valley by the sea. A ria coastline is one featuring a branching network of inlets, created by the sea gradually flooding across lowland areas and valleys, leaving hills as islands.

Salt marsh A low-lying area of coastline that is often flooded by the sea. Salt marshes usually form in sheltered areas, such as deltas or estuaries. They are home to grasses and shrubs that grow in salt water.

Sea arch A section of headland that is shaped like a arch. A sea arch is formed when a sea cave is gouged through.

Sea cave A cave near the base of a cliff. Sea caves form when the sea crashes against cracks in a cliff’s surface, pushing water and air into the cracks and forcing them to open wider.

Spit A mound of sand or pebbles that extends out from the land into the sea. Spits are formed by currents that carry sand and shingle along the coast. When the current’s path is interrupted, by meeting a headland or entering an estuary, the current weakens and drops the sediment.

Spring tide A tide with a very large difference between high tide and low tide. Spring tides occur when the Sun and Moon are in line, at a full moon or new moon. The Sun’s gravity combines with that of the Moon to increase the pull on the water.

Stack A column of rock, created when the roof of a sea arch collapses, leaving one side of the arch standing alone.

Strait A narrow stretch of sea between two areas of land.

Tide The rise and fall of the sea usually every 12 hours 30 minutes. Tides are caused by the gravitational pull of the Sun and Moon. Ocean waters on the side of the Earth closest to the Moon (and the opposite side) bulge outwards, causing a high tide. At the same time, the rest of the Earth has a low tide. The Sun may either increase or lessen the effect of the Moon.

Wave The surging motion of the sea as it approaches the shore. Waves are caused by wind moving over the surface of the ocean. The water itself does not move but spins around on the spot. When a wave approaches the shore, the lower part drags on the seabed, while the upper part moves on. Eventually it topples over, or breaks, on the shore.

Consultant: Ian Fairchild