Rivers and coasts, Year 10: waves, weathering and landforms of erosion (Coastal landscapes option)

A destructive wave

HintTall, steep and close together; common in winter storms.

The whyThe swash is the water running up the beach and the backwash is the water draining back. When the backwash is the stronger of the two, more material is taken away than is brought in. Destructive waves are steep and arrive close together; constructive waves are low and further apart, with the stronger swash.

Hydraulic power (also called hydraulic action)

HintThe first word names the fluid-driven brakes and lifts on machines.

The whyThe force of the water alone does the work: no pebbles are needed. Each wave squeezes the air in a crack and then releases it as the water falls back. Repeated thousands of times, this widens the crack and loosens blocks of rock.

attrition

HintIt shares its opening with "attack", and is also used for a war that slowly wears both sides down.

The whyAttrition wears down the load itself, not the cliff. It is why pebbles on a beach are smooth and rounded, while rock that has just fallen from a cliff is sharp and angular.

Straight down the beach, at right angles to the shoreline

HintThink about which way gravity pulls water on a slope.

The whyWaves usually approach at an angle, driven by the prevailing wind, so the swash runs up the beach diagonally. The backwash simply drains down the steepest slope. Each wave therefore moves a pebble a little further along the shore in a zigzag.

Waves in a bay have little energy, so they can no longer carry their load

HintCompare how hard the water is moving in each place.

The whyMoving water needs energy to carry sand and shingle. Waves lose it in sheltered bays, in shallow water and where the wind drops, so that is where beaches and other landforms of deposition build up.

Movement: the rock is worn away and carried off by the sea

HintAsk whether the broken pieces stay where they are.

The whyWeathering breaks rock down where it stands, through the action of the weather, chemicals and living things. Erosion is the wearing away and removal of rock by something that moves, such as waves. On a cliff the two work together: weathering loosens the rock and the sea removes it.

carbon dioxide

HintThe same gas makes fizzy drinks slightly sharp to taste.

The whyThis is chemical weathering: the rock is changed and removed by a chemical reaction, not broken by force. The weak acid reacts with the calcium carbonate in chalk and limestone and carries it away in solution.

Slumping (a rotational slide)

HintThe verb also describes a tired person dropping into an armchair.

The whyRain soaks into soft rock, making it heavier and weaker. The cliff then fails along a curved, spoon-shaped surface, and the block tilts backwards as it rotates downwards. Slumped cliffs often look like a series of steps.

It is flat (a straight plane), not curved

HintPicture a book slipping down a tilted tray.

The whyA slide happens along a straight line of weakness in the rock, such as a bedding plane or joint that slopes towards the sea. The block keeps its shape and moves as one piece. In a slump the surface is curved, so the block rotates as it moves.

Rock fall

HintTwo short words: the material, then what an apple does from a tree.

The whyRock falls happen on steep or vertical cliffs of hard, jointed rock. Weathering widens the joints and waves undercut the cliff foot until blocks break away. The fallen rock piles up at the base as scree.

A discordant coastline

HintThe first word is also used in music for notes that clash.

The whyWhere the rock bands meet the sea end-on, the waves reach hard and soft rock side by side. The soft rock is cut back into bays and the hard rock is left as headlands. Where the bands run parallel to the shore (a concordant coastline), one rock type faces the sea and the coast is straighter.

It is exposed to the full force of the waves, while the bays are sheltered

HintCompare standing at the end of a pier with standing in a harbour.

The whyBays are sheltered by the headlands, so their waves have less energy and drop sand to make beaches. The headland meets high-energy waves on three sides. That is why cliffs, caves, arches and stacks are found on headlands.

notch

HintThe same word names the V you cut in a stick with a knife.

The whyAbrasion and hydraulic power are concentrated at the base of the cliff, where the waves break. The hollow grows until the overhanging rock falls. The sea clears the debris and starts again, so the cliff slowly retreats inland.

A wave-cut platform

HintThree words: who made it, how, and a flat place where you stand to wait for a train.

The whyThe platform is the base of the old cliff, left behind as the cliff face moved inland. It slopes gently towards the sea and is usually covered at high tide. The wider it becomes, the more wave energy it absorbs, so the cliff retreats more slowly.

cave; arch; stump

HintIn order: a bear's home, the shape of a bridge, and what is left of a felled tree.

The whyHydraulic power and abrasion do the work at each stage. The arch roof falls when it becomes too heavy to be supported. A stump is so low that it may be covered at high tide.