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

A destructive wave

提示Tall, steep and close together; common in winter storms.

为什么The 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)

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

为什么The 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

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

为什么Attrition 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

提示Think about which way gravity pulls water on a slope.

为什么Waves 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

提示Compare how hard the water is moving in each place.

为什么Moving 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

提示Ask whether the broken pieces stay where they are.

为什么Weathering 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

提示The same gas makes fizzy drinks slightly sharp to taste.

为什么This 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)

提示The verb also describes a tired person dropping into an armchair.

为什么Rain 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

提示Picture a book slipping down a tilted tray.

为什么A 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

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

为什么Rock 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

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

为什么Where 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

提示Compare standing at the end of a pier with standing in a harbour.

为什么Bays 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

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

为什么Abrasion 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

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

为什么The 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

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

为什么Hydraulic 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.