difference between constructive and destructive waves-
- Destructive waves are created in storm conditions.
- They are created from big, strong waves when the wind is powerful and has been blowing for a long time.
- They occur when wave energy is high and the wave has travelled over a long fetch.
- They tend to erode the coast.
- They have a stronger backwash than swash.
- They have a short wave length and are high and steep.
- They are created in calm weather and are less powerful than destructive waves.
- They break on the shore and deposit material, building up beaches.
- They have a swash that is stronger than the backwash.
- They have a long wavelength, and are low in height.
- Hydraulic action. Air may become trapped in joints and cracks on a cliff face. When a wave breaks, the trapped air is compressed which weakens the cliff and causes erosion.
- Abrasion. Bits of rock and sand in waves grind down cliff surfaces like sandpaper.
- Attrition. Waves smash rocks and pebbles on the shore into each other, and they break and become smoother.
- Solution. Acids contained in sea water will dissolve some types of rock such as chalk or limestone.
mass movement processess:
mass movement- the down slope movement of material due to gravity
A slump is a type of mass wasting that results in the sliding of coherent rock material along a curved surface.
Sliding is where the land on a steep hill slides because of the ground being too saturated.
There are various sources of the material in the sea. The material has been:
- eroded from cliffs
- transported by longshore drift along the coastline
- brought inland from offshore by constructive waves
- carried to the coastline by rivers
where and why does deposition happen
When the sea loses energy, it drops the sand, rock particles and pebbles it has been carrying. This is called deposition. Deposition happens when the swash is stronger than the backwash and is associated with constructive waves.
Deposition is likely to occur when:
- waves enter an area of shallow water.
- waves enter a sheltered area, eg a cove or bay.
- there is little wind.
- there is a good supply of material.
Formations of headlands, bays, cliffs, caves and arches
headlands and bays:Headlands are formed when the sea attacks a section of coast with alternating bands of hard and soft rock. The bands of soft rock, such as sand and clay, erode more quickly than those of more resistant rock, such as chalk. This leaves a section of land jutting out into the sea called a headland.
Caves occur when waves force their way into cracks in the cliff face. The water contains sand and other materials that grind away at the rock until the cracks become a cave. Hydraulic action is the predominant process.
Arches:If the cave is formed in a headland, it may eventually break through to the other side forming an arch
formation of spits and bars
Spits are also created by deposition. A spit is an extended stretch of beach material that projects out to sea and is joined to the mainland at one end.
Spits are formed where the prevailing wind blows at an angle to the coastline, resulting in longshore drift.
bays: formed by a spit growing across a bay. A sand bank develops offshore, parrallel to the shore until it joins the mainland.
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