oceans and seas

oceans and seas

• An ocean is a large and extensive body of saline water occupying a basin between continents while a sea is a large body of saline water on the margins of continents.

• The coastal zone is a narrow stretch between the land and the sea. The sea, land and air constantly change its shape and form.

The importance of waves

• The power of waves is one of the most important forces that changes the shape of the coast. Waves are created by wind blowing over the surface of the sea.

• The size of a wave depends on:

• length of time the wind has been blowing

• strength of the wind

• 'fetch' - how far the wind has travelled

• Wave typesWaves can be constructive or destructive.

  When a wave breaks, water is washed up the beach. This is called the swash. Then the water runs back down the beach, which is called the backwash. With a constructive wave, the swash is stronger than the backwash. With a destructive wave, the backwash is stronger than the swash.

  The table below outlines the key differences between the two types of wave.

Erosion

• Erosion is the wearing away of rock along the coastline. Destructive waves are responsible for erosion on the coastline. There are four types of erosion:

• Hydraulic action - this is the sheer power of the waves as they smash against the cliff. Air becomes trapped in the cracks in the rock and causes the rock to break apart.

• Abrasion - this is when pebbles grind along a rock platform, much like sandpaper. Over time the rock becomes smooth.

• Attrition - this is when rocks that the sea is carrying knock against each other. They break apart to become smaller and more rounded.

• Solution - this is when sea water dissolves certain types of rocks. In the UK, chalk and limestone cliffs are prone to this type of erosion.

Headlands and bays

• Headlands are usually formed of more resistant rock types than bays.

  If there are different bands of rock along a coastline, the weaker or softer rock, such as clay, is eroded fastest. This leaves more resistant rock types, such as granite, sticking out.

Transportation

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• Sediment is carried by the waves along the coastline. The movement of the material is known as longshore drift. Waves approach the coast at an angle because of the direction of prevailing wind. The swash will carry the material towards the beach at an angle. The backwash then flows back to the sea, down the slope of the beach. The process repeats itself along the coast in the zigzag movement.

Deposition

• When the sea loses energy, it drops the material it has been carrying. This is known as deposition. Deposition can occur on coastlines that have constructive waves.

  Factors leading to deposition include:

• waves starting to slow down and lose energy

• shallow water

• sheltered areas, eg bays

• little or no wind

Depositional landforms

• Beaches are a common feature of a coastline.

• Beaches are made up of eroded material that has been transported from elsewhere and deposited by the sea.

  Constructive waves help to build up beaches. The material found on a beach (ie sand or shingle) depends on the geology of the area and wave energy.

Spits

• 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.

• Longshore drift moves material along the coastline.

• A spit forms when the material is deposited.

• Over time, the spit grows and develops a hook if wind direction changes further out.

• Waves cannot get past a spit, which creates a sheltered area where silt is deposited and mud flats or salt marshes form

Multiple Choice

Which type of coastline has fewer headlands and bays?

• Concordant

• Discordant

• Both concordant and discordant

Multiple Choice

Which of the following coastal features is NOT created through erosion?

• Tombolos

• Bays

• Caves

Multiple Choice

What is the correct definition of the coastal zone?

• Where the land meets the sea

• Where people go on holiday

• Where destructive waves are common

Multiple Choice

Which of the following is typical of a destructive wave?

• Strong swash, weak backwash

• Weak swash, strong backwash

• Equal swash and backwash

Multiple Choice

Which of the following factors affect the strength of waves?

• The length of the fetch

• The amount of water

• The distance of the swash

Multiple Choice

Which of the following is typical of a constructive wave?

• 10-14 waves per minute

• Strong swash

• Steep shape

Multiple Choice

How does a discordant coastline erode?

• Evenly, at the same rate

• Rapidly

• At different rates

Multiple Choice

When is deposition likely to occur?

• When the headlands reach far out into the sea

• When there are calm conditions with little wind

• At the base of steep cliffs

Fill in the Blank

Pebbles grinding along a rock platform is known as which type of erosion?

Fill in the Blank

Which type of erosion is the sheer power of the waves hitting the cliffs?

Fill in the Blank

Which type of coastal erosion occurs when rocks crash against each other, breaking them down into smaller and rounder pieces.

Multiple Choice

What type of rock is usually found at a headland?

• Soft, less resistant rock

• Hard, more resistant rock

• Fossilised rock

Multiple Choice

Which is the correct order for the formation of a stump?

• Stack, arch, cave, stump

• Arch, cave, stack, stump

• Cave, arch, stack, stump

Multiple Choice

What is cliff retreat?

• When cliffs move further forward towards the sea over time

• When cliffs move further away from the sea over time

• When cliffs turn into beaches

Multiple Choice

What is longshore drift?

• A process of erosion

• A process of deposition

• A process of transportation

Multiple Choice

What is a spit?

• A beach found within a bay

• An extended stretch of beach material that only joins the mainland at one end

• An extended stretch of beach forming around a headland

Multiple Choice

What feature is often found behind a spit?

• bay

• A salt marsh

• A stack

Fill in the Blank

The distance a wave has travelled is called the: