Lesson video

Hello, and welcome.

My name is Ms. Harrison.

I'm so looking forward to learning with you today.

Today's lesson is called Landforms of coastal deposition.

Grab everything that you might need, and let's begin our learning.

By the end of today's lesson, you will understand the characteristics and formation of landforms of coastal deposition.

Before we can begin this learning, we need to define the keywords that we'll be using throughout today's lesson.

The keywords in today's lesson are deposition, longshore drift, and constructive waves.

Deposition.

This is when materials, such as sand and pebbles, are dropped by waves, wind, or water when they lose energy.

Longshore drift.

This is the movement of sediment along the coast by wave action in a zigzag pattern.

Constructive waves.

These are low waves that are typically formed by distant storms that deposit sediment onto beaches.

Fantastic! Now that we've defined these keywords, we can begin our learning.

The first question we are going to explore in today's lesson is what depositional landforms are created by waves? Now that we understand the key processes, such as longshore drift and deposition, let's look at how they shape our coastline.

Coastal deposition occurs in areas where the sea has less energy and deposits material like sand, shingle, or silt.

This leads to the formation of depositional landforms such as beaches, spits, and bars.

Each of these features has unique characteristics, but they all share one thing in common, they are built up over time by the movement and settling of sediment.

As we explore the different landforms, I would like you to think about why deposition might dominate in certain areas, while erosion might take over in others.

Let's begin with beaches.

These are one of the most common depositional landforms, and beaches are found along the coast where the waves deposit sand and pebbles.

Sandy beaches, which are often wide and gently sloping, are typically found in sheltered bays.

These areas are protected from strong wave energy, allowing constructive waves to build up the sediment.

Pebble beaches, like those on England's south coast, are steeper and found in high-energy environments where finer material is washed away.

Seawater soaks through pebbles easily, meaning the swash can deposit pebbles, but the backwash cannot pull the pebbles off the beach as the water has soaked into the beach.

This makes pebble beaches much steeper.

Beaches can also change shape throughout the year, and this is dependent on the type of waves they experience.

The photo shows a berm.

A berm is a ridge on the beach.

And berms are formed when high tides push sediment into a ridge.

A beach profile shows the gradient from the back of the beach to the sea and the characteristics in between.

A pebble beach often has a steep, stepped profile, like you can see in the image on the screen.

And a sandy beach generally has a gentle, fairly flat profile, again, like the image on the screen.

Beach profiles change throughout the year, and beaches are often eroded by destructive waves during winter storms. A key feature here is a berm.

We know it's a ridge of sediment that's created during high tide.

In winter, when destructive waves dominate, berms are often eroded as powerful backwash drags sediment offshore.

The destructive waves reshape winter profiles to be steeper, and the beaches narrow at high tide, like you can see in the image on your screen.

The powerful backwash has dragged the sediment offshore, making the beach lower and creating an offshore bar.

And we can see that the berm has been eroded by the waves, and the offshore bar has now been created.

In spring and summer, calmer conditions allow constructive waves to rebuild the berm, restoring the beach's flatter, wider profile.

Understanding these changes helps us to see how beaches constantly evolve.

Let's go through it with this diagram.

The strong swash restores the beach's gentle, flatter profile.

The beach is now wider at high tide.

The offshore bar is worked by the waves to rebuild the berm, and, as we can see, we have an established berm again.

Let's test our knowledge.

What is a berm? Is it A, a raised area of sand on the beach formed by high tide waves? Is it B, a large, flat area of land behind a beach formed by low tide waves? Or C, a type of coastal cliff formed by erosion? Pause the video here whilst you decide, and press play when you're ready to check your answer.

Excellent! The answer to what is a berm is A.

It's a raised area of sand on the beach formed by high tide waves.

Well done if you managed to get that correct.

True or false? Beach profiles are steeper and beaches are narrower in the summer due to more destructive waves.

Pause the video here whilst you attempt this task, and press play when you're ready to continue.

Excellent! This statement is false.

I would now like you to pause the video here and try and explain why this statement is false.

Press play when you're ready to check your answer.

Excellent! The reason why this statement is false is because winter storms lead to more destructive waves, which creates a steep beach profile and a narrow beach in winter, not in summer.

Well done on this task.

Let's now try and look at some of our other landforms, a spits.

We can see a salt marsh also form part of it.

Spits are formed by longshore drift.

Waves approach the coast at an angle due to the wind direction, and they carry sediment along the shoreline.

The prevailing wind is the most common wind direction at a location.

If the coastline changes direction or a river mouth is reached, longshore drift then deposits material from the beach into the sea.

Over time, more and more sediment builds up along where the coast changes direction, like you can see in the image on the screen.

Over time, as longshore drift continues, the sand deposited will build up until it is above sea level, forming a narrow stretch of sand or shingle known as a spit.

If the wind or wave direction changes over time, the spit will develop a curved end.

The spit will create a sheltered area from the sea.

This will allow mud and silt to settle.

Over time, this builds up and salt-tolerant plants begin to grow.

A salt marsh will then form in the calm, protected waters.

Let's take a closer look at a fantastic real-world example of a depositional landform, Spurn Head.

Spurn Head is located in East Yorkshire in England.

This is a sand and shingle spit, and it's formed by the process of longshore drift, erosion and deposition.

It's one of the best examples in the UK of how dynamic coastal processes shape our landscape over time.

Firstly, let's talk about how Spurn Head was formed.

It all starts with longshore drift.

Remember, longshore drift is a process where waves approach the shore at an angle, moving sediment like sand and shingle in a zigzag pattern.

At Spurn Head, sediment is carried southward by longshore drift along the Holderness Coast.

This coast is one of the fastest eroding coastlines in Europe because of its soft boulder clay cliffs.

As the cliffs erode, the material is transported along the shore by the waves.

Now, here's where the deposition comes into play.

When the coastline suddenly changes direction or where the energy of the waves decreases, the transported material is deposited, forming a narrow, elongated ridge of sand and shingle that extends out into the sea.

Over time, the ridge grows farther out, creating what we call a spit.

At Spurn Head, you'll notice a curve at the end of the spit.

This happens because the prevailing winds and wind direction shift, causing the end of the spit to curve inward almost like a hook.

This feature is typical of many spits.

Spurn Head is also a great example of how deposition landforms are constantly changing due to erosion and deposition.

The spit has shifted position and shape many times throughout history because of the tides, waves, and the erosion of the Holderness Coast.

In fact, it has even been breached by the sea on multiple occasions, most recently in 2013 during a major storm surge.

This shows how fragile and dynamic our coastlines can be.

If erosion continues at the Holderness Coast, there may not be enough sediment to maintain Spurn Head in the future.

This highlights the ongoing challenge of managing and protecting depositional features.

You can see the change on the image on your screen.

It's a historic map from 1890 and a modern-day map.

Let's now test our knowledge.

True or false? Spits form wherever longshore drift transports sediment along a beach.

Pause the video here whilst you attempt this task, and press play when you're ready to continue.

Excellent! The answer is false.

I would now like you to explain why the statement is false.

Pause the video here and press play when you're ready to check your answer.

Excellent! The reason why the statement is false is because spits do form where longshore drift transports sediment along a beach, but there needs to be a sharp change in the direction of the coastline in order for longshore drift to continue to deposit sediment out into the sea to form a spit.

Well done if you managed to explain that correctly.

Excellent, let's go through our answers.

Number 1, longshore drift moves sediment along the coast.

Number 2, sediment is deposited where the coastline changes direction.

Number 3, a spit extends further out into the sea as more sediment is deposited.

Number 4, sediment builds up in the sheltered area behind the spit, leading to the formation of a salt marsh.

Number 5, a hook forms if there is a long-term change in the wind direction.

Well done if you managed to get that all answered correctly.

We're now going to start to look at a bar.

Bars are fascinating examples of how a longshore drift can reshape the coastline.

A bar forms when sediment is transported by longshore drift and it stretches across the bay, connecting two headlands.

This process effectively traps water behind it, creating a lagoon.

Lagoons are calm and shallow bodies of water that can become important ecosystems. While bars are less common than spits, they show the same principle of sediment being deposited over time to create a new landform.

Let's now test our knowledge.

True or false? Lagoons develop behind bars.

Pause the video here whilst you attempt this task, and press play when you're ready to continue.

Excellent! This statement is true.

I would now like you to explain why this statement is true.

Pause the video here and press play when you're ready to continue.

Fantastic! The reason why the statement is true is because bars form when longshore drift moves sediment across the bay through longshore drift.

The sediment deposited will eventually connect two headlands, trapping a lagoon behind it.

Well done on this task.

I would now like you to add the missing labels to this diagram.

Pause the video here whilst you attempt this task, and press play when you're ready to check your answers.

Fantastic! Let's look at our answers.

A is the direction of longshore drift.

B is a bar.

C is a lagoon.

D is a salt marsh.

And E is a spit.

Well done on this.

I would now like you to explain the formation of a spit.

Jun has made a really important point here.

He is going to make sure that he uses geographical terminology like longshore drift in his answer.

Pause the video here whilst you attempt this task and press play when you're ready to check your answers.

Fantastic! Let's look at our answers.

Your answer might include some of the following points.

A spit forms through the process of longshore drift.

Waves approach the coast at an angle due to the wind direction, and move sediment along the shoreline.

When the coastline changes direction, longshore drift does not follow the new direction but continues to move sediment out into the sea, where it is deposited.

Over time, as sediment builds up above sea level, a narrow stretch of sand develops, known as a spit.

The spit extends further out into the sea as more sediment accumulates.

If a long-term change in wind direction occurs, the spit may develop a hooked end.

Well done on this task.

Let's now explore our second question of this lesson.

What depositional landforms are created by wind? Sand dunes are large piles of sand that form at the back of sandy beaches.

They provide habitat for a variety of different wildlife, including plants and insects.

Some of these species are so highly specialised that without these dune habitats, they may even be driven to the point of extinction.

The largest sand dune system in the UK is Braunton Burrows in North Devon.

GIS can be used to measure the length of dunes.

Izzy has cleverly noted that through GIS, she's been able to measure the length of Braunton Burrows, and she can see that it is 5.

21 kilometres long.

Sand dunes require specific conditions to form.

They need a large, wide, flat beach, plenty of sand, a wide tidal range, so there is enough time for sand to dry before the tide comes in.

Onshore winds, which pick up the dry sediment and move it to the back of the beach.

This is called aeolian transport.

Aeolian means wind.

Obstacles on the beach that trap sand, such as tree roots or driftwood.

Sand dunes are formed when the wind collects grains of sand and transports them.

Obstacles slow the wind and cause it to deposit its load.

The heaviest grains of sand are deposited first, and they create a small ridge at the obstacle, like you can see on the image on the screen.

The ridge slows the wind more, and more sand is deposited.

Over time, a crest will form on the side facing the wind because the pile of sand has become steep.

This makes it unstable, and eventually, the top of the dune will collapse.

Once it has collapsed, the light grains of sand will slip down the leeward side.

This is the side facing away from the wind.

Let's now look at it annotated on our diagram.

The dune builds up until it becomes unstable, and we can see where the leeward side is, where the grains of sand will slip down.

The wind will blow more material to build up the windward side, and this is the side facing the wind.

The crest will collapse again, and this will cause more sand to slip down the leeward side.

This will be repeated and will cause the sand dune to move inland.

As you can see on the image, the process is continuously repeated, causing the sand dunes to move inland.

Plants like marram grass begin to grow in the sand, and they help to stabilise the dunes.

Their roots help to trap more sand, leading to the gradual buildup of the dune.

Over time, layers of sand accumulate and grow into larger sand dunes, and the process can take many, many years.

Older sand dunes are called mature dunes, and newer sand dunes are called embryo dunes.

On the diagram on your screen, you can see what mature sand dunes are and what embryo sand dunes are.

Let's now test our knowledge.

What conditions do sand dunes need to form? Is it A, a flat beach, plenty of sand, destructive waves, onshore winds, and few obstacles? Is it B, flat beach, little sand, wide tidal range, offshore winds, and obstacles? C, a steep beach, plenty of sand, short tidal range, offshore winds, and obstacles? Or D, flat beach, plenty of sand, wide tidal range, onshore winds, and obstacles? Pause the video here whilst you attempt this task, and press play when you're ready to check your answers.

Excellent! The answer is D.

Sand dunes need particular conditions to form, and these are a flat beach, plenty of sand, wide tidal range, onshore winds, and obstacles.

Well done if you managed to correctly identify that.

True or false? Sand dunes are formed when wind blows sand onto the land and vegetation helps to stabilise it.

Pause the video here whilst you attempt this task and press play when you're ready to continue.

Excellent! The statement is true.

I would now like you to explain why this statement is true.

Pause the video here whilst you attempt the task, and press play when you're ready to continue.

Excellent! The reason why this statement is true is because sand dunes form when wind blows sand onto the land, and plants like marram grass grow to stabilise the sand, trapping more sediment and allowing the sand dune to grow over time.

Well done if you managed to explain that correctly.

I would like you now to explain how a sand dune is formed.

Izzy has cleverly said that she knows that sand dunes need certain conditions to grow, like strong winds.

I would like you to pause the video here and explain how sand dunes are formed.

Press play when you're ready to check your answer.

Fantastic! Let's now check our answer.

Your answer could include some of the following points.

Sand dunes are formed by wind transporting and depositing sand from the beach.

For dunes to grow, there needs to be a large supply of dry sand, strong winds, and obstacles to trap the sand.

As wind blows across the beach, it picks up loose sand particles and carries them inland.

When the wind meets an obstacle, its speed decreases, it drops the sand, which begins to accumulate around the obstacle.

Over time, this builds up into a small mound.

Dunes move inland as winds blow onto the shore move sand from the windward to the leeward side.

Plants like marram grass start growing on the dune, which helps to stabilise it.

Excellent work on this task.

This answer is great because it has combined different elements of how sand dunes form.

It's mentioned the conditions that they need and a step-by-step process.

Well done if you managed to include some of the following points.

We've now come to the end of our lesson on landforms of coastal deposition.

Well done, you've done brilliantly in today's lesson.

Before we end this lesson, let's summarise everything we've learned today.

Beaches, spits, bars, and sand dunes are coastal landforms created by deposition.

Beaches form from the deposition of sand and pebbles brought to shore by waves.

A spit forms when longshore drift moves sand along the coast, creating a narrow feature that often curves.

A bar forms when a spit connects two headlands across the bay, and a lagoon is formed behind the bar.

Sand dunes form when wind blows sand inland and deposits it around obstacles.

Plants like marram grass help to stabilise the sand.

Well done on your learning in today's lesson.

I look forward to learning with you again very soon.