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 Weathering and Mass Movement at the Coast.

Grab everything you might need for today's lesson and let's begin our learning.

By the end of today's lesson, you will understand how weathering and mass movement shape the coast.

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

The key words that we'll be using throughout today's lesson are weathering, mechanical weathering, chemical weathering, and mass movement.

Weathering.

This is the breakdown or disintegration of rocks at or close to the earth's surface.

Mechanical weathering.

This is the physical disintegration of rocks, for example, through freeze-thaw.

Chemical weathering.

This is the chemical breakdown of rocks usually involving slightly acidic rainwater.

And mass movement.

This is the downhill movement of material under influence of gravity.

Brilliant.

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

The first question that we are going to explore in today's lesson is how does weathering shape the coast? Weathering is the breakdown of rocks and minerals at or near the earth's surface, and there are three types of weathering.

There's mechanical weathering, and this involves physically breaking rocks into smaller pieces without changing their chemical structure.

There's chemical weathering, and this happens when chemical reactions occur in rocks often involving weak acids.

And finally, there's biological weathering.

Here living organisms like plants and animals contribute to breaking rocks apart.

What are the three types of weathering found at the coast? Pause the video here whilst you decide and press play when you're ready to continue.

Excellent.

The three types of weathering found at the coast are mechanical weathering, chemical weathering, and biological weathering.

Well done if you manage to remember those correctly.

Mechanical weathering is the breakdown of rocks into smaller pieces without chemical change.

Let's look a bit more closely at freeze-thaw weathering.

This process starts when water enters cracks in rocks.

When the temperature drops below freezing, the water turns to ice and it begins to expand.

This expansion puts pressure on the surrounding rock, widening the crack.

When the ice melts the water seeps deeper into the crack.

If this freezing and thawing cycle happens repeatedly, the rock eventually breaks into smaller pieces.

Freeze-thaw is very common in coastal areas with cold climates because of the fluctuating temperatures and the availability of water from waves and rain.

An easy way to remember this is thinking about water bottles in the summer.

In the summer, you might fill up the water bottle and put it in the freezer so it's nice and cold for you in the morning.

You'll wait for it to thaw so you can drink it, and when you're finished you'll fill it up again and freeze it.

This continued process of freezing and thawing on the same water bottle will cause this water bottle to eventually break, similar to the process we've just learned about here.

Chemical weathering occurs when rocks are broken down through chemical reactions.

Acid in rainwater can react with rocks like limestone, which contain calcium carbonate.

Aisha has cleverly noted that when carbon dioxide dissolves in rainwater, it creates carbonic acid.

Chemical weathering is more common in coastal areas because of the moist conditions and the presence of salty or slightly acidic sea spray, which can speed up the process.

Biological weathering is caused by living organisms. For example, plant roots can grow into cracks in rocks, and as the roots grow thicker, they force the cracks to widen and the rock then breaks apart.

Another example is animals that burrow into softer rock.

They loosen the material and make it more vulnerable to other types of weathering.

They type of weathering is especially noticeable in coastal areas where plants like seaweed and organisms like mollusks attach to rocks and contribute to their breakdown.

Let's now test our knowledge.

Which of the following best describes the difference between chemical weathering and biological weathering? Is it A, chemical weathering involves chemical reactions, while biological weathering is caused by living organisms. Is it B, chemical weathering is caused by living organisms, while biological weathering involves chemical reactions.

Or is it C, chemical weathering only occurs in hot climates, while biological weathering happens in cold climates.

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

Excellent.

The statement that best describes the difference between chemical weathering and biological weathering is A.

Chemical weathering involves chemical reactions, while biological weathering is caused by living organisms like plants and animals.

Well done on this task.

We are now going to complete two different tasks before we review our answers.

For this first task, I would like you to number the descriptions to match the steps shown in the diagram of freeze-thaw weathering.

Remember, freeze-thaw weathering is a type of mechanical weathering.

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

Well done for attempting this task.

Let's now attempt at the second task.

I would like you to explain the difference between mechanical weathering and chemical weathering at the coast.

I provided you with some hints to help you formulate your answer.

For this question you need to make sure you make two distinct points.

One needs to be for mechanical weathering, and the other needs to be for chemical weathering.

You also need to make sure that you include a detailed description for each of your points, and an example of how the process occurs.

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

Excellent effort on this task.

Let's review our answers.

For the first task I asked you to number the descriptions to match the steps shown in the diagram of freeze-thaw weathering.

Let's check to see if you manage to sequence them correctly.

The first one is water enters cracks in rocks.

The second, the water freezes when temperatures drop.

The third, freezing water expands and puts pressure on the rock.

The fourth, repeated freeze-thaw cycles widen the cracks.

And lastly, the rock breaks into smaller pieces.

Well done if you managed to complete this task correctly.

I then asked you to explain the difference between mechanical weathering and chemical weathering at the coast.

Your answers could include some of the following points.

Mechanical weathering is the process where rocks are broken down into smaller pieces without any chemical change.

This often occurs through processes such as freeze-thaw weathering, where water enters cracks in the rock, freezes and expands, causing the rock to break apart.

Chemical weathering, on the other hand, involves a breakdown of rocks through chemical reactions.

One example is when weak acids in the rainwater gradually dissolve minerals, like the calcium carbonate in limestone.

Well done if you manage to include some of these points in your answer.

This answer is good because it is clearly explained what happens in the mechanical weathering process and the chemical weathering process, and it even provided an example in the chemical weathering when it said weak acids dissolved minerals like calcium carbonate in limestone.

Well done.

We're now going to explore our final question of this lesson.

How does mass movement shape the coast? Mass movement is a key process in coastal geography.

Mass movement refers to the downward movement of rock, soil, or debris under the influence of gravity.

This process is extremely important for shaping the coastlines as it moves the material that has slowly become weakened.

The result is often really dramatic.

Think about cliff collapses, landslides, or slumping slopes.

At the coast mass movement is influenced by factors like the type of rock, the slope steepness, and the presence of water, such as after heavy rainfall.

Understanding these processes is really important in helping us to understand how coastal landscapes constantly evolve, and for predicting and managing hazards in vulnerable areas.

Rock falls occur when rocks or fragments of rock break away from a cliff face and fall directly to the base.

This often happens for a number of reasons, and mainly because freeze-thaw weathering has weakened the rocks, or wave action has undercut the base of the cliff, and sometimes human activities, like construction or quarry, can trigger rock rock falls by destabilising the cliff.

The fallen material is called scree, and the scree piles up at the base, and can eventually be carried away by waves, further altering the cliffs and increasing erosion.

Slumping is when material moves down a slope along a curved surface, and it happens like this.

Heavy rainfall will infiltrate and saturate the cliff, making it really, really heavy.

The saturated material will then move downwards under gravity along a curved slip plain within the cliff.

The curved movement then means the material can tip back on itself to form what looks like terraces or steps at the top of the slump, like you can see in the image on the screen.

The base of the slump is called the toe, and this is often eroded by waves.

The slump often leaves a distinctive curved, concaved scar at the top of the cliff.

Sliding is different from slumping.

Here blocks of rock or soil will move straight down a slope rather than in a curved motion, and this usually occurs along a bedding plane, which is a layer of weaker rock parallel to the slope.

sliding happens when the upper layers of the rock become saturated and heavy, causing them to slide over the weaker layer.

This process is going to leave a jagged edge at the top And a large amount of debris at the base of the cliff.

Disaster response teams rely heavily on geographic information systems, GIS, to effectively manage and coordinate their efforts during emergencies.

GIS technology allows responders to map out the paths and impacts of natural disasters such as mass movement events, but in real time.

By analysing these maps, teams can identify the most affected areas, prioritise rescue operations, and allocate resources more efficiently.

One example of this occurred during the devastating landslide in Sierra Leone in 2017.

In August of that year, after heavy rainfall, a massive landslide struck the Regent area which is near the capital Freetown.

This catastrophic event tragically resulted in the deaths of over 500 people and left approximately 3,000 homeless.

GIS is really important in mapping the extent of disasters.

It helps responders to identify areas that are buried under mud and debris, coordinates search and rescue missions, and assess which routes are still accessible.

This mapping process helped disaster teams plan how to deliver aid to survivors and evacuate those in immediate danger.

GIS maps were also used to estimate the scale of the destruction and assist in long-term recovery and rebuilding efforts.

GIS plays a really important role in assisting in disaster response.

It provides accurate real-time data, and it also shows teams how to respond more effectively, and ultimately save lives.

The 2017 Sierra Leone landslide serves as a really good example of how this technology can be used in the real world emergencies.

What is the key difference between sliding and slumping? Is it A, sliding involves rotational movement along a curved surface, while slumping occurs straight down a slope? Is it B, slumping involves a rotational movement along a curved surface, while sliding moves material down a slope? Or is it C, sliding occurs when rock falls off a cliff while slumping involves a rotational movement along a curved surface? Pause the video here whilst you decide, and press play when you're ready to check your answer.

Excellent.

The key difference between sliding and slumping is B.

Slumping involves a rotational movement along a curved surface, while sliding moves material straight down a slope.

Well done if you manage to get that correct.

True or false, rock falls occur when loose rocks and debris slide slowly down a slope due to the force of gravity.

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 explain why this statement is false.

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

Excellent.

The reason why this statement is false is because rock falls involve rock or debris falling freely from a steep slope or cliff, rather than sliding slowly down a cliff.

Well done.

The photo on the screen shows slumping at the cliffs of Happisburgh.

I would now like you to explain the process of slumping at the coast.

Izzy has cleverly identified that at the top of the cliff she can see the scar where the material has recently moved down from.

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

Excellent.

Let's check our answers.

Your answer could include some of the following points.

Slumping often happens after heavy rainfall.

When water infiltrates into a cliff, it makes the material in the cliff heavier and reduces the cohesion holding the material together.

The saturated material moves downwards under gravity along a curved slip plane within the cliff.

This curved movement leaves a curved scar behind the slump, and this can be seen in the photo on the screen and it can tip the slump material back on itself to form what looks like steps or terraces.

The base of the slump is called the toe, and this is often eroded by waves.

Well done if you managed to answer this question correctly, include some of the following points.

This answer is good because it has clearly explained the process of slumping in a step-by-step process, and it has also referred back to the image that was in the question.

Well done on this task.

We've now come to the end of our lesson on weathering and mass movement at the coast, and you've done brilliantly.

But let's summarise our lesson before we finish.

Weathering and mass movement are key processes that shape the coast.

Weathering breaks down rocks into smaller particles through physical, chemical, and biological processes.

Mass movement is the downward movement of rock, soil, or debris due to gravity.

Sliding, slumping, and rock falls are types of mass movement that are found at the coast.

Together, weathering and mass movement gradually reshape the coastal landscapes that we know.

I really enjoyed learning with you today, and I look forward to our next lesson.