Liz Bonnin introduces a clip exploring the tectonic plate movement and geological significance of Anglesey.
LIZ BONNIN: Hi, I’m Liz Bonnin. When we think about plate tectonics, we normally picture erupting volcanos, gigantic mountain ranges like the Himalayas, or terrifying tsunamis and earthquakes, but rarely do we picture scenes from around the coast of the UK.
Well time to change that thinking, as Nick Crane discovers the fault lines and earthquakes around Anglesey on Wales’ north coast…
NICK CRANE: Many make their way to these cliffs for the glorious sights looking out to sea, but what’s brought me here are the rocks beneath my feet.
On the island’s edge, you see a slice right through the Earth’s geological history. An extraordinary collection of rocks are exposed here.
Just to show you how different Anglesey is, look at this geological map of southern Britain. Great swathes of it are all the same colour, meaning they’re all the same rock type.
Here’s this great band of chalk running up here in green, there’s another huge band of limestone running down here. But up here on Anglesey, something different is happening. There’s an intense mosaic of different colours, meaning there are many different rock types.
Much of the mystery of Anglesey’s formation is buried below the turf. But the coast reveals the island’s subterranean secrets. The most stunning geological feature is the long channel of water that separates Anglesey from the mainland: the Menai Strait.
To understand its significance, I’m with David Schofield, from the British Geological Survey.
What part does this gulf play in Anglesey’s geology?
DAVID SCHOFIELD: Well this is actually a long fault zone which we call the Menai Straits Fault System. I mean, it separates very much older rocks to the north-west than those to the south-east. We’re looking at a fundamental geological divide here, which we know is still active today because we’re seeing some of Britain’s biggest earthquakes just happening along this fault line.
NICK CRANE: Right where we’re standing?
DAVID SCHOFIELD: Right where we’re standing, yes.
NICK CRANE: So the shore we’re on here is moving in relation to the shore over there?
DAVID SCHOFIELD: It certainly is, yes. It’s at a very slow rate every year, and every now and then it takes a bit of a jump and then there’s an earthquake.
NICK CRANE: Around 300 small earthquakes shake Britain each year. Often felt most strongly here, caused as the mainland grinds against Anglesey.
It’s part of the bigger movement of landmasses around the globe. The Earth’s crust is made up of separate distinct plates, which are constantly moving against each other.
Where the edges of the plate move apart, new crust is created about as fast as your fingernails grow. The plates of crust pull apart at one edge but collide at the other edge.
As they crush into each other, a jumble of different rocks is left behind. Local geologist, Margaret Wood, is my guide.
Wow! Just look at that! Those colours, Margaret!
MARGARET WOOD: It’s fantastic, isn’t it!
NICK CRANE: So many shapes too. It looks like a great big blancmange.
MARGARET WOOD: It’s wonderful isn’t it. Those are quartz rich rocks, you’ve got limestone over there, and you’ve got schists, you’ve got conglomerate. And the colours are fantastic, aren’t they?
NICK CRANE: So this is two plates of the Earth’s crust colliding?
MARGARET WOOD: Exactly.
NICK CRANE: In the hundreds of millions of years Anglesey’s been moving around the globe, collisions and splits in the Earth’s crust have created an astonishing array of rocks.
LIZ BONNIN: A couple of amazing facts in that clip: Anglesey is its own tiny tectonic plate and we get 300 mini earthquakes in the UK every year. Almost one a day. That’s just my camera man mucking about.
Liz Bonnin introduces the geological significance of Anglesey and its links to tectonics.
Nick Crane uses a map to compare the geology of Anglesey to that of the rest of Britain - highlighting how it is different because of the diversity of rock types.
The team visit the fault line where some of the biggest earthquakes in the UK occur and discuss how the land either side is moving (very slowly)!
A visualisation of the Earth’s tectonic plates is shown to demonstrate what is happening at the fault line.
This short film explains how a mixture of different rock types is left behind from the forces at a tectonic fault.
This short film is from the Â鶹ԼÅÄ series, Physical Geography with Liz Bonnin.
Teacher Notes
Students could follow up this short film with a presentation about the specifics of the geology of Anglesey - considering the specific geological structure of some of the rocks found there.
They could also consider how it is similar or different to other locations on tectonic faults around the world.
Curriculum Notes
This topic appears in geography at KS3 and KS4 / GCSE in England, Wales and Northern Ireland and National 4/5 in Scotland.
More geography clips with Liz Bonnin:
What is the water cycle? video
Iain Stewart describes the water cycle and explains that water is constantly suspended in the atmosphere, yet we only notice it when it falls as rain.
How does a river change as it travels downstream? video
Liz Bonnin introduces a Â鶹ԼÅÄ archive clip of Sir David Attenborough as he follows the Amazon River downstream.
The erosion of the Grand Canyon. video
Liz Bonnin introduces the Grand Canyon with its complex and very ancient geology.
What coastal management techniques are being used on Hayling Island? video
This short film introduces the coastal management techniques used on Hayling Island in Hampshire.
What is a ‘spit’ and how does it form through longshore drift? video
Presenter Katie Knapman explains how a spit forms through longshore drift and is a dynamic feature- constantly changing the coastline.
The geological significance of the Jurassic Coast. video
A look at the Jurassic coastline and its geological significance with rocks spanning the Cretaceous, Jurassic and Triassic periods.
How has ice and other processes impacted the landscape of Yorkshire? video
Wildlife presenter Julia Bradbury explains how Malham Cove and the limestone pavement formed, highlighting the significance of glaciers on the landscape.
What does the North Norfolk coastline tell us about how glaciation shaped Britain? video
Presenter and biologist Alice Roberts explains how Britain used to be connected to Europe via a land-bridge but has changed with sea-level rise since the last Ice Age.
Glaciation of the Northern Hemisphere. video
Presenter Iain Stewart explains the glaciation of the Northern Hemisphere, looking at the El Capitan rock face.
What evidence is there for a changing climate in the UK? video
Countryfile presenter Tom Heap introduces the idea that the UK climate might be changing, with increased droughts, increased summer temperatures but wetter winters.
The continued impact of plate tectonics on our oceans. video
A look at how our oceans are constantly changing due to the underlying plate tectonics.
Deforestation and soya growth in Paraguay. video
Simon Reeves visits Paraguay to consider the deforestation that has occurred to grow soy and the challenge of conversation vs exploitation.
