Liz Bonnin introduces a video clip explaining the glaciation of the Northern Hemisphere.
LIZ BONNIN: Hi, I’m Liz Bonnin. It’s strange to think it but technically speaking we are in the middle of an ice age right now. Fortunately though, it’s a relatively warm part of one. During Earth’s 4.5 billion year history, ice ages have come and gone, with the ice sheets sometimes reaching as far as the equator.
And where that’s occurred, it’s created some of the most spectacular landscapes on the planet. So let’s look at how glaciation has created a climbers paradise in Yosemite National Park, in California. Oh and this clip comes with a warning. Watching it might require a head for heights.
IAIN STEWART: Around 3 million years ago, the continents of North and South America collided. The result? A warm ocean current that flowed around the equator was cut off. So now the warm water travelled north. Today we know this current as the Gulf Stream. Strange as it may seem, it was this warm current that tipped the planet into an ice age.
As the warm waters evaporated, this supplied more moisture to the cold northern regions of the planet, so more snow fell. And slowly, the northern hemisphere iced over, triggering a global cooling. Over the last 3 million years, the ice has advanced and retreated more than 50 times.
In a cycle governed by small changes in Earth’s orbit. If I was standing here 20,000 years ago, there would be over a kilometre of ice above my head. And even though much of that has melted and retreated away, permanent ice still covers 10 percent of the planet’s surface. So ice is still well and truly with us.
Although a few million years is just the blink of an eye in the planet’s life, this recent ice age has had an extraordinary influence on our world and on us. As we’ll discover, it changed the climate across the planet, and in doing so, it drove human evolution. And it carved out many of the most dramatic landscapes we know today.
If you head to Yosemite National Park, in California, you get a good idea just how effective ice is at shaping the landscape on a gigantic scale. Glaciers are responsible for carving out many cliffs, but few are as epic as this one: El Capitan.
It’s ice that has made El Capitan into the greatest challenge in rock climbing. And for Leo Houlding, one of the world’s top climbers, nothing quite matches it.
LEO HOULDING: We call El Cap the 'Big Daddy'. This is 1000 metres high and it’s damn near vertical the whole way. Your initial reaction is terror. Just the scale of it is really intimidating even to extremely experienced climbers. There’s basically no easy way up it, it’s the hardest cliff to climb in the world.
IAIN STEWART: 2 million years ago, Yosemite Valley looked very different. A landscape of steep V-shaped valleys carved out by rivers. But then glaciers formed in these mountains. Slowly they flowed down the valleys, grinding sideways into the hard granite rock. Gradually steepening the sides of the valley.
When the ice retreated, it left behind a deep U-shaped valley. The classic signs of glacial activity are everywhere. There are huge boulders plucked from the cliffs and carried for kilometres by the ice. Waterfalls reveal where ancient river valleys were cut off midstream. Sheer cliffs like this are absolutely typical of recent glacial activity. The rock face is almost vertical. The ice took a mountain of granite and over tens of thousands of years, cut one side of it away, which is why this cliff is so steep.
The glacier moved across the granite, grinding it with a force of over a hundred kilograms on every square centimetre. It polished the rock up a treat.
LEO HOULDING: Whoa, I’m slipping, I’m slipping. Right at the limit of friction. Urgh! (Gasps) Urgh! It’s just so smooth and slippery, urgh. You have to keep your weight close in to the wall.
IAIN STEWART: But when bad weather closes in… This rock face becomes a climbers nightmare.
LEO HOULDING: It’s getting really wet and … this glassy rock is just turning into an ice rink. In fact I might fall off here. Oh, my god. Like, there’s quite a good chance I’m gonna fall.
IAIN STEWART: It would be reckless to keep on climbing.
LEO HOULDING: Urgh! Jesus Christ.
IAIN STEWART: Leo must find one of the few refuges that El Capitan has to offer.
LEO HOULDING: We might have to … It’s alright, we’re nearly there. Even when it’s raining it’s just such an awesome sensation to be up here. (To climbing partner) Okay, Dean, I’m safe! Brilliant. What an awesome climb. Magical place. It’s like mother nature created this place for rock climbers.
LIZ BONNIN: Well this is all about physical geography and that was both. A bit of geography and a lot of physical.
Presenter Iain Stewart introduces the idea of huge changes in the climate over Earth’s history, with ice sheets sometimes reaching as far as the equator - resulting in varied landscapes.
A visualisation of the Gulf Stream is shown to explain the significance of this air current to the temperature of the UK.
This short film focuses on the El Capitan landmark in the Yosemite National Park, California.
This national park shows the impact that ice can have on the landscape.
Iain shows what the landscape would have looked like before the ice with interweaving V-shaped valleys curved out by rivers.
Then, when glaciers filled the valleys, they were eroded sideways to become a deep U-shaped valley.
The formation of the vertical face of El Capitan is explained and it’s difficulty as a climbing wall linked to the glaciation of the area.
This short film is from the Â鶹ԼÅÄ series, Physical Geography with Liz Bonnin.
Teacher Notes
Key Stage 3
This short film can be used to introduce students to the impacts of glaciation on a valley.
After watching the clip, students could label features of a U-shaped valley to explain how each one results from the impact of the ice.
Key Stage 4
This short film can be used to reinforce students’ knowledge of the impacts of glaciation on a valley.
After watching the clip, they could label features of a U-shaped valley to explain how each one results from the impact of the ice.
Students could explore in more detail the impact of air currents on the climate - considering the link between the Gulf Stream and the climate of the UK.
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.
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.
What can Anglesey tell us about the plate tectonics of Britain? video
Presenter Nick Crane uses a map to compare the geology of Anglesey to that of the rest of Britain - highlighting the diversity of rock types.
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.
