Liz Bonnin introduces a video clip exploring how landforms have been shaped by glaciation in the Northern Hemisphere.
LIZ BONNIN: Hi, I鈥檓 Liz Bonnin. It鈥檚 strange to think it but technically speaking we are in the middle of an ice age right now. Fortunately though, it鈥檚 a relatively warm part of one. During Earth鈥檚 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鈥檚 occurred, it鈥檚 created some of the most spectacular landscapes on the planet. So let鈥檚 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鈥檚 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鈥檚 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鈥檚 life, this recent ice age has had an extraordinary influence on our world and on us. As we鈥檒l 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鈥檚 ice that has made El Capitan into the greatest challenge in rock climbing. And for Leo Houlding, one of the world鈥檚 top climbers, nothing quite matches it.
LEO HOULDING: We call El Cap the 'Big Daddy'. This is 1000 metres high and it鈥檚 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鈥檚 basically no easy way up it, it鈥檚 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鈥檓 slipping, I鈥檓 slipping. Right at the limit of friction. Urgh! (Gasps) Urgh! It鈥檚 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鈥 This rock face becomes a climbers nightmare.
LEO HOULDING: It鈥檚 getting really wet and 鈥 this glassy rock is just turning into an ice rink. In fact I might fall off here. Oh, my god. Like, there鈥檚 quite a good chance I鈥檓 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 鈥 It鈥檚 alright, we鈥檙e nearly there. Even when it鈥檚 raining it鈥檚 just such an awesome sensation to be up here. (To climbing partner) Okay, Dean, I鈥檓 safe! Brilliant. What an awesome climb. Magical place. It鈥檚 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.
Professor Iain Stewart considers how the Northern Hemisphere was once covered in ice - a major factor in shaping the landforms seen today.
A visualisation of the Gulf Stream is shown to explain the significance of this air current to the temperature of the UK. The film then focuses on El Capitan in the Yosemite National Park, California. The region demonstrates the impact of ice on the landscape and how glaciers erode the rock to create U-shaped valleys.
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鈥 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 (Hydrology) and KS4 / GCSE (Rivers and water) 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 including evaporation, condensation and precipitation.
How does a river change as it travels downstream? video
An archive clip of Sir David Attenborough as he follows the course of the Amazon River as it travels downstream.
The erosion of the Grand Canyon. video
Liz Bonnin introduces the Grand Canyon - its ancient geology and what can be learned from the erosion of the rocks.
What coastal management techniques are being used on Hayling Island? video
Introduces the coastal management techniques used on Hayling Island in Hampshire to control drift and flooding.
What is a 鈥榮pit鈥 and how does it form through longshore drift? video
Katie Knapman explains how a spit forms through longshore drift and is a dynamic physical process, constantly changing the coastline.
The geology of the Jurassic Coast. video
Exploring the Jurassic coastline and its geological significance with rocks spanning the Cretaceous, Jurassic and Triassic periods.
How have physical processes impacted the landscape of Yorkshire? video
Julia Bradbury explains the formation of Malham Cove including limestone pavement, highlighting the impact of glaciers on the landscape.
Glaciation and the UK coastline. video
Alice Roberts explains how Britain was once connected to Europe, but changed due to rising sea-levels following the Ice Age.
What evidence is there for climate change in the UK? video
Tom Heap considers the evidence that the UK climate might be changing - with more droughts, higher summer temperatures, but wetter winters.
How can plate tectonics impact oceans? video
Exploring how the plate tectonics impacts the coastline, focusing on California through study of the San Andreas fault.
Plate tectonics in the UK - Anglesey. video
Nick Crane explores the geology and seismology of Anglesey - earthquake hot spot of the UK.
Deforestation and the growth of soya in Paraguay. video
Simon Reeves visits Paraguay to consider the deforestation that has occurred there to grow soy and the challenge of conservation vs development.
