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This would be a big iceberg in the Arctic

Updated Wednesday, 7th March 2007

Mark Brandon explains how icebergs are formed and how they contribute to rising sea levels.

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When you are working on an icebreaker, after a while you forget just how strange it is to be sailing through a landscape of ice in all its forms. Here I thought I would have a go at talking about a small iceberg we sailed past. I say small because by Antarctic standards it is, although at about 50-60m high the International Ice Patrol who operate in the Arctic would classify it as a large berg.

Text version

Just coming into the frame in a minute, you’ll see a big iceberg behind me. Now when snow falls on Antarctica, eventually the weight of the snow on top of the snow underneath crushes the snow into ice, and then eventually that ice flows away from the centre of the island in glaciers. When these glaciers come down o the edge of the water, they break off, like this thing – yeah, you can see that over my shoulder. Eventually these glaciers flow down to the edge of Antarctica and break off forming these icebergs. 

So, the ice in that iceberg, well for a start how much of the iceberg is underwater? That’s the perennial favourite. It could be four-fifths, nine-tenths, I would guess probably about nine-tenths is more likely from measurements I’ve made in the past.   But the freeboard on that glacier, that’s probably about 60 metres high. Nine-tenths, probably about 400-500 metres beneath the water. There’s probably, well an awful lot of fresh water stored in there. And that’s one of the key things. The key things about these icebergs is that they’re made of frozen snow, that’s freshwater. And frozen snow falls on Antarctica, eventually reaches the edge of the continent and breaks off into these icebergs where they drift away. 

Now, the floating ice shelves around Antarctica, when they melt and decay they don’t do anything to sea level, they’re floating on the sea already so the water’s already displaced. If you want to do an experiment of that at home, what you can do is get yourself a lemonade, or a gin if you like, drop in some ice cubes, see what happens to the water level, mark off on the side of the cup and then just let it melt. So if you’ve got a floating ice shelf that doesn’t affect the sea level, but where the glaciers flow down from the middle of Antarctica towards the edge of the continent and break off as these icebergs, this was snow on land, this wasn’t floating on Antarctica so it wasn’t displaced. So when it breaks off and when it melts it does increase sea level. 

And we do know that Antarctica is contributing to sea level rise around the planet. We also know that pretty soon there’s going to be, there’s going to – we also know that pretty soon scientists are going to be releasing the Inter-Governmental Panel on Climate Change report, the new one, on how fast they think sea level around the planet is going to increase, and what we do know is a lot of these things you can see behind me are going to contribute to sea level rise.





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