I've heard that Britain is sinking in the south and rising in the north - how can that happen

asks MScott:
A. You're right. It's happening because of something called 'isostatic rebound'.

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Q. Sounds scary - is it
A. Could be. It's happening because the north of Britain is recovering from having the weight of an enormous amount of ice pressing down on it after the last Ice Age.�That part of the country is merely 'bouncing back'.

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Q. Wasn't the ice age a very long time ago
A. Yes it was. But even though the earth's crust is slightly elastic, it takes thousands of years for�it to adjust to a huge amount of weight being added or removed.

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Q. How much ice are we talking about
A. Scotland was under more than 300 metres of ice during the ice ages. And Scotland is rising fairly quickly.

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Q. How quickly
A. About a metre a century.

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Q. So you can see the effects
A. Yes. Along the coast of north-east Scotland in particular, you can see 'raised beaches' which sit several feet above the current sea level.

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Q. So is Scotland pushing England down
A. Not exactly. When the ice weighed Scotland down, it also had the effect of raising England up - in a see-saw kind of motion. Now that the ice has gone, England is returning to its pre-ice age level .

Also, the sea level is rising worldwide as global warming melts glaciers and releases more water into the oceans.

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And, as oceans get warmer they expand, raising the sea level further - about 3mm a year.

This is, of course, causing great concern to those living on the south coasts of England.

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Q. Is London particularly vulnerable
A. Yes, it couldn't be sited in a worse place. As well as the rising sea level and the fact that England is sinking, the Thames valley is a syncline (an area of locally subsided crust), and is suffering from subsidence because of groundwater extraction - plus storm surges in the Thames estuary are greater because of the funnel shape of the North Sea.

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By Sheena Miller