The earth has experienced numerous glaciations over its history, however, the most significant for us have been the glaciations of the last 2.58 million years (Ma)(the Quaternary) during much of which the earth has flipped between cold states (Glacial) and warm states (Interglacials), probably because of the regular changes in the relationship of the earth to the sun (the so-called Milankovitch Cycles). Human-caused climate change aside, we should be dipping down into another glacial cycle, peak interglacial warmth being around 6000 years ago.

During the glacials, water tends to be deposited as snow and ice at high latitudes. This removes water that would otherwise return to the oceans so sea-level drops. However, at the same time the ice, which weighs a lot, pushes down the earth's crust under it. An ice cap 1000m thick and 300km wide would weight 64765 billion tons; and this would be a relatively small ice cap! The molten rock deep under the landmass appears to move to the edges of the ice, causing a "forebulge" where the land rises, with a point between the depression and rise where there is no change. Not only this, but the pressure of the ice is enough to activate local faults, allowing some areas to move down further than others.

As you can see, the local sea level is therefore a complicated result of local ice, global sea level drops, and local geology. Not only this, but as the ice freezes or melts there will be a lag; global sea level will be faster than the depression of the crust. For example, even though all glaciers had probably left Britain by c.10000 years ago, the crust is still moving - up in Scotland, where most of the ice was, and down in the south, where the forebudge was.

On to Raised Beaches...