September 17, 2009

Unusual ancient ice sheet movement studied

British scientists say they have created a model of the British and Irish ice sheets that shows they moved in unexpected ways.

Durham University researchers said their model reveals for the first time how the glaciers reversed their flows and retreated back into upland regions from where they originated.

During the last glacial maximum, around 21,500 years ago, the ice sheets built up on the high land of the Lake District, north Pennines and Scottish Southern Uplands, the researchers said. As more snow fell and local ice caps thickened, glaciers flowed into surrounding lowlands as expected.

But the new model reveals an unusual twist. As the ice sheet evolved it flowed out towards the Irish Sea, eventually becoming so thick it reversed its flow back up the valleys, re-adjusting the landforms it had created during earlier stages of growth.

The stereotypical image of Ice-age Britain is of ice rolling in from the Arctic, said lead scientist David Evans. But this is not an accurate description of what happened.

Evans said the new model shows an ice sheet can reverse its flow in a hundred or so years and when that happens, it creates unique features in the landscape.

Elongated drumlins and meltwater channels in northern England and southern Scotland provide evidence of this unique phenomenon, he said.

The findings appear in the journal Quaternary Science Reviews.