A global positioning system (GPS) deployed in remote west Antarctica to measure the motion of its bedrock.

A global positioning system (GPS) deployed in remote west Antarctica to measure the motion of its bedrock. The bedrock is responding to past and present changes in the weight of ice upon it. Credit: Matt Burke.

Professor Matt A King was awarded 2015 Kavli Medal and Lecture speaking at the Royal Society on ‘Continental loss: the quest to determine Antarctica’s contribution to sea-level change’. Here he tells us some interesting facts about glaciers.

How fast can glaciers move?

The fastest glacier in the world is in Greenland and it flows more than 10 miles (17 kilometres) per year. This is four times faster than it flowed two decades ago.

What is largest glacier in the world?

Our understanding of the longest glacier in the world has changed in recent years. The Lambert Glacier in Antarctica was thought to be the longest glacier, but new airborne and satellite data has shown that the glacier begins to float hundreds of kilometres earlier than thought. The title of the world’s longest glacier is now owned by Byrd Glacier in Antarctica, which stretches more than 1,000 kilometres inland.

What does melting ice do to the bedrock below it?

When a glacier melts, the weight of ice on the bedrock below is reduced. That causes the bedrock to bounce up. Global positioning system (GPS) receivers have measured a rate of rebound of more than 2 inches (50 mm) per year – that’s half a metre over a decade! As glaciers melt faster and faster, I expect we’ll soon be measuring rebound rates that are double that figure.

How much water is being added to the ocean each year due to glacier melting?

Over the last 20 years the oceans have risen by 3 millimetres per year on average. Small glaciers, like those in the Alps, contribute about one-third of that. The ice melting in Greenland and Antarctica combined contributes about another third, but that is increasing over time.

What’s the most surprising thing you’ve learned about glaciers?

I’ve been amazed to see the speed at which glaciers can change their behaviour. We’ve shown with GPS that some finely tuned glaciers can stop flowing, or even flow backwards. Other glaciers have gone from not thinning at all to thinning by 30 metres per year, almost overnight.

Watch Matt’s 2015 Kavli Lecture