Study cracks lake loss riddle

IN Greenland there are large lakes, more than 1km long and tens of metres deep, which have been vanishing before researchers’ eyes, as massive cracks appear in the ice beneath them.

Matt King a Professor of Polar Geodesy says global sea levels are rising at slightly less than 3mm a year and that the melting of Greenland’s ice is contributing about one third of that rise, a lot more than Antarctica.

Prof King said the deaths of Greenland’s supra-glacial lakes, with water gushing out at rates more rapid than Niagara Falls, were significant because the discharge helped to lubricate the glacial ice where it met the rock below, causing the glaciers to slide even faster into the sea.

He was a member of an international research team that monitored three rapid lake drainage events between 2011 and 2013, to work out how it happened.

Prof King’s role had been to supervise 16 GPS receivers placed on the ice around the lakes to watch how the ice moved and deformed with millimetre accuracy, before the sudden cracking of 1km thick ice beneath.

He was able to do this from his Sandy Bay office, and wasn’t present when the ice gave way, causing a jolt similar to a magnitude 5-5.5 earthquake.

“The big advance in this study has come from measuring the relatively tiny change that occurs just before the ice cracks — we’ve been able to nail down the trigger and that gives us a better view as to how Greenland will influence sea level in the future.”

The team, whose research paper was published in Nature last week, discovered the trigger had been water that had run down beneath the glacial ice from Greenland’s interior, which accumulated underneath the icy lake bed and forcing it upward until it cracked.

Supra-glacial lakes further inland were less likely to suffer the same fate.