Biggest ‘calving’ in years
Photos have emerged of huge chunks of ice which have broken off the Tasman Glacier.
The photos were posted to Facebook by two local guides who were alerted to the event in the Aoraki/Mount Cook National Park early on Wednesday morning.
‘‘Glacier Explorers called us about the event so we got there after they had cleaned up some of the chaos,’’ Anthony Harris, a guide at Southern Alps Guiding, said. ‘‘Luckily the kayaks were racked and above the height of the waterline.’’
A tidal surge up to 2 metres high smashed the jetty about and lifted a boat trailer upside down on to another trailer, Harris said. ‘‘All in all, this is the most significant event I’ve seen in the last five years on the Tasman.
‘‘The present SE [southeasterly] is holding these bergs in the northern section of the lake and will do so for at least another day or two.
‘‘Once we get a NW [northwester] they will begin to fill the lake with bergs of all sizes ... some of these are really big.’’
The breaking of ice chunks from the edge of glaciers is known as glacial calving.
University of Canterbury glaciologist Heather Purdie said large calving events like this one happened about once every two years on the Tasman Glacier.
They were caused by glacial ice above the water melting, putting pressure on the ice beneath it still under the water.
When the pressure became too much, the ice eventually snapped off.
‘‘The water gets in underneath the ice and sort of jacks it up, and it snaps off,’’ Purdie said.
‘‘Large calving events are less frequent but the icebergs that come up are really big.’’
The calving was not necessarily the result of global warming, although the glacier retreating and becoming smaller was attributable to warming, Purdie said.