Icy blasts swell glacier by 3m a day

Franz Josef glacier is growing as much as 3m a day, thanks to a cold spring and fickle summer.

More snow and ice is flowing into the top of the glacier than is melting at the bottom, causing the glacier to expand upwards and outwards, becoming steeper at its front.

It is difficult to predict how long the glacier's advance will continue, but experts say the significant thickening of the ice just behind its face suggests it may last for several years.

The advance means more work for the glacier's two guiding companies, who must predict changes to the icy landscape daily to make safe pathways for climbing tourists.

Franz Josef's front, or terminal face, is now wedged against a mass of bedrock that in 1990 was the site of a Department of Conservation viewing platform.

But the steady pace of the glacier's growth will soon mean the ice is higher than the rock and will start to spill over, eventually covering the rock altogether and moving forward.

That process may take only weeks.

A glacier in a state of advance is a different terrain to one in retreat. The pressure of the rapid growth causes the ice to "open like a zip", says Franz Josef Glacier Guides manager Mark Mellsop.

"So from one day to the next the changes are quite marked. A stepline you might have made will become impassable because the ice has split and fallen in, so you have to be able to predict what will happen a couple of days out."

That kind of quick change means Mr Mellsop's company must send teams of guides up before the day's paying clients arrive, to ensure the steps cut into the ice the day before are still usable.

Ropes are nailed into the ice to help climbers up the sometimes-vertical steps. As the groups climb, their guides carry ice picks and often have to clear the way through crevasses or define steps more clearly before the group can move on.

The change in the terrain - when a glacier is retreating the face is less steep and much easier to climb - is dramatic enough that clients are now being discreetly screened.

Mr Mellsop says those assessed as being less able to manage the perilous climb up the sheer ice face are discouraged from attempting it, although no one is flatly refused.

"It's a safety issue. The climb is tougher now and you have to remember it's not sturdy rock, it's slippery ice. You fall, you're gone.

"In saying that, we have never had a serious accident on the ice.

"There is a difference to being fit and able to walk the streets of New York than to climb the terminal face of an advancing glacier."

Franz Josef is a flexible glacier and has advanced and retreated significantly over the past 100 years.

Nearby Fox Glacier is also advancing but its wider valley means it travels at a much slower rate.