Trampers warned away from slip 

Experts are warning trampers to stay away from an area hit by one of the biggest landslides in New Zealand in more than a decade.

They blame the hot dry summer for the spectacular slip at Aoraki-Mount Cook National Park more than a week ago.

The wall of rock broke away from Vampire Peak at the head of the Mueller Glacier leaving a massive trail of debris in the valley below. 

The gash is 70 metres wide and as high as a 30 storey building.

Scientists say it broke away with such force it dumped a million cubic metres of debris into the glacier valley.
 
"It goes down the glacier for nearly two kilometres and it goes right from one side to the other," says Don Bogie, DOC acting area manager at Aoraki-Mount Cook National Park.

In the mess there are rocks as big as houses around five to 10 metres high.

A rock slide like this is a rare event.  The last big one was 17 years ago and broke off the eastern face of Aoraki-Mount Cook, changing it forever.
 
For years the snow and ice have held the fragile rocks together and experts believe the warmer than usual temperatures in the Southern Alps probably caused the slip.

"It's very loose, soft rock in the Mount Cook area.  It's being twisted and deformed and pushed up and fractured and it's held together a bit by ice and occasionally, when some of the ice melts, that may have the affect," says GNS Scientist Dr Simon Cox.

Brian Carter from Alpine Guides says the rock is quite friable and has never seen the light of day before so it is probably going to be a little more unstable as a result.

The glacier valley is popular with trampers and climbers but they are now being warned it is not safe.

"We've told climbers the Mount Vampire avalanche has occurred and walking up and down the Mueller Glacier will be probably if not very hard, and potentially dangerous at the moment," says Bogie.

A team will move in next week to try to work out exactly why the rock fell.

There will be no moves to clean up and what has happened will be visible for decades to come.