KEY POINTS:
Part of Mt Cook National Park has been declared unsafe for trampers after boulders the size of cars fell in a massive landslide that could have filled half of Eden Park with rubble.
Up to one million cubic metres of rock and debris came down in the slip on Mt Vampire.
GNS Scientist Simon Cox compared the slip to smearing half of the Eden Park stadium down 2km of road.
"Some boulders were the size of cars while others were broken down to dust," Mr Cox said.
He said the scar left on the side of Mt Vampire was about 120 metres high, up to 80 wide and 30 deep.
Mr Cox said there had been multiple slips on Mt Vampire - about 20km south of the Aoraki-Mt Cook.
He said the first slip happened two weeks ago and there had been more slips since.
Mr Cox said GNS picked up an earthquake measuring 2.5 on the Richter scale after one of the slips.
"It's probably the equivalent of a double-decker truck going past your office. It's a rumbling and we can pick it up with sensitive instruments but most people would not have felt it," he said.
Mr Cox said it was dry in the region at this time of year and there was no ice to support the rock.
"You don't need to have a trigger but when you do have a trigger - like a big earthquake - then all hell breaks lose. When we get a big earthquake in the Mt Cook National Park lots of mountains are going to fall down," Mr Cox said.
Department of Conservation Mt Cook area manager Don Bogie said the slip came down a side glacier and across the Mueller Glacier.
Mr Bogie said Mt Vampire was usually climbed in the winter and so the slip would not disturb many climbers. He said the Mueller Glacier hut - popular with trampers - was still open.
Mr Bogie said the slip was large but not as big as the 12 million cubic metres that came off Mt Cook in 1991.
Mr Cox said the Mt Cook slide of 1991 could be repeated. "We can expect that sort of thing again and usually without warning."
