While the "immediate" risk has passed at the Moonlight Track, near Queenstown, a permanent solution is being investigated to stabilise an area which, in heavy rain, could wipe out two houses.
Queenstown Lakes District Council roading manager Ian Marshall said the track was closed on Wednesday night while a section of the road above McChesney St was stabilised.
A large section of rock, estimated at 90 tonnes-100 tonnes, was brought down by an excavator on Thursday.
"There was quite a large rock formation that was hanging directly above the road that was brought down.
"It looked like a big, solid, stable rock, but when it started to move it fell into thousands of pieces," Mr Marshall said.
The rock had been affected by recent heavy rain and thawing, and in an alpine setting at this time of year the situation was not uncommon.
Mr Marshall said the council had temporarily fixed the problem, but design work was planned to come up with a permanent solution.
"The contractors have cleared the immediate risk, but now we've got some material that's unstable.
"The whole area in there is old, historic landslip material from thousands of years ago - when it's exposed to rain . . . it's susceptible to being eroded away."
The most concerning area of the track was only about 30m-40m in length.
Adding to the concern was an existing residence directly above the unstable area and another house under construction directly below it.
The risk to the house above the track, which is occupied, could be serious.
"[The risk is low] right now, but if we were to do nothing and there was to be a heavy rain event, there would be a real risk.
"We've had more engineers per square metre out there [last week] than there are at most universities."
The temporary solution involved covering the slip with tarpaulin to secure it.
However, long-term "geotextile material" would be required.
"There have been two or three jobs along Frankton Rd where they've effectively sprayed concrete on the face.
That wouldn't be an appropriate solution here.
"It's not like you would have seen in other places where we have done construction jobs that have left exposed batters and then [we've] sprayed . . . mashed up paper with hydroseeds on it [to help grass grow].
"On this sort of soil the grass won't grow on it anyway."
