State Highway 6 south of Makarora was closed to motorists again yesterday after the second major slip in less than two weeks.
Heavy rain and wind was believed to have caused a September 5 slip of between 1000 and 2000 cubic metres, which blocked the highway about 2km south of the Boundary Creek reserve.
One lane was opened the following day but efforts were still being made to clear the remaining material from the other lane when the second slip occurred on the same section of road on Saturday night.
Opus senior geotechnical engineer Rob Bond said further heavy rain over a 48-hour period had triggered the latest slip.
"Once the first slip occurred, the remaining material became very unstable."
Efforts to stabilise the bluff above the road and remove the material so both lanes could reopen continued last week.
"But unfortunately, the weather, basically, beat us," Mr Bond said.
New Zealand Transport Agency (NZTA) Central Otago area manager John Jarvis said he was advised of the slip about 7am yesterday and Fulton Hogan and Opus had worked all day to clear the material.
The new slip was about half the size of the original one but included some large boulders the length of two cars. More rocks "about as big as a soccer ball" had continued to fall throughout the day.
The highway, the only direct road link between Otago and Westland, was reopened about 7pm yesterday.
Mr Jarvis said NZTA was continually having to reassess the slip area.
"We'll get there eventually but the nature of the geology of that country up there, it's a very unstable area right through Lake Wanaka on the Haast road, so from time to time we have these issues. And of course, once a slip starts, it can generate into other areas and continue to fret away and that's the situation we've got at the moment.
"We're going to have to do some more work once it's settled down to stabilise it all."
He understood there were about 30 vehicles on either side of the the slip yesterday.
