He said the dam failure was not unexpected and scientists had expected the wall would give way at about the level it did. The dam had filled to an estimated 60,000 cubic metres of water before the dam wall failed after heavy rain at 12.30am on Sunday.
The resulting lahar of mud and rocks was between three and five metres high and flowed 12 kilometres down the valley, Dr Keys said.
It caused significant damage to 200m of the Tongariro Alpine Crossing on the section of track which passes through the bush near the Ketetahi carpark end.
Mud was also spread over a further 1.3km of track and DOC is warning visitors to expect conditions to be muddy and uneven underfoot on that section. The lahar flowed onto State Highway 46 but did not reach Lake Rotoaira.
Dr Keys said DOC would continue to monitor the dam but the dam's outlet now appeared "really stable" and the lake level had dropped to about 10,000cu metres of water. The lahar had all but eliminated any risk to visitors using the track from lahars and mudflows.
DOC is warning people that although the Tongariro Alpine Crossing has been repaired, in some places it may be a little soft and rocky. Visitors would still need to consider winter conditions, with snow cover and avalanche conditions remaining on many high parts of the track.
Local transport operators, i-Sites, the Mountain Safety Council website and the Whakapapa Visitor Centre have regular updates on weather, avalanche and track conditions.
A public ceremony to open the final complete track section from Mangatepopo to Ketetahi track entrances will take place this Friday with kaumatua from local hapu Ngati Hikairo ki Tongariro.
The ceremony will lift the rahui (closure) over the Tongariro Alpine Crossing track, but a rahui will remain in place around a 1km hazard zone of the Te Maari crater. Signs showing the location of the remaining rahui will be in place on the track, and safety flyers regarding the volcanic hazard will be available at the Mangatepopo and Ketetahi road ends.
