A lahar on Mt Tongariro early on Sunday morning has helped to make the Tongariro Alpine Crossing track safe to reopen.
The track will reopen this Friday in time for Labour Weekend. It was closed after Mt Tongariro's Te Maari Crater erupted on August 6, and partially reopened from Mangatepopo to Red Crater on August 31.
The eruption caused a landslide which flowed 2km down the mountain and blocked three streams. One of them formed a dam, posing a threat to people further down the mountain, including on the Tongariro Alpine Crossing.
Conservation Department scientist Harry Keys said that while safety systems, including a lake level sensor on the dam, had been put in place, he was pleased that nature had taken its course and made the dam safe before the section of the track from Red Crater to Ketetahi reopened this weekend.
"It's a load off that it failed when it did."