Remnants of the world-famous White Terraces have been rediscovered in Lake Rotomahana near Rotorua.
The cascading Pink and White Terraces were buried by the eruption of Mt Tarawera in 1886. Up to then, they had been New Zealand's premier tourist attraction.
A joint New Zealand-American project mapped the floor of the lake using two unmanned submarines over 10 days last summer.
Project leader Cornel de Ronde of GNS Science says the team only realised they had also found the White Terraces weeks after the mapping had finished.
He says the team had gone back on the last day of their mapping operation to the area of the White Terraces.
The sonar found something very similar to the Pink Terraces, a section of which was rediscovered earlier this year, but the team was not able to look at the data for several weeks.
Dr de Ronde says they believe the Terraces are deeper than first thought, at about 60 metres, which indicates large-scale slumping may have occurred. The cascading silica terraces are not as intact as they were, he says.
Local iwi were notified of the discovery on Thursday. About 200 iwi members were spending part of Friday on Mt Tarawera to commemorate the 125th anniversary of its eruption.