Nearly all of the Pink Terraces survived the devastating 1886 eruption of Mt Tarawera.
They now lie beneath 2m of sediment and 60m of water in Lake Rotomahana, GNS scientists have found.
Using free-swimming robotic missiles, they discovered the bottom two layers of the terraces while mapping out the floor of Lake Rotomahana early last year. Results of sonar and seismic surveys of the lake floor undertaken last week to re-map the topography of the lake floor show more of the terraces.
Seismic lines over the location of the Pink Terraces show hard surfaces at the same depth they found the two layers last year, according to GNS scientist and project leader Cornel de Ronde.
A stack of hard material covered by a 2m-thick layer of sediment sits on top of the terraces.
Seismic data showed a 40m wide, three-storey-high stack of hard material exactly where the terraces were estimated to be, Mr de Ronde said.
"We believe this represents a substantial portion of the Pink Terraces although we were not able to determine their state of preservation. We were unable to image individual terraces."
Mr de Ronde said the new map revealed a number of volcanic craters, fault lines and pockmarks on the lake floor which resulted from the 1886 eruption but had not been seen before.
This information would help scientists put into context existing information about the eruption and the two geothermal systems under the lake, he said.
"Most of the newly identified lake-floor volcanic features have been hidden for over 100 years. Their discovery provides much greater insight into sequences of events that made up the 1886 eruption. In particular, the data shows the volcanic craters and the deep rift that formed when the lake floor unzipped violently during the eruption," he said.
Te Arawa Lakes Trust Board is supporting the project. Chairman Toby Curtis said Te Arawa were excited about the find and had expressed their gratitude to the scientists.
"We have been given a wonderful source of valuable information in terms of knowledge around geothermal structures and the situation that was there before the eruption and after. It is the most detailed picture of a geothermal lake in the world," he said.
The find would be a valuable resource benefiting not only Te Arawa but everybody in the district.
"It is a treasure for future generations to come. For all of us who live here," he said. "Our job is to find out how we can capitalise on that in as many ways as possible."
Meanwhile, Waimangu Volcanic Valley manager Harvey James said it was an exciting find as everyone thought the terraces, which drew people from all around the world to see them, had been devastated in the massive eruption in June 1886.
"It's like a boy's own adventure. It's so cool," he said.
People visiting the valley were very interested in the find, Mr James said.
"It's thrown up many points of interest about what actually happened here during and after the eruption, which nobody had a clue about. It's just amazing," he said.
"In the last 12 months the information about the lake has tripled and so have the questions ...
"It's several new chapters of the story. We are here to help understand how [the lake] got here."