An eruption underneath Lake Rotorua would be catastrophic, says GNS Science, as a burst of geothermal activity on the lake this week coincides with a new study of the volcanic lake floor.
This week's eruptions are thought to be part of a natural cycle, with no obvious link to the recent earthquakes.
But the lake itself could be a timebomb of sorts.
It occupies part of a caldera, or giant volcanic cauldron, which is expected to erupt one day down the track.
"It could well be a small cone that pops up anywhere. If you had any eruption underneath the lake that would be quite devastating because magma and water don't mix very well and it would be catastrophic," said Cornel de Ronde, GNS principal scientist.
"But the odds on it happening any time soon are very remote," he added.
For the last month the Royal New Zealand Navy has been mapping the geothermally active lake floor in minute detail, for use by researchers at GNS Science.
"The maps are the basis of everything that we do. So, if you don't have a decent map you don't have a framework in which to hang other things off," Mr de Ronde said.
The boat trawls up and down the lake, equipment on board capturing all the detail below.
"We're projecting sonar or sound waves, if you like, down onto the lake and they'll hit the lake floor and they'll bounce back," Mr de Ronde said.
Lieutenant Commander Tim Garvan of the navy said: "You can see things like thermal vents, gas upwellings and things, which is really interesting."
Technicians are processing the results bit by bit and helping to identify where future research could be focused.
It's not the first time the lake has been surveyed. But this operation is the most extensive, the mapping the most detailed.
"We can see bubble streams coming through the water column. But we'll come back at a later date and we'll put heat probes down there to try and determine the flux of the heat through the lake floor," Mr de Ronde said.