Last year's volcanic eruption in Tonga triggered the fastest underwater debris flow ever recorded - at 122 kmph.
The research, by NIWA and the UK's National Oceanography Centre, sought to find out how the eruption of Hunga-Tonga Hunga-Ha'apai had broken underwater telecommunications cables 80-kilometres away on the seabed.
When the volcano blew, it spewed rock and ash 57-kilometres into the mesosphere. It was when some of that material returned to earth that it rapidly spread out deep underwater, smothering everything in its path.
NIWA marine geologist and voyage leader Kevin Mackay spoke to Corin Dann.
