A research vessel has mapped the full extent of a canyon system beneath the waters of the Great South Basin.
The National Institute of Water and Atmospheric Research (NIWA) says the system, off the coast of Otago, probably formed about 60 million years ago.
Research manager Rob Murdoch says scientists knew the canyon itself was there but not its shape or where it went.
"This new survey has just shown immense detail of how all of the small channel systems coming off the continental shelf actually flow down and into this large trough system, the Bounty Trough," he says.
The deepwater research ship Tangaroa mapped 16,000 square kilometres of seabed in July.
The overall canyon system ends 1100 kilometres east of New Zealand in a large, deep sediment deposit in the Bounty Trough.
The systems are like underwater river networks, transporting sediment from the coast far out to sea.