Methane seeps off Gisborne linked to submarine landslides, tsunamis

Methane bubbling up from the sea floor off the coast of Gisborne is being investigated over its link to submarine landslides and potential tsunamis.

NIWA marine geologist Dr Joshu Mountjoy is researching how submarine landslides move, which will help understand their tsunami hazard potential.

He was leading the team of scientists which discovered a field of methane seeps in 2014 in the Hikurangi Subduction Zone, where the Pacific plate is subducting beneath the Indo-Australian plate.

The Hikurangi Subduction Zone is potentially the largest source of earthquake and tsunami hazard in New Zealand and is being intensely studied by scientists.

The team named the field of more than 630 methane seeps the 'Tuaheni Seep Field'. Dr Mountjoy says the field is a sign that there is a "significant underground gas source", which is suspected of "destabilising underwater slopes and causing landslides".

"The team published a paper in 2016 showing that the same underground gas reservoir is linked to submarine landslides," he says.

"A lot of landslides have happened here in the past, so it looks like this gas is a piece in the puzzle of what is going on."

The gas may also be related to deeper fluids in the subduction zone that can in turn influence earthquake behaviour.

Dr Mountjoy says his best hypothesis is that tectonic behaviour in the subduction system is controlling the seeps.

"I think it's all linked into the seamounts making their way through the subduction zone and potentially even slow slip processes in the area," he says.