NZ - German 3D survey reveals massive seabed gas hydrate and methane system
A joint New Zealand-German research team has discovered a huge network of frozen methane and methane gas in sediments
and in the ocean near New Zealand’s east coast. The 16-strong team is using state-of-the-art 3D and 2D seismic and
echosounder technology to map both forms of methane within the ocean and beneath the seafloor.
The area off the North Island’s east coast is known to have very large active landslides, up to 15km long and 100m
thick, and the team set out to discover what is causing them to move.
What they discovered was direct evidence of widespread gas in the sediment and ocean, and indications of large areas of
methane hydrate, ice-like frozen methane, below the seafloor.
The team has identified 99 gas flares in a 50 km2 area, venting from the seabed in columns up to 250 m high. This is
believed to be the densest concentration of seafloor gas vents known in New Zealand. 3D seismic data show that
landslides and faults allow the gas built up in the sediment to be released into the ocean.
This discovery reveals a hydrate and gas field very different from others known in New Zealand.
“Previously all gas venting sites have been in deeper water and associated with large earthquake faults” say NIWA marine
geologist and voyage leader Dr Joshu Mountjoy.
“What we have found is high density methane flares in very shallow water, as well as gas building up beneath a large
landslide and being released along the landslide margins”.
In a recently submitted scientific paper the team proposed that these landslides might be the seafloor equivalent of
glaciers, but with frozen methane instead of water ice, or alternatively that pressurized gas is causing them to
progressively move downslope. The results from this expedition indicate that both of these are possibilities and provide
data to carefully test these hypotheses.
The expedition took the opportunity to deploy the German research institute GEOMAR’s high resolution 3D seismic
equipment known as the P-Cable from NIWA’s research vessel Tangaroa.
“This equipment is the best available for imaging fluid systems within the seafloor,” says co-leader Professor Sebastian
Krastel of the University of Kiel. “The sediment, rocks and fluids we have mapped here are perfectly suited to this
equipment, and the area mapped is one of the biggest ever mapped with the P-Cable seismic system.”
The work forms part of a larger project focused on understanding the dynamic interaction of gas hydrates and slow moving
active landslides. Dubbed SCHLIP (Submarine Clathrate Hydrate Landslide Imaging Project), ongoing investigations in the
project over the next decade will including drilling into the landslides themselves in 2016.
This first part of the project, SCHLIP-3D, is a collaboration between NIWA, GNS Science and the University of Auckland
from New Zealand, GEOMAR and the University of Kiel from Germany, Oregon State University from the USA, and the
University of Malta.
“The initial findings are very important” says Dr Mountjoy. “Methane is a very effective greenhouse gas and seabed
methane release has the potential to dramatically alter the earth’s climate. As ocean temperatures change the methane
hydrate system has the potential to become unstable.”
“In terms of natural hazards, the occurrence of very large slow landslides, rather than catastrophic ones, has major
implications for the tsunami generating potential of landslides globally as slow landslides are unlikely to cause
tsunami.”
“This type of slow moving submarine landslide is essentially unknown around the world, but it is very likely that they
do occur widely and are an important process shaping continental margins”.
The team set off from Wellington on 14 April and finished the voyage on 8 May. The work is funded from New Zealand by
MBIE and Germany by DFG.
ENDS