Survey reveals seabed gas hydrate system
A joint New Zealand-German research team has discovered a network of frozen methane and methane gas in sediments and in the ocean near New Zealand’s east coast.
The team is using 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 f lares in a 50 km2 area, venting from the seabed in columns up to 250m high. This is believed to be the densest concentration of seafloor gas vents known in New Zealand. 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.” says NIWA marine geologist and voyage leader Dr Joshu Mountjoy.
“What we have found is high density methane f lares in very shallow water, as well as gas building up beneath a large landslide and being released along the landslide margins.”
In a 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 f luid systems within the seafloor,” says co-leader professor Sebastian Krastel of the University of Kiel. “The sediment, rocks and f luids 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, SCHLIP3D, 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.