Home / News and Events / Media Releases / New map reveals secrets of previously unknown offshore region - 25/09/2015

New map reveals secrets of previously unknown offshore region - 25/09/2015

Scientists have returned from a three-week mission to map the seafloor of the Colville Ridge, northeast of Auckland, as part of a long-term programme to survey regions within New Zealand’s offshore territory considered prospective for seafloor minerals.

View looking towards the southeast down the Colville Ridge, mapped during the expedition. The topography in this image has been exaggerated by a factor of four.

View looking towards the southeast down the Colville Ridge, mapped during the expedition. The topography in this image has been exaggerated by a factor of four.

The voyage over the middle part of the Colville Ridge was led by GNS Science in collaboration with Oregon State University. It took place on NIWA’s deepwater research ship Tangaroa and was funded by the Ministry of Business Innovation and Employment.

Scientists on the ship used the ‘holy trinity’ of seafloor mapping techniques - sonar mapping plus measurements of magnetism and gravity. The trio complement each other and are considered essential to obtain meaningful information on the seafloor and its underlying structures.

The area of seafloor mapped was just over 20,000km2 , equivalent to the size of Israel. The scientists stepped off the ship today having produced a stunning seafloor map with a resolution of 30m, which is 30 times better than the previous map of the area which was compiled from satellite data.

Combined with a similar survey of the southern part of the Colville Ridge in 2013, GNS Science has now mapped almost 38,000km2 of what was previously unmapped New Zealand territory.

The new high definition maps of the region, together with geophysical data, will be valuable as a guide to future voyages which are likely to focus on particular areas for more detailed investigations.

A key finding during the voyage were seafloor rocks that had been ‘hydrothermally altered’.

This means hot fluids containing dissolved elements such as silica had once passed through them.

Often these same fluids carry dissolved metals that, on mixing with cold seawater, precipitate out and accumulate on the seafloor.

"

The southern end of this large geological feature lies within 500km of New Zealand’s largest city, and yet prior to this mapping expedition and the one we completed in 2013, we knew almost nothing about it.

Dr Cornel de Ronde

"

Voyage leader, Cornel de Ronde of GNS Science, said the find indicated that parts of the submerged Colville Ridge, which is estimated to cover about 100,000km2 , could be prospective for metallic minerals such as copper and gold.

“This find is a real bonus as our mission was to produce a detailed bathymetric map of the area, backed up by gravity and magnetic measurements,” Dr de Ronde said.

The shallowest point on the new map is just 390m below the surface, and the deepest is 3,730m.

“A dominant feature of the area we surveyed is a large mountain chain that when viewed from the northwest looks almost like an alligator snaking its way towards Auckland.

“We believe this survey will show that the Colville Ridge and Kermadec Ridge were once joined and they rifted apart at some unknown time in the past.”

The older Colville Ridge and neighbouring Kermadec Ridge have formed as a result of subduction of the Pacific tectonic plate. Both ridges stretch northeast from New Zealand toward Fiji and Tonga respectively.

Scientists now plan to review the gravity and magnetic data and analyse the rocks they recovered from the seafloor. This will tell them more about how and when the Colville Ridge formed and when the two ridges rifted apart.

Dr de Ronde said it was amazing to think that so little was known about the Colville Ridge.

“The southern end of this large geological feature lies within 500km of New Zealand’s largest city, and yet prior to this mapping expedition and the one we completed in 2013, we knew almost nothing about it.”

There were four or five major ridge features in New Zealand’s offshore territory and until now Colville was arguably the least known of them, Dr de Ronde said.