Australasian Science: Australia's authority on science since 1938

Deep Sea Volcano Found in Bight

By Stephen Luntz

Extinct volcano found in waters 2 km deep.

An unexpected deep sea volcano has been discovered in the Great Australian Bight Marine Park’s Benthic Protection Zone (BPZ). The BPZ is a narrow strip of the sea floor stretching south from near the Western Australian border to the edge of Australia’s exclusive economic zone.

Dr David Currie was leading an exploratory expedition through the area on the RV Southern Surveyor when postgraduate student Anna Hill noticed that the seismic data was producing a clear peak in what is otherwise a featureless sedimentary plain. The peak sits about half-way between the edge of the continent and the 200 nautical mile limit.

“It’s a phenomenal find, and quite remarkable that we passed right over the top of it 100 nautical miles offshore in the middle of the BPZ,” Currie says. “We were mapping a strip of seabed less than two nautical miles wide, and it could have taken us hundreds of survey lines to locate it.”

The object is believed to be an extinct volcano 200 metres in height and 600–800 metres in diameter. The water at this point is around 2 km deep.

Previous work by Geoscience Australia has uncovered larger such objects to the north-west and to the east. However, this find is of particular significance because of its location in the BPZ. The remote location of Anna’s Pimple, as it is tentatively being called, means it has probably not been damaged by human activity, and the marine park location ensures this will continue.

The peak is too deep to receive noticeably more sunlight than the seafloor around it, but as a solid igneous projection it should be far more suitable for life than the shifting sediments that surround it. Its isolation means that the local ecosystem may have evolved independently of other seamounts.

“When the Benthic Protection Zone, which covers a total area of 4000 square nautical miles, was initially declared in the late 1990s, it wasn’t known exactly what it was that we were really protecting,” Currie says. “This expedition is helping to provide data on the composition and distribution of the fauna inhabiting some of the deepest parts of the Marine Park to 4000 metres. By comparing it to other places around the world we will know if the fauna is endemic to this area.”

Rocks taken from similar objects in the Bight suggest they were formed 48 million years ago.