A team of Australian and American geologists has discovered several active undersea volcanoes, ridges and hot springs off the coast of Fiji.

The geologists located them with the help of high-tech, multi-beam sonar mapping equipment, while exploring uncharted areas. Digital images of the seafloor revealed formerly unknown features.

For example, summits of the volcanoes, named ‘Dugong’ and ‘Lobster’, are dominated by large calderas at depths of 1,100 and 1,500 metres.

Calderas are volcanic craters that have diameters many times that of the vent and is formed by collapse of the central part of a volcano or by extremely violent explosions.

During the six-week expedition, the scientists analyzed rock types and formation around North Lau Basin, 400 km northeast of Fiji.

The project’s chief scientist, Richard Arculus, described the terrain — the result of extreme volcanic and tectonic activity — as spectacular, with some of the features looking like "the volcanic blisters seen on the surface of Venus."

"These active volcanoes are modern-day evidence of mineral deposition such as copper, zinc, and lead and give an insight into the geological make-up of Australia," he noted.

"It provides a model of what happened millions of years ago to explain the formation of the deposits of precious minerals that are currently exploited.’

It could also provide geologists with clues about new undiscovered mineral deposits.

The discovery, Arculus said, highlighted man’s lack of knowledge about the world’s oceans.

"We know more about the surface of Mars than we know about the ocean floor," Arculus said.

"These deep-sea features are important in understanding the influences that have shaped not only our unique continent but indeed the whole planet," Professor Arculus says.

CSIRO’s Director of Research Vessels, Captain Fred Stein, says the expedition was a humbling experience. "It was a reminder that at the beginning of the twenty-first century it is still possible — on what is often regarded as a thoroughly explored planet — to discover a previously unknown massif larger than Mt Kosciuszko," he says.

"We are fortunate that we can offer the scientific capability of the Southern Surveyor to Australian scientists. It’s the only Australian research vessel that can provide the opportunity to conduct such valuable research to make these kinds of discoveries possible."