Scientists have used a remotely-operated submarine that helped discover the wreck of the Titanic to peer inside a massive underwater volcano north-east of New Zealand.
Using a remotely operated vehicle equipped with a high-definition video camera and an array of scientific measuring equipment, the international team observed copper-rich veins in the inner crater walls of Brothers volcano in the Kermadec arc at a depth of 1550m.
"This confirms that the veins in the rocks mark the route fluids and dissolved metals travelled through the volcano to the seafloor to form the hundreds of metal-rich chimneys that grow up from the various ledges on the walls," said voyage co-leader Dr Cornel de Ronde, of GNS Science.
"This would have occurred decades or perhaps hundreds of years ago before the veins were exposed by faulting."
The observations were made during a 21-day US-New Zealand mission on the US research ship R/V Thompson at the volcano, which lies about 400km northeast of White Island in the Kermadec Arc.
This was the most hydrothermally active undersea volcano system on Earth and it harboured extreme environments where unusual life forms thrived.
"Brothers has some the of extremes you see in the hot springs in New Zealand, and represents an unexplored frontier for new extremophilic microbial life that thrives in acid and metal-rich, high-temperature fluids," said voyage chief scientist Professor Anna-Louise Reysenbach from Portland State University.
The scientists investigated how an undersea volcano releases heat, chemicals, and metals into the ocean and how they affect the life around it.
"The expedition is all about how these remarkable, yet poorly understood, submarine hydrothermal systems work," de Ronde said.
Volcanoes like Brothers form where two of the Earth's tectonic plates, in this case the Pacific Plate and the Australian Plate, were colliding.
Cracks at the surface of the volcano allowed seawater to circulate deep into the Earth's crust.
The water was heated up by the underlying magma chamber and chemical reactions between the seawater and rocks resulted in hot springs that vented mineral-rich fluids from the seafloor.
"The fluids can hold important clues about the formation and evolution of volcanoes and how significant mineral deposits can be formed, and about life itself," de Ronde said.
Part of the mission was to sample the hot fluids coming out of hydrothermal vents to see how much metal and various other chemicals are contained within them.
Incredibly, these vents often harboured a vast array of life.
So far, around 50 species of animals, including shrimp, crabs, worms, and various species of fish have been identified at Brothers volcano.
Large vent fields occur perched on the inner walls of the caldera and atop a volcanic cone that has grown up from the caldera floor.
De Ronde said it featured two very different types of hot springs, each of which gave different clues about the volcano's inner workings.
One expelled hot, metal-rich fluids up to 318C and the other gas-rich, metal-poor fluids that are extremely acidic.
"Very few other volcanoes on the seafloor provide such an opportunity to see multiple vent systems in action at the same place," he said.
"To geologists and microbiologists, Brothers is nirvana."
De Ronde, who has visited Brothers 11 times before, said they saw dozens of "black smoker chimneys" up to 20m tall perched on the steep walls of volcano's crater.
The fluid coming out of the metal-rich fluid is rich in iron, copper, zinc, and gold that precipitate on the seafloor, commonly forming tall chimney structures.
"Amazingly, these vents often harbour a vast array of life. So far, around 50 species of animals, including shrimp, crabs, worms, and various species of fish have been identified at Brothers volcano."
"In addition, many types of microbes live at Brothers, and on this voyage it is likely we will discover some that have never been recorded by science before."
De Ronde said the knowledge they gleaned about what metals were being transported within the volcano and how they are distributed provided insights into the formation of large mineral deposits.
Investigations such as this provided valuable insights as world demand for green technologies gathers pace and explorers look to the ocean for new supplies of critical metals.
The voyage was a US National Science Foundation-funded project involving Woods Hole Oceanographic Institution and Portland State University, in collaboration with GNS Science.