Discovered only in 1977, the vents are home to extraordinarily diverse forms of life while they are active. Tube worms more than two metres high (6.6ft) with vivid red tips, deathly white crabs and fish, and countless species of microorganisms are uniquely adapted to the hot, dark conditions of life at the vents.

These vents don’t last forever. Over thousands of years, tectonic forces carry the vents further from the plate boundaries. The sites become less and less active, growing cold and silent.

Near these dormant sites, the mineral deposits – including copper, zinc, lead, gold and silver – remain at or close to the seafloor. An individual mound can contain millions of tonnes of metallic ore.

For Japan, these large deposits are seen as a potential resource for supplying the country’s demand for basic metals. The Japanese government initiated a research project to seek out these deposits in 2013. But despite their large size, finding the deposits can be difficult.

“There is no hot metallic discharge to detect with remote sensing exploration tools,” Paul Lusty, team leader of the ore deposits and commodities group at the British Geological Survey, wrote by email from a research ship investigating a site at the Rio Grande Rise off the coast of Brazil.

“As they age they are also likely to be altered and covered by sediment, resulting in eventual burial and no obvious expression on the seafloor.”

The conditions at the seafloor are also extremely harsh. The work can take place at depths of up to 3,000m (10,000ft) and the currents at the bottom of the ocean can be rough.

As well as the challenge of finding out where the deposits are, finding out how large they are is crucial. They can extend for tens to hundreds of metres below the seafloor. Determining their size helps to figure out how much they could offer in terms of mineral resources.