Oceanographers uncover more than 19,000 previously unknown undersea volcanoes

The demand to create legislation and safeguards over deep ocean seabed mining has received new urgency with the mapping of thousands of new undersea volcanoes – which are said to contain vast quantities of valuable, rare-earth minerals.

Ships have only managed to map 20% of the world’s sea floor, and many undersea volcanoes – also known as seamounts – remain hidden deep beneath the waves.

This poses a major risk to submarines and their crews and in fact, two separate US submarines have previously collided with seamounts.

Now, oceanographers using radar satellite data to map these seamounts have identified 19,325 new seamounts to the catalogue of known undersea volcanoes.

The results are described in a new study in the journal Earth and Space Science.

The researchers suggest that these findings will have important implications for creating models depicting the flow of ocean water around the world — and for potential deep seabed mining.

“Seamounts are valuable characteristics of the ocean floor since they provide insight on many of the Earth’s geological, oceanographical, and ecological cycles and processes,” the authors write.

What are seamounts?

According to the study seamounts are “active or extinct volcanoes with heights that reach at least 1,000 metres,”  although this definition has been broadened to include much smaller isolated volcanoes.

Found in every ocean on Earth, seamounts can form at mid-tectonic plate regions.  Volcanic hotspots are zones where plumes of molten magma rise from deep within the Earth’s mantle to the surface and erupt out of the crust.

Seamounts can also occur at tectonic plate boundaries; this includes subduction zones — where two tectonic plates collide and one dives under the other into the Earth’s mantle — and at seafloor spreading centres where magma rises from between two plates which are moving away from each other.

So how do you discover new seamounts?

Satellite radar altimeters gauge the ocean surface height, or sea level, by measuring the time it takes for a radar pulse to travel to the sea surface and bounce back again.

Sea levels can vary, in an effect known as sea mounding, because of changes in gravitational force that occur due to variations in the seafloor landscape. In areas with more mass – such as a seamount – gravitational forces are stronger, and the sea level will be higher since the ocean has been pulled away from areas of lower gravitational force.

“We used the latest vertical gravity gradient maps to update and refine a global seamount catalogue, finding 19,325 new seamounts,” the authors write.

“Due to the impact that seamounts have on the ocean and ecosystems, they are important features to study, map, and classify.”

Seamounts provide insight into the composition and temperature of the mantle, and studying them can be used to further understand the eruption process in volcanoes.

They also contain vast amounts of rare-earth minerals, which are an attractive target for potential, but controversial, deep seabed mining.

Read more: Seabed mining might be the next big environmental campaign – what you need to know

They’re also centres for diverse ecological communities, since the ocean upwelling that occurs in their presence brings valuable nutrients from the deep water to the surface.

With currents mixing in unknown ways after running into seamounts, they also have a strong impact on deep-sea ocean flow. Understanding this impact is important for climate change research, since more than 90% of the extra heating caused by global warming is absorbed by and circulated in the ocean.