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Researchers may have discovered why some areas of the seafloor have more volcanic activity than others

Thousands of mountains lie hidden in the ocean depths. Researchers have now found a connection between two deep structures in Earth’s interior and the formation of seamounts.

Sunbeams illuminate a rugged volcanic seamount on the deep ocean floor.

The seafloor of the world’s oceans is covered with large and small seamounts. Most of them have a volcanic origin.

(Stock photo: Johan Holmdahl / iStock)

Gunn Kristin Tjoflot Gunn Kristin Tjoflot SENIOR ADVISER

Presented by: Presented by: University of Oslo

Published 16 November 2026 - 00:01

The ocean covers around 70 per cent of the Earth’s surface, but large parts of the seafloor remain largely unexplored.

“The deep oceans and the life they host are still something we know surprisingly little about,” says Clint Conrad.

He is a professor at the University of Oslo's Department of Geosciences.

Among the features hidden in the depths are underwater mountains called seamounts, often ancient extinct volcanoes. They can form long mountain ranges on the seafloor and can rise as much as 4,000 metres above it.

“Researchers can locate them by using satellites to detect small variations in gravity,” says Mathew Domeier.

He is an associate professor at the Department of Geosciences and the PHAB Centre.

Conrad and Domeier have recently published a scientific article. They uncovered new insights into how Earth’s interior creates the conditions for the formation of these important seamounts.

Portraits of Mathew Domeier and Clint Conrad — From left: Mathew Domeier and Clint Conrad are both researchers at the Department of Geosciences and the PHAB Centre at the University of Oslo.

Seamounts in Norwegian waters

We tend to think of mountains as something that rises above sea level. But the seafloor is just as rugged as the landscape on land.

“Many of the mountains beneath the ocean are completely hidden because they never reach the surface. Some, however, come close to sea level and can sometimes rise above to create islands,” says Conrad.

What the researchers have focused on in their study is the large seamounts located in the deep oceans, far from land. They can be enormous.

“In Norwegian waters, there are a number of such seamounts near Svalbard, and several in areas around other Norwegian islands such as Jan Mayen and Bouvet Island,” says Conrad.

These underwater mountain structures are also of interest to initiatives such as the Norwegian government's Arctic Ocean 2050.

About seamounts

Seamounts are usually extinct volcanoes that rise steeply up to 4,000 metres above the seafloor.

Some are so large that they rise above the ocean surface. Some of these can then have their tops eroded down, so that the seamount ends up with a flat summit below sea level. These are called guyots or tablemounts.

Earth’s oceans contain more than 43,000 identified seamounts, more than half of which are higher than 1,000 metres.

Volcanic activity is more extensive here

Beneath the seafloor lies the Earth’s mantle. This is a thick layer of solid but viscous and hot rock.

Within this layer, large structures and heat flows can influence where volcanic activity occurs on the seafloor.

The researchers examined two enormous structures at the very bottom of the mantle, near the boundary with Earth’s core.

They are called LLSVPs, short for Large Low Seismic Velocity Provinces. These are large regions where seismic S-waves travel more slowly.

Seismic S-waves are earthquake waves that travel through Earth and shake the ground side to side or up and down.

“We see that volcanic activity on seamounts is more extensive on seafloor that has previously passed over such LLSVPs,” says Domeier.

There are two LLSVPs located in the lowermost part of the mantle beneath Africa and the Pacific.

"They are like two island‑like hot zones near Earth’s core – enigmatic but important structures that may have existed for billions of years,” says Conrad.

The two enormous structures in the deep mantle are hotter than their surroundings and therefore less rigid, the researcher explains.

In their study, Conrad and Domeier propose that weak plumes rising from both LLSVPs interact with the seafloor and promote volcanic activity on seamounts.

They believe this process may be particularly strong in the Pacific region. There, the rocks in the mantle may be hotter and wetter, and therefore more dynamic.

Oval world map showing slow seismic regions beneath the mantle and seamount locations marked by dots. — The figure shows the two regions of the mantle where seismic signals travel unusually slowly. Conrad and Domeier discovered that these two regions are connected to the formation of seamounts at the surface (shown by dots).

Important for life in the deep sea

As with mountains on land, it is important for us to understand seamounts, the researchers point out.

Submarines, for example, have crashed into previously unknown seamounts.

Seamounts also create special habitats in the ocean.

They provide hard surfaces and shelter. Sometimes there are favourable currents around them, and often an abundace of nutrients. They can also be important stopovers for migrating species, Conrad explains.

Seamounts also affect ocean currents. When water flows over and around these structures, both circulation and the mixing of nutrients in the ocean are altered.

Currents that are forced upwards along the seamounts bring nutrients towards the surface and create rich feeding grounds for fish, marine mammals, and seabirds.

They also show how our planet has evolved

Seamounts also provide researchers with important information about how Earth has developed as a planet, both in the past and into the future.

In the new study, Conrad and Domeier show that plumes transporting heat from the LLSVPs are likely responsible for most of the volcanic activity within oceanic plates. This includes scattered seamounts.

This connection to the deep mantle means that volcanism on seamounts is sensitive to and can help us understand how the dynamics of Earth’s deepest mantle have changed over geological time.

Geological time is the period extending from Earth's formation approximately 4.6 billion years ago to the present day.

A small purple deep-sea organism lies among dark, rugged rocks. — Example of rocks and deep‑sea life observed on the Polarstern seamount in the Arctic Ocean during a GoNorth expedition to the Arctic in 2025. The remotely operated vehicle Ægir 6000 (ROV) was used.

The Pacific’s famous volcanic island chain

Mathew Domeier has previously researched the volcanic island chain off Hawaii known as the Hawaiian–Emperor chain.

“It's an undersea mountain range in the Pacific Ocean. It lies below sea level, but the Hawaiian ridge rises above sea level and forms the Hawaiian Islands. Altogether, this chain contains more than 80 identified submarine volcanoes,” says Domeier.

This mountain chain has moved over one of the LLSVP structures in the deep mantle. This has produced long‑lasting volcanic activity on the seafloor and built up a series of mountains as the oceanic plates have passed over this mantle zone.

“The Hawaiian–Emperor seamounts chain is a good example of how the deep mantle can control where and when seamounts form. In our study, we show that similar processes may have been important in many places on the seafloor,” says Domeier.

Watch the video on YouTube below to learn more about the Hawaiian–Emperor seamounts chain and how such mountain chains form: