Imagine two colossal mountains, each towering over 1,000 kilometers high—one hundred times taller than Mount Everest—yet completely invisible to the human eye because they lie buried deep beneath our feet.
This astonishing discovery comes from a research team at Utrecht University in the Netherlands and was published in the scientific journal Nature. Hidden 2,000 kilometers beneath the Earth’s surface—right under the Pacific Ocean, not far from the Indonesian archipelago—scientists have identified two mysterious “mega-mountains” deep within the Earth's mantle.
These structures are known as Large Low Seismic Velocity Provinces (LLSVPs)—vast regions where seismic waves travel significantly slower than in the surrounding mantle.
But this discovery is about more than just size. LLSVPs are not only much larger and hotter than surrounding mantle regions—they are also far older. Researchers estimate that these structures may have formed over 4 billion years, longer than most supposed geological formations.
What Are LLSVPs?
LLSVPs are vast regions in the lower mantle, first detected in the late 20th century through seismic wave analysis from large earthquakes. They are located beneath the Pacific Ocean and Africa, regions that are close to the Indonesian archipelago. When seismic waves travel through these areas, they slow down drastically—hence the name “low shear velocity.”
However, recent findings have revealed that it's not just the speed that changes. By analyzing the amount of energy lost by seismic waves—called damping—scientists are gaining new insights into Earth's internal structure.
The Mystery of Ancient Islands Within the Earth
For decades, scientists have believed that the Earth's mantle is a dynamic system, where hot material rises and cooler material sinks in a continuous cycle. But this new study challenges that view. The Utrecht team found that these two “hidden islands” within the mantle appear to be remarkably stable and have changed very little since their formation.
LLSVPs were first detected through the analysis of seismic waves from major earthquakes. When an earthquake occurs, the Earth vibrates like a giant bell. These vibrations propagate as waves, and the way they travel allows scientists to glimpse what lies deep inside our planet.
In LLSVP regions, these waves move more slowly—an indication that the material is hotter and compositionally different.
What’s most surprising, according to researcher Sujania Talavera-Soza, is that the waves did not dampen significantly as they passed through the LLSVPs—unlike the surrounding regions, which act like “graveyards of tectonic plates” and heavily absorb seismic energy.
This means that, despite being hotter, LLSVPs do not dampen seismic waves as previously assumed.
What Causes This Phenomenon?
To understand why seismic waves behave strangely in these regions, researchers investigated the microscopic structure of the LLSVPs. It turns out that the size of the mineral grains is the key factor.
In areas where tectonic plates have sunk into the mantle, the cold material recrystallizes into fine-grained structures. As seismic waves travel through these regions, their energy is absorbed because the waves must pass through numerous grain boundaries. This is why seismic energy rapidly diminishes in these areas.
In contrast, LLSVPs are composed of much larger grains, allowing seismic waves to pass through without losing much energy. And because these large grains grow extremely slowly, it suggests that the LLSVP structures are incredibly ancient—possibly even older than the continental crust itself.
How Earth’s Core Shapes Us
The existence of these two “mega-mountains” could fundamentally reshape how we understand Earth’s geological evolution. LLSVPs are believed to be the origin points of mantle plumes—columns of hot material that rise toward the surface and trigger volcanic activity, such as what occurs in Hawaii.
In other words, these ancient structures may be the hidden drivers behind major geological events on the Earth’s surface. They are the “engines within,” powering the formation of mountains, volcanic eruptions, and the movement of tectonic plates.
The Unseen World Below
This research not only opens up new insights into the Earth's internal structure, but also highlights just how many mysteries remain hidden beneath our feet. Although these features cannot yet be excavated or directly explored, seismic technology continues to provide valuable clues about this exotic underground world.
Since 1975, seismographs have recorded thousands of high-quality earthquakes. One of the most significant was the 1994 Bolivia earthquake, which occurred at a depth of 650 kilometers—too deep to cause surface damage, but ideal for sending seismic waves rippling across the entire planet.
With increasingly advanced technology, scientists hope to uncover even more hidden structures and gain deeper understanding of the origins of the planet we call home.
