New research reveals that the massive, mysterious structure beneath Hawaii—scientifically termed a mega-ultralow velocity zone (mega-ULVZ)—is not the molten mass previously suspected, but rather a dense, solid formation rich in iron. This discovery fundamentally shifts our understanding of how volcanic hotspots like Hawaii are sustained and offers unprecedented insights into Earth’s deep interior.
The Mega-ULVZ: What It Is, and Why It Matters
Ultralow velocity zones (ULVZs) are enormous regions found near the Earth’s mantle-core boundary, approximately 1,800 miles (2,900 kilometers) below the surface. They’re characterized by dramatically slowed seismic waves—the very reason they were first detected. Mega-ULVZs are the largest of these zones, stretching hundreds of kilometers across and frequently associated with volcanic hotspots in locations like Hawaii, Iceland, and the Marquesas Islands.
This matters because these zones represent a direct line of sight into the deep Earth’s composition and behavior. Studying them helps us understand not just how Earth formed, but also how other planets evolve.
Solid Iron, Not Molten Goo
For years, one leading theory suggested that mega-ULVZs were primarily composed of partially molten material. However, the latest study, published January 28 in Science Advances, disproves this. Researchers led by Doyeon Kim of Imperial College London used a novel approach combining both compressional (P) and shear (S) seismic waves to analyze the mega-ULVZ under Hawaii.
The data strongly indicate that the structure is predominantly solid rock with high iron content. According to Kim, “Because it’s iron-rich material, it is going to be electrically more conductive, and that will actually promote thermal conduction—so it will actually help localize the plume to last longer.”
Implications for Volcanic Activity and Earth’s History
The solid, iron-rich composition has significant implications. The high thermal conductivity of iron helps stabilize the Hawaiian hotspot, ensuring a long-lasting source of volcanic activity.
The mega-ULVZ’s origins remain debated, but the study proposes two main possibilities:
- Remnants of Earth’s early evolution: The structure could be a relic from the planet’s formation, specifically from the crystallization of an ancient magma ocean or recrystallized melts.
- Subducted oceanic crust: Material from deep within the mantle, including water-rich oceanic crust pushed down through subduction zones, may contribute to its formation.
Kim notes that not all mega-ULVZs are alike, and that some may even contain material originating from the Earth’s core itself. The new analytical approach allows scientists to differentiate these types of ULVZs across the globe.
“We have to first clearly understand what’s happening on Earth to understand fully what’s happening on other planets.” – Doyeon Kim
This research is not just about Hawaii; it’s a crucial step toward understanding planetary formation and the dynamics of Earth’s deep interior. The composition and behavior of these hidden structures will shape our understanding of the planet for years to come.
