Beneath Hawaii: Iron-Rich 'Mega-Blob' May Anchor Volcanic Hotspot
A recent study suggests that a massive, iron-rich 'mega-blob' located deep beneath Hawaii may be contributing to the area's volcanic hotspot activity.
Scientifically known as a mega-ultralow velocity zone (ULVZ), this structure is believed to be solid and rich in iron. Researchers propose that its properties could help anchor the Hawaii hotspot, a region where hot material rises through the Earth's mantle, driving the volcanic activity responsible for the Hawaiian Islands.
According to Doyeon Kim, a seismologist at Imperial College London and lead author of the study published in Science Advances, the iron-rich material's electrical conductivity may promote thermal conduction, thereby helping to localize and sustain the plume over time.
Understanding ULVZs
ULVZs are large geological formations situated near the boundary between the Earth's mantle and core, approximately 1,800 miles (2,900 kilometers) below the surface. They are identified by the significant slowing of seismic waves in these regions. Mega-ULVZs are the largest of these zones, often spanning hundreds of kilometers, and are frequently found near volcanic hotspots like Hawaii, Iceland, and the Marquesas Islands.
A Novel Approach to Deep Earth Study
Scientists typically study these deep structures using compressional waves (P waves) generated by earthquakes, which offer limited data. Kim and his team utilized a novel method developed in 2020 that integrates data from both P waves and shear waves (S waves). By combining and modeling these data, the researchers gained a clearer understanding of the material composition causing the seismic wave slowdown.
Key Findings: Solid, Iron-Rich Composition
The findings indicate that the mega-ULVZ under Hawaii is likely composed of solid, iron-rich rock, disproving a previous hypothesis that suggested the area might be extra-melty. This information provides insights into the origin of the blob, potentially linking it to the Earth's early evolution, such as the crystallization of a basal magma ocean or recrystallized melt from past mantle melting.
Broader Implications for Planetary Formation
Kim noted that not all mega-ULVZs may have the same origin; some could form from subducted oceanic crust, while others might involve material from the core. The methodology presented in the study could help differentiate these various types of ULVZs globally, contributing to a broader understanding of planetary formation processes.