An enormous reservoir of partially molten rock, described by scientists as a “blob” and located deep underground, might be the fuel and substance that caused Iceland.
The blob, 15 km high, 800 km in diameter, and located roughly 2,800 km below ground, at the Earth’s core-mantle boundary, sits directly beneath the Iceland Plume, a massive upwelling of molten rock that, over millions of years, created Iceland (as well as parts of Scotland and Norway).
The blob’s likely key role in powering the plume emerged when scientists Kaiqing Yuan and Barbara Romanowicz of the Berkeley Seismological Laboratory in California used an imaging method known as seismic tomography to uncover a detailed picture of it.
The pair were attracted to the feature because it is an example of what’s known as an ultralow-velocity zone (ULVZ), a section of the core–mantle boundary through which the seismic waves of earthquakes pass through 30% more slowly than in neighbouring areas.
ULVZs are rare, and their extreme depth makes them challenging targets for analysis – in particular, mapping their shapes.
Other major ULVZs have been detected beneath the Pacific island nation of Samoa and the Hawaiian island chain. Like Iceland, these are volcanic land masses fed by plumes, leading geologists to suspect the zones may be integral parts of active volcanic hotspots.
Andrew Masterson is a former editor of Cosmos.
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