Scientists seeking to understand the forces at work beneath the Earth’s surface have detected previously unknown “fingers” of heat,some of them thousands of miles long,in our planet’s upper mantle.
The discovery helps explain the “hotspot volcanoes” that give birth to island chains such as Hawaii and Tahiti.
Many volcanoes arise at collision zones between the tectonic plates,but hotspot volcanoes form in the middle of the plates,researchers said.
Geologists have hypothesised that upwellings of hot,buoyant rock rise as plumes from deep within Earth’s mantle – the layer between the crust and the core that makes up most of Earth’s volume – and supply the heat that feeds these mid-plate volcanoes.
Computer modelling approach,developed by University of Maryland seismologist Vedran Lekic and colleagues at the University of California Berkeley,has produced new seismic wave imagery which reveals that the rising plumes are,in fact,influenced by a pattern of finger-like structures carrying heat deep beneath Earth’s oceanic plates.
Seismic waves are waves of energy produced by earthquakes,explosions and volcanic eruptions,which can travel long distances below Earth’s surface.
As they travel through layers of different density and elasticity,their shape changes.
A research team led by Scott French found finger-like channels of low-speed seismic waves flowing about 193 to 354 kilometres below the sea floor,and stretching out in bands about 1127km wide and 2253km apart.
The researchers also discovered a subtle but important difference in speed: at this depth,seismic waves typically travel about 4 to 4.8 kilometres per second,but the average seismic velocity in the channels was 4 per cent slower.
Because higher temperatures slow down seismic waves,the researchers infer that the channels are hotter than the surrounding material.
“We estimate that the slowdown we’re seeing could represent a temperature increase of up to 200 degrees Celsius,” said French,the study’s lead author.
At these depths,absolute temperatures in the mantle are about 1,300 degrees Celsius,the researchers said.
The study was published in the journal Science Express.