Earth's Pulse Felt at Hot Spots

/ Source: Discovery Channel

Enigmatic volcanic hot spots around the world might be pulsating together -- like a great planetary heartbeat -- at the rates of five and 10 million years, say researchers from Norway, Hawaii and Australia.

The discovery suggests that hot spots are responding to regular fluctuations that come from way down in the Earth's core. It's from the core that pulses of heat are thought to be launched through the mantle, which rise and melt rocks nearer the surface to create hot-spot eruptions.

Among the most famous hot spots are Hawaii, Yellowstone and Iceland. All of these sites have long histories of eruptive pulses that have burned through the slowly moving crust above like a cutting torch -- leaving a long, telltale wake of dead volcanoes made of progressively older rocks.

This is in contrast to other sorts of volcanoes, which are caused by shallower things, like one tectonic plate being shoved under another, then melting.

"Hot spots ... remain some of the greatest enigmas in earth science," commented geologist Mike Coffin of the University of Tasmania, Australia. "Plate tectonic theory does not explain them."

What's more, some of these hot spots have been linked to vast eruptions that have covered large areas with lava, Coffin said. These larger eruptions, in turn, are suspected of having something to do with some of the greatest mass extinctions in the history of life on Earth.

So while they are mysterious, they are crucial for understanding the history of Earth.

The discovery of the co-pulsating hot spots came after geologist Rolf Mjelde of the University of Bergen in Norway, and colleagues looked at the timing of eruptions at all the major hot spots that are thought to be caused by plumes of heat from the depths.

These include Hawaii, Easter Island, Iceland, La Runion, Tristan, the Galpagos, Samoa, Ontong Java, Tasmantid, Society Islands, the Azores, Madeira, Canary Islands, Cape Verde Islands, St. Helena, Kerguelen in the Indian Ocean, as well as Afar-Kenya, Yellowstone, and some European hot spots.

The team found eruption peaks at 10, 22, 30, 40, 49 and 60 million years ago. They also found a secondary series of eruptions at four, 15, 34, 45 and 65 million years ago. Analyzing those dates suggests a main eruption pulse period of approximately 10 million years, with a secondary period of about five million years.

"The periodicity appeared to be the same, which was surprising," Mjelde told Discovery News. "It seems that if these global pulsations are true, it must be something at the core-mantle boundary."

The results of the study by Mjelde, Paul Wessel of the University of Hawaii and Dietmar Mller of the University of Sydney are published in the October issue of the journal Lithosphere.

If the co-pulsation of hot spots is confirmed, it could serve as a window into the behavior of Earth's core.

"If global hot-spot pulsation does turn out to be real, then energy transfer processes at the core-mantle boundary would seem to be the most reasonable cause," said Coffin.

It's confirming the discovery that's really the hard part, he said, and Mjelde agrees.

"Earth scientists commonly suffer from a paucity of data and benefit from a plethora of ideas," said Coffin. "Mjelde et al's work is not atypical in this regard. I regard the pulsation hypothesis as interesting and stimulating, but not necessarily convincing."