Why Supercontinents Self-Destruct

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May 1, 2007 — Earth's mega-volcanic eruptions may be the direct result of mega continents getting in the way.

A new computer simulation that looks at how heat moves out from the center of our planet confirms the idea that the supercontinent Pangea could have acted like a thermal dam to that heat flow.

When the dam burst, Pangea experienced a gigantic, continent-melting flood of basalt lava that not only busted the place up, but likely vented enormous amounts of carbon into the atmosphere and caused rapid global warming — all at the time of the dinosaurs' demise.

"(Pangea) was sort of a blanket that prevented cooling," said Ben Phillips, a geophysical modeler at Los Alamos National Laboratory in New Mexico. "It was insulating almost a hemisphere." Phillips coauthored a paper on the new simulation in the May issue of the journal Geology.

What's more, when there are many land masses, there is more cooling in the mantle because there's more crust being pushed into the mantle, explained Phillips. It's a lot like dropping ice cubes in hot tea. But when there's just one big continent, he said, there's less cooling in the mantle.

The big question, of course, is whether the big continental blanket and fewer ice cubes could build up enough heat to melt a lot of rock and split up Pangea. The computer simulation indicates it could.

If it's correct, then supercontinents are their own worst enemies — literally creating the conditions which lead to their own demise.

On the other hand, the biggest breach in Pangea — today’s Atlantic Ocean — may hold clues to another continent-wrecker. The Atlantic has quite a few volcanic hot spots that indicate that there are plumes of extra heat rising from deeper in the Earth, says geochemist Kent Condie of the New Mexico Institute of Mining and Technology in Socorro.

These hot spots — like the Azores, Bermuda and Iceland — might be the leftovers of a much larger plume and upwelling that was the cause of the continental break-up.

This plume and upwelling idea is the way geologists have previously explained the massive flood basalt eruptions that wrenched the continent apart and might have led to global warming that killed the dinosaurs.

"(Phillips and his colleagues) have suggested that you don't need to have a mantle plume to have flood basalt," said Condie. What seems more likely, he said, is that there was a combination of things going on — including plumes.

More evidence that plumes are at work is the fact that parts of Pangea are still in the process of breaking up, said Condie. Places like the east African Rift or the ever-widening Red Sea are examples of the continuing break up of Pangea.

Either way, figuring out what ended Pangea is important because its story could help explain other massive events. A billion years ago there was another supercontinent, Rodinia, which didn't last either, said Phillips.