Geologists debate volcano origins

Where did Hawaii’s volcanoes come from? Scientists have long believed that “hotspot” volcanoes that are located away from the edges of the earth’s plates — like Hawai`i — are caused by plumes of molten lava rising from deep within the Earth. But a recent article in the journal Science has cast some doubt on that theory.

Gillian Foulger of the University of Durham in England and James Natland of the University of Miami believe that many hotspot volcanoes may be a by-product of plate tectonics, like most other volcanoes.

Plate tectonics is the process by which the Earth’s gigantic continental and oceanic plates move. Gigantic masses of rock scrape together and slip under each other where the plates meet, creating the incredible heat and lava that results in volcanoes. Geologists have generally agreed that most volcanoes, located near the edges of the Earth’s plates, are the result of plate tectonics.

For volcanoes located away from the plate boundaries, scientists came up with the hotspot theory. And in the same issue of Science, other scientists defended it.

Donald DePaolo and Michael Manga of the University of California-Berkley argued that volcanoes like Hawai`i cannot be explained by plate tectonics. Because of their location far from the plate edges and because of the very high volume of lava exuded, they conclude, there must be a separate process driving this type of volcano.

Hawai`i geologist Ken Hon agreed.

“If there is a true plume-driven hotspot, we’re sitting on it (here in Hawai`i),” Hon told “To me the evidence is still that there must be some deep driven source for this (Hawaiian) hotspot, not associated with any tectonic features.”

Hon, an assistant professor of geology at the University of Hawai`i-Hilo, explained that although Hawai`i is most likely the result of a deep-rooted hotspot, it is still unclear whether or not the hotspot is completely stationary. There is some evidence suggesting that about 40 million years ago, the Hawaiian hotspot may have been located much further North of its present position, he said.

Hon said he believes that some other hotspots areas may be explained as the by-products of plate tectonics, as Foulger and Natland asserted. He said Yellowstone and Iceland are both hotspot areas located near the edges of plates, and can be explained as the result of cracks radiating out from the plate edges.

This argument doesn’t work for Hawai`i, Hon explained, because there are no cracks radiating out from the plate edges all the way to Hawai`i, located in the center of the Pacific plate.

There are a lot of big questions still unanswered about the hotspots, Hon said, adding that the technology needed to “see” clearly into the earth to try to answer these questions doesn’t exist yet.

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