Volcanoes' Mantle Plumes Debunked

According to a typical textbook picture of how volcanoes work, they erupt when magma gushes out as narrow jets from deep inside Earth. However, new research has debunked this widely held belief.

In fact, these narrow jet streams, or mantle plumes, may not even exist.

"Mantle plumes have never had a sound physical or logical basis," Don Anderson of the California Institute of Technology said in a statement.

According to the currently held theory, heat from Earth's core generates narrow jets of hot magma that gush through the mantle and to the surface. While it isn't clear exactly how these jets are created, scientists have long assumed that they exist. Supposedly they are no more than 300 kilometers wide and located almost 3,000 kilometers underground - nearly halfway to the planet's center.

"Much of solid-Earth science for the past 20 years - and large amounts of money - have been spent looking for elusive narrow mantle plumes that wind their way upward through the mantle," Anderson explained.

Instead, researchers behind this latest study - published in the journal Proceedings of the National Academy of Sciences - argue that there are broad upwellings, rather than narrow jets, driving volcanic behavior.

After analyzing global seismic activity, the research team failed to find evidence of mantle plumes, but did discover large, slow, upward-moving chunks of mantle a thousand kilometers wide. Anderson describes their behavior like that of a lava lamp, in which the heat that is transferred upward via jets - like blobs of wax - is balanced by the slower downward motion of cooled, broad, uniform chunks of mantle.

"What's new is incredibly simple: upwellings in the mantle are thousands of kilometers across," Anderson said.

While this may not seem like a huge revelation, it disproves what scientists had long believed about the mechanisms behind a volcanic eruption. What is driving this motion is not heat from the core, but cooling at Earth's surface. This cooling and plate tectonics drives mantle convection, the cooling of the core, and Earth's magnetic field - volcanoes are simply a side effect.

Still, some continue to support the mantle plume theory. Another recent study even claims that this phenomenon can crack continents under certain conditions, contributing to the distribution of land across Earth's oceans that we see today.