Text book volcano pictures all wrong: Scientiststext_fields
New York: We have all grown up looking at pictures of erupting volcanoes in textbooks. But those pictures are wrongful depiction of volcanic eruptions, geophysicists say.
In the typical textbook picture, volcanoes, such as those that line the Hawaiian islands, are seen to be spewing magma, which gush out in the form of narrow jets from deep inside Earth.
"New seismology data are now confirming that such narrow jets do not actually exist," said Don Anderson, a professor emeritus of geophysics from the California Institute of Technology.
In fact, he adds, basic physics does not support the presence of these jets - called mantle plumes - and the new results corroborate those fundamental ideas.
"Mantle plumes have never had a sound physical or logical basis. They are akin to Rudyard Kipling's 'Just So Stories' about how giraffes got their long necks," Anderson added.
The new measurements suggest that what is really happening is just the opposite: Instead of narrow jets, there are broad upwellings which are balanced by narrow channels of sinking material called slabs.
What is driving this motion is not heat from the core but cooling at Earth's surface.
"When material in the planet's crust cools, it sinks, displacing material deeper in the mantle and forcing it upward," informed James Natland, a professor emeritus of marine geology and geophysics from the University of Miami in Florida.
"What's new is incredibly simple: upwellings in the mantle are thousands of kms across," Anderson noted, calling his theory "top-down plate tectonics".
"Volcanoes and cracks in the plate are simply side effects," the authors concluded in their analysis that appeared in the journal Proceedings of the National Academy of Sciences.