Yellowstone's hotspot theory heats up
supervolcano A new study may have finally resolved debate on how America's famous Yellowstone supervolcano was formed.
The research conducted by scientists including Professor Ross Griffiths of the Australian National University, shows features associated with Yellowstone were caused by a volcanic hot spot affected by a subduction zone.
Reporting in the journal Nature Geoscience, they suggest a mantle plume originated to the northeast of Yellowstone, and is being sucked southwest into the subduction zone caused by the Pacific plate.
Hotspots occur where plumes of hot mantle material from deep inside the Earth rise to the surface by convection.
"Hot spot volcanism is commonly out in the centre of an oceanic plate like Hawaii or at the spreading ridges between two oceanic plates like Iceland," says Griffiths.
"But they can come up anywhere as far as we know, and so they'll often occur in the vicinity of subduction zones, such as the Ring of Fire around the Pacific."
Subduction zones occur on the Earth's crustal plate boundaries where heavy basaltic oceanic crust is subducted under lighter granite-based continental crust.
"We chose Yellowstone because it's been cited by many other researchers as a place where the volcanism couldn't possibly be due to a mantle plume," says Griffiths.
"It just doesn't fit the usual picture as in Hawaii where you have an active centre and a chain of islands of increasing age extending along the Pacific plate."
The Yellowstone supervolcano has a 72-kilometre-wide caldera created by the collapse of the volcano's magma chamber.
But the causes of this volcanism over the past 20 million years have been strongly debated by scientists.
There are several large and apparently unconnected local flood basalt volcanic features that occur in different areas, directions and timescales.
These have been interpreted as being associated with different subduction events, and are often used to argue against a single hot spot origin for Yellowstone's volcanism.
And to date, seismic studies haven't detected any mantle plume structure under Yellowstone.
"We felt the seismic surveys were being carried out in the wrong area, and we also though we could demonstrate a connection between the Columbia River basalts and the Yellowstone plume," says Griffiths.
Viscous syrup study
To investigate their theory, Griffiths and colleagues undertook laboratory simulations using a viscous syrup that can be heated or cooled to act in a way similar to the Earth's mantle.
"It has the consistency of honey and behaves on timescales analogues to geologic time, allowing us to recreate a range of scenarios, something like what occurred in the northwest," says Griffiths.
The experiments showed how a single hot spot interacting with a subducting plate could produce the range of different and apparently unconnected features seen at Yellowstone.
"Because of the way the solid mantle is swept around the edges of the subducting Pacific plate, there would be an apparent disconnection between the flood basalt province and the volcanic chain leading to Yellowstone," says Griffiths.
"It all seemed to fit together very nicely allowing us to explain much of the activity in the northwest US with a plume model and the way it interacts with the subduction zone."