While we read stories in the national media of a possible catastrophic eruption of the Yellowstone volcanic area, scientists are not so sure of the likelihood of such an event. In an effort to better understand the region’s subsurface geology, geologists are taking another look at geologic history.
“The heat needed to drive volcanism usually occurs in areas where tectonic plates meet and one slab of crust slides, or subducts, under another.
“However, Yellowstone and other volcanic areas of the inland western U.S. are far away from the active plate boundaries along the west coast.
“In these inland cases, a deep-seated heat source known as a mantle plume is suspected of driving crustal melting and surface volcanism.”
In new study, which was published in the journal Nature Geoscience, the researchers used a method called seismic tomography to see deep into the subsurface of the western U.S. This helped to piece together the geologic history behind the volcanism.
The team then used supercomputers to run different tectonic scenarios to detect a range of possible geologic histories over the past 20 million years. The results showed little support for the traditional mantle plume hypothesis. Graduate student Quan Zhou, who was part of the team, explained:
“Our goal is to develop a model that matches up with what we see both below ground and on the surface today.
“We call it a hybrid geodynamic model because most of the earlier models either start with an initial condition and move forward, or start with the current conditions and move backward. Our model does both, which gives us more control over the relevant mantle processes.”
One of the variables entered into their model was heat, because hot subsurface material like what you would find in a mantle plume should rise vertically toward the surface. However, in their model, that was not what they saw: Liu explained:
“It appears that the mantle plume under the western U.S. is sinking deeper into the earth through time, which seems counterintuitive.
“This suggests that something closer to the surface — an oceanic slab originating from the western tectonic boundary — is interfering with the rise of the plume.”
For many years, the mantle plume hypothesis has been contentious; nevertheless, this new finding adds to the evidence for a revised tectonic scenario, the researchers said, adding:
“A robust result from these models is that the heat source behind the extensive inland volcanism actually originated from the shallow oceanic mantle to the west of the Pacific Northwest coast.
“This directly challenges the traditional view that most of the heat came from the plume below Yellowstone.”
“Eventually, we hope to consider the chemical data from the volcanic rocks in our model.
“That will help us further constrain the source of the magma because rocks from deep mantle plumes and near-surface tectonic plates could have different chemistries,” Zhou added.
As for the recent stories in the national media, researchers say it is still too early to know the possibility of a violent demise of Yellowstone occurring anytime soon, Liu went on to say:
“Of course, our model can’t predict specific future super-eruptions.
“However, looking back through 20 million years of history, we do not see anything that makes the present-day Yellowstone region particularly special – at least not enough to make us suspect that it may do something different from the past when many catastrophic eruptions have occurred.
“More importantly, this work will give us a better understanding of some of the mysterious processes deep within the earth, which will help us better understand the consequences of plate tectonics, including the mechanism of earthquakes and volcanoes.”
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