Scientists studied "fingers of heat" that creep beneath the Earth's surface to uncover the secrets of volcanic hot spots, such as the one that created Hawaii.
The majority of volcanoes sit in areas where the Earth's tectonic plates collide, hot spot volcanos form in the center of the plates. Some geologists believe that "hot buoyant rock" rising from the Earth's mantle provides heat to feed these mid-plate volcanoes, a University of Maryland press release reported.
A research team believed the explanation was more complex in the case of large volcanoes like the ones that formed Hawaii. Using a computer model, the team found the rising plumes of scalding rock were triggered by "fingers" of heat moving within the Earth's crust.
Researchers can "make inferences" to the path seismic waves (which travel beneath the Earth's surface triggered by volcanic activity) have travelled, by comparing records of past seismic events. The waves change shape as they pass through areas with different "density and elasticity."
The process used to map these wave forms, known as seismic tomography, is similar to a CT scan used to look inside the human body. Since less is known about the Earth's innermost structures, the "scans are harder to interpret.
"The Earth's crust varies a lot, and being able to represent that variation is difficult, much less the structure deeper below," Vedran Lekic, an assistant professor of geology at the College Park campus, said.
Through a refined process, that once would have taken 19 years to complete, scientists were able to analyze the "finger-like channels of low-speed seismic waves flowing about 120 to 220 miles below the sea floor, and stretching out in bands about 700 miles wide and 1,400 miles apart.," the press release reported.
The team also noticed the waves travelled four percent slower (at speeds of 2.5 to three miles-per-second) than average in lower depths.
"We estimate that the slowdown we're seeing could represent a temperature increase of up to 200 degrees Celsius (390 degrees Fahrenheit)," lead author Scott French, said.
Scientists had already suggested the existence of the "fingers of heat," but this study allowed them to analyze their size and shape.
"This global pattern of finger-like structures that we're seeing, which has not been documented before, appears to reflect interactions between the upwelling plumes and the motion of the overlying plates," Lekic said. "The deflection of the plumes into these finger-like channels represents an intermediate scale of convection in the mantle, between the large-scale circulation that drives plate motions and the smaller scale plumes, which we are now starting to image."
"The exact nature of those interactions will need further study," said French, "but we now have a clearer picture that can help us understand the 'plumbing' of Earth's mantle responsible for hotspot volcano islands like Tahiti, Reunion and Samoa."
