Credit: Vadim Levin/Rutgers University-New Brunswick
In the figure, measurements of the strength of mantle flow are shown along with the colored map of seismic wave speed at 195 kilometers (121 miles) beneath the Earth's surface, under the North American tectonic plate. The warm colors indicate lower speed, implying that rock in those regions is less dense, likely warmer and rising toward the surface. The key finding is that mantle flow indicators are smallest above the warm region, likely because warmer rock flows upward and disrupts the horizontal flow.