Meet the Yellowstone PlumeGeophysicists can use seismic waves as a tool to probe the interior of the

Meet the Yellowstone PlumeGeophysicists can use seismic waves as a tool to probe the interior of the Earth, to far greater depths than humans have ever traveled. Seismic waves travel through rock and interact with that rock as they go. If the rock is cold, or has certain compositions, it will speed up; if the rock is warm or has different compositions, the wave will slow down.When an Earthquake happens, it sends seismic energy out in all directions and seismometers at the surface detect the arrival of those waves. If a wave arrives a little bit early at one spot, that means it traveled through a slightly faster layer. If a wave is a bit late, then it hit a slow layer. If there are enough seismometers deployed on the planet’s surface, measurements of wave arrivals can be turned into 3-D pictures of the interior of the Earth; a technique known as Seismic Tomography.One of the features in Earth’s lower mantle that was sought for decades was evidence of Plumes. At Earth’s Surface we see evidence in places like Hawaii, Iceland, and Yellowstone, that there is something exceptionally hot rising up through the mantle and hitting the surface at single points. However, these vertical columns are thin and hard to detect with this technique. The first ever seismic detection of plumes heading all the way down to the bottom of the mantle happened only in 2015 (See our post here: https://tmblr.co/Zyv2Js1tcYzwU). That paper explored a number of plumes including Iceland, but it was unable to image anything heading into the deep mantle from Yellowstone.Since that paper was published, the United States conducted a huge seismic experiment with the USArray – a series of hundreds of seismometers that was deployed in part of the country and then moved – marching across the continent from East to West. This huge seismic deployment has allowed scientists to image the deep mantle in ways they never could before. Using data from the USArray, Scientists at UT Austin just published this image – the first ever shot of the Yellowstone Mantle Plume reaching all the way down to the Core.The Yellowstone Plume is a column of seismically slow material that starts somewhere near the border between California and Mexico. About 1000 kilometers below the surface, it kinks and is bent to the North. This seismically slow material is shown in red in this shot, which is traditional as seismically slow material is often interpreted as “hot”. It eventually strikes the surface and spreads out beneath Yellowstone, delivering hot material from the Core-Mantle Boundary to the Yellowstone system. Yellowstone is marked with a volcano on this cross section.The scientists note that the kink in the center of the plume is probably driven by something else happening around the plume, a “mantle wind” or a flow in the mantle around it. The Earth’s mantle convects on its own and plumes would have to punch through this convection, so it’s not surprising that the plume might have some bends in it. The plume also has to reach the surface after traveling through an area where the Farallon plate recently subducted, which may also play a role in bending this plume to the North.To the south of Yellowstone, these scientists imaged another “slow” area in the upper mantle, just beneath the Basin and Range province where North America is slowly faulting and forming rifts. The scientists tested and were able to verify that this region is not connected to the Yellowstone plume; the slow seismic velocities there are caused by something else, such as mantle flow triggered by plate tectonic processes above.-JBBImage credit and original paper:https://www.nature.com/articles/s41561-018-0075-y -- source link
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