Transition region resists the movement of magma plumes, sinking plates
M.L. Rudolph, V. Lekić and C. Lithgow-Bertelloni
A sixth of the way to the center of the Earth, things get goopy. Using variations in the planet’s gravitational tug, geophysicists have discovered that the viscosity of Earth’s mantle rapidly increases about 1,000 kilometers below ground.
The increasingly viscous rock acts like geologic molasses, slowing down anything trying to push through it. That includes sinking tectonic plates and the rising plumes of hot rock that fuel volcanoes, geophysicist Maxwell Rudolph of Portland State University in Oregon and colleagues report in the Dec. 11 Science. While the origins of the viscosity increase remain unknown, its discovery should help geologists better understand the flow of heat and rock through the planet’s interior.
The depth of the viscosity jump may even be a more suitable dividing line between the upper and lower mantle than the 660-kilometer-deep region