High-Viscosity Zone (image) Arizona State University Share Print E-Mail Caption As slabs of Earth's crust decend into the mantle, they encounter a zone about 1,100 kilometers down where the mantle rock abruptly becomes stiffer, flowing less easily. Similarly, rising plumes of molten rock encounter the same layer and have difficulty punching through from below. Credit Dan Shim Usage Restrictions No restrictions if used in connection with reportage on this discovery. Share Print E-Mail Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.