Lithosphere-Asthenosphere boundary found to become deeper under older crust, thus supporting the suggestion that the discontinuity is closely interrelated to the LAB. Beneath oceanic crust, the LAB ranges anywhere from 50 to 140 km in depth except at mid-ocean ridges where the LAB is no deeper than the depth of the new crust being created. Seismic evidence shows that oceanic plates do thicken with age. This would suggest that the Lithosphere-Asthenosphere boundary underneath oceanic lithosphere also deepens with plate age. Data from ocean seismometers indicate a sharp age-dependent LAB beneath the Pacific and Philippine plates and has been interpreted as evidence for
Geology of the Pacific Northwest spot, an extremely hot plume of deep mantle material, is rising to the surface beneath the Columbia Plateau Province. Geologists know that beneath Hawaii and Iceland, a temperature instability develops (for reasons not yet well understood) at the boundary between the core and mantle. The concentrated heat triggers a plume hundreds of kilometers in diameter that ascends directly through to the surface of the Earth. When the hot plume arrives at the base of the lithosphere, some of the lighter rock of the lithosphere rapidly melts. It is this molten lithosphere that becomes the basalt lavas that gush onto the