Seismic measurements reveal a saturated porous layer beneath an active Antarctic ice stream

Seismic reflection studies recently conducted on ice stream B, part of the marine ice sheet of West Antarctica, show a metres-thick layer immediately beneath the ice in which both compressional (P) and shear (S) wave speeds are very low. These low wave speeds imply that the material in the layer is highly porous and is saturated with water at a high pore pressure. From this, and from arguments presented in an accompanying paper¹ to the effect that the layer would be too weak to support the shear stress exerted by the overlying ice, we conclude that the layer is deforming and that the ice stream probably moves principally by such deformation.