CompuServe Messages

<<If an ice sheet is pushed or pulled underwater at roughly a 45 degree angle, bubbles trapped in the ice when freed by melting might rise straight up instead of angling to follow the "weakness" made by ice penetrating water.>> My understanding is that in the case of a denser oceanic crust subducting under the edge of a less dense continental crust and the subsequent flow of magma to the surface, we should remember that at the boundary, both plates are in compression. As the edge of the continental crust is turned up as the oceanic crust turns down, at some distance back from the boundary the lower portion of the the continental crust goes into tension and bending, and cracks. The magma takes the easy route and follows the cracks to the surface; it would be contrary to the laws of physics for it to fight its way back through the zone of compression to vent at the actual "edge" of the subduction zone.