Dr Ken Ridgway of Purdue University and, previously, Chevron, spoke on a unique subduction zone in south-central Alaska. Here, in a situation similar to that at the Ontong Java Trench in the southwestern Pacific, a large oceanic plateau is subducting under the continent. Because the majority of oceanic crust is relatively thin and dense, it readily slides under continental crust, which is thicker and more buoyant. When a thick deposit of undersea lavas reaches a subduction zone, however, it causes problems, since such volcanic provinces are different from normal oceanic crust. Such a situation is called “flat slab subduction” because of the tendency of the subducting crust to go under the continent at a much shallower angle than normal.