Ridge crest volcanism

Developments in this area have preceeded very rapidly. Much of this progress has resulted from sophisticated multi‐channel seismic surveys of the ridge axes and especially from the detailed investigation or mapping of small areas using multibeam arrays, towed cameras and submersibles. The Magma Chamber The depth‐lateral dimensions of the magma chamber remain unconstrained. Multi‐channel seismic reflections from the mantle and from the top of the magma chamber under the crest of the East Pacific Rise at 9°N have been reported by Stoffa et al. [1980] and Herron et al. [1980]. These have been re‐interpreted by Hale et al. [1982] as showing an assymetric chamber caused perhaps by assymetric spreading or by the intersections of the profile with an unmapped fracture zone. Herron [1982] using the same data has resolved the transition from the pillow basalt layer to the sheeted dyke complex at a depth of about 400 m. All interpretations are consistent with the top of the magma chamber being at a depth of between 1.5 and 2 km below the sea floor in this area.