The 75km long Puna Ridge is the submarine extension of the East Rift Zone of Kilauea Volcano, Hawaii. The 060¡ trending ridge extends from sea level at the east cape of Hawaii to approximately 5000m depth along it's axis, and is buttressed to the northwest by the older Hilo Ridge; the southeast flank of the ridge is unbuttressed. Pillow lavas and fragments derived from submarine eruptions define a very irregular surface, interrupted along the ridge axis by numerous constructional cones, and along the flanks by plateaus thought to represent ponded lavas. To date, little is known about the subsurface structure of the Puna Ridge, which might inform us about the magmatic and tectonic processes active in this zone.

Multi-channel seismic reflection data collected across the Puna Ridge with the R/V Maurice Ewing in January and February 1998 provide a first look beneath the surface. Three ridge parallel and seven ridge perpendicular 2-D seismic reflection lines were collected over the ridge. The irregular surface morphology and volcanic origin of the Puna Ridge reduces the resolution of most shallow reflection events. Several narrow plateaus along the flanks of the ridge show strong, continuous horizontal reflections, perhaps indicative of lava ponds or shield like vents. Directly beneath the crest of the ridge lies an area of discontinuous and irregular reflections presumably due to the highly fractured and porous nature of the rocks in this zone of magma resupply. Deep reflections interpreted as the top of the Cretaceous oceanic crust can be traced continuously beneath the ridge and in many cases across the entire sections. The existence of these well defined deep reflections, especially directly beneath the axis of the ridge, supports the idea that the ocean crust is unbroken beneath the ridge, and that magma derives from lateral migration along the ridge. A broad bench near the toe of the southeastern flank is revealed to overlap onto the older, sedimented sea floor, suggesting that it represents a local slump.