Mid-Atlantic Ridge axis cross section. Beneath the surface, dikes (magma conduits) rise vertically and propagate along the axis from a magma body. Three dikes are shown in detail. The most recent is the one to the right, shaded yellow-orange. Where a dike breaches the surface, a fissure eruption occurs. Older flows are transparent. Hummocky ridges and seamounts are built along the axis. Seamounts and flat-topped highs on the flanks of the axial volcanic ridge are fed by lava tubes from the summit.
Three-dimensional perspective view of side-scan sonar data mapped onto the color bathymetric surface for a portion of the inner valley floor of a spreading segment near 29° N at the Mid-Atlantic Ridge. The area of the image is 15 kilometers east to west and 13 kilometers north to south. Several side-scan sonar swaths have been merged together across the image. Bright is a reflection, and dark is a shadow or attenuated return from sediment-covered terrain. The cratered seamount (volcano) marked on the image is about 220 meters in relief with a summit crater some 600 meters in diameter. A hummocky-textured axial volcanic ridge winds its way along the valley floor, and volcanic highs extend to the east and west from the axial volcanic ridge into its flanking deeps.
Side-scan sonar image of a small volcanic ridge that is located within the central low of a spreading segment near 25° N. Illumination is from the right. The ridge is about 3.3 kilometers long, 400 meters wide, and 30 meters high. The along-axis orientation of the ridge mimics neighboring faults and fissures, and it is inferred to have erupted from similar fissures. The smooth, unfaulted flows surrounding the ridge are interpreted to be part of the eruption that built the ridge. These flows cover pre-existing faults and fissures. Information about the small-scale volcanic products and faults gained from images such as these provide insight into the processes of magmatism and tectonism at the axis of the Mid-Atlantic Ridge.
Three-dimensional perspective view of side-scan sonar data mapped on to a color bathymetric surface for a portion of the inner valley floor of a spreading segment near 25° N at the Mid-Atlantic Ridge. The area of the image is 15 kilometers east to west and 22 kilometers north to south. The morphological center of this segment is a topographic low filled with smooth-textured flows that are extensively fissured and faulted. Isolated volcanic features sit strati-graphically on top of the smooth flows.