Loihi seamount, the youngest volcano of the Hawaiian chain, lies about 35 kilometers off the SouthEast coast of the island of Hawaii. Loihi has an elongated morphology dominated by two curving rift zones extending north and south of the summit. The summit region contains a caldera about 3 x 4 kilometers wide and is dotted with numerous lava cones, the highest of which is about 975 meters below the sea surface. The summit platform includes two well defined pit craters, sediment-free glassy lava, and low temperature hydrothermal venting. An arcuate chain of small cones on the western edge of the summit extends north and south of the pit craters and merges into the crests of Loihis prominent rift zones.