Sulfur deposited from fumarolic vents coats lava flows on Loihi seamount. Loihi, the youngest Hawaiian volcano, rises to within 975 m of the sea surface 35 km off the SE coast of the island of Hawaii. Two rift zones, oriented N-S, give the volcano an elongated form, and prompted its name, which is the Hawaiian word for "long." Fresh, sediment-free lava flows indicate the young age of the submarine volcano, and seismic swarms related to intrusive or eruptive activity have been recorded frequently.

Photo by the Hawaii Undersea Research Laboratory (University of Hawaii).

Submarine extrusion of magma produces a characteristic "pillow lava" morphology, as seen here on Loihi seamount SE of the island of Hawaii. Thin streams of molten lava are extruded in a form that resembles toothpaste squeezed out of a tube. The outer surface of the molten lava is quickly chilled by the water and solidifies, while the interior remains molten and continues to flow, lengthening the tubes. Lava flows with similar textures on land can be recognized as being uplifted submarine (or sublacustral) lavas.

Photo by the Hawaii Undersea Research Laboratory (University of Hawaii).