Submarine Eruption

Eruptions beneath the sea surface are the most common type on Earth, but are significantly underrepresented in the historical record. Submarine eruptions display characteristics that differ from their on-land equivalents. Submarine lava flows are emplaced by incremental extrusion of lobes that are rapidly chilled in contact with the water, forming structures known as pillow lavas. Explosive fragmentation of lavas forms thick fragmental deposits known as hyaloclastites. Deep-sea submarine eruptions are common along mid-ocean ridges, where an estimated 75% of Earth's magmas erupt. Shallow submarine eruptions can produce explosive columns of steam and ash, known as Surtseyan eruptions from the new island Surtsey formed off the coast of Iceland in 1967. Explosive submarine eruptions often produce large amounts of pumice, which can form long-lived rafts of floating pumice carried long distances from the volcano by ocean currents. Lava flows entering the sea can cause explosions that create cones of ash and debris that resemble cinder cones, although they were formed from rootless vents not connected to a volcanic conduit.

Photo by W.G. Muller, 1977 (courtesy of Wally Johnson, Australia Bureau of Mineral Resources).

Kavachi

A spectacular shallow-water phreatomagmatic, or surtseyan eruption from Kavachi volcano is observed from a small boat on July 17 or 18, 1977. Sprays of dark ash can be seen emerging from white vapor clouds. Numerous individual blocks ejected at high velocity are trailed by clouds of steam. Similar activity was observed from boats and airplanes for a period of less than one week.

A burst of incandescent magma rises above the sea surface at Kavachi volcano in the Solomon Islands. By the time of this June 30, 1978 photo, the vent of the submarine volcano had reached the sea surface. Dark blocks of extruded lava can be seen through the clouds of steam. No sign of the submarine volcano had been observed on June 20, but the following day an eruption was seen. By the 22nd, a 30-50 m wide island was observed, from which incandescent lava was emerging. Vapor and ash rose a few thousand meters into the air.

Photo by C.E. Stehn, 1930 (courtesy Volcanological Survey of Indonesia).

Krakatau

A dark, ash-laden cloud is ejected from a submarine vent at Anak Krakatau (Child of Krakatau) on June 12, 1930. A white steam column rises above a pyroclastic-surge that travels horizontally along the sea surface in a radial direction from the vent. "Base surges" such as these are a common phenomenon of submarine eruptions. The first eruptions of Anak Krakatau to breach the surface were seen in December 1927.

Photo courtesy of Ryohei Morimoto (University of Tokyo), 1952.

Bayonnaise Rock

An explosion from the Bayonnaise Rocks submarine volcano in Japan's central Izu Islands breaches the sea surface on September 23, 1952. These cockscomb-like projections of blocks and ash are characteristic of shallow submarine explosions. This photo was taken 5 seconds after the explosion penetrated the sea surface. Five minutes later the eruption was over and the sea was again calm. The suddeness of these powerful explosions proved to be fatal to 31 persons on a research vessel that sailed over the vent the following day.