Loihi Seamount

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Lōʻihi Seamount

Elevation:	-975 meters (-3,199 feet)
Coordinates:	18.92° N 155.27° W
Location:	Hawaiian Islands
Type:	Submarine volcano
Last eruption:	2007 (active)

Lōʻihi is a seamount and undersea volcano in the Hawaiian archipelago, located at 18.92°N, 155.27°W—roughly 30 km (19 mi) south of the southeast coast of the Island of Hawaiʻi. It is one of three active volcanoes (the other two are Mauna Loa and Kīlauea) thought to presently sit over the Hawaiian hotspot. The greatest distance between the summits of these volcanoes is about 80 km (50 mi), approximately the diameter of the hot spot. Lōʻihi has yet to build to the surface of the ocean, although it is now over 3000 m (10,000 ft) high (taller than Mount St. Helens). The top of Lōʻihi lies 969 m (3,178 ft) below the surface. If the rate of upward building is about the same as nearby Kīlauea, Lōʻihi should appear at the surface in several tens of thousands of years.

Yellow iron oxide covered lava rock on the flank of Lōʻihi submarine volcano.

Like Kīlauea, Lōʻihi lies on the flank of Mauna Loa, the largest shield volcano on the planet. The summit has a caldera-like depression, and three craters. The crater called Pele's Pit is known to have formed in July 1996 when a vent collapsed forming a depression with 200 m (660 ft) high, vertical walls. The rift zone for this volcano is about 31 km (19 mi) long and oriented northwest-southeast across the 2.8 by 3.7 km (1.7 × 2.3 mi) caldera. The eruption in 1996 was confirmed by scientists at the University of Hawaiʻi, becoming the first such confirmation of an active eruption occurring on a seamount. Another active undersea volcano, named Vailuʻuluʻu, was confirmed in 2001 in the Manuʻa Group, Samoa.

Lōʻihi is being studied by manned submersible dives to its surface and placement of recording instruments and remote observatories on the summit. The volcano is actively venting hydrothermal fluids and thermal vents there are being studied for thermophilic extremophiles: (micro)organisms associated with extreme temperature conditions. In 1999, a never before seen jelly-like organism surrounding the 160°C vents was collected for incubation and study at NSF's Marine Bioproducts Engineering Center (MarBEC).