page_title: Lōʻihi Seamount
section_title: Geology
hierarchical_section_title: Lōʻihi Seamount / Characteristics / Geology
caption_attribution_description: English: bathemetric Map of Loihi Seamount
context_page_description: Lōʻihi Seamount is an active submarine volcano about 35 km off the southeast coast of the island of Hawaii. The top of the seamount is about 975 m below sea level. This seamount is on the flank of Mauna Loa, the largest shield volcano on Earth. Lōʻihi, meaning "long" in Hawaiian, is the newest volcano in the Hawaiian–Emperor seamount chain, a string of volcanoes that stretches about 6,200 km northwest of Lōʻihi. Unlike most active volcanoes in the Pacific Ocean that make up the active plate margins on the Pacific Ring of Fire, Lōʻihi and the other volcanoes of the Hawaiian–Emperor seamount chain are hotspot volcanoes and formed well away from the nearest plate boundary. Volcanoes in the Hawaiian Islands arise from the Hawaii hotspot, and as the youngest volcano in the chain, Lōʻihi is the only Hawaiian volcano in the deep submarine preshield stage of development.
  Lōʻihi began forming around 400,000 years ago and is expected to begin emerging above sea level about 10,000–100,000 years from now. At its summit, Lōʻihi Seamount stands more than 3,000 m above the seafloor, making it taller than Mount St. Helens was before its catastrophic 1980 eruption.
context_section_description: Lōʻihi is a seamount, or underwater volcano, on the flank of Mauna Loa, the Earth's largest shield volcano. It is the newest volcano created by the Hawaiʻi hotspot in the extensive Hawaiian–Emperor seamount chain. The distance between the summit of the older Mauna Loa and the summit of Lōʻihi is about 80 km (50 mi), which is, coincidentally, also the approximate diameter of the Hawaiʻi hotspot. Lōʻihi consists of a summit area with three pit craters, an 11 km (7 mi) long rift zone extending north from the summit, and a 19 km (12 mi) long rift zone extending south-southeast from the summit.
  The summit's pit craters are named West Pit, East Pit, and Pele's Pit. Pele's Pit is the youngest of this group and is located at the southern part of the summit. The walls of Pele's Pit stand 200 m (700 ft) high and were formed in July 1996 when its predecessor, Pele's Vent, a hydrothermal field near Lōʻihi's summit, collapsed into a large depression. The thick crater walls of Pele's Pit – averaging 20 m (70 ft) in width, unusually thick for Hawaiian volcanic craters – suggest its craters have filled with lava multiple times in the past.
  Lōʻihi's north–south trending rift zones create a distinctive elongated shape, from which the volcano's Hawaiian name, meaning "long", derives. The north rift zone consists of a longer western portion and a shorter eastern rift zone. Observations show that both the north and south rift zones lack sediment cover, indicating recent activity. A bulge in the western part of the north rift zone contains three 60–80 m (200–260 ft) cone-shaped prominences.
  Until 1970, Lōʻihi was thought to be an inactive volcano that had been transported to its current location by sea-floor spreading. The seafloor under Hawaii is 80–100 million years old and was created at the East Pacific Rise, an oceanic spreading center where new sea floor forms from magma that erupts from the mantle. New oceanic crust moves away from the spreading center. Over a period of 80–100 million years, the sea floor under Hawaii moved from the East Pacific Rise to its present location 6,000 km (4,000 mi) west, carrying ancient seamounts with it. When scientists investigated a series of earthquakes off Hawaii in 1970, they discovered that Lōʻihi was an active member of the Hawaiian–Emperor seamount chain.
  Lōʻihi is built on the seafloor with a slope of about five degrees. Its northern base on the flank of Mauna Loa is 1,900 m (6,200 ft) below sea level, but its southern base is a more substantial 4,755 m (15,600 ft) below the surface. Thus, the summit is 931 m (3,054 ft) above the seafloor as measured from the base of its north flank, but 3,786 m (12,421 ft) high when measured from the base of its southern flank.
  Lōʻihi is following the pattern of development that is characteristic of all Hawaiian volcanoes. Geochemical evidence from Lōʻihi lavas indicates that Lōʻihi is in transition between the preshield and shield volcano stage, providing valuable clues to the early development of Hawaiian volcanoes. In the preshield stage, Hawaiian volcanoes have steeper sides and a lower level of activity, producing an alkali basalt lava. Continued volcanism is expected to eventually create an island at Lōʻihi. Lōʻihi experiences frequent landslides; the growth of the volcano has destabilized its slopes, and extensive areas of debris inhabit the steep southeastern face. Similar deposits from other Hawaiian volcanoes indicate that landslide debris is an important product of the early development of Hawaiian volcanoes. Lōʻihi is predicted to rise above the surface in 10,000 to 100,000 years.
caption: Bathymetric mapping of Lōʻihi; the arrow points to Pele's Pit.
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