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<title>Loihi Seamount</title>
<authors>Wikipedia</authors>
<publisher>wikipedia.org</publisher>
<publishedplace>network</publishedplace>
<publishedyear>2010</publishedyear>
<edition></edition>
<category>Volcanoes of Hawaii</category>
<section id="24764" fatherid="0" title="" lv="" priority="-1" level="1">
Lōihi Seamount is an active undersea volcano located around  off the southeast coast of the island of Hawaii. It lies on the flank of Mauna Loa, the largest shield volcano on Earth. Lōihi Seamount is the newest volcano in the Hawaiian-Emperor seamount chain, a string of volcanoes that stretches over  northwest of Lōihi and the island of Hawaii. Unlike most active volcanoes in the Pacific ocean that make up the active plate margins on the Pacific Ring of Fire, Lōihi 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, Lōihi is the only Hawaiian volcano in the deep submarine preshield stage of development. Lōihi  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, Lōihi Seamount stands more than  above the seafloor, making it taller than Mount St. Helens was before its catastrophic 1980 eruption. A diverse microbial community resides around Lōihi's many hydrothermal vents.
In the summer of 1996, a swarm of 4,070 earthquakes was recorded at Lōihi. This series included more earthquakes than any other swarm in Hawaiian history. The swarm altered  of the seamount's summit; one section, Pele's Vents, collapsed entirely upon itself and formed the renamed Pele's Pit. The volcano has remained relatively active since the 1996 swarm and is monitored by the National Oceanic and Atmospheric Administration (NOAA) and the United States Geological Survey (USGS).  The Hawaii Undersea Geological Observatory (HUGO) provided real-time data on Lōihi between 1997 and 2002. Lōihi last erupted in 1996, before a summer earthquake swarm.

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<section id="24765" fatherid="0" title="Characteristics" lv="" priority="-2" level="1">
<section id="24766" fatherid="24765" title="Geology" lv="" priority="-1" level="2">
Lōihi 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 Hawaii hotspot in the extensive Hawaiian-Emperor seamount chain. The distance between the summit of the older Mauna Loa and the summit of Lōihi is about , which is, coincidentally, also the approximate diameter of the Hawaii hotspot.
  Lōihi consists of a summit area with three pit craters, an  long rift zone extending north from the summit, and a  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  high and were formed in July 1996 when its predecessor, Pele's Vent, a hydrothermal field near Lōihi's summit, collapsed into a large depression. The thick crater walls of Pele's Pit-averaging  in width, unusually thick for Hawaiian volcanic craters-suggest its craters have filled with lava multiple times in the past.
Lōihi'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  cone-shaped prominences.
Until 1970, Lōihi was thought to be inactive that was transported by sea-floor spreading to its current location. 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  west, carrying ancient seamounts with it. When scientists investigated a series of earthquakes off Hawaii in 1970, they discovered that Lōihi was an active member of the Hawaiian-Emperor seamount chain. The age pattern Lōihi's summit craters confirms that volcanism at Lōihi has slowly been moving east as Lōihi moves away from its origins over the Hawaii hotspot.
Lōihi rises more than  from the ocean floor, but its peak is still  below the ocean surface. Lōihi is built on the seafloor with a slope of about five degrees. Its northern base on the flank of Mauna Loa is  below sea level, but its southern base is a more substantial  below the surface. Thus, the summit is  above the seafloor as measured from the base of its north flank, but  high when measured from the base of its southern flank.
Lōihi is following the pattern of development that is characteristic of all Hawaiian volcanoes. Geochemical evidence from Lōihi lavas indicates that Lōihi 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 Lōihi. Lōihi 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 Hawaiian volcanos' early development. Lōihi is predicted to rise above the surface in 10,000 to 100,000 years.

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<section id="24767" fatherid="24765" title="Age and growth" lv="" priority="2" level="2">
Radiometric dating was used to determine the age of rock samples from Lōihi. The Hawaii Center for Volcanology tested samples recovered by various expeditions, notably the 1978 expedition, which provided 17 dredge samples. Most of the samples were found to be of ancient origin; the oldest dated rock is around 300,000 years old. Following the 1996 event, some young breccia was also collected. Based on the samples, scientists estimate Lōihi is about 400,000 years old. A few samples collected from the younger, eastern section (where there is volcanic activity) have been unreliably dated as between 4,000 to 21,000 years old. The rock accumulates at an average rate of  per year near the base, and  near the summit. If the data model from other volcanoes such as Kīlauea holds true for Lōihi, 40% of the volcano's mass formed within the last 100,000 years.  Assuming a linear growth rate, Lōihi is 250,000 years old. However, as with all hotspot volcanoes, Lōihi's level of activity has increased with time; therefore, it would take at least 400,000 years for such a volcano to reach Lōihi's mass.   As Hawaiian volcanoes drift northwest at a rate of about  a year, Lōihi was  southeast of its current position at the time of its initial eruption.
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<section id="24768" fatherid="0" title="Activity" lv="" priority="3" level="1">
<section id="24769" fatherid="24768" title="" lv="" priority="-1" level="2">
Lōihi is a young and fairly active volcano, although less so than nearby Kīlauea. In the past few decades, several earthquake swarms have been attributed to Lōihi, the largest of which are summarized in the table below. The volcano's activity is now known to predate scientific record keeping of its activity, which commenced in 1959. Most earthquake swarms at Lōihi have lasted less than two days; the two exceptions are the 1991–92 earthquake, lasting several months, and the 1996 event, which was shorter but much more pronounced. Both of the earthquakes followed a pattern of activity that began on the flank and migrated to the summit. The 1996 event was directly observed by an autonomous ocean bottom observatory (OBO), allowing scientists to calculate the depth of the earthquakes as  to  below the summit, approximating to the position of Lōihi's extremely shallow magma chamber. This is evidence that Lōihi's seismicity is volcanic in origin.
The low-level seismic activity documented on Lōihi  since 1959  has shown that between two and ten earthquakes per month are traceable to the summit.  Earthquake swarm data have been used to analyze how well Lōihi's rocks propagate seismic waves and to investigate the relationship between earthquakes and eruptions. This low level activity is periodically punctuated by large swarms of earthquakes, each swarm comprising up to hundreds of earthquakes. The majority of the earthquakes are not distributed close to the summit, though they follow a north-south trend. Rather, most of the earthquakes occur in the southwest portion of Lōihi. The largest recorded swarms took place on Lōihi in 1971, 1972, 1975, 1991–92 and 1996. The nearest seismic station is around  from Lōihi, on the south coast of Hawaii. Seismic events that have a magnitude under 2 are recorded often, but their location cannot be determined precisely as it can for larger events. In fact, HUGO (Hawaii Undersea Geological Observatory), positioned on Lōihi's flank, detected ten times as many earthquakes  as were recorded by the Hawaiian Volcano Observatory (HVO) seismic network.

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<section id="24770" fatherid="24768" title="1996 earthquake swarm" lv="" priority="2" level="2">
The largest amount of activity recorded for the Lōihi seamount was a swarm of 4,070 earthquakes between July 16 and August 9, 1996.  This series of earthquakes was the largest recorded for any Hawaiian volcano to date in both amount and intensity. Most of the earthquakes had moment magnitudes of less than 3.0. "Several hundred" had a magnitude greater than 3.0, including more than 40 greater than 4.0 and a 5.0 tremor.
The final two weeks of the earthquake swarm were observed by a quick response cruise launched in August 1996. The National Science Foundation funded an expedition by University of Hawaii scientists, led by Frederick Duennebier, that began investigating the swarm and its origin in August 1996. The scientists' assessment laid the groundwork for many of the expeditions that followed.  Follow-up expeditions to Lōihi took place, including a series of manned-submersible dives in August and September.
These were supplemented by a great deal of shore-based research. Fresh rock collected during the expedition revealed that an eruption occurred before the earthquake swarm.
Submersible dives in August were followed by NOAA-funded research in September and October 1996. These more detailed studies showed the southern portion of Lōihi's summit had collapsed, a result of a swarm of earthquakes and the rapid withdrawal of magma from the volcano. A crater  across and  deep formed out of the rubble. The event involved the movement of 100 million cubic meters of volcanic material. A region of 10 to 13 km² (4 to 5 sq mi) of the summit was altered and populated by bus-sized pillow lava blocks, precariously perched along the outer rim of the newly formed crater. "Pele's Vents," an area on the southern side, previously considered stable, collapsed completely into a giant pit, renamed "Pele's Pit". Seawater flowed into the newborn pit on the northern end of the volcano, mixing with loose minerals and bacterial matter before flowing over Lōihi's western edge. The resulting strong current made submersible diving hazardous in the region.
The researchers were continually met by clouds of sulfide and sulfate. The sudden collapse of Pele's Vents caused a large discharge of hydrothermal material. The presence of certain indicator minerals in the mixture suggested temperatures exceeded 250 °C, a record for an underwater volcano. The composition of the materials was similar to that of black smokers, the hydrothermal vent plumes located along mid-ocean ridges. Samples from mounds built by discharges from the hydrothermal plumes resembled white smokers.
The studies demonstrated that the most volcanically and hydrothermally active area was along the southern rift. Dives on the less active northern rim indicated that the terrain was more stable there, and high lava columns were still standing up. A new hydrothermal vent field (Naha Vents) was located in the upper-south rift zone, at a depth of .

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<section id="24771" fatherid="24768" title="Recent activity" lv="" priority="3" level="2">
Lōihi has remained largely quiet since the 1996 event; no activity was recorded from 2002 to 2004. The seamount showed signs of life again in 2005 by generating an earthquake bigger than any previously recorded there.  USGS-ANSS (Advanced National Seismic System) reported two earthquakes, magnitudes 5.1 and 5.4, on May 13 and July 17. Both originated from a depth of . On April 23, a magnitude 4.3 earthquake was recorded at a depth of approximately . Between December 7, 2005 and January 18, 2006, a swarm of around 100 earthquakes occurred, the largest measuring 4 on the Moment magnitude scale and   to  deep. Another earthquake measuring 4.7 was later recorded approximately midway between Lōihi and Pāhala (on the south coast of the island of Hawaii).
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</section>
<section id="24772" fatherid="0" title="Exploration" lv="" priority="-4" level="1">
<section id="24773" fatherid="24772" title="Early work" lv="" priority="1" level="2">
Expedition Timeline
Lōihi Seamount's first depiction on a map was on Survey Chart 4115, a bathymetric rendering of part of Hawaii compiled by the US Coast and Geodetic Survey in 1940. At the time, the seamount was non-notable, being one of many in the region. A large earthquake swarm first brought attention to it in 1952. That same year, geologist Gordon A. Macdonald hypothesized the seamount was an active submarine shield volcano, similar to the two active Hawaiian volcanoes, Mauna Loa and Kīlauea. Macdonald's hypothesis placed the seamount as the newest volcano in the Hawaiian-Emperor seamount chain, created by the Hawaii hotspot. However, because the earthquakes were oriented east-west (the direction of the volcanic fault) and there was no volcanic tremor in seismometers distant from the seamount, Macdonald attributed the earthquake to faulting rather than a volcanic eruption.
Geologists suspected the seamount could be an active undersea volcano, but without evidence the idea remained speculative. The volcano was largely ignored after the 1952 event, and was often mislabeled as an "older volcanic feature" in subsequent charts. Geologist Kenneth O. Emery is credited with naming the seamount in 1955, describing the long and narrow shape of the volcano as Lōihi, the Hawaiian word for "long".Lōihi, meaning "length, height, distance; long".  See:  In 1978, an expedition studied intense, repeated seismic activity known as earthquake swarms in and around the Lōihi area. Rather than finding an old, extinct seamount, data collected revealed Lōihi to be a young, possibly active volcano. Observations showed volcano to be encrusted with young and old lava flows as well as actively venting hydrothermal fluids.
In 1978, a US Geological Survey research ship collected dredge samples and photographed Lōihi's summit with the goal of studying whether  Lōihi is active. Analysis of the photos and testing of pillow lava rock samples appeared to show that the material was "fresh", yielding more evidence that Lōihi is still active. An expedition from October 1980 to January 1981 collected further dredge samples and photographs, providing additional confirmation. Studies indicated that the eruptions came from the southern part of the rift crater. This area is closest to the Hawaii hotspot, which supplies Lōihi with magma. Following a 1986 seismic event, a network of five ocean bottom observatories (OBOs) were deployed on Lōihi for a month.  Lōihi's frequent seismicity makes it an ideal candidate for seismic study through OBOs. In 1987, the submersible DSV Alvin was used to survey Lōihi.
Another autonomous observatory was positioned on Lōihi in 1991 to track earthquake swarms.

</section>
<section id="24774" fatherid="24772" title="1996 to present" lv="" priority="2" level="2">
The bulk of information about Lōihi comes from dives made in response to the 1996 eruption. In a dive conducted almost immediately after seismic activity was reported, visibility was greatly reduced by high concentrations of displaced minerals and large floating mats of bacteria in the water. The bacteria that feed on the dissolved nutrients had already begun colonizing the new hydrothermal vents at Pele's Pit (formed from the collapse of the old ones), and may be indicators of the kinds of material ejected from the newly formed vents. They were carefully sampled for further analysis in a laboratory. An OBO briefly sat on the summit before a more permanent probe could be installed.
Repeated multibeam bathymetric mapping was used to measure the changes in the summit following the 1996 collapse. Hydrothermal plume surveys confirmed changes in the energy, and dissolved minerals emanating from Lōihi. Hawaii Undersea Research Laboratory, HURL's   submersible Pisces V allowed scientists to sample the vent waters, microorganisms and hydrothermal mineral deposits. 
In 1997, scientists from the University of Hawaii installed an ocean bottom observatory (OBO) on the summit of Lōihi Seamount. The submarine observatory was nicknamed HUGO, (Hawaii Undersea Geological Observatory).  HUGO was connected to the shore,  away, by a fiber optic cable. It gave scientists real-time seismic, chemical and visual data about the state of Lōihi, which had by then become an international laboratory for the study of undersea volcanism. The cable that provided HUGO with power and communications broke in October 1998, effectively shutting it down. On January 19 of the following year, HUGO was visited by Pisces V. The observatory functioned for four years before it went dead again in 2002.
Since 2006, the Fe-Oxidizing Microbial Observatory Project (FeMO), funded by the National Science Foundation and Microbial Observatory Program, has led cruises to Lōihi investigate its microbiology every October. The first cruise, on the ship R/V Melville and exploiting the submersible  JASON2, lasted from September 22 to October 9. These cruises study the large number of Fe-oxidizing bacteria that have colonized Lōihi. Lōihi's extensive vent system is characterized by a high concentration of CO2 and Iron, while being low in sulfide. These characteristics make a perfect environment for iron-oxidizing bacteria, called FeOB, to thrive in.

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</section>
<section id="24775" fatherid="0" title="Ecology" lv="" priority="-5" level="1">
<section id="24776" fatherid="24775" title="Hydrothermal vent geochemistry" lv="" priority="1" level="2">
Lōihi's mid-Pacific location and its well-sustained hydrothermal system contribute to a rich oasis for a microbial ecosystem.  Areas of extensive hydrothermal venting are found on Lōihi's crater floor and north slope, and along the summit of Lōihi itself. Active hydrothermal vents were first discovered at Lōihi in the late 1980s. These vents are remarkably similar to those found at the mid-ocean ridges, with similar composition and thermal differences. The two most prominent vent fields are at the summit: Pele's Pit (formally Pele's Vents) and Kapo's Vents. They are named after the Hawaiian deity Pele and her sister Kapo. These vents were considered "low temperature vents" because their waters were only about 30 °C. The volcanic eruption of 1996 and the creation of Pele's Pit changed this, and initiated high temperature venting; exit temperatures were measured at 77 °C in 1996.
</section>
<section id="24777" fatherid="24775" title="Microorganisms" lv="" priority="-2" level="2">
The vents lie  to  below the surface, and range in temperature from 10 to over . The vent fluids are characterized by a high concentration of  (up to 17 mM) and Fe (Iron), but low in sulfide. Low oxygen and pH levels are important factors in supporting the high amounts of Fe (iron), one of the hallmark features of Lōihi. These characteristics make a perfect environment for iron-oxidizing bacteria, called FeOB, to thrive in. The composition of the materials was similar to that of black smokers, that are a habitat of archea extremophiles. Dissolution and oxidation of the mineral observed over the next two years  suggests the sulfate is not easily preserved.
A diverse community of microbial mats surround the vents and virtually cover Pele's Pit.
The Hawaii Undersea Research Laboratory (HURL), NOAA's Research Center for Hawaii and the Western Pacific, monitors and researches the hydrothermal systems and studies the local community.
The National Science Foundation (NSF) funded an extremophile sampling expedition to Lōihi in 1999. Microbial mats surrounded the 160 °C vents, and included a novel jelly-like organism. Samples were collected for study at NSF's Marine Bioproducts Engineering Center (MarBEC). In 2001, Pisces V collected samples of the organisms and brought them to the surface for study.
NOAA's National Undersea Research Center and NSF's Marine Bioproducts Engineering Center are cooperating to sample and research the local bacteria and archea extremophiles. There is also a FeMO (Fe-Oxidizing Microbial Observatory) cruise planned for October 2009.

</section>
<section id="24778" fatherid="24775" title="Macroorganisms" lv="" priority="-3" level="2">
Marine life inhabiting the waters around Lōihi is not as diverse as life at other, less active seamounts. Fish found living near Lōihi include the Celebes monkfish  (Sladenia remiger) , and members of the Cutthroat eel family, Synaphobranchidae.  Invertebrates identified in the area include two species endemic to the hydrothermal vents, a bresiliid shrimp (Opaepele loihi) of the family Alvinocarididae (described in 1995), and a tube or pogonophoran worm.  Dives conducted after the 1996 earthquake swarms were unable to find either the shrimp or the worm, and it is not known if there are lasting effects on these species.
From 1982 to 1992, divers in Hawaii Undersea Research Laboratory submersibles deployed near Johnston Atoll and Cross Seamount photographed the fish of Lōihi Seamount, Johnston Atoll and Cross Seamount at depths between  and .  A small number of species identified at Loihi were newly recorded sightings in Hawaii including the Tassled coffinfish (Chaunax fimbriatus), and the Celebes monkfish.

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<section id="24779" fatherid="0" title="References" lv="" priority="-6" level="1">
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<section id="24780" fatherid="0" title="Further reading" lv="" priority="-7" level="1">
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<section id="24781" fatherid="0" title="External links" lv="" priority="-8" level="1">
Loihi
Loihi
Category:Seamounts of the Pacific Ocean
Category:Hotspot volcanoes
Loihi

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