TheGardner Pinnacles (Hawaiian:Pūhāhonu) are two barrenrock outcrops surrounded by a reef and located in theNorthwestern Hawaiian Islands. The large and small rocks have been namedʻŌnūnui andʻŌnūiki, respectively.
ThePūhāhonu volcano responsible for the pinnacles is 511nautical miles (946 km; 588 mi) northwest ofHonolulu and 108 miles (94 nmi; 174 km) fromFrench Frigate Shoals. The total area of the two small islets, remnants of an ancientshield volcano, the world's largest, is 5.939 acres (24,030 m2).[1] The highest peak is 170 feet (52 meters).[2][a] The surrounding reef has an area in excess of 1,904 square kilometres (470,000 acres; 735 sq mi).[3]
The Gardner Pinnacles were discovered and named in 1820 by thewhaling shipMaro.[4] The island may be the last remnant of one of the largest volcanoes on Earth.[5] It holds the record for the largest and hottestshield volcano.[2][b]
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The Gardner Pinnacles were first discovered on June 2, 1820, by the AmericanwhalerMaro, commanded by Captain Joseph Allen.[4]
In 1859, the position of the Gardner Pinnacles was determined by the survey schoonerUSSFenimore Cooper.[6]
The Gardner Pinnacles are home to the giantopihi (Cellana talcosa), a limpet known inHawaiian as the'opihi ko'ele, which is not found anywhere else in the world outside the Hawaiian Islands.[3] Numerous insects live on the island.[3][7]
In 1903 the Gardner Pinnacles became a part of the Hawaiian Islands Bird Reservation.[6] In 1940 it became a part of the Hawaiian Islands National Wildlife Refuge.[8] In the 21st century it is part ofPapahānaumokuākea Marine National Monument wildlife refuge.[2][a]
The Gardner Pinnacles were used as an emergency helicopter landing spot for the Hawaiian HIRAN project, an effort to determine the locations of area islands with great precision for navigational purposes.[9] In the Hawaiian Archipelago, adjacent islands/reefs areFrench Frigate Shoals to the southeast, andMaro Reef to the northwest.
The island is made up ofbasalt rock,[6] which comes from lava erupted between 14 and 12 million years ago.[2][c] The rock is dark grey and dense,[6] and has a highforsterite content implying themagma source was at 1,703 ± 56 °C (3,097 ± 101 °F).[2][d]
According to a 2020 report inEarth and Planetary Science Letters, Pūhāhonu contains approximately 150,000 cubic kilometres (36,000 cu mi) of rock, based on a 2014 sonar survey.[2][e] This would make it Earth's largest single volcano. Only about one-third of that volume is exposed above the sea floor while the rest is buried beneath a ring of debris, broken coral, and other material that has eroded from the peak. By comparison, from sea floor to peak,Mauna Kea, on Hawaii's Big Island, is the tallestshield volcano on Earth, but it is nowhere near as massive as Pūhāhonu. Another volcano on the Big Island isMauna Loa; a 2013 study estimates Mauna Loa's volume at 83,000 cubic kilometres (20,000 cu mi) which is believed to be an overestimate.[2][e] Pūhāhonu is so heavy, researchers note, that it has caused Earth's crust nearby—and thus the volcano itself—to sink hundreds of meters over millions of years.[10] The Puhahonu volcano (Gardner) would be twice as big as Mauna Loa's based on that research.[5][f]
The Pūhāhonu and West Pūhāhonu volcanoes result from theHawaii hotspot which is fed by the Hawaiian plume which had a major magmatic flux pulse at the time.[2][c] A longer magmatic flux pulse produced the Hawaiian Islands.[2][c] The five seamounts of the Naifeh Chain to the north of Pūhāhonu have a completely different tectonic origin, and are older (Late Cretaceous).[11] At one time they were hypothesised to be related to the Pūhāhonu volcano because of arch volcanism, which can not be the case, given the newly determined age difference.[11]
The island has one plant known to grow on it, the succulentsea purslane.[12] However, there are over a dozen species of bird observed here, many nesting.[12] There is also a variety of insect species on the island.[12]
In the surrounding waters there is a variety of sealife, which is noted as habitat for a limpet, the giant ophi which lives in tidal areas of the rocky island.[12] There are many species of fish and coral life in the nearby waters.[12]
The large numbers of birds have coated many surfaces of the island inguano, giving it a whitish appearance.[6]
Some of the fish species in the nearby waters includered lip parrotfish, doublebargoatfish, andreef triggerfish.[13]
The name Gardner comes from its discovery in 1820, when the Captain Joseph Allen of the shipMaro named it Gardner's Island.[12] They also discoveredMaro Reef, which is named for that sailing ship.[14]
It has sometimes been called Gardner Rock or Gardner Island, besides the Gardner Pinnacles.[15]
The Hawaiian name,Pūhāhonu, means 'turtle surfacing for air', frompūhā 'to breathe at the surface' andhonu 'turtle'.[16]
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