Gardner Pinnacles

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The guano-coated Gardner Pinnacles.
Map showing the location of Gardner Pinnacles in the Hawaiian island chain
Gardner Pinnacles in 1909

The Gardner Pinnacles (Hawaiian: Pūhāhonu) are two barren rock outcrops surrounded by a reef and located in the Northwestern Hawaiian Islands at 24°59′56″N 167°59′58″W / 24.99889°N 167.99944°W / 24.99889; -167.99944Coordinates: 24°59′56″N 167°59′58″W / 24.99889°N 167.99944°W / 24.99889; -167.99944.

The volcano is 511 nautical miles (946 km; 588 mi) northwest of Honolulu and 108 miles (94 nmi; 174 km) from French Frigate Shoals. The total area of the two small islets—remnants of an ancient volcano that is the world's largest shield volcano—is 5.939 acres (24,030 m2).[1] The highest peak is 170 feet (52 meters). The surrounding reef has an area in excess of 600,000 acres (2,400 km2; 940 sq mi).

Gardner Pinnacles was first discovered on June 2, 1820, by the American whaler Maro, commanded by Captain Joseph Allen.

The Gardner Pinnacles are home to some species of fish not found anywhere else in the Northwestern Hawaiian Islands, and have more species of coral than two rocky neighbors to the south, Necker Island and Nihoa. Numerous insects live on the island, and a researcher[who?] claims to have found two new species of spiders here.

Since this is part of Papahanaumokuakea Marine National Monument wildlife refuge, Gardner Pinnacles is off limits to even the military, although they made an unauthorized landing in 1961 or 1962 and blew off the tip of the outcrop to create an emergency helicopter landing spot for the Hawaiian HIRAN project, an effort to determine location of area islands with great precision for navigational purposes.[2] To this day the tip has not been replaced, and debris from the blast can be found scattered throughout the island. In the Hawaiian Archipelago, adjacent islands/reefs are French Frigate Shoals to the southeast, and Maro Reef to the northwest.


According to a 2020 report in Earth and Planetary Science Letters, Pūhāhonu contains approximately 150,000 cubic kilometers of rock, based on a 2014 sonar survey. This would make it Earth's largest single volcano. Only about one-third of that volume is exposed above the sea floor. The rest is buried beneath a ring of debris, broken coral, and other material that has eroded from the peak. 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.

By comparison, from sea floor to peak, Mauna Loa, on Hawaii’s Big Island, is the tallest shield volcano on Earth. But it’s nowhere near as big as Pūhāhonu; a 2013 study estimates Mauna Loa’s volume at 83,000 cubic kilometers. The Tamu Massif, a 4-kilometer-tall volcanic feature the size of the British Isles on the sea floor east of Japan, contains almost 7 million cubic kilometers of material and was once thought to be the world’s largest shield volcano. But Tamu Massif is now believed to have formed along a midocean ridge rather than over a single source of magma. That makes Pūhāhonu the largest known shield volcano on Earth.[3]


The Hawaiian name, Pūhāhonu, means 'turtle surfacing for air', from pūhā 'to breathe at the surface' and honu 'turtle'.[4]

See also[edit]


  1. ^ Giuliani-Hoffman, Francesca. "The largest volcano in the world sits beneath two small rocky peaks in Hawaii". CNN. Retrieved 2020-05-26.
  2. ^ King, Warren B. (March 1973). "Conservation Status of Birds of Central Pacific Islands". The Wilson Bulletin. Wilson Ornithological Society. 85 (1): 89–103. JSTOR 4160286.
  3. ^ World’s biggest volcano is barely visible, Science Magazine, May. 12, 2020. doi:10.1126/science.abc7615
  4. ^ Ulukau Hawaiian Electronic Dictionary

External links[edit]