The new largest shield volcano found by scientists is more than twice the size of the previous record-holder, the Mauna Loa.

Beneath the peaks that tower 52 meters above sea level, stretches the world’s largest volcano. credit: NOAA Northwestern Hawaiian Islands Coral Reef Ecosystem Reserve

Mauna Loa, the towering giant on the island of Hawaii, has long been considered the world’s largest volcano: from its base on the seabed to its summit, it’s more than 30,000 feet (9170 meters) high and 19,200 cubic miles (83,000 cubic kilometers) wide. However, experts now believe that they have found an even bigger volcano.

In the middle of the Pacific Ocean, 590 miles (952 kilometers) northwest of Honolulu, rise the peaks of Gardner Pinnacles, 170 feet (52 meters) above sea level. Beneath the seemingly insignificant barren rocks lies the ancient behemoth Pūhāhonu, the world’s single largest volcano.

Pūhāhonu is barely visible above the water. Image credit: Live Science/Google Earth

Recent seafloor mapping revealed that the small pinnacles are actually the tips of Pūhāhonu: a volcano, part of the Hawaiian–Emperor seamount mountain chain, that stretches for over 3,700 miles between the Hawaiian Islands and the east coast of Russia. The chain of mostly submerged mountains contains more than 80 underwater volcanoes, most of which are no longer active, although relatively younger peaks still rise above the land and occasionally erupt.

Michael Garcia of the University of Hawaii at Manoa and his team have studied Pūhāhonu, using sonar and gravity detectors. The team of researchers found that the ancient volcano contains about 36,000 cubic miles (150,000 cubic kilometers) of rock. Even though only a small part the volcano is visible above the sea level, it’s twice the size of Mauna Loa. The vast majority of Pūhāhonu lies in extreme depths and its overall height is equivalent to five Eiffel towers. Due to its size, the crust beneath the volcano has sunk hundreds of miles since it was formed over millions of years ago. Hence the name Pūhāhonu, the Hawai’ian word for ‘turtle rising for breath’.

Shield volcanos, such as Pūhāhonu or Mauna Loa, are the largest known volcano types. These dome-shaped mountains with gently sloping sides were formed by the eruption of very fluid lava that flows farther, thus creating volcanoes that resemble a shield lying on the ground. Pūhāhonu formed around 14 million years ago by a single magma plume that surged through the solid bulk of Earth’s interior layer. Over the long years, the magma built the volcano to a height of 14,764 feet (4500 meters), spanning an area of 171 miles (275 kilometers) long and 56 miles (90 kilometers) wide.

It also seems that Pūhāhonu is not only the largest volcano on Earth, but it may be one of the hottest as well. Garcia and his team conducted analysis over several samples of olivine, a crystallized magma they collected from different parts of the volcano. Based on the olivine’s composition, the team was able to infer the temperature at which the magma crystallized into the olivine. According to their results, Pūhāhonu’s magma must have been around 3100 degrees Fahrenheit (1700 degrees Celsius) when it first flowed. This makes it the hottest recorded magma ever, which can reflect the volcano’s extreme size.

The small peak of the great Pūhāhonu is also the home of many bird species that build their nests on these stones. In the surrounding waters there is a variety of marine life: many species of fish and coral can be found here. Gardner Pinnacles is also noted as habitat for the giant opihi, a limpet which lives in tidal areas of the volcano.