Beneath the cyan and waxy waters of the northwest Hawaiian Islands hides a leviathan. Its true scope has been hidden for many years, but not anymore. What geologists have discovered is a wonder: the largest and best known volcano in the world.
Surprisingly, it is more than double the size of the previous record holder, Mauna Loa on the island of Hawai & # 39; i. And that could change our understanding of the vast Hawaiian Emperor Underwater Chain volcanoes spanning the North Pacific Ocean.
The new record stretches to approximately 148,000 cubic kilometers (35,507 cubic miles) under the waves of the Papahānaumokuākea National Marine Monument, against 74,000 for Mauna Loa.
Only relatively small rock pinnacles called Pinnacles Gardner breaking the surface, giving the volcano its name – Pūhāhonu, the Hawaiian word for "turtle that rises to breathe".
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"We share with the scientific community and the public that we should call this volcano by the name that the Hawaiians gave it, rather than the western name of the two small rocky islands which are the only remains above the sea level of this time. majestic volcano " said geologist Michael Garcia of the University of Hawai & # 39; i in Manoa
.
In the 1970s, low-resolution bathymetric data suggested that Pūhāhonu was approximately 54,000 cubic kilometers in size, later considered to be the largest volcano before further study of Mauna Loa revealed its real size.
Pūhāhonu recovers his crown only after extensive studies of the area, high resolution multibeam bathymetric sounder data has been added to our current understanding of the northwestern chain of Hawaii, hence the volcano rises.
Geologists combined this with the petrological analysis of rock samples recovered from the volcano, refining the volume calculations and modeling based on these parameters.
"Hotspots that produce chains of volcanoes like Hawaii have been suggested to cool gradually over 1-2 million years, and then die." Said Garcia.
"However, we learned from this study that hotspots can undergo impulses of melting production. A small impulse created the Midway group of now extinct volcanoes and another, much larger one, created Pūhāhonu. This will rewrite the manuals on how the mantle feathers work. "
(García et al., EPSL, 2020)
Pūhāhonu is a volcano shield, 12.5 to 14.1 million years old, formed from a single plume of magma that emerges through the mantle. Over the millennia, this source gradually built the volcano to a height of 4,500 meters (14,764 feet) from its lowest point, covering an area of 275 kilometers (171 miles) long and 90 kilometers (56 miles) wide. .
Chemical analysis of the rock collected from the volcano revealed a higher concentration of an olivine mineral called forsterite that we saw on a Hawaiian volcano. This mineral indicates magma at the upper end of the temperature range.
The calcium oxide content of forsterite allowed the team to deduce the depth at which it formed, confirming that it formed in the magma. The simulations allowed the team to calculate the pressure at which the forsterite formed and the temperature.
According to these calculations, the magma recorded 1,703 degrees Celsius (3,097 degrees Fahrenheit), hotter than any other Hawaiian basalt. This extreme temperature is reflected in the size of the volcano, the researchers said.
It is an impressive beast in its own right. But it also has important implications for our understanding of the processes that create these incredible formations.
"The Hawaiian-Emperor chain is perhaps the world's best-studied shallow expression of a mantle plume." investigators wrote in their article.
However, new perspectives on its magmatic and thermal history continue to be revealed as the chain of the Hawaiian emperor is mapped and sampled. This knowledge provides a more complete understanding of the mechanics and thermal evolution of feathers. of the coat. "
The research was published in Letters from Earth and planetary sciences.