Two rocky pinnacles in the North Pacific, 1,100 km northwest of Honolulu, the Gardner Pinnacles, are in fact the tip of a huge shield volcano, called Pūhāhonu, meaning "the turtle rising to the surface to breathe ".
Gardner Pinnacles, guano covered rocks - photo Andy Collins, NOAA Northwestern Hawaiian Islands Coral Reef Ecosystem Reserve
He competes at MaunaLoa, on Big Island, for the title of the largest shield volcano in the world.
Impressive in size, because its base is 4,500 meters below the ocean surface, its mass is even more so: according to a sonar analysis made in 2004, its total volume would be 150,000 km³, causing the subsidence of the crust which supports.
New bathymetric and gravimetric maps, refined volume calculations and petrological analyzes show that the Hawaiian volcano Pūhāhonu, dated from 12.5 to 14.1 Ma, located in the northwest of the Hawaiian ridge (NWHR) has twice the size of the Mauna Loa volcano.
Its gigantic size would be due to a warmer mantle, particularly a solitary wave in the Hawaiian mantle plume, capable of supplying large volumes of magma, consistent with the compositions of highly forsteritic olivine phenocrysts (more than 91.8% of forsterite, a magnesium silicate) and the high percentage of fusion (24% according to calculations).
Source: Earth and Planetary Science letters - Pūhāhonu: Earth's biggest and hottest shield volcano - M.O. Garcia & al.