World's largest and hottest shield volcano revealed

A new study has found that Mauna Loa on Hawaii’s Big Island is not the world’s largest shield volcano, as experts have believed for many years.

Scientists at the University of Hawaii at Mānoa have now determined that Pūhāhonu, a volcano that has been extinct for more than 12 million years, is two times larger than Mauna Loa.

The research team, which included volcanologists and oceanographers, surveyed the ocean floor along the Hawaiian volcano chain using sonar and gravity sensors to measure mass. The experts also chemically analyzed rocks preserved in the UH Mānoa rock collection. 

The researchers then modeled the results of these studies to estimate the size of Pūhāhonu.

The Hawaiian islands formed over a hotspot in the Earth’s mantle. Volcanoes in this region have been erupting some of the hottest magma on the planet for millions of years. 

Based on the chemical analysis of rocks from Pūhāhonu, the team found that the volcano was once the source of the hottest magma that is known in the past 66 million years. 

“It has been proposed that hotspots that produce volcano chains like Hawaii undergo progressive cooling over 1-2 million years and then die,” said study lead author Michael Garcia. 

“However, we have learned from this study that hotspots can undergo pulses of melt production. A small pulse created the Midway cluster of now extinct volcanoes and another, much bigger one created Pūhāhonu. This will rewrite the textbooks on how mantle plumes work.”  

In 1974, limited survey data indicated that Pūhāhonu was the largest Hawaiian volcano, but subsequent studies concluded that Mauna Loa was larger. 

The advanced surveying and modeling techniques used for the current study were similar to the methods used to examine Mauna Loa. 

The findings confirm that Pūhāhonu is the world’s largest and hottest shield volcano.

The research draws attention to an often overlooked part of Hawaii that has ecological, historical, and cultural importance.

“We are sharing with the science community and the public that we should be calling this volcano by the name the Hawaiians have given to it, rather than the western name for the two rocky small islands that are the only above sea level remnants of this once majestic volcano,” said Garcia.

The study is published in the journal Earth and Planetary Science Letters.

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By Chrissy Sexton, Earth.com Staff Writer