LIHUE — Scientists at the University of Hawai‘i at Manoa have successfully mapped out the past eruptions of Kama‘ehuakanaloa (formerly known as Lo‘ihi Seamount), an undersea Hawaiian volcano approximately 20 miles off Hawai‘i Island’s southern coast.
Hawaiian volcanoes are thought to transition through a series of growth stages, beginning with a submarine “pre-shield” stage. As the only active and exposed Hawaiian volcano in this phase, Kama‘ehuakanaloa provides researchers a unique opportunity to study young, budding volcanoes.
“On the other Hawaiian volcanoes, this early part of the volcanic history is covered by the great outpouring of lava that occurs during the shield stage,” said Aaron Pietruszka, lead author of the study and associate earth sciences professor at UH Manoa. “Thus, there is great interest in learning about the growth and evolution of Kama‘ehu.”
Previously, the only known and confirmed eruption of Kama‘ehuakanaloa occurred in 1996, and was only discovered after
seisometers on Hawai‘i Island detected a swarm of earthquakes.
While seismometers, which measure vibrations caused by seismic waves, are great for measuring active and ongoing undersea eruptions, they are useless for studying volcanic history.
To measure Kama‘ehuakanaloa’s past eruptions, the researchers had to instead analyze the content of its lava. Radium-226, an isotope that naturally occurs in magma, radioactively decays at a predictable rate.
By measuring how much radium-226 was still in lava samples, Pietruzska and the study’s co-authors were able to infer the approximate time period of each eruption. Paired with visual analyses of the seafloor, the team created a more precise timeframe of the volcano’s history.
“The lavas with the freshest appearance also had the most radium-226, and vice versa for the lavas with the ‘older’ appearance — that is, fractured and broken, and/or covered with marine sediment,” Pietruzska explained.
“I was surprised to discover that Kama‘ehu had erupted five times within the last (approximately) 150 years, which implies a frequency of about 30 years between eruptions at this volcano,” he continued. “This is much slower than at Kilauea, which erupts almost continuously, with infrequent pauses of only a few years.”
While both Kama‘ehuakanaloa and Kilauea share Hawai‘i’s volcanic hotspot, Pietruzska explained that their positions over the hotspot may be to blame for the differences in eruption frequency.
“This is an area of Earth’s mantle that is rising toward the surface — a ‘mantle plume’ that ultimately melts to form the magma that supplies Hawaiian volcanoes,” he explained. “Models and other isotope data from thorium-230 suggest that the center of a mantle plume should rise faster than its margin. Our results … provide independent confirmation of this idea.”
Using their findings as a baseline, the researchers hope to better understand how Hawaiian volcanoes work, from their earliest growth stages to their full — and frequently active — maturity.
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Jackson Healy, reporter, can be reached at 808-647-4966 or jhealy@thegardenisland.com.
