History of Deep Sea Hawaii Volcano Revealed by Scientists

The history of an underwater volcano in Hawaii has been revealed by researchers in a new study.

For the first time, scientists at the University of Hawaii (UH) have estimated how many eruptions have occurred in the Kamaʻehuakanaloa volcano, or Kamaʻehu—previously known as the Lōʻihi Seamount. It lies underwater about 20 miles off the coast of Hawaii's Big Island, on the flank of Mauna Loa, the largest shield volcano on the planet. The top of the seamount lies 3,200 feet below sea level.

The volcano has erupted five times in the past 150 years, according to a study published in the journal Geology.

To determine the volcano's history, scientists measured the loss of basalts (hard, black volcanic rock) from Kama'ehuakanaloa to estimate the ages of recent eruptions.

Before now, only one eruption known was known to have occurred at the volcano, in 1996. Eruptions at this volcano are extremely hard to monitor. Because its summit lies thousands of feet below sea level, no monitoring instruments are inside, although scientists can record its activity using seismometers on the land.

The 1996 eruption was detected only because of an intense seismic swarm that seismologists picked up from afar.

Scientists do not know much about the underwater volcano's magmatic evolution, but the study says it is very important to their understanding of the evolution of Hawaii's volcanoes as a whole.

"Kamaʻehu is the only active and exposed example of a pre-shield Hawaiian volcano," Aaron Pietruszka, lead author of the study, told local news outlet Big Island Now.

"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. Thus, there is great interest in learning about the growth and evolution of Kamaʻehu," said Pietruszka, an associate professor at UH Mānoa's School of Ocean and Earth Science and Technology.

Scientists assessed the underwater volcano's growth stages, which are typical of Hawaiian volcanoes. They found that Kamaʻehuakanaloa is in an early stage of growth known as "pre-shield." This is different from neighboring volcanoes like Kīlauea, which is in its main shield-building stage.

The underwater volcano also has very different lava fluctuations, compared with Kīlauea. Scientists found that Kamaʻehuakanaloa's timescale for lava chemistry is about 1,200 years, while Kīlauea's is about 200 years.

"We think that the origin of this difference is related to the position of the two volcanoes over the Hawaiian hot spot," Pietruszka told Big Island Now. "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."

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