New research conducted by Earth scientists at the University of Hawai'i at Mānoa has revealed fascinating insights about Kamaʻehuakanaloa, formerly known as Lōʻihi Seamount. This submarine Hawaiian volcano, located around 20 miles off the south coast of the Big Island of Hawai'i, has erupted at least five times in the last 150 years. The study provided estimates for the ages of these recent eruptions and also identified eight older eruptions dating back approximately 2,000 years.
What makes Kamaʻehu stand out is its current stage of growth. It is in the earliest submarine “pre-shield” stage, which is quite distinct from its active neighboring volcano, Kīlauea, currently in its main shield-building stage. This unique characteristic makes Kamaʻehu the only active and exposed example of a pre-shield Hawaiian volcano.
The volcanic history of Kamaʻehu is of particular interest because on other Hawaiian volcanoes, the early stages are typically obscured by the extensive lava outpouring during the shield stage. Understanding the growth and evolution of Kama'ehu provides valuable knowledge about this intriguing geological process. The findings of this study were published in the scientific journal Geology.
Kama'ehu's history revealed with chemistry and underwater videos
Until recently, the only confirmed eruption of Kamaʻehuakanaloa was the one in 1996, which came to light due to its coincidental association with a large earthquake swarm detected remotely by seismometers on the Big Island. However, Earth scientists led by Aaron Pietruszka from the University of Hawai'i at Mānoa took a different approach to uncover the ages of older eruptions at Kamaʻehu.
By using a mass spectrometer, they measured tiny amounts of the isotope radium-226 in quenched glassy lava pieces collected from the seafloor outcrops of Kamaʻehu via a submersible. Magma naturally contains radium-226, which decays radioactively at a predictable rate. Analyzing the amount of radium-226 in each sample allowed them to estimate the eruption age of the lava.
Pietruszka had been working on this investigation since his postdoctoral days at the Carnegie Institution for Science, and after returning to UH Mānoa in 2019, he gained access to submersible dive videos and photos around Kama'ehu, which helped confirm their estimates of eruption ages.
Surprisingly, they discovered that Kama'ehu had erupted at least five times in the last ~150 years, indicating a slower eruption frequency of approximately once every 30 years compared to the almost continuous eruptions of its neighboring volcano, Kīlauea, which only has infrequent pauses of a few years. This newfound knowledge sheds light on the growth and evolution of this intriguing pre-shield Hawaiian volcano.
Chemical changes in lava over time
The chemistry of lava erupted from Hawaiian volcanoes undergoes significant changes over time. Recent eruption age estimates for lavas from Kama'ehuakanaloa, along with lava chemistry measurements, reveal that this pre-shield volcano experiences variations in lava chemistry over a timescale of approximately 1200 years. In contrast, Kīlauea's lava chemistry changes on a much shorter timescale, ranging from a few years to decades, with a complete cycle occurring over about 200 years.
Scientists believe that the difference in lava chemistry timescales between the two volcanoes is linked to their positions over the Hawaiian hotspot. The hotspot is an area in Earth's mantle where molten rock rises toward the surface, creating a “mantle plume” that eventually forms the magma feeding Hawaiian volcanoes. According to models and thorium-230 isotope data, the center of a mantle plume should rise faster than its edges. The six times longer timescale of lava chemistry variation observed at Kama'ehu independently supports this concept.
The research team aims to gain a better understanding of how Hawaiian volcanoes evolve from their early stages to their fully mature and frequently active states. By doing so, they hope to unravel the underlying factors influencing volcanic eruptions that originate within the enigmatic and upwelling mantle plume beneath the Hawaiian hotspot. This research sheds light on the complex processes shaping volcanic activity in this dynamic region.
Source: University of Hawaii at Manoa