PAHOA, Hawaii – Despite Kilauea currently not erupting and the USGS Volcano Alert Level remaining at ADVISORY, ongoing unrest is being observed beneath Halemaʻumaʻu, the south caldera, and the upper East Rift Zone. Recent activity has seen an increase in earthquakes clustered below the summit and upper East Rift Zone. The USGS Hawaiian Volcano Observatory has stated that it is uncertain whether this heightened activity will lead to an eruption in the near future or continue as seismic unrest at depth.
However, this week’s focus is not on the present activity but rather on the explosive eruptions that took place a century ago. HVO geologist Kendra J. Lynn and University of Hawaiʻi at Mānoa student Reed Mershon have shared new discoveries made while examining the ash deposited during the 1924 eruptions.
Geologists at the USGS Hawaiian Volcano Observatory have been studying the 1924 explosive deposits for several years, conducting field and laboratory studies on the ash layers around Halema‘uma‘u. These ash layers have remained largely undisturbed for the past 100 years. Analysis of the ash samples has revealed that most of the 1924 ash layers contain recycled lavas, indicating that the eruptions were primarily driven by water-rock interactions known as phreatic explosions.
Further research on the 1924 ash deposits has shown that some layers contain fresh magma, contrary to the initial interpretation of the explosions being steam-driven. Collaboration between HVO scientists and colleagues at the University of Hawai‘i at Mānoa has led to the identification of distinct chemical and textural differences in the 1924 grains, suggesting the interaction of multiple magmas beneath Halema‘uma‘u during the explosive eruptions.
The presence of olivine crystals in the juvenile component of the 1924 eruptions indicates a variety of mineral groups with different histories prior to eruption. The discovery of zoned olivine crystals with varying chemistry further confirms the mixing of magmas just before the volcanic events. Despite 100 years having passed since the 1924 eruptions, ongoing research aims to uncover more insights into the interactions of different magmas and the factors that led to the explosive eruptions at Kīlauea.