Hazardous Explosive Eruption Cycles at Kīlauea Volcano, Hawai’i

Kīlauea, on the island of Hawaiʻi, is one of the most active volcanoes on Earth. The volcano is ranked as the highest-threat volcano in the U.S. because of the large population and large number of visitors to Hawaiʻi Volcanoes National Park. For the past two centuries, Kīlauea has produced mostly gentle lava flows. However, long periods of explosive, ash-producing eruptions have also occurred. Explosive eruptions may be part of the volcano’s normal behavior rather than a rare exception. Only the two most recent explosive periods of the last 2,500 years have been studied in detail. Scientists do not yet understand what triggers the shifts between quiet and explosive activity. This project will investigate a 10,000-year-long explosive episode known as the Pahala Tephra. Research will determine when the episode occurred and what conditions inside the volcano allowed it to happen. This research will help scientists recognize warning signs of explosive activity. Results will improve long-term hazard planning for Hawaiʻi communities and visitors. This project investigates the origins, duration, and spatial distribution of the Pahala Tephra, a proposed ~10,000-year-long explosive eruptive cycle of Kīlauea Volcano. The ash and pyroclastic deposits were emplaced between approximately 30,000 to 3,500 years ago. Kīlauea’s stratigraphy indicates that alternating explosive-effusive cycles may represent the volcano’s typical long-term behavior, rather than the sustained effusive activity observed over the last two centuries. However, only the two most recent explosive cycles in the last 2,500 years have been characterized in detail. The investigators will use a multidisciplinary approach that combines field stratigraphic and dispersal mapping of tephra units; radiocarbon dating of intercalated charcoal to constrain eruption timing and cycle duration; textural analysis of pyroclast groundmass and vesicles to estimate magma decompression rates; and geochemical analysis of volatile contents, degassing state, and mantle source characteristics. Results will be used to reconstruct the magma storage and supply configuration that were active during the Pahala period. Comparison of these deposits with the overlying and underlying effusive units will test whether explosive activity is driven primarily by elevated magmatic volatile content or requires interaction between rising magma and groundwater within a deep summit caldera. By identifying recurring physical and geochemical indicators associated with the onset, duration, and cessation of explosive cycles, this project will help establish the mechanisms that govern transitions between explosive and effusive behavior at Kīlauea and provide a basis for assessing the likelihood and character of future long-lived explosive activity. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.