Onset and evolution of summit lava fountaining during the Mauna Loa 2022 eruption
The start of the Mauna Loa 2022 eruption in the Mokuʻāweoweo summit caldera was entirely captured through webcam videos. We analyzed footage from the ~ 7-h summit episode, processing > 87,000 frames using a newly automated method to measure fountain heights, fissure lengths, and inflight ejecta volumes. The summit episode comprised four phases. In Phase 1 (~ 1 h ), a ~ 1 km long fissure propagated from southwest to northeast, with steady fountain heights reaching 125 m. In Phase 2 (~ 50 min ), two further fissure segments extended the total length to ~ 2.4 km, with fountains focused into point sources reaching up to 70 m. In Phase 3 (~ 70 min ), the eruption was steady with no major changes in eruptive behavior. In Phase 4 (~ 4 h ), fountains became unsteady and weak (< 30 m). Fissure growth rates varied from ~ 20 to -9 m/min, and bulk magma flux peaked at 2.7 × 10 4 m 3 /s. An inverse relationship between maximum fountain heights and fissure lengths suggests that total magma flux was nearly constant until Phase 4. We propose an interconnected feeding system for the summit episode with a preferential pathway for gas-rich magma in the southwest portion of the caldera. The sustained nature of the episode was likely driven by the fast rise of melt coupled with small bubbles, with trains of decoupled larger bubbles producing pulsations. Webcam videography was an effective tool to quantify early-stage eruption parameters and could be further explored for rapid response and fine-tuning of hazard mitigation strategies on erupting basaltic volcanoes.