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 (