https://www.youtube.com/watch?v=zymINXCAMw0
Early in the 2021 eruption, lava spilled from a fissure-fed vent and cascaded into Geldingadalur, steadily raising a growing lava pond on the valley floor.
Valley-filling eruptions reshape topography quickly: successive overflows bury older crust, divert channels, and eventually spill into neighboring valleys as volume accumulates.