Abstract Three voluminous inflated lobate lava flow complexes on the distal rifts of Axial Seamount are much larger than other known flows in the global spreading system. Each complex is 65–100 km 2 , is up to 130 m thick, and is ∼3.0–4.6 km 3 , almost 100 times the volumes of historical Axial flows. These extraordinary flows are 5–7 times thicker than typical drained ponds in sheet flows. They thickened as impounded lava accumulated under chilled crusts. As flows expanded, molten interiors partially drained and flow tops collapsed. Levees built around collapses when interiors are repressurized. This formation sequence was preserved when the levee around one deep pond breached and drained the interconnected ponds. The complexes formed during moderately high‐rate eruptions. Lavas from the south rift complex are plagioclase phyric mid‐ocean ridge basalt (MORB) and those from the north rift complex are nearly aphyric and slightly more evolved. Glass compositions are similar to those of the summit and most rift lavas, implying that they resided in the summit magma reservoir where depleted ridge‐derived magma and more enriched hot‐spot‐derived magma mixed. The distal south rift complex formed ∼1259 ± 119 years BP (or ∼691 CE; based on 14 C dating of planktic foraminifera from core bases), a date that is statistically indistinguishable from the dates of phreatomagmatic deposits at the summit and formation of the present‐day caldera. The north rift voluminous flows erupted ∼12,870 ± 173 years BP. The southwest complex, although partly mapped, remains unsampled, and is still older. Eruptions of these earlier voluminous lava complexes may also have coincided with prior caldera collapses.
Paduan et al. (Thu,) studied this question.