Steam explosions ejecting country rock and lake-floor sediments from Rotomahana-Waimangu accompanied eruption of basaltic scoria from Tarawera Volcanic Complex during the early morning of 1886 June 10. The near-source Rotomahana ejecta displays wave-like internal bed forms typical of base surge eruption mechanisms. Deposition occurred from high velocity, steam-fluidised density currents, which carried ejecta laterally outwards from the base of a large vertical eruption column. The surges extended at least 6 km west of the source and passed over steep hills that rise to 350 m above the eruptive vents.