Thin beds of explosive debris in the Keanakako`i Ash Member exposed in bluffs west of Keanakako`i Crater. The debris was exploded from unknown vents on the floor of Kilauea Caldera when the caldera was hundreds of meters deeper than at present. Steam derived from heating of ground or surface water was the propellant for the many different explosions.
The most recent explosive eruption of Kilauea was in 1924, but the Keanakako`i deposits record scores of much larger explosions probably distributed over a period of decades to centuries and ending in about A.D. 1790. The explosions were very powerful, mostly consisting of a mixture of material torn from rocks within the volcano with that derived from fresh magma. One thick layer of pumice (smooth brown ledge just above the most prominent shadow in right center of photo) records a mighty lava fountain interspersed between far more powerful, steam-driven explosions.