The Uwekahuna Ash was erupted about 1,500 years ago and may be related to an older caldera that filled with lava prior to the development of the present caldera. The Keanakakoi Ash was erupted during weeks or months of activity in 1790. The early activity was driven by degassing magma that interacted with groundwater. Later eruptions were driven by steam explosions. Hawaiian warriors were killed near the end of the eruption by what geologists call a base surge.
Surges are gas-rich and have little volcanic material.
Note that these explosive eruptions are infrequent. Steve Mattox Account of the 1790 eruption The footprints of Hawaiian warriors are preserved in a layer of ash and accretionary lapilli in the Kau Desert southwest of the summit of Kilauea. Photo by Steve Mattox, July 1995. The company in advance had not preceded far before the ground began to shake and rock beneath their feet and it became impossible to stand. Soon a dense cloud of darkness was seen to rise out of the crater, and almost at the same instant the electrical effect upon the air was so great that the thunder began to roar in the heavens and the lightening to flash.