This map shows recent changes to Kīlauea’s East Rift Zone lava flow field at the coast. The area of the active flow field as of September 12 is shown in pink, while widening and advancement of the active flow as mapped on September 20 is shown in red. The dashed blue line shows the pre-1983 coastline. The base is a Digital Globe image from January 2016.
Lava deltas – the new land accreted to the front of an older sea cliff – are prone to collapse because the loose underwater lava rubble on which they are built can sometimes become unstable and slide. The interaction of the hot rock composing the delta and cold seawater has led to violent explosions that blasted rocks in all directions, caused local tsunami, and produced billowing plumes of ash and hot, acidic steam.
The dotted line surrounding the Kamokuna lava delta indicates a distance of 300 m (790 ft), which is the maximum documented distance that rocks and spatter have been thrown inland from the older sea cliff by delta explosions that occurred during the Puʻu ʻŌʻō eruption. It is possible that debris could be thrown even farther during exceptionally large explosions.