Kīlauea south vent cone within Halema‘uma‘u

A closeup view of the south cone at the summit of Kīlauea, showing the semi-molten nature of the cone flanks. During fountaining, lava accumulates on the cone's flanks at such a high rate that the material remains hot and semi-molten, despite the appearance of cooled, solid material on the surface. On the steep slopes of the cone, this semi-molten material can then reach a critical thickness and begin flowing downhill, in a kind of secondary lava flow. During the Pu‘u‘ō‘ō eruption, these flows were called agglutinated spatter flows, or rootless spatter flows. Several zones of striations on the cone also show where large chunks separated and slid downwards, leaving grooves in the flank. USGS photo by M. Patrick.