Sideromelane from the upper Holocene of Hawaii. (field of view ~3.2 cm across)

Mt. Kilauea is the world’s most active volcano. It sits atop the Hawaii Hotspot in the central Pacific Ocean. It had a decades-long eruption from 1983 to 2018. Kilauea lavas are basaltic in composition, but the physical appearance of Kilauea’s output varies tremendously. Many of Kilauea’s ongoing basaltic eruptions have occurred along its East Rift Zone, a fracture system extending ~eastward from the summit vent area.

The rock shown here is from the thin ceiling of a lava tube that was active during the 1969 to 1974 eruption of the Mauna Ulu Vent. The Mauna Ulu Lava Field is located along Kilauea’s East Rift Zone. This lava tube ceiling specimen ranges from 1 to 3.5 cm thick.

The photo depicts the exterior (upper) surface of a lava tube ceiling. Abundant, consolidated basalt glass filaments are present, formed by stretching. In cross-section view, the rock is seen to be a highly vesiculated basaltic glass. Rich golden brown-colored basaltic glass is called sideromelane.