Pāhoehoe
Pāhoehoe is a basaltic lava-flow surface with smooth, billowing, or ropy forms. Its crust forms while hot lava continues moving beneath it.
Lava crust: A solid or partly solid layer that forms at the surface of a lava flow. Pāhoehoe’s smooth surface is a thin crust shaped by lava moving underneath.
Basalt: A dark, fine-grained volcanic rock formed when low-silica lava cools. Pāhoehoe is a surface form typically produced by basaltic lava.
ʻAʻā: A basaltic lava-flow surface of rough, broken, clinkery blocks. ʻAʻā is the contrasting rough surface texture to pāhoehoe’s smooth, ropy crust.
Kīlauea: An active shield volcano on Hawaiʻi Island that has produced extensive basaltic lava flows. Its eruptions provide well-documented examples of pāhoehoe emplacement.
Lava inflation: The thickening of a lava flow as molten lava enters and lifts its insulating crust. Inflation can raise pāhoehoe crust into rounded, billowing forms.
Mafic rock: An igneous rock relatively rich in magnesium and iron and relatively low in silica. Basalt belongs to this broad rock family, which commonly produces fluid lava.
Block lava: A lava-flow surface covered in large, angular blocks, commonly formed by more viscous lava. Its angular blocks contrast with pāhoehoe’s continuous, deformable crust.
Mauna Loa: A massive active shield volcano on Hawaiʻi Island built mainly from basaltic lava. Its broad flows include extensive fields of pāhoehoe.
Lava tube: A conduit formed when the surface of a lava flow solidifies around a channel of moving lava. Pāhoehoe crust can roof active channels, helping them develop into lava tubes.
Lava: Molten or partly molten rock that has erupted onto Earth’s surface. Pāhoehoe is a surface texture formed by lava after it erupts.