Global Volcanism Program | Image GVP-04746
The ropy texture of pahoehoe lava flows is produced when the thin solidifying surface of the flow is pushed by the advancing, still-molten interior. This pleated pahoehoe lobe, on a lava flow at Santiago shield volcano in the Galápagos Islands, advanced slowly from the bottom left to the top right. Pahoehoe lavas are the least viscous of common lava types, and thus form diverse surface structures.
Photo by Lee Siebert, 1978 (Smithsonian Institution).