Slabs of basaltic pahoehoe lava are tilted along a pressure ridge of the Carrizozo lava flow in New Mexico. This massive tube-fed pahoehoe flow displays abundant evidence of inflation features such as tumuli, pressure ridges, and lava pits. Tumuli form when brittle crust buckles to accommodate the inflating core of the flow, thus creating a central crack along the length of the tumulus. These structures sometimes grade into elongated features called pressure ridges.

Photo by Lee Siebert, 1999 (Smithsonian Institution).

This image is made available under the Public Domain Dedication CC0 license, but proper attribution is appreciated.

Carrizozo