Photo Information

Pahoehoe lava flow, Kilauea Volcano, Hawaii
Photograph by L. Simmons on November 29, 1988
Tube-fed pahoehoe flow creeps across flat-lying ground near the coast. A crust forms on these flows as soon as lava is exposed to air. As the flow front slowly advances, the crust at the margins of the flow lifts and molten material oozes out, further extending the flow.

`A`a lava flow, Kilauea Volcano, Hawaii

Photograph by T. Mattox on August 16, 1990
This photo shows examples of both forms of basaltic lava: a rubbly `a`a flow advances over smooth silvery pahoehoe. There is no difference in the composition of these two forms, and a single flow can start as pahoehoe and change to `a`a as it loses heat and gas and starts to crystallize. Flowing down steep slopes, or very rapidly, also accelerates the transition from pahoehoe to `a`a.