LAVA FLOW TRAIL STOP 9

Aa and pahoehoe

Basically basalt
Virtually all of Sunset Crater Volcano National Monument is covered with basalt flows and cinders. Despite the fact that it's all pretty much the same stuff, the black and red basalt surface exhibits a remarkable variety of form and texture.

After gasses escape from the magma during the eruption of the cinders, lava flows push out from weak locations at the base of the cinder cone. The lava flows are denser and more viscous than the magma forming the cinders, even though both are the same composition - basalt.

Lava flows can be one of two basic types. Pahoehoe (pa-hoy-hoy) or Aa. Pahoehoe is a Hawaiian term for a smooth, ropey-looking lava that is not commonly found here at Sunset Crater. Aa is a Hawaiian term for the jagged, blocky, rough lava that makes up most of the lava flows around Sunset crater. You might say "Aa " if you walked over this without shoes!

This site is a cooperative endeavor of the
US Geological Survey Western Earth Surface Processes Team
and the National Park Service.

This page was last updated on 8/28/2003.