pahoehoe

noun1

1. •
   A form of lava flow of basaltic rock, usually dark-colored with a smooth or ropey surface. It is one of two chief forms of lava flow emitted from volcanoes of the Hawaiian type, the other form being aa.

   • We [...] saw ‘pahoihoi’ or solid lava forming, and also ‘aa’ or clinkers. — 1859