Galway Kinnell captures the marked differences in the congealed flows of the two types of lava erupted by Hawaiian volcanoes in his poem “Lava”: smooth, ropy pāhoehoe is “a clear brazened surface/one can cross barefooted,” while jagged ‘a‘ā resembles “a mass of rubble still/ tumbling.” These terms are now standard for Western geologists describing the highly fluid basalt erupted by shield volcanoes (though Icelanders have their own names: helluhraun for pāhoehoe and apalhraun for ‘a‘ā). As it cools, a slow-moving pāhoehoe flow may solidify into fantastic forms: geologists speak of entrail, as well as filamented, corded, sharkskin, slab, and shelly pāhoehoe. What Hawai‘i residents call blue rock is an unusually dense basalt sometimes encountered when cutting roads through old lava.

Pamela Frierson