The distinction between lava and magma is a fine one. Both terms refer to molten rock, but once magma leaves the earth’s interior and flows out the open air, it becomes lava. It’s sort of like the alchemy of “meteor" into “meteorite" once a chunk of space rock touches ground—a linguistic metamorphosis as much as, or more than, a physical one.
The ongoing eruption of Kilauea in Hawaii has brought volcano jargon to the surface, like an effusion of mafic (that’s low-silica, oozing magma to you). Maybe you’ve heard of “laze," the haze that issues forth when hot lava hits seawater, billowing clouds of hydrochloric acid and particles of glass that can be toxic to inhale. There’s also “vog”—volcanic smog that drifts from active volcanoes like Kilauea, reacting with sunlight and oxygen to form a hazy fug that often reaches the far end of the Hawaiian island chain.
But if you want to sound like a volcanologist, you’ll need to get a few more terms under your belt. Here’s a quick guide to help you mind your ‘pahoehoe’s and ‘coulee’s.
Pahoehoe & A’a
There are two kinds of lava. Pahoehoe—basaltic, iron-rich lava that moves quickly and smoothly, forming ropy masses and hollow tunnels—and a’a, a viscous, chunky lava that hardens into a rough or spiky surface. Both names come from Hawaiian language: hoe (pronounced “hoo-ee”) means “to paddle,” for the way the swirling lava resembles eddying water. A’a comes from the Hawaiian word for “to burn.”