Pāhoehoe lava flow on the Big Island of Hawaii. The picture shows overflows from a main lava channel. The channel is crusting over with a v-shaped opening pointing upstream (top left). The main channel and overflows show the perched nature of this kind of lava channel. Red liquid lava is breaking through ephemeral levees at the overflows.
A lava channel is a stream of fluid lava contained within marginal zones of static (i.e., solid and stationary) lava or lava levees. The initial channel may not contain levees per se, until the parental flow solidifies over what develops into the channel and creates natural levees. This initial levee allows for the building of a more complex levee and channel. As the lava flows though the channel, the elevation of the surface of the lava flow pulsates and lava can possibly flood the associated channel walls spilling out of the channel and over the existing levees, creating what is known as overflow levees. Overflow levees increase the height and width of the original levee. The lava that flows in lava channels is commonly basaltic in composition.