Aa is basaltic lava and is characterized by a rough, jagged surface. It forms rare but large gas bubbles which, as the lava solidifies during flow, promote its fracturing into large blocks. The temperature of this type of lava is usually between 1000 and 1100 °C (1830 and 2000 °F).
The name aa (ʻaʻā) was originally applied only to Hawaiian lavas. However, it has been adopted to refer to all lavas of this type. In Iceland this type of lava is called apalhraun.
