Aā (also spelled aa, aa, aa, and a-aa; or , from Hawaiian meaning "stony rough lava", but also to "burn" or "blaze") is one of three basic types of flow lava. Aā is basaltic lava characterized by a rough or rubbly surface composed of broken lava blocks called clinker. The Hawaiian word was introduced as a technical term in geology by Clarence Dutton. Accretionary lava balls as large as 3 metres (10 feet) are common on aā flows. Aā is usually of higher viscosity than pāhoehoe. Pāhoehoe can turn into aā if it becomes turbulent from meeting impediments or steep slopes.