lahar definition
Freebase(5.00 / 1 vote)Rate this definition: A lahar is a type of mudflow or debris flow composed of a slurry of pyroclastic material, rocky debris, and water. The material flows down from a volcano, typically along a river valley. Lahars are extremely destructive: they can flow tens of meters per second, be 140 metres deep, and destroy any structures in their path.