Volcanic activity in Haruj has been subdivided into a variable number of phases, including one six generation scheme and a four class scheme based on composition and age. Radiometric dating has yielded a Late Pliocene age for the oldest lava flow generation, and ages established by paleomagnetic analysis are coherent with those established on the basis of the degree of erosion of flows. The oldest generation of lava flows makes up the bulk of the field and has been completely flattened by erosion, save some exceptions. Pre-existent valleys have influenced the emplacement of the oldest generation lava flows, and also that of the second oldest albeit to a lesser degree.