Other parts of the East Arm were active by 15 million years ago and by 10 million years ago there was activity along all four arms. volcanic phase in the Afar Triangle started around 4 million years ago; it lasted until 0.5-1 million years ago. The fact that Ethiopia and Yemen both show the outpourings of the flood basalt of 30 million year ago, but the plateau in Yemen lacks the 24 million year event suggests that their split happened in between these times.