It is generally believed that the Mangatepopo Valley was glacially carved out during the last ice age and subsequently partially in-filled by lava flows from Ngauruhoe. Note the different colours on the lava flows as you walk up the valley. The surface colour of younger lava is darker and absorbs much of the suns' heat - this is a harsh environment for plants to grow and the reason why the youngest flows only have a few plants, lichens and moss. The older flows have progressively more species and large plants, which take advantage of the slow build up of precious soil. The vegetation has also been modified by fire and farming.