Mangatepopo Hut Area

The hut is on the Tongariro Alpine Crossing. It provides a great vantage point of some of the youngest and oldest lavas of Tongariro Volcano. The older lavas are intercallated with moraines, and both were kept out of the Mangatepopo Valley by thick ice for most of the history of the volcano. The youngest lavas are from Ngauruhoe, which was able to grown where the glacier had been once temperatures rose after the end of the last glaciation.

The high slope and ridge close by to the north is mostly moraine from the last glaciation about 17,000 years ago, with a few thin lavas in it. These were kept out of the valley by the same thick glacier than formed the moraine.
A similar process formed Pukekaikiore but quite a bit earlier, at least 140,000 years ago during the second-to-last glaciation. In both glaciations the ice occupied the same Mangatepopo Valley. The ice in this valley may not even have entirely disappeared between those two glaciations because the temperature never got as warm as it is today.
Since the last glaciation lava has finally been able to flow in the valley bottom. The hut is on Ngauruhoe lava that is more than about 1800 years old (we know this because the pumice from the most recent Taupo Eruption is on top). And to your east you can see the flow front of a younger Ngauruhoe lava that is on top of Taupo Eruption pumice (the track deviates there to the north around the younger flow front).