The Tongariro land mass was formed by a multitude of eruptions from at least six different cones which all share the same alignment. The oldest lava started flowing about 275,000 years ago, near what is now the Tama Lakes on the southern flanks of Mt Ngauruhoe. The eruptions continued for the next 200,000 years until the Ice Age. As the ice retreated, it carved out valleys clearly visible in the lower Mangatepopo and Oturere valleys.
Red Crater and Mt Ngauruhoe are the most recently formed features on the Tongariro Alpine Crossing.
Red Crater was formed about 3000 years ago. It lies within a scoria cone which rests on top of the older Tongariro lava flows. The red colour is due to the presence of oxidised iron in the rock.
The most recent confirmed volcanic activity from Red Crater was reported between 1855 and 1890. The dike on the Southern Wall has been exposed by erosion. Lava would have flowed through this dike and poured into the Oturere Valley.
Mt Ngauruhoe is the youngest volcano in the area having begun to form about 2,500 years ago. It is the most active vent in the Tongariro area with its last eruption recorded in 1975. The most recent flows from Mt Ngauruhoe are easily visible on the way to South Crater.