The Tongariro area has grown over last 300,000 years.  The land mass was formed by many different eruptions from at least six cones.   They 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 200,0000 years until the Ice Age.   As the ice retreated it carved our valleys clearly visiable in the lower Mangatepopo and Oturere Valley.

The Red Crater and Mt Ngauruhoe are the most recently formed features on the Crossing.

Red Crater was formed about 3000 years ago and lies within a scoria cone which rests on top of the older Tongairo lava flows. The red colouring is due to the presence of oxidized iron in the rock.  The most recent confirmed volcanic activity from Red Crater was reported between 1855 and 1890.  Exposed by erosion is the dike on the southern wall, lava would have flowed through this dike  and pored into the Oturere Valley.

Mt Ngauruhoe is the youngest volcano and started to form about 2500 years ago, it is the most active vent in the Tongariro area, it last erupted in 1975. The most recent flows from Ngauruhoe are very easy to identify on the way to South Crater.

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