Mount Ngauruhoe

Mount Ngauruhoe (Māori: Ngāuruhoe) is a volcanic cone in New Zealand. It is the youngest vent in the Tongariro stratovolcano complex on the Central Plateau of the North Island and first erupted about 2,500 years ago. Although often regarded as a separate mountain, geologically, it is a secondary cone of Mount Tongariro.

The volcano lies between the active volcanoes of Mount Tongariro to the north and Mount Ruapehu to the south, to the west of the Rangipo Desert and 25 kilometres (16 miles) to the south of the southern shore of Lake Taupō.

Before the initial mapping of the area introduced labelling confusion, the local Māori name for the cone was Tongariro, and its summit crater was known as Ngāuruhoe.

The local Māori traditions state that the volcano was named by Ngātoro-i-rangi, an ancestor of the local Māori iwi, Ngāti Tūwharetoa. Ngātoro-i-rangi called volcanic fire from his homeland Hawaiki, which eventually emerged at Ngauruhoe. The name given by Ngātoro-i-rangi (Ngāuruhoe) either commemorates his slave, who had died from the cold before the fire arrived, or refers to the insertions (ngā uru) of Ngātoro-i-rangi's hoe (paddle-like staff) into the ground during his summoning of the volcanic fire.

In this region of the southern Taupō Rift, the Tertiary greywacke basement is tens to hundreds of metres thick and hundreds of metres above sea level. The magma reservoir is about 5 km (3.1 mi) deep although other historic Tongariro vents to the south had much deeper magma sources.

Ngauruhoe was New Zealand's most active volcano in the 20th century with 45 eruptions, the most recent in 1977. Fumaroles exist inside the inner crater and on the rim of the eastern, outer crater. Climbers who suffer from asthma may be affected by the strong sulphurous gases emitted from the crater.

A significant increase in earthquake activity in May 2006 prompted the alert level to be raised from zero (typical background activity, no signs of significant unrest) to one (signs of volcano unrest). Over the next two years GeoNet recorded an average of 5 to 30 earthquakes a day close to Ngauruhoe, though the maximum daily number was as high as 80.

After mid-2008, the number of volcanic earthquakes close to Ngauruhoe declined to the background level. Regular measurements of volcanic gas levels and the temperature of a summit gas vent failed to record any significant changes over the subsequent two and a half years. GNS Science accordingly reduced the alert level for Ngauruhoe to Level 0 on 2 December 2008. “The reduction in earthquake activity means that an eruption in the near future is unlikely without further earthquakes or other changes and the appropriate alert level is therefore zero”, said GNS Science Volcano Section Manager Gill Jolly.