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Mount Ruapehu erupts

On this page: Photograph of Mount Ruapehu erupting, 1995Mount Ruapehu, Recent major eruptions, Current activity and monitoring, Useful links

Mount Ruapehu is an active volcano in the Waikato region. Mount Ruapehu can produce lahars (mudflows) and ashfall following eruptions, which threaten people and property as well as the area’s tourist industry.

Mount Ruapehu

Mount Ruapehu is one of the more active volcanoes within the Taupo Volcanic Zone (others include Mount Tongariro and Mount Ngauruhoe). It has been erupting regularly since 1969, with the latest events in 1995 and 1996. Ruapehu’s eruptions pose a risk to life and disruption to major power, economic and transport services.

  • Mount Ruapehu usually erupts ‘andesitic’ material - fine-grained brown or greyish volcanic rock.
  • Ashfall travels further than most other material, particularly when carried by the wind.
  • Lahars (mudflows comprised of mainly volcanic debris) are likely to occur when the crater lake over flows or the crater rim collapses and the water then mixes with snow and volcanic debris from the crater and valley floor. Lahars can travel very fast over long distances.
  • Mount Ruapehu’s crater lake fills the volcano’s vent, and contains 8-10 million cubic metres of acidic water. This is a potential hazard to people climbing up to the crater lake.

A lahar was the cause of the 1953 ‘Tangiwai Disaster’, New Zealand’s worst rail disaster. The lahar rushed down the Whangaehu River and damaged the rail bridge, derailing the train and killing 151 people. To prevent a similar event happening again, the crater and its lake are regularly monitored with the aim of warning people in the potential path of a lahar. The Whakapapa ski area is also at risk and sirens warn skiers. Find out more about the crater lake's current status.

Recent major eruptions

Ruapehu’s most recent major eruptions in 1995 and 1996 affected 100,000 people in the central North Island:

  • The 1996 eruption produced at least seven million tonnes of ash, with 2.3 million tonnes falling on Lake Taupo.
  • Drinking water contamination affected people and animals, particularly in rural areas.
  • Ash got into waterways, reducing water clarity in some streams and increasing acidity in others.
  • Metal structures and vehicles were damaged by ash.
  • Tourism activities were disrupted, causing a downturn in the area’s economy.
  • Dangerous levels of sulphur dioxide (SO2) were found on the mountain.
  • Ash in Tongariro River resulted in damage to the Rangipo Power Station.
  • Ashfall lowered visibility, disrupting air travel at times, as the plume (which could be seen by satellite) travelled north east to the coast and across the Bay of Plenty.

Find out about the effect of Mount Ruapehu’s eruptions on Lake Taupo.

These events also threaten ‘lifeline’ services such as water, power, telecommunication and transportation networks. Find out more about managing Lifelines to deal with unexpected emergency or natural hazard events.

Current activity and monitoring

The Institute of Geological and Nuclear Sciences (GNS) monitors volcanic activity in New Zealand and updates alert levels. These alert levels give an indication of how active a volcano is, on a scale of 0-5. Normal background levels are ‘0’, while ‘5’ indicates a large volcanic eruption is in progress. Ruapehu is currently active at Alert Level 1. Check out the latest volcano bulletins from GNS.

Waikato Regional Council is involved in discussions and planning for an alarm system to reduce the risk from a lahar. See our map for more information about lahar zones in the Waikato region.

The potential impact of future eruptions can be minimised by:

  • monitoring the volcano for any advanced signs of impending eruption. For example:
    • earthquake activity
    • crater lake temperature
    • crater lake level
    • crater lake water chemistry.
    This allows early warning so suitable action can be taken.

  • analysing Ruapehu’s past volcanic history to create an eruption profile. Understanding the size, type and frequency of eruptions, lahars, lava flows and ashfall emissions helps us to:
    • detect patterns and identify potential volcanic activity on the Mountain
    • prepare more effective and suitable responses to future threats (such as emergency responses and mitigation).

Find out more about Waikato Regional Council’s risk mitigation plans.

For policy information on natural hazards, see section 3.8 of our Regional Policy Statement.

Useful links