Volcanic activity threatens people and property. The Waikato region has many volcanic centres that vary in activity and risk.
The central North Island features many landforms that have been created over the last 1.6 million years through volcanic activity (‘volcanism’). Volcanic soils are important in supporting farming and forestry.
Volcanism is the biggest source of death from natural disasters in New Zealand over the last 150 years. Over 100 people died when Mount Tarawera erupted in 1886, and 151 people were killed after a mudflow (‘lahar’) derailed their train at Tangiwai following Mount Ruapehu’s eruption in 1953. We need to monitor volcanic zones in our region to prepare for and minimise any effects from future volcanic activity.
Most of New Zealand’s volcanic activity has taken place in the Taupo Volcanic Zone (TVZ), a long rectangular area from White Island to Ruapehu.
Volcanic centres in the Waikato region include:
- Maroa - north of Lake Taupo.
- Ruapehu is New Zealand’s largest andesite cone volcano. It is unusual because it has a warm and highly acidic crater lake. Even small eruptions may cause potentially hazardous mudflows or lahars.
- Ngauruhoe’s distinctive ‘cone shape’ has been built up by layers of eruptive material, mainly lava flows and pyroclastic flows. Ngauruhoe is also an andesitic volcano. Although the vent has been active, it’s currently quiet and has not erupted since 1975 - its longest period of inactivity in recorded history.
- The Maroa Volcanic Centre is made up of rhyolite domes and calderas. Although active, this is not a major hazard area. Eruptions have been mostly of rhyolitic material.
Ruapehu, Ngauruhoe and White Island are considered very active compared with other volcanoes around the world. The Taupo Volcanic Zone also includes the two most explosive caldera volcanoes, Taupo and Okataina.
Lake Taupo was formed by a series of eruptions, the most recent - around 1800 years ago - blasted out about 60 cubic kilometres of earth, rock and mud, leaving a massive crater. Lake Taupo:
- has more than 30 rivers and streams flowing into it, but only one outlet – the Waikato River
- has a catchment about five times the size of the Lake (3,487 square kilometres – or 14 percent of the Waikato region)
- was sinking at a rate of up to 7 millimetres a year from 1983 to 1999
- has a number of active fault lines running through it, such as the Waihi Fault, the Horomatangi Fault and the Kaiapo Fault.
Other volcanic centres such as Auckland and White Island are close to our region and could also affect people and property in the Waikato.
Volcanic hazards include ashfall, lava flows, lahars (mudflows) and pyroclastic flows.
As well as potentially threatening lives and property, any of these hazards may also damage our region’s:
- lifeline facilities, such as electricity supplies, rail networks and road access
- economy, affecting agriculture and tourist attractions, such as fishing and skiing
- air carrier network, if ‘no-fly’ zones are put in place.
The Institute of Geological and Nuclear Sciences has more information about what to do in the event of a volcanic eruption.
Ash is made up of small particles of exploded volcanic glass (less than 2 mm in size), which erupt from a volcano. Clouds of ash are carried by the wind, with the ash plume from a volcano often reaching high up into the atmosphere and showing up on satellite images.
Ashfall effects include:
- Disruption to air travel through poor visibility and/or the risk of engine failure, causing planes to be diverted around the area of ash.
- Damage to roofs and other structures due to the acidic effects and weight of ash. Ash becomes heavy as it absorbs moisture and should be removed before it reaches 100 mm.
- Irritations to people’s breathing passages, eyes and skin. Animals may also be affected. This is why fine ash can be more dangerous than coarse ash.
- Contamination of drinking water (affecting people, farm and other domestic animals, and pets).
Use our map to find out about volcanic ashfall zones in the Waikato region.
A lahar is a fast moving mixture of water and volcanic material which travels down the slopes of a volcano, concentrating in valleys and riverbeds. Lahars can also carry larger material within their flows as debris is ripped from the valley floor. Lahars are created when:
- rain and snow-melt mixes with loose ash to form a ‘river of mud’
- water from a volcano’s crater lake flows down the mountain, mixing with ash and other material along the way.
Mount Ruapehu has a crater lake and is particularly vulnerable to lahars. This was the cause of the Tangiwai disaster in 1953. Warning systems are currently being installed and various authorities and agencies are drafting contingency plans to ensure a co-ordinated approach when the next lahar occurs.
Lava flow rates can vary from 0.5 to 5,000 cubic metres per second (depending on the type of magma) but generally lava flows seen in New Zealand are slow moving. Magma is made up of molten material including rock, crystals and liquid that forms beneath the upper mantle or crust of the Earth. A black crust forms where the surface of the lava flow comes into contact with cooling air. This crust thickens and hardens into volcanic rock once the lava has cooled completely.
Most deaths resulting from lava flows are from burns. Some countries have had limited success with diverting lava flows by cooling them with seawater in an attempt to protect people and property.
Pyroclastic flows occur when an eruption plume collapses or is directed at ground level. This type of flow (made up of gases, molten glass and rock fragments) has a number of destructive effects:
- Intense heat near the flow source can instantly destroy anything in its path.
- Volcanic material travelling at speeds of up to 200 km per hour can pulverise anything near the flow’s initial impact area.
- The flow itself can be so hot that it glows and burns everything in its path as it follows the contours of hills and valleys, while large amounts of volcanic material can bury the surrounding landscape.
Lake Taupo (essentially a huge crater lake) is our region’s most likely source of a pyroclastic flow should an eruption happen from beneath the Lake. Such an event would totally destroy the Taupo township and surrounding areas, as well as causing significant damage to the central North Island’s heavily forested areas.
The Institute of Geological and Nuclear Sciences (GNS) regularly monitors Lake Taupo as part of its volcano surveillance programme. Their studies show that Taupo has erupted 28 times during the past 26,500 years, with its last eruption 1800 years ago. Intervals between eruptions vary. At one stage a period of 3,000 years went by with no eruption, followed by two in 500 years.
The Institute of Geological and Nuclear Sciences (GNS) monitors and assesses New Zealand’s volcanoes regularly and issues scientific alerts. 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. Scientists look for changes in:
- the composition of the gases produced by the volcano
- the amount of gas being produced by the volcano
- water temperature
- ground water level changes
- topography (land features).
Changes in the above do not necessarily mean an eruption will happen. However, they are good indicators that something might happen. Find out more about what alert levels mean.
There are five volcano-seismic monitoring networks around New Zealand’s volcanoes - three of these are within the Taupo Volcanic Zone. Regular ground deformation surveys and water sampling are carried out on the Ruapehu Crater Lake. Geochemical surveys (such as sampling volcanic gases) are done on Mount Tongariro and the summit crater of Ngauruhoe.
- identifying hazards through the resource consent and regional planning processes
- ensuring risk assessments are undertaken if further site-specific research is required
- preparing and implementing risk mitigation plans which aim to minimise the effect of natural hazards on the Waikato economy and community
- providing information on natural hazards to the public
- passing on (promulgating) warnings of volcanic hazard events
- planning for emergency response.
We've also been:
- working with other agencies to monitor volcanic risks
- assisting Civil Defence and the Taupo District Council to ensure contingency plans are kept up to date.
- developing and examining hypothetical scenarios in order to identify various potential risks and likely problems that may occur during a volcanic event.
- working with key members of the Central Plateau Volcanic Advisory Group (CPVAG) and Caldera Advisory Group (CAG) - scientific advisory groups that provide oversight and advice on volcanic hazard issues in the region.
For policy information on natural hazards, see our Regional Policy Statement.
- Geothermal activity
- Waikato Civil Defence and Emergency Management Group
- Institute of Geological and Nuclear Sciences – a New Zealand website with information about all things volcanic.
- New Zealand GeoNet Project - real-time monitoring and data collection for rapid response and research into earthquake, volcano, landslide and tsunami hazards.
- Volcano World - an international website featuring information on all aspects of volcanoes.
- United States National Landslide Information Centre has earth hazards information including teacher/student resources.