Taranaki Blowout is a community exercise based on a fictional but fact-based eruption scenario on Mount Taranaki. This page has general information on volcanoes.
What are volcanoes and what causes them?
Why talk about volcanoes?
What hazards result from a volcanic eruption?
What is the best source of information?
Volcanic alert levels
What are volcanoes and what causes them?
A volcano is a landform that results from magma (molten rock within the earth) erupting at the surface.
The size and shape of a volcano reflect how often it erupts, the size and type of eruptions, and the composition of the magma it produces.
When pressure from gases within the molten rock becomes too great, gases drive the molten rock to the surface and an eruption occurs.
Why talk about volcanoes?
Volcanoes produce a wide variety of hazards that can kill people and destroy property.
Volcanic eruptions fall into two broad types: explosive and quiet.
Hazards from large explosive eruptions include widespread ashfall (sand and dust-sized pieces of fractured rock and glass), pyroclastic flows (very fast flowing mixtures of hot gases and volcanic rock) and massive lahars (volcanic mud flows — fast-flowing mixtures of muddy water and volcanic rock) that can endanger people and property nearby as well as tens to hundreds of kilometres away.
Eruptions can even affect the global climate. Hazards from quiet lava flows include fires, building and other structural collapse, and acidic gas clouds.
New Zealand has a high density of active volcanoes and a high frequency of eruptions.
Cone volcanoes such as Mt Taranaki are characterised by a series of small to large eruptions from roughly the same point on the earth's surface. The products of successive eruptions accumulate close to the vents to form a large cone, which is the volcano itself.
Over a long period of time, several cones may form which overlap and build up. The cone shape can be modified by partial collapse due to oversteepening (Mt Taranaki is a good example) or by collapse of the summit area to form a caldera.
Because the magma tends to follow the same route to the surface each time, sites of future eruptions can largely be predicted.
What hazards result from a volcanic eruption?
Typically, a number of different types of hazards will result from a single volcanic eruption. These hazards can be divided into two categories:
Near-vent destructive hazards
- Pyroclastic falls (ashfall).
- Pyroclastic flows (surface-hugging eruption clouds of very hot gas and volcanic particles that move rapidly across the ground surface, away from the vent).
- Lava flows.
- Lahars (volcanic mudflows) and flooding.
- Debris avalanches (volcanic landslides).
- Volcanic gases.
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- Pyroclastic falls (ashfall).
- Lahars.
Volcanic eruptions can also cause other natural hazards, including earthquakes, wildfires, and (given certain conditions) tsunamis.
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What is the best source of information in case of a volcanic alert?
In New Zealand a system of volcanic alert levels is used to define the current status of each volcano.
The alert levels range from 0 to 5. There are two tables, one for the frequently active volcanoes like Ruapehu and White Island, and one that deals with the reawakening of dormant volcanoes such as Mount Taranaki. The alert levels are used by the public and responding agencies to set their response. GNS Science is responsible for setting volcanic alert levels.
When there is a change in volcanic activity, such as observation of geophysical signals which indicate a volcano may erupt, GNS Science will issue a 'Scientific Alert Bulletin' and may change the volcanic alert level.
The bulletins are released to the media, civil defence emergency management organisations, and posted on the GeoNet website for public viewing (www.geonet.org.nz).
If an eruption has occurred, the GeoNet website will also contain information on the likely dispersal of ashfall.
In a volcanic emergency, information will be broadcast on radio and other media.
Alert levels for reawakening volcanoes
Alert level What scientists are seeing Volcano status 0
Typical background surface activity; deformation, seismicity, and heat flow at low levels.
Usual dormant, or quiescent state.
1
Apparent seismic, geodetic, thermal or other unrest indicators.
Initial signs of possible volcano unrest. No eruption threat.
2
Increase in number or intensity of unrest indicators (seismicity, deformation, heat flow and so on).
Confirmation of volcano unrest. Eruption threat.
3
Minor steam eruptions. High increasing trends of unrest indicators, significant effects on volcano, possible beyond.
Minor eruptions commenced. Real possibility of hazardous eruptions.
4
Eruption of new magma. Sustained high levels of unrest indicators, significant effects beyond volcano.
Hazardous local eruption in progress. Large-scale eruption now possible.
5
Destruction with major damage beyond active volcano. Significant risk over wider areas.
Large hazardous volcanic eruption in progress.
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Who was behind this exercise?
The exercise is being run by the Taranaki Civil Defence Emergency Management Group in partnership with New Zealand Red Cross and with input from GNS Science. 
The CDEM Group acknowledges the support of these organisations:
GNS Science
Ministry of Civil Defence
and Emergency Management
M&O Pacific
Powerco
Classic Hits
90FM Taranaki
93.2 More FM
Taranaki
Methanex
New Zealand Ltd
Pace Engineering Ltd