Taranaki Blowout background info

This page has scientific background information on the fictional eruption scenario unfolding on the Taranaki Blowout pages.

Tarnaki Blowout
Week 6 background info
Week 5 scientific background
Week 4 scientific background
Week 3 scientific background
Week 2 scientific background
Week 1 scientific background

Seismic monitoring
Volcano Alert Levels

Week 6 background information

There's a real chance that there'll be recurring periods of volcanic activity after the mountain reawakes. How would we adapt to life with an active volcano in our back yard?


The plus side of volcanoes


Why people live near volcanoes


Volcano & Geothermal Tourism book details


Volcano & Geothermal Tourism book review

Some possible answers may be found in the Japanese city of Kagoshima (population 600,000), which is only 10 km from a volcano called Sakurajima.

The people of Kagoshima have had to adapt to ash fall, volcanic gases, acid rain, landslides and occasional volcanic explosions that have broken windows and sent rocks and even a 5,000 kg boulder raining down on buildings.

Adaptations have included:
  • Construction of concrete shelters for protection against volcanic "ballistics".

  • Building houses without roof gutters and with a stormwater channel immediately below the roof. This allows ash to be swept off easily.

  • Building large overhang roofs over balconies.

  • Using ash-resistant tiles and heavy-duty window and door seals in buildings.

  • Developing a natural ventilation system incorporating an ash-resistant device.

  • Establishing ash collection depots.

  • Developing an extensive system of man-made channels and dams to slow and divert lahars and debris flows.

  • Regular patrols by firefighters during periods of volcanic activity.

  • Regular evacuation drills.

  • Issuing hard-hats to children walking to school.

On the plus side, the volcano has generated significant tourist traffic for the city, while the fertile volcanic soils produce massive daikon radishes and other produce.


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Week 5 background information

Mount Merapi. This Week 5 photo on the Taranaki Blowout home page looks eerily like Mount Taranaki. But in fact it's Taranaki's Indonesian "twin",  Mount Merapi. It dramatically shows the effect of a lahar down a river that rises on the mountain, where volcanic ash is remobilised off the slopes by tropical rain. An equivalent here could be the Waiwhakaiho.

Merapi - which has been erupting on and off since 1994, killing more than 150 people and causing the evacuation of thousands at times - is by many measures  identical to Taranaki.

Sending searing rivers of rock and ash down its flanks, Merapi has laid villages to waste and has even killed a couple of scientists studying it - they were sheltering in a bunker that was supposed to protect them.

Volcanologists expect that like Merapi, Taranaki will be volcanically active for years if not decades once reawakened.

That's a characteristic of volcanoes of this type, which is marked by "cone-forming" eruptions that produce lava flows, steep slopes, landslides, slips or lahars.

Merapi's primary eruptions (block and ash flows, volcanologists call them) would not extend beyond the Egmont National Park boundaries if replicated here. But lahars made up of mud, water and volcanic debris extended for 45km and have been a far greater problem in Indonesia, as indeed they would be in Taranaki.

The Taranaki Blowout eruption scenario realistically keeps the "fireworks" — lava and pyroclastic flows, and hot-rock avalanches — inside the boundaries of Egmont National Park.

But lahars, floods and ashfall will have a significant effect on the region as a whole, with the potential to cause major disruption.

Pyroclastic flows

The devastating nature of pyroclastic flows is illustrated in a video from Japan (see link below).

Bear in mind that in an eruption of Mount Taranaki, such flows would not extend beyond the boundaries of Egmont National Park and would not threaten built-up areas.

Location of Week 5 earthquakes

Location of Week 5 earthquakes. Click on graphic for large version.
Graphic: GNS Science

Red circles show location of Week 5 earthquakes
Black circles show locations of normal earthquakes over 12 months

TF: Taranaki Fault (learn more)
Click on graphic for large version


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 Week 4 background information

Location of Week 4 earthquakes

Location of Week 4 earthquakes. Click for large versionl
Graphic: GNS Science
Red circles show earthquakes occurring in Week 4
Black circles show normal earthquakes recorded over 12 months
TF: Taranaki Fault (learn more)
Click on graphic for large version

An eruption is now perceived as likely and GNS Science raises the alert level to 2. The Taranaki Civil Defence Emergency Management Group declares a local state of emergency.

This follows continued seismicity under the volcano, with an increase in the number of earthquakes, and some at shallower depths. 

 The first volcanic earthquakes are recorded, indicating that magma may be present. This is a major factor in the decision to raise the alert level to 2.


Volcano alert levels


Volcanic hazards at Egmont Volcano


Emergency Declaration (425 KB)

Continous GPS monitoring station. Pictue: Alaska Volcano Observatory. The Continuous GPS monitoring is now under way (see picture at left, courtesy of Alaska Volcano Observatory). It is recording minor indications of ground movement.

Trampers also report that water on the volcano smells like sulphur.

A major rockfall occurs in the headwaters of the Stony River.  Coarse debris forms a partial dam across the river.  A large rumbling sound is heard one night.

The bed of the Stony River has risen four to five metres due to deposits of material in the waterway, and the Blue Rata reserve is flooded as a result.

More rockfalls are heard on the western slopes of the volcano and aerial observations show more water building behind the rockfall dam in the Stony River, causing the dam to break.  Large debris flows in the river remove the Wiremu Road bridge and exposes and damages the gas pipeline.

Low-lying areas and roads around the Stony River at the SH45 bridge are covered with thick sandy deposits. Many of the roads are impassible.

The declaration of a state of emergency means that emergency powers are available to the Civil Defence Controller and police.

This allows them to implement evacuation plans and road closures in high-risk areas, especially around the upper flanks of the western side of the mountain. Civil Defence also responds to the flooding in the Stony River area, by co-ordinating relief and repairs.

Media interest is high, with national TV news and current affairs shows broadcast live from Taranaki. Civil Defence works to ensure that media personnel do not hinder the emergency response or put themselves in danger, and to ensure that all media have ready access to informed comment and analysis.


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Week 3 background information

Locations of Week 3 earthquakes

Locations of Week 3 earthquakes. Click on graphic for large version.
Graphic: GNS Science
Red circles show earthquakes occurring in Week 3
Black circles show normal earthquakes recorded over 12 months

TF: Taranaki Fault (learn more)
Click on graphic for large version

The mountain's a suspense story, with scientists still lacking conclusive evidence that an eruption may be imminent. While Mount Taranaki has been asleep for a couple of centuries, it's important to remember that "unrest" is common at many other volcanies, and most times this unrest does not lead to eruptions.

Maero Stream lahar aftermath on the slopes of Mt Taranaki. In the meantime, a heavy rainstorm causes more instabilty along the fragile, erosion-prone headwaters of the Stony River.

The unstable nature of this area was dramatically illustrated during and after an intense rainstorm in April 2008. This resulted in rain-triggered lahars thundering through streams, climbing banks and slicing out sections of forest and tracks on the slopes of Mt Taranaki (see photo at right).

270 mm of rain fell over three days and sent one great mix of sand, shingle, rock and water surging down the Little Maketawa Stream on the mountain's north-eastern slopes. Another muddy mixture rumbled down the Maero Stream around the north-western side. Both cut deep channels before ending just before the boundary of the Egmont National Park.

The Department of Conservation says the lahars travelled at an estimated 40 km/h from high up on the mountain. Sediment can bulk up a river until the concentrated mix of water and sand is able to carry boulders weighing up to a tonne. One such mix took out vegetation and changed the course of the Mangahume Stream leaving a hunters' bivvy perched on an island.

The flow down the Maero stream headed for the Stony River and ploughed straight ahead at a sharp right-hand bend climbing a bank and knocking over a segment of 1km long and about 200 metres wide. All the major streams within the Egmont National Park sustained serious damage or erosion, and there were problems throughout the Stony catchment.


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Week 2 background information

By Week 2, scientists are seeing enough clues to suggest our volcano might be stirring, though the evidence is still not rigorous enough for them to be sure an eruption is imminent.

While the Cape Egmont fault belt earthquakes decline, irregular swarms continue under the volcano. A few are felt by the public, and some report their experience on the GeoNet website.

Locations of Week 2 earthquakes

Locations of Week 2 earthquakes. Click on graphic for large version.
Graphic: GNS Science
Red circles show earthquakes occurring in Week 2
Black circles show normal earthquakes recorded over 12 months
TF: Taranaki Fault (learn more)
Click on graphic for large version

Two large landslides are reported on the mountain itself, along Pyramid Stream at the headwaters of the Stony River. While such events are not unusual in this area, the assumption is that these ones have been caused by the ground shaking.

GNS Science raises the Volcanic Alert Level from 0 to 1, which signifies initial signs of possible volcanic unrest, but no eruption threat. The irregular swarms of earthquakes under the mountain are significant, but volcanologists need to know a lot more.


Monitoring ground deformation

So GeoNet supplements its monitoring with continuous GPS gear to detect any deformation on the mountain, as well as chemical testing of water samples from streams flowing off the mountain, and interprets all the data.

Still unknown is how long this sort of activity will go on for, and whether it will amount to anything. It could go on for a few months then peter out. Or it could be the precursor to an eruption. Scientists can't make that call until they have more conclusive evidence.

But among the public, rumours are starting to do the rounds. They're fuelled as some of the shaking empties shelves and causes landslides that bring minor traffic disruption on roads near Egmont National Park.

Civil Defence tells the public what the scientists are doing and stresses that an eruption threat has not been identified. Panic buying - or any other sort of panic -  is the last thing anyone needs.


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Week 1 background information

Slightly above-normal seismic activity is recorded by GeoNet in the Taranaki region.  This includes a sequence of moderate main shocks and aftershocks in the Cape Egmont Fault Belt and a few small deeper events under the volcano.

Most of us don't realise just how many earthquakes are recorded in Taranaki, because we feel very few of them. In the 12 months to June 30 this year, there were 309, and in the previous year there were 420.

Not only are very few felt, but very few occur right under the mountain - just one out of the latest year's 309, for example, was under the mountain.

Think of the zone under today's mountain as an earthquake dead spot. The magma may have cooled since the last eruption in 1755, but it is still flexible rather than brittle. So it won't fracture sharply, producing earthquakes. But if the magma warms up and starts moving towards the surface, the ground will shake as fissures are filled or created by the rising magma.

 As with most science, though, this can't be reduced to a simple formula of "earthquakes under mountain = magma on the move = eruption on the way".


How volcanoes are monitored in NZ


All about seismographs


There are no hard and fast rules for assessing whether an earthquake or series of quakes under the mountain indicates volcanic activity. Volcanologists look at the number of earthquakes, their size and the frequency of the shockwaves for clues.

The occasional quakes recorded under the mountain so far have not been classed as significant in volcanology terms. That also applies to Week 1 events.

Location of Week 1 earthquakes

Red dots show locations of Week 1 earthquakes. Click on graphic for big version.
Graphic: GNS Science
Red circles show location of Week 1 earthquakes
Black circles show locations of normal earthquakes over 12 months

TF: Taranaki Fault (learn more)
Click on graphic for large version


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Seismic monitoring

GeoNet has completed a major upgrade and expension of the 16-year-old network of seismic detectors on and surrounding the mountain.

The three-year  project means the region is the best-equipped it's ever been to keep a finger on the earth's pulse.

All nine recording stations now have state-of-the-art digital seismographs that can record three directions of quake movement - up-down and, for example, north-south and east-west. Originally there were six seismographs that recorded only the up-down movement.

The system for obtaining readings from the seismographs is also more robust. Previously, radio links fed data from each site through to the Taranaki Emergency Management Office (TEMO) in New Plymouth. Now, with hubs at TEMO, Kahui Road and Eltham, the communications network has built-in back-up.

The only limiting factor now is one that exists everywhere - ambient noise level from both natural and human causes - things like heavy equipment, or crashing waves in a westerly storm. These cause vibrations that the seismographs pick up.

The network's expansion includes new monitoring stations at Mangahewa and Lake Rotokare, well to the east of the mountain. This signals an expanded focus and changed status for what started in 1994 as a local initiative aimed squarely at the mountain.

Taranaki's monitoring stations are now part of the national GeoNet seismic monitoring system, which didn't exist when the network here was first established. And the focus now isn't solely on the mountain. The Taranaki equipment is providing essential earthquake recording capability for the western part of the North Island.

GeoNet, a joint venture between GNS Science and the Earthquake Commission, monitors all geological hazards in New Zealand. Go to www.geonet.org.nz for more information.


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Alert levels for reawakening volcanoes

Alert level What scientists are seeing
Volcano status


Typical background surface activity; deformation, seismicity, and heat flow at low levels. Usual dormant, or quiescent state.


Apparent seismic, geodetic, thermal or other unrest indicators. Initial signs of possible volcano unrest. No eruption threat.


Increase in number or intensity of unrest indicators (seismicity, deformation, heat flow and so on). Confirmation of volcano unrest. Eruption threat.


Minor steam eruptions. High increasing trends of unrest indicators, significant effects on volcano, possible beyond. Minor eruptions commenced. Real possibility of hazardous eruptions.


Eruption of new magma. Sustained high levels of unrest indicators, significant effects beyond volcano. Hazardous local eruption in progress. Large-scale eruption now possible.


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 was run by the Taranaki Civil Defence Emergency Management Group in partnership with New Zealand Red Cross and with input from GNS Science. Red Cross logo.
The CDEM Group acknowledges the support of these organisations:
GNS Science logo.
GNS Science
Ministry of Civil Defence logo.
Ministry of Civil Defence
and Emergency Management

M&O Pacific
Powerco logo.


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Methanex NZ Ltd. Click to go to website.
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