VOLCANIC

RISK
Although there are no volcanoes in Hawke's Bay, the area has been affected by over 20,000 years of volcanic activity, mainly in the form of ash falls. The North Island of New Zealand has both a high density of active volcanoes and a high frequency of eruptions. Five of these volcanoes have erupted, often repeatedly, in the past 300 years.


LOCATIONvolcano ruheapu
As the Hawke's Bay region lies many kilometres from any active volcano it will be spared many of the highly damaging near-source effects of a volcanic eruption, except in the event of a very large eruption from the Taupo Volcanic Centre. However, the region is vulnerable to volcanic ash-falls and their associated hazards, because the prevailing winds in the North Island are from the west and south.

Based on our understanding of New Zealand's volcanoes, we can conclude that eruptions from the Okataina and Taupo volcanic centres may produce sufficient volcanic ash to have significant impacts on Hawke's Bay. Large eruptions from Ruapehu, Tongariro, Ngauruhoe and Taranaki may also produce enough ash to impact on the region but will have a lesser impact. Eruptions from White Island and other volcanoes are not likely to affect Hawke's Bay.

ERUPTION IMPACTS
The impacts from ashfall vary with the thickness of ash and the type of ash. Because Hawke’s Bay is far from volcanic sources it can be expected that only, fine, easily transported ash will reach the region. The major problems from fine ash are likely to be interruption or failure of lifeline utilities, including transport and clean up costs. If ashfall is over a few millimetres, disruption to traffic is likely as road markings will be covered, road surfaces will be slippery and air filters will get clogged. The greater the thickness the more impacts - see the Ash Impacts table below.  Health issues can be managed by staying indoors and sealing doors and windows, and the use of masks and protective clothing. Clean up costs will be significant as correct handling and disposal of ash is important to avoid blocked sewage or storm-water systems, and having capacity to store the large volumes of ash in landfills is also important for environmental reasons.

Based on national research it is estimated Hawke’s Bay might expect the following ash fall depths at coastal locations for different return period in the future.

volcano ashdepth

In New Zealand a system of volcanic alert levels is used to define the current status of each volcano and give warning of eruptions. The alert levels range from 0 to 5 and you can find out more information about alerts and volcanic emergency information on the GeoNet website 


The Hawke’s Bay CDEM is the lead agency for managing any natural hazard event, like ash fall affecting the people of Hawke’s Bay.


HISTORY
In historic times, ashfalls from Ruapehu have affected the region in 1945, 1975, 1995 and 1996; and from Tongariro in 1896 and 2012. Peat bogs and swamps record a complex sequence of older ash layers from Taupo, Okataina, Ruapehu and Taranaki volcanoes dating back over 20,000 years.


Eruptions from Ruapehu in 1995 and 1996 dispersed ash over much of the North Island, including Hawke’s Bay, closing the airport and creating a nuisance to other sectors.

An eruption from Tongariro in August 2012, resulted in a large cloud of fine ash beign dispersed across Hawke’s Bay, particularly in the northwest. The ash closed the Hawke’s Bay Airport and dusted the region in a grey coat. Cars, houses, streets and lawns were dusted with a 1mm layer of fine grey ash from Wairoa to inland Napier, combined with a noticeable smell of sulphur. Hospitals reported no admissions due to respiratory problems, but pharmacies sold a lot of masks.

volcano photos
WHAT CAN YOU DO?

You can do many things to protect yourself and your family from the dangers a volcanic eruption can cause, including storing masks with your emergency survival items.
GNS Science is responsible for monitoring volcanic activity and setting alert levels. If a life-threatening eruption is likely to occur, a civil defence emergency will be declared and you be given information on how to prepare for a volcanic eruption.

Learn more at Get Thru

Some other useful links are

 

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ASHFALL IMPACTS ZONES

The impact of ash-fall on people, structures and equipment depends largely on ash thickness. Five levels of ash thickness are given below.  Thicknesses given are for uncompacted ash. 

<1 mm thickness 

  • Falling ash will act as an irritant to lungs and eyes

  • Airports will close due to the potential damage to aircraft.

  • Possible minor damage to vehicles, houses and equipment caused by fine abrasive ash.

  • Possible contamination of water supplies, particularly roof-fed tank supplies.

  • Dust (or mud) affects road visibility and traction. 

1-5 mm thickness 

Effects that occur with < 1 mm of ash will be amplified, plus: 

  • Most livestock will not be unduly stressed but may suffer from lack of feed, wear on teeth, and possible contamination of stock water supplies.

  • Minor damage to houses will occur if fine ash enters buildings, soiling interiors, blocking air-conditioning filters etc.

  • Electricity may be cut; shorting occurs at substations if the ash is wet and therefore conductive. Low voltage systems more vulnerable than high.

  • Water supplies may be cut or limited due to failure of electricity supply to pumps.

  • Contamination of water supplies by chemical leachates may occur.

  • High water-usage will result from ash clean-up operations.

  • Roads may need to be cleared to reduce the ash nuisance and prevent storm-water systems becoming blocked.

  • Sewage systems may be blocked by ash or disrupted by loss of electrical supplies.

  • Damage to electrical equipment and machinery may occur.  

5-100 mm thickness 

Effects that occur with < 5 mm of ash will be amplified, plus: 

  • Ash will affect vegetation, burying pasture and low plants. Foliage may be stripped off some trees but most trees will survive.

  • Most pastures will be killed by over 50 mm of ash.

  • Major ash removal operations will need to be organised in urban areas.

  • Most buildings will support the ash load but weaker roof structures may collapse at 100 mm ash thickness, particularly if wet.

  • Road transport may be stopped due to the build up of ash on roads or clogging of air-filters.

  • Rail transport may be forced to stop due to signal failure bought on by short circuiting if ash becomes wet. 

100 -300 mm thickness 

Effects that occur with  < 100 mm of ash will be amplified, plus: 

  • Buildings that are not cleared of ash will run the risk of roof collapse, especially large flat roofed structures and if ash becomes wet.

  • Severe damage to trees, stripping of foliage and breaking of branches.

  • Loss of electricity supplies due to falling tree branches and shorting of power lines. 

> 300 mm thickness 

Effects that occur with < 300 mm will be amplified, plus: 

  • Heavy kill of vegetation.

  • Complete burial of soil horizon creating a layer in the soil profile.

  • Livestock and other animals killed or heavily distressed.

  • Aquatic life in lakes and rivers killed.

  • Major collapse of roofs due to ash loading.

  • Loading and possible breakage of power and telephone lines.

 

 

 

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