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.
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.
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.
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.
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.
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
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
1-5 mm thickness
Effects that occur with < 1 mm of ash will be amplified, plus:
5-100 mm thickness
Effects that occur with < 5 mm of ash will be amplified, plus:
100 -300 mm thickness
Effects that occur with < 100 mm of ash will be amplified, plus:
> 300 mm thickness
Effects that occur with < 300 mm will be amplified, plus: