Aucklanders may get only a day or two warning of a volcanic eruption and will know just hours before where it will explode, a scientific paper says.
The 1.4 million people living on the Auckland volcanic field make too much noise for existing instruments to hear what is happening below the surface.
"This means that localisation of a future eruption site is only likely to occur within a few hours or days of an eruption," the paper in the Journal of Remote Sensing of Environment says.
Each new vent in Auckland will occur at a new location, rather than an existing volcano, creating uncertainty over where it will hit.
The scientists say they have used a variety of devices and models to explore in a new way the lava flows of the 360 square kilometre volcanic field which holds 50 monogenetic volcanoes - that is single vents that erupt in one go. Polygenetic volcanoes - such as Ruapehu - erupt from the same craters regularly.
They say the city, especially south Auckland, will probably suffer more damage from lava flows during the early stages of the eruption.
"The city of Auckland is highly susceptible to lava flows, which are likely to travel further, and be potentially more destructive to infrastructure over longer periods, than the products of explosive opening phases of monogenetic eruptions at Auckland."
The paper says Auckland has two different areas for lava danger.
"The southern part of the city is predominantly flat, without hindrance to lava flow, whereas the hilly northern and central part has many ridges that can limit or channelise lavas."
The lava flows in central Auckland are likely to be longer in length as the topography forces lava into river-like channels.
"The volcanism in Auckland in New Zealand differs from large, polygenetic volcanoes because future eruptions will likely take place within a densely populated city, there are no rift zones that indicate areas of elevated hazard, and the future vent area is therefore unknown, and due to the generally low-lying topography, there are few opportunities to use mitigation options, such as artificial dams.
"Hence, future vent forming eruptions will very likely occur within the city limits or its outskirts, allowing few mitigation or preparation options. The majority of previous scoria cones and lava flows are located in the heart of the city, upon a presently slightly elevated ridge-system."
The paper says most studies so far have been about the location, nature and the possible effect of future eruptions on the city.
"Detailed evaluation of lava flow hazards and delimitation of potentially safe places from lava flow inundation have not yet been attempted, in spite of the relatively high level of their potential risk."
Studies to date have focussed on the creation of the vent and the ash fall over the city.
"Knowledge of lava flow susceptibility is an essential addition, because over half of the eruptions in Auckland have produced lava flows or lakes."
The paper was written by scientists from Massey University's Institute of Natural Resources, Gabor Kereszturi, Jonathan Procter, Shane Cronin, Karoly Nemeth and Mark Babbington with Auckland University School of Environment's Jan Lindsay.
- © Fairfax NZ News
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