Ash to ashes


Lava being deposited on Hawaii’s Big Island in July 2003.

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Few New Zealanders have any idea how much destruction a moderate-scale volcanic eruption could wreak. Volcanologist Shane Cronin says even a relatively small ash eruption would severely disrupt energy distribution, agriculture and air travel.

When the Mt Ruapehu’s Crater Lake dam broke in 2007, a massive lahar up to eight metres high swept down the precipitous eastern flanks of the volcano and into the Whangaehu River. Volcanologist Professor Shane Cronin and his team of 20 researchers was on-site to collect raw data, and their research has since revealed a multi-faceted picture of how lahars behave.

If there is a flip-side to the damage volcanic eruptions cause, it may be in the contributions they make to the fertility of volcanic soils. As Ruapehu finished discharging lahars from its Crater Lake in 1995 and 1996, it began erupting ash, which was swept by the prevailing winds over vast areas of the central and northern North Island. Cronin (a PhD student at the time) followed it, mapping the distribution of where it fell.

The maps turned out to be a critical piece in the puzzle of understanding the environmental impacts of the eruption for farmers, fertiliser companies and health authorities. Massey scientists analysed the ash chemistry and found it carried fertility-promoting elements, especially selenium and sulphur, which are naturally low in North Island pastoral soils.

But, as some farmers discovered, not everything the ash brought was beneficial. Out on the Rangitaiki plains east of Taupo, a number of sheep and cattle died soon after ashfalls, and when Taupo veterinarian Don Shanks performed autopsies, he found their guts contained masses of ash, and their kidneys were pale and swollen – a classic signature of fluoride poisoning.

Fluoride is a Jekyll-and-Hyde ion. Small doses in drinking water and in toothpaste can protect against tooth decay. In greater concentrations it can progressively cause dental fluorosis which stains teeth, and skeletal fluorosis, a painful bone disease.

Being highly reactive, fluoride is quickly bound by the soil, and most plants do not take up fluoride readily. The risks lie in ash that is eaten when it covers pasture or when it contaminates drinking water.

Around Ruapehu, the risk of fluorosis passed soon after the ashfalls did. In other locations, such as Ambrym in Vanuatu, ashfall on a daily basis causes major human and animal health impacts due to fluoride; here the long-term answer, says Cronin, lies in a shift to reticulated groundwater-based systems and ongoing environmental monitoring.

In 2003, Cronin’s six-year programme Living with Volcanic Risk received $4,248,000 for 2004-2009 from the Public Good Science and Technology Fund from the Foundation for Research, Science and Technology. This program has now been incorporated as a component within the $14.6 million New Zealand Natural Hazards Research Platform, due to run over the next 10 years.

Enlisting economists, statisticians, Mäori studies experts, geologists and soil scientists, the project continues to provide “probabilistic hazard forecasts and new risk management tools in order to reduce socioeconomic losses from volcanic events to New Zealand”. Cronin and his team focus on the scenarios likely to arise from eruptions of Ruapehu, Nga-uruhoe and Taranaki and what any renewed activity might mean for us.

Volcanic Risk Solutions, the Massey-based multidisciplinary centre for applied volcanic hazard and risk management research, now numbers more than 20 staff, 13 at Massey, with the remainder at other New Zealand, Australian, German, British and United States universities. Postgraduate placements with the centre are highly sought after and students come from all over the world to work within the unit.

Cronin and his colleagues, particularly Garry McDonald, of the New Zealand Centre for Ecological Economics and Market Economics Ltd, and Professor Anton Meister (Applied Economics), have conducted a number of sectoral and regional analyses projecting the economic loss for various eruptive scenarios.

Ruapehu’s eruptions in 1995 and 1996 were a cause of serious inconvenience, but in the scale of what might have been, did not amount to much.

Even a relatively small ash eruption at the present time would severely disrupt energy distribution, agriculture and air travel.

If Mt. Taranaki awakes again soon, Massey research shows that it will undoubtedly erupt over durations of many years and perhaps decades, creating a host of new and ongoing environmental challenges for land users around it.

Cronin knows what happens when volcanoes behave badly. In reviewing one of two e-mail bulletins that go out weekly to volcanologists worldwide, he notes that 16 different conspicuously active volcanoes are listed in various localities.

Today New Zealand is absent. It won’t be always.

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