Chemicals detected in ash from past volcanic eruptions may help us forecast the effects of the next major eruption.
Volcanic ash from the past may help forecast the likely health and environmental effects of New Zealand’s next major eruption. That could come from any of our volcanic centres, such as Whakaari White Island, Ruapehu or Taranaki.
Every volcano produces ash with unique characteristics and we can use these ash ‘fingerprints’ to understand the potential effects of future eruptions, says Dr Jenni Hopkins, a geochemist and volcanologist at Te Herenga Waka—Victoria University of Wellington.
Past research suggests there is a 30 to 50 percent chance of a large rhyolitic eruption in New Zealand in the next 50 years. Rhyolite is a type of volcanic rock, associated with explosive eruptions.
Ash fall from these events can be widespread and contain chemicals hazardous to human health and the environment.
The last big New Zealand eruption, in terms of its explosivity and the volume of ash ejected, was the rhyolitic Kaharoa eruption at Mount Tarawera in about 1314, Dr Hopkins says.
The ash from this event is distributed widely across the east and north of the North Island.
Dr Hopkins has developed the TephraNZ database, which categorises ash from major rhyolitic eruptions during the past million years.
She now wants to collect data on ash deposited by less violent eruptions from non-rhyolitic volcanoes, such as Mount Taranaki.
“We can take a handful of these ash deposits and using a process where we gently grind the surface of the historic ash to reveal a fresh face—basically to make the deposits how they would have been when they first came out of the volcano—we can compare their chemical composition and how it links to different eruption types.”
Hazardous elements in volcanic ash can include arsenic, fluorine, and sulphur, as well as carcinogenic silicate minerals, such as cristobalite.
Dr Hopkins says finding out about these chemicals will help communities plan for future volcanic eruptions.
“We can take a sample of ash and analyse it in the days after an eruption has occurred, so we can say, ‘it’s got these components, it’s got this chemistry, it’s going to put this into the environment’. But by the time you’ve done the analysis, it’s a few days later and almost getting too late for the advice to be particularly useful.
“The added difficulty with volcanic ash is that the chemicals it contains can start to be released when the ash hits a river, lake or stream, or gets rained on—or even interacts with biological fluids, for example, being breathed in.
“So even if you collect ash a few hours after an eruption has occurred, it could be that it’s already lost quite a lot of those toxic elements. Or nutritional elements—we need to remember that ash can contain beneficial chemicals such as iron, potassium, and phosphorus, which can be fertilisers for the environment,” she says.
Dr Hopkins hopes to secure additional funding to expand the TephraNZ database, model the effects of past eruptions, and provide guidance on safety precautions before and during ash-fall events.
