Shake, rattle, boom - monitoring Auckland's volcanic field

07 December 2012

Jan Lindsay (right) and PhD student Lucy McGee

The recent eruption at Mt Tongariro and concern surrounding Ruapehu’s stability are timely reminders for Auckland which is built on one of the world’s youngest volcanic fields. What would a major volcanic eruption look like here and how would we respond?

This is something University of Auckland volcanologist Jan Lindsay thinks about every day. Together with a GNS scientist, she leads a major seven-year project DEtermining VOlcanic Risk in Auckland (DEVORA).

Working with 30 senior researchers and 10 doctoral students, Jan is dating the city’s 50 volcanoes to see if there is a pattern to past eruptions. At Lake Pupuke in Takapuna, a painstaking assessment of sediment in ash layers has changed thinking about Rangitoto, the youngest and largest volcano in Auckland. Rather than erupting once 600 years ago, the island may have erupted three times starting about 1,500 years ago.

“Traditionally, it has always been said that once a volcano has erupted in the Auckland field it’s done, but the fact Rangitoto has erupted a few times is really challenging this traditional view of how the field might behave,” says Jan.

DEVORA researchers have also been trying to understand what an eruption might look like.
“The first sign will be a swarm of earthquakes triggered by magma rising from a depth of about 80 kilometres,” says Jan. “As it gets closer to the surface, the earthquakes will become shallower and centre on a particular site. The chances are an eruption will start with an explosion and then we’ll get base surges as hot magma meets water in or above the ground.”

As Jan and her team process this geological information it is fed through to Auckland Council and the Earthquake Commission who are both funding DEVORA. “We want everything we have learned to make its way into policy,” says Jan.

Although volcanic hazard is very low in Auckland with chances of an eruption once every 2,500 years on average, if it does happen our vulnerability will be extremely high. So another key focus of DEVORA is to assess the impact of an eruption on Auckland society and a tangible outcome will be the customisation of a new computer-based, risk evaluation tool called Riskscape for the Auckland volcanic field, which can predict the impact of an eruption on things like building collapse, transformer failure, economic loss and ash clean-up costs. “It’ll be a fantastic tool for planning. If we were about to have an eruption it could simulate it in advance and predict what would be effected on the day aiding evacuation and contingency planning,” says Jan.

She is also working directly with Civil Defence to develop a decision-making tool that can be used to decide when to evacuate people. “It’s been a two-way discussion and invaluable process,” says Clive Manley, head of Auckland Civil Defence.

Jan started her career with GNS Science during the 1995-1996 Ruapehu eruption and has since studied Chile’s La Pacana caldera, one of the world’s biggest volcanoes, and spent four years working in a volcano observatory in Trinidad.

She and her team are now using a DEVORA-style approach with researchers at King Abdulaziz University in Saudi Arabia to study a volcanic field near the holy city of Medina.

“New Zealand is a leader in this integrated approach to a hazard,” says Jan.