Determining Auckland’s volcanic risk

New Zealand’s biggest city is built on an active volcanic field. What risks does this mean for the inhabitants, and how should these risks be managed? Could there be an explosion tomorrow?

Dr Jan Lindsay from The University of Auckland studies all aspects of volcanoes, including the chemical composition of their magmas, the deposits they generate and the hazards they pose. She has worked in Chile and the Caribbean and is now working on the DEVORA Project in Auckland. DEVORA stands for DEtermining VOlcanic Risk in Auckland. The DEVORA scientists are trying to find out much more about the Auckland volcanic field with the aim of keeping Auckland and Aucklanders safe in the unlikely event of a volcanic eruption. The DEVORA project is split into 3 important parts:

• Understanding Auckland’s geology.
• Determining the risk of a volcanic eruption.
• Assessing and managing the risks to people and Auckland’s infrastructure.

Understanding Auckland’s geology

Auckland was first settled by Māori around 1350, and they valued the land’s ability to grow crops – volcanic soil is rich, containing elements and nutrients essential for plant growth. The many volcanic peaks also made ideal pā sites that were easily defended against invading tribes. Today, Auckland is home to about 1.3 million people. Many are aware they live on a volcanic field and may think the volcanoes are dormant or extinct, but scientists now know that the volcanic field that lies under Auckland is far from dormant. So when will the field erupt again? How often do the volcanoes in Auckland erupt? Does one eruption trigger another?

To answer these questions, scientists are working on a number of projects. For example, Dr Phil Shane from The University of Auckland uses rock cores from areas such as Onepoto Basin to map when different volcanoes have erupted in Auckland. From this data, scientists are starting to determine how often eruptions occur and if there are any patterns.

What’s the risk of future eruptions?

Dr Jan Lindsay uses techniques such as gas monitoring, seismic measurements and ground deformation monitoring to monitor the volcanoes in Auckland and predict future eruptions. This information would be used to warn the city about a possible eruption.

Evidence suggests that an eruption in the next 50–100 years is very unlikely. The Auckland volcanic field seems to have had clusters of eruptions happening every 3,000 years. Within a cluster, there may be 2 or 3 new eruptions about 100 years apart, then everything tends to go quiet again. So are we in one of these clusters? Rangitoto last erupted just 600 years ago –does this mean we are safe for another 2,400 years? These are just some of the questions that Jan is seeking answers to. She suggests that the Auckland volcanic field is a low probability but high risk situation – that means it’s unlikely we will experience an eruption in Auckland within our lifetime, but if it did, it would cause widespread damage and disruption.

Managing the risk

What would happen if a volcano did erupt in Auckland tomorrow? Imagine having a volcano erupt in your backyard that throws up ash and rocks. How would Auckland respond? How would the rest of the country be affected? Scientists are working with organisations such as Civil Defence, electricity companies, local government and transport providers to make sure Auckland is ready. If an eruption did occur in Auckland, all these groups would be involved to try and minimise the impact on the city. To be more prepared, they take part in practice runs like Exercise Ruaumoko. Accurate risk assessment is only possible when a large group of people get together to make sense of various bits of information.