Heart of fire

Sometimes we forget what’s beneath our feet

This week, in the very heart of Africa, the earth gave us a frightening reminder that solid ground is something of an illusion. Mount Nyiragongo, which lies near the eastern border of the Democratic Republic of Congo, erupted, sending a stream of fast flowing lava down its flanks and towards the city of Goma. Thousands fled their homes, and at least 32 people died. This time, though, the people of Goma were relatively lucky. So far, the lava has largely stopped short of the city, and most of the tragedy has been confined to outlying villages. In a previous eruption, in 2002, Nyiragongo’s crater lake emptied and lava flowed right into the heart of Goma. Hundreds died, and tens of thousands lost their homes.

I’ve been listening to overseas media reports about the eruption, and I was struck by a question that one reporter asked – why would so many people live so close to such a dangerous volcano? On the one hand, it seems like a reasonable question. More than 30,000 people live within 10 kilometres of Nyiragongo, and a million live within 30 kilometres. Why take the risk? On the other hand, the reporter who asked the question was British, and it’s understandable that someone from Britain would find living next to a volcano a foreign concept. Had the reporter been from Italy, or Indonesia, or New Zealand, for example, it’s hard to imagine them asking that question.

As New Zealanders, we can, I hope, empathise more than most with the people of Goma. Less than two years ago we had our own deadly reminder of what it means to live with volcanoes, when Whakaari/ White Island erupted. We know what it’s like to live with dangerous and largely unpredictable natural hazards. I grew up in Auckland, a city where you can see a volcano in any direction you look. Although I no longer live there (I’m in Wellington, which, of course, has its own hazards), the eruption of Nyiragongo has prompted me to think more about what it means to live in a volcanic zone.

Nyiragongo is a very different type of volcano from the ones in Auckland. It’s a stratovolcano, also known as a composite cone, with layers of different types of volcanic materials – ash, lava, different types of rock – surrounding a central lava tube. New Zealand has a number of stratovolcanos, such as Taranaki and Ruapehu, but Auckland’s volcanoes aren’t of this type. Instead, they are scoria cones, also called cinder cones. Scoria cones result from lava which is full of gas bubbles, and they are typically small. The majority of scoria cones erupt only once, meaning that Auckland’s 53 volcanoes are probably all extinct.

But before you breathe a sigh of relief, there’s another important point about scoria cones. Many, Auckland’s volcanoes included, occur on volcanic fields. A volcanic field is a hot spot in the earth’s crust, where rock slowly melts, then periodically works its way to the surface, causing an eruption. Although Auckland’s individual volcanoes are extinct, the Auckland volcanic field is not. It has been active for 250,000 years, and there is every reason to think that there will be another eruption, and a brand new volcano, at some point in the next couple of thousand years.

Living in Wellington, where the frequency of large earthquakes is around once every 150 years, Auckland actually sounds rather safe. But Wellington’s buildings have, mostly, been built with such earthquakes in mind, something I remind myself of whenever there’s a small shake. How on earth do you prepare for a volcanic eruption, especially when you don’t know exactly where it will be?

The answer to this question is simple, but frightening. Just as with Nyiragongo, the safest thing to do is get out of the way. But anyone who has negotiated Auckland’s traffic will know that getting a lot of people from one part of the city to another is far from easy. On land, most of the traffic in and out of Auckland goes over one of four motorway bridges – the Harbour Bridge, the North-Western Motorway Bridge, Mangere Bridge and the Southern Motorway Bridge. Auckland struggles to move people around during a normal rush hour – so what would happen if a volcano was threatening to erupt?

Part of the problem in planning to evacuate part of Auckland is that the exact location of any future eruption is uncertain. Pupuke is one of the oldest volcanoes, nearby, Rangitoto is the youngest. To the south, in Māngere, Pūkaki is old, while Waitomokia, not too far away, is relatively young. There’s no obvious pattern in where the eruptions occur. The only consistent pattern is that there are a lot of volcanoes aged from 28,000 to 34,000 years. However, that age range is consistent with the limits of carbon-14 dating, and so the authors who reviewed the data were sceptical of the results. That leaves us with the unsettling conclusion that the location of the last eruption gives us no information about the location of the next.

Photo: the remains of a lava flow from one of Auckland’s oldest volcanoes, Pupuke, with the youngest volcano, Rangitoto, in the background

Another difficulty, described in a paper by scientists from the Universities of Auckland and Canterbury, is that we don’t really know how the people of Auckland will behave when they receive the advice that part of their city is about to erupt. Most of the systematic research about how people behave in mass evacuation situations comes from American cities responding to hurricane warnings, not quite the same as a volcano. It’s most likely that some people in designated evacuation areas will refuse to go, while others who are outside the evacuation area will want to leave. Planning for evacuation routes is difficult too. People might take the most familiar route, even if it isn’t the shortest.

In order to better understand the risks, and how to manage them, New Zealand ran a simulation exercise back in 2008, known as Exercise Ruaumoko. In that exercise, Auckland endured a couple of weeks of gradually-intensifying earthquakes before a new volcano erupted in the Māngere Inlet. The exercise highlighted a difficult tradeoff in any evacuation plan – the longer you wait before evacuating, the more certain you can be of the location, but the less time you have to evacuate. Since that time, we’ve learned more about the amount of warning we would have before an eruption, and the news isn’t reassuring. Exercise Ruaumoko was on the optimistic side – recent research estimates warning times ranging from 5-15 days.

On the positive side, the Auckland Volcanic Field is active, on average, once every 2,600 years. Rangitoto was active around 550 years ago, so the odds are in our favour. While there’s no guarantee that there won’t be an eruption sometime soon, it’s not likely. There’s no harm in making a plan, though. And spare a thought for the people of Goma, because their fate could be ours one day.

The Red Cross has an office in Goma (although like the city’s residents they have had to relocate temporarily). They and the UNHCR appear to be the main aid agencies active in this disaster.

The Turnstone comes out once a week. Usually, I write an original article once a fortnight and on alternate weeks I follow up with more information or some related links.

As always, let me know if you have any questions that you’d like me to answer through my articles.

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