Volcanoes can kill you in many different ways. Are you on their slopes? A volcanic avalanche of superheated ash and gas or a sneaky lava flow would do it. Far across the bay? A tsunami caused by a collapsing flank will be delivered to your door. On the other side of the planet? The aerosols jettisoned into the stratosphere will tamper with the climate, leading to deadly droughts in one place and fatal floods in another.
Volcanoes can also launch chunks of freshly baked volcanic rock into the sky that, even before they have cooled down and properly solidified, can land on you and send you into the great beyond.
A team of scientists in New Zealand wanted to know how roofs in Auckland — the country’s largest city and one that sits on a huge field of volcanoes — would stand up to a future ballistics-throwing eruption. They couldn’t just walk around the streets lobbing volcanic rock at people’s houses, so they did the next best thing: They built a cannon, loaded it up with volcanic rocks, and blasted them at replica-but-realistic roofs, watching to see what it takes to dent, bent, and break them.
Volcanologists conduct experiments in laboratories all the time to try to shrink complex natural phenomena down to a scale at which scientific interrogation is possible. But it’s safe to say that this project is arguably one of the most fun. “Come on,” said Rebecca Williams, a volcanologist at the University of Hull in England who wasn’t involved with the research. “Who doesn’t want to fire volcanic cannonballs at roofs?”
Volcanic bombs (still partially molten when ejected) and blocks (already solid chunks) can and have hit people. Kīlauea’s prolific 2018 eruption sequence, which mostly involved lava flows, did occasionally surprise everyone with an explosion. A volcanic bomb the size of a basketball shot out of the sea at one point, crashing through the roof of a tour boat like a shotgun blast from hell, injuring over a dozen people. Back on land, another bomb smashed through a man’s shin, shattering the bones all the way down to his foot.
You may think the scariest feature of these ballistics is that they can be several times hotter than boiling water. True, the sautéed skin part is grim, but more often than not, the deadliest factor is that both bombs and blocks can weigh as much as a refrigerator and can easily travel at 370 km per hour. They pack one heck of a punch and can hit someone 10 km away from the volcano itself. “That’s astonishing, for something that goes from fist-size to van-size,” said Williams.
It hasn’t escaped the attention of volcanologists that New Zealand’s North Island and its surroundings are profoundly volcanic. Some of these volcanoes, being near people and capable of all kinds of eruptions, can be hazardous.
Auckland, home to 1.7 million humans, overlaps the appropriately named Auckland Volcanic Field, a zone of 53 individual volcanic centres that have erupted in a cornucopia of ways. The most recent eruption, about 600 years ago, was the only one witnessed by people. During a violent eruption in which lava mingled explosively with seawater, it created the 6 km Rangitoto Island, a rubbly, undulating spot draped by hardened lava.
Another Auckland Volcanic Field eruption at some point in the future is inevitable, which won’t be great news for the city that now sits atop it. “It’s not just the normal uncertainty of what the eruption is going to be like,” Nicole Allen, a PhD student at the University of Canterbury in New Zealand, told Gizmodo. “It’s where it’s going to be, and we just don’t know.”
This inevitable future disaster is why DEVORA — that’s DEtermining VOlcanic Risk in Auckland — was launched in 2008. Led by volcanologists at the University of Auckland and GNS Science, a vast number of scientists, engineers, emergency managers, economists, social scientists and others are cooperating to better understand the risks to the metropolis from the next eruption. This work includes improving their understanding of how the volcanoes work and the effects their eruptions may have on the city’s infrastructure, from short-circuiting its power grid to blocking up sewers.
Firing volcanic ballistics at roofs falls under DEVORA’s umbrella. Involving Allen and led by Tom Wilson, a disaster risk and resilience researcher at the University of Canterbury, this project wants to answer a pretty simple question: Can local roofs hold up against an onslaught of volcanic debris?
The university put together a ballistic cannon for this sort of work a couple of years ago. “We really wanted to make it bigger and better and do some more experiments with it,” said Allen — although, initially, they had a very different experimental setup. “It started as a trebuchet, actually, but it wasn’t very accurate.”
It turned out to be easier (if a bit less recklessly fun) to get two shipping containers, cut a hole in the floors and roofs of them both, stick roof targets at the bottom and position a downward-facing cannon at the top. A bona fide volcanic block — anywhere from 1 to 9 kilograms — is attached to a rod stuck to a piston inside the cannon. The cannon is pressurised, a trigger is pulled, and the sudden decompression propels the rock toward the roof at over 161 km per hour.
The work is ongoing, but surprising results are already emerging. As part of this set of experiments, ash is being sprinkled onto some of the roofs. Being far denser than water, it sometimes only takes a moderate dusting of ash to cause a roof to buckle and even collapse.
But the group’s work seems to indicate that “if you’ve got an eruption that’s going to pump out some ballistics, some volcanic bombs, you actually want a layer of ash,” said Williams. The team’s tests show that a thin layer of ash reduces the damage caused by some incoming bombs. “It acts like a cushion on the roof, which is really cool. And that’s completely counterintuitive.” The question they want to know now is, at what point does the ash turn from a help into a hindrance?
The setup is not a perfect model of reality. But reality is “so complicated that if you did, you wouldn’t get anything meaningful out of the data anyway,” said Williams. “You’d never know what’s doing what.” Scientists need to simplify things in order to isolate individual processes to study. And the work done with this relatively straightforward but nevertheless pioneering ballistics-versus-roofs project will be used to protect lives when one of the volcanoes below Auckland awakens — not just by helping engineers to design better roofs, but by giving authorities a sense of the damage an eruption may cause.
Allen explained that she studied geochemistry not too long ago, an unquestionably important way to find out what makes volcanoes tick. But she seems to prefer this more practical approach to understanding their explosive power. “I’d rather that people, non-scientists, knew what I was doing and how it was helpful,” she said.