Tongan volcano eruption leaves scientists with unanswered questions

Host: Benjamin Thompson

Welcome back to the Nature Podcast. This time, the science of the Tongan volcano eruption…

Host: Nick Petrić Howe

And modelling how societal changes could alter carbon emissions. I’m Nick Petrić Howe.

Host: Benjamin Thompson

And I’m Benjamin Thompson.

[Jingle]

Host: Benjamin Thompson

On 15 January this year, shockwaves went around the world as a volcano in the South Pacific Ocean, close to Tonga, erupted, sending debris high up into the atmosphere. Resulting tsunamis and ash have devastated the nearby islands and prompted a humanitarian crisis. Since then, scientists have been trying to work out exactly what happened during the cataclysmic explosion, and what it means for future volcanic risks. Alex Witze has been writing about these efforts for Nature, and reporter Ariana Remmel has been speaking to her to find out more. Ariana started by asking about the history of the volcano that erupted.

Interviewee: Alex Witze

This volcano has been active in the past. It had big eruptions in the year 200-ish and around the year 1100-ish. So, about every 900-1,000 years it’s had a very large explosive eruption. More recently, it’s been active several times in the last couple of years. In 2009, it had a small eruption. Again, in 2014-2015, it had a small eruption. So, that’s where we were until December of last year when it began erupting again, so we mean ash plumes going up a little way, activity in general, nothing major but big enough that you could tell. So, in January, the Tonga Geological Services were warning that this volcano was active, there was ash coming from it, it could do some things that could be bad. In fact, the day before the giant eruption, the Tongan geologists took boats and went over to do a survey and then on 15 January, fortunately nobody was there – they’d gone back to Tonga – that’s when the enormous planet-altering blast went off.

Interviewee: Ariana Remmel

Now, this volcano is a submarine volcano. It’s underneath the ocean. I mean, is it common for underwater volcanoes to have this kind of a blast?

Interviewee: Alex Witze

It is and it isn’t. So, submarine volcanoes are a big threat, we just don’t think about them because they’re below the water. We don’t necessarily see them. And often, when there are underwater eruptions, they’re deep enough that essentially the pressure of the water above them kind of suppresses the eruption, so it happens really deep and nothing really makes it to the surface. What you might get is suddenly, weirdly, you have a bunch of light volcanic rocks like pumice, like the stuff you use on your hands and feet, might suddenly appear at the ocean surface, but all you get is floating rocks. It’s really pretty rare that you have a submarine volcano actually erupt all the way through the surface of the water and up.

Interviewee: Ariana Remmel

So, how high did the eruption plume from this blast actually go?

Interviewee: Alex Witze

It got at least 30 kilometres high, so that puts it in the stratosphere or the upper atmosphere. And the reason that’s important is when you have a really powerful volcanic eruption that puts things very high into the atmosphere, it can affect global climate. So, right after the eruption, the number one question was how do we help the Tongans? What is the disaster there? How can we get aid on the ground to assist with people? The number two question is what are the long-term impacts of this? So, when stuff gets 30 kilometres high, I mean, that’s way up there, right? There were even satellite images that suggested some parts of the plume might have gotten essentially almost all the way to the edge of space – 55 kilometres or so. It was just like a straight jet all the way up.

Interviewee: Ariana Remmel

It seems like one of the other really remarkable aspects of this eruption is the atmospheric waves that occurred afterwards that went across the globe.

Interviewee: Alex Witze

Yeah, it was really wild. So, there were all sorts of atmospheric ripples that went outward. Things called gravity waves that we haven’t really seen from eruptions before, effects all the way up into the ionosphere, which is even above the stratosphere. It was messing with the GPS signals up there. Pressure waves rippled all the way around the world. People who were observing atmospheric pressure anywhere could see it change dramatically as these pressure waves came through. It was really extraordinary. There were atmospheric effects that triggered tsunamis in other ocean basins as well too. It was like the oceans and the atmosphere were ringing all the way around the world after this thing.

Interviewee: Ariana Remmel

So, given that the island is really challenging to get to by land, are there other ways that scientists are trying to answer questions and get more data to better understand what happened?

Interviewee: Alex Witze

Yeah, there’s a lot of efforts going on right now to see what data they can get, what information they can get, about what happened. So, closest to the eruption itself, the Tongan Geological Services have been working really hard to get samples of ash from different islands and sending them to colleagues primarily in New Zealand where they can analyse them and figure out what was the ash like that erupted. A little bit farther out, there have been some teams that have been doing things like launching balloons into the eruption plume. So, there are a couple of teams, for instance, that were on the island of La Réunion in the Indian Ocean that basically got there as fast as they could, attached instruments to measure aerosol particles, lofted them up and measured just how high stuff was. And then of course, from an even broader perspective, Earth-observing satellites are continuing to monitor the after effects and that plume as it goes around the world.

Interviewee: Ariana Remmel

With a blast this size, you’ve got ash that presumably is really iron-rich going into the ocean and yet, at the same time, you’ve got all this water vapour pulling seawater into the atmosphere. I mean, what are the effects of that kind of chemical exchange?

Interviewee: Alex Witze

There is a lot of really interesting geochemistry that goes on after an eruption like this. So, one of those things that you mentioned – ash falling onto the ocean – at least one scientist that I talked to is looking to see whether that iron is going to fertilise a plankton bloom, essentially stimulate plankton to grow in the ocean more than it would have otherwise because it’s acting as a nutrient. There are other sort of crazy things that can happen during the eruption. For instance, the fact that it erupted through seawater, it brought lots of salt with it, and so there was in the eruption plume there were a lot of salt crystals and salt compounds, which made it much more electrically conductive than normal. So, another crazy thing about this eruption is the number of lightening strokes that were recorded in this eruption plume. Just think of this giant plume towering out of the ocean and it’s just getting nailed with flash after flash of lightning. I think there were tens of thousands of lightning strikes in a fraction of an hour, just absolutely ripping away, and that’s because there’s salts in the plume, the salts are electrically conductive and you get lots of lightning.

Interviewee: Ariana Remmel

What do we know about what’s next for this particular volcano, and does this eruption give us a new way of thinking about other submarine volcanoes around the world?

Interviewee: Alex Witze

What happens next with this volcano is pretty much anyone’s guess. There are a lot of people watching it very closely and trying to game out what might happen. Will it just kind of burble along? Will it be fairly active? What are the chances of another enormous eruption like this? We don’t really know that yet. It’s really just a question of watching and waiting at this point. But this eruption does point out that there are a lot of these volcanoes, especially around the Pacific, and we probably need to pay more attention to them than we have until now. What happened on 15 January is really underscoring that these underwater things that we don’t see, so we don’t think about them very often, can be incredibly dangerous as well.

Host: Benjamin Thompson

That was Alex Witze talking to Ariana Remmel. For more on this story, check out the show notes for a link to a feature article written by Alex.

Host: Nick Petrić Howe

Coming up, we’ll be hearing about research that’s trying to figure out what humans might do in the face of climate change. Right now, though, it’s time for the Research Highlights with Dan Fox.

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Dan Fox

When it comes to reindeer, it seems only some have been bitten by the travel bug, because while many make epic migrations of more than 1,000 kilometres a year, others are content to stick closer to home. Now, scientists have linked a reindeer’s tendency to migrate with its genetic heritage. Researchers tracked 139 reindeer moving throughout western North America. The team then looked for genes that could explain the differences in animals’ movement patterns. They found genetic vestiges of the last ice age, when an ice sheet divided the North American reindeer into northern and southern populations. In modern reindeer, those bearing greater genetic similarity to the northern group are more migratory than those more closely related to the ancient southern population. Fifty-seven genetic mutations seemed to have especially strong associations with migration. Many are in genes that, in other animals, affect brain activity and fat storage — logical connections, given that metabolism and a sense of time could influence migration. However, because humans have fragmented reindeer habitats, the populations most inclined to migration could die out. Read that research in full in PLoS Genetics.

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Dan Fox

An analysis of fossilised vomit is providing clues to the diet and anatomy of extinct pterosaurs. Researchers examined the fossilised remains of two winged reptiles and two preserved regurgitated pellets found in an ancient rock formation in northeast China. The researchers found that the pellets contained the scales of a type of extinct fish. The pterosaurs, a juvenile and an adult, probably vomited them shortly before they died. Modern birds have stomachs divided into two chambers: one secretes digestive acids while the other helps to break down food and stores bones, scales and other indigestible elements which some birds then regurgitate in the form of pellets. The authors say that their findings suggest that pterosaurs also had a two-part stomach and were able to contract it to force swallowed food up into their mouths. Read that research in full in Philosophical Transactions of the Royal Society B.

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Interviewer: Nick Petrić Howe

Now, it’s time to talk about climate change. You’re probably familiar with climate models –these sort of mathematical simulations of how Earth’s systems come together to make the climate. These give us an idea of how the climate was, is and, importantly, will be. This is of course key to understanding how the climate is changing as a result of human activity. However, that human activity is tricky to model. In many models, the amount of carbon humans emit tends to follow a static trajectory, but the world is a complex place and sometimes things can change very rapidly, altering our carbon emissions. To give a recent example, in my home of the UK, coal use for electricity has rapidly declined. Last year it was under 2%, down from 25% 5 years ago. Such rapid changes and the diverse ways in which society can act leave a vast range of future possibilities for human-caused emissions. And with such complexity, they are often left out of models.

Interviewee: Fran Moore

I think people are rightly nervous about taking something that seems complex, past-dependent, and to try and model that in any kind of confident way. And I think that is a kind of legitimate concern, but if the motivation for doing that is high enough, maybe we should have a go at it.

Interviewer: Nick Petrić Howe

This is Fran Moore, a climate economist from the University of California, Davis. And Fran and her team have had a go at it and have published a paper in this week’s Nature, looking at what societal, political and technological changes might happen in the face of climate change, and how these changes would affect emissions. Now, if modelling all this sounds tricky, it’s because it is. So, Fran was part of an interdisciplinary team, who came up with a number of societal factors that could influence emissions. Key to this was an idea of feedback processes. These are processes that can again and again increase or decrease a certain effect. In a system as complex as society, feedbacks are going to be the things that really drive change. Here’s Fran with an example.

Interviewee: Fran Moore

So, one example is, what's sometimes called the learning-by-doing feedback. And so this is an effect where, initially, new energy technologies are often very expensive for a variety of reasons. But what you observe is that some installation, initially, you get going on them, and what happens is suppliers, the installers, the customers kind of learn, the supply chains kind of improve, and what happens is those costs of that energy technology tend to decline over time as a function of installation, right? So, you have some initial installation that drives down the cost of that technology, that drives further installation, that drives down the cost, that drives further installation.

Interviewer: Nick Petrić Howe

So, by including feedbacks like this one, Fran and her team were able to come up with a model that can represent how society could change in the face of climate change, and how this would impact our carbon emissions. There were several components, but to give you a flavour, here’s one that they named cognition. This describes how climatic changes are perceived by people as evidence for or against climate change. Will extreme weather make people take climate change more seriously or would people bury their heads in the sand and deny that climate change is occurring? Fran and her team ran the model 100,000 times, each time tweaking slightly the different components – turning up or turning down how their virtual people perceived different aspects of climate change and how they might act. From that they could get an idea of how emissions would change and, as a result, what amount of warming we might expect by the end of the century.

Interviewee: Fran Moore

The bulk of our probability mass is kind of coming in for 2100, warming somewhere slightly less than 2 degrees to up to kind of 2.5-2.8 degrees maybe.

Interviewer: Nick Petrić Howe

Most of the time, warming was coming in at under 2.8 degrees, which would still lead to a range of disastrous impacts. However, in the model, it was rare that emissions didn’t come down at all, and about a quarter of the time the model suggested that emissions would decline rapidly, as in this case, more policies would be pursued to strictly limit carbon emissions. This kind of breaking down of behaviours and how they might alter emission levels is a relatively novel approach. And being able to take these known behavioural insights and play them out on a global scale impressed Ganga Shreedhar, a behavioural scientist who wasn’t associated with this study.

Interviewee: Ganga Shreedhar

It sort of does address the limitation of the literature. Rather than thinking, how do you design an intervention or what motivates people in particular contexts, really takes a system-level perspective. What's the net effect, if these sort of behavioural drivers kick in, and how does it sort of result in different emission scenarios, and I think that's super useful.

Interviewer: Nick Petrić Howe

But is doing so realistic? Taking these behavioural insights and letting them play out over decades in a virtual world? Ganga believed so.

Interviewee: Ganga Shreedhar

I think it is realistic. And I think it's an important exercise as well, because I think by doing so you get a sense of, actually, what are the environmental implications, at least in terms of emissions, of these microprocesses and how they actually add up?

Interviewer: Nick Petrić Howe

Now, the paper doesn’t necessarily show us what we should be doing. It was more focusing on showing what could happen. But Ganga and Fran did say it could give us some insights on what policies to focus on. By looking at the model, you can see which aspects of it were the biggest drivers of emissions. For example, the cognition component I mentioned earlier –how changes in climate are perceived by people as evidence for or against climate change. In the model, this could have a huge impact on future emissions.

Interviewee: Fran Moore

If you think people are able to kind of directly kind of perceive climate change and that that has some effect on their opinion about climate change, then that kind of leads to these more aggressive, kind of very rapidly decreasing emissions. Whereas if you think people have these cognitive biases, they have imperfect perceptions of climate change, and in particular their political worldviews might colour their perception of the weather anomalies that they face, then in those cases you get kind of delayed climate policy.

Interviewer: Nick Petrić Howe

That was Fran Moore from the University of California, Davis in the US. You also heard from Ganga Shreedhar from the London School of Economics and Political Science here in the UK. To find out more about this study, check out a link to the paper in the show notes.

Host: Benjamin Thompson

Finally on this week’s show, it’s time for the Briefing chat, were we discuss a couple of science stories from the Nature Briefing. Nick, what have you brought for us to discuss this time?

Host: Nick Petrić Howe

So, Ben, I’ve been reading in Nature about China’s decision to have more approval for gene-edited crops.

Host: Benjamin Thompson

And when we say gene-edited crops then, Nick, what do we mean?

Host: Nick Petrić Howe

Well, it’s a good question, Ben, because there are some subtleties that are important here. So, gene-edited crops are developed using technologies like CRISPR, and they make small tweaks to DNA sequences. Now, they differ from crops obtained from genetic modification because that involves moving entire parts of genes or DNA sequences from other plants or animal species. So, until now, in China, they have both had the same legislation, but the new rules coming in are going to make a distinction between the two.

Host: Benjamin Thompson

Right, okay, so, I mean, what was the situation before then and what’s been approved now?

Host: Nick Petrić Howe

So, currently, it takes around six years for approval to be reached and you need to do extensive trials and meet all sorts of criteria. These criteria are being sort of reduced somewhat and the timeline for such crops to go from lab into the real world is being reduced, so it should take about a year or two, people reckon. So, where this sits in terms of the amount of restrictions in place on gene-edited crops is somewhere between the European Union’s stance and somewhere between the US’s stance. So, for example, in the US, small changes that could occur naturally are allowed, whereas in the EU, all gene-edited crops are treated as genetically modified organisms. So, China is sitting somewhere in between there.

Host: Benjamin Thompson

And what sort of crops then, Nick, are researchers in China looking to work on now these rules are being changed?

Host: Nick Petrić Howe

So, it’s a range of different things. So, since the preliminary guidelines came out on 24 January, researchers have been submitting lots and lots of applications for a variety of different things. So, it could be more disease-tolerant crops, it could be more drought-tolerant crops, it could even be crops that have better flavours. The one specific example – and there was a paper that came out on this in Nature last week – is about a crop that is resistant to powdery mildew. So, this is a disease that can really devastate crops. Now, making it resistant to this disease can also make its growth not as good, but by combining different edits, you’re able to make it so it grows really well and it’s also resistant to this disease. So, this could be one of the first examples of something that’s approved under the new guidelines.

Host: Benjamin Thompson

And what are researchers saying then, Nick, about these new regulations?

Host: Nick Petrić Howe

Well, some researchers in China are quoted in this article as saying this is very good news. It really opens the door for commercialisation, so actually getting things into the field. But what’s your story this week, Ben?

Host: Benjamin Thompson

Well, Nick, I’ve got a story that was also covered in Nature and it’s a good news story. It’s the lowest ever recorded numbers of a very painful parasitic disease called guinea worm.

Host: Nick Petrić Howe

Well, that does sound like a good news story but, I must confess, I don’t know much about this. Can you tell me what guinea worm is?

Host: Benjamin Thompson

So, people and animals can be infected with guinea worm by drinking water contaminated with its larvae, and the parasite spends about a year growing inside the host, sometimes reaching a metre long before poking out of the skin, maybe the feet or the legs, and it waits for the host to go near water so it can release its larvae and start the cycle again. And this emergence, Nick, is extremely painful and can take up to six weeks, from what I understand, and can be hugely debilitating and can prevent people working or even walking in some cases.

Host: Nick Petrić Howe

Well, it certainly sounds nasty. So, what are the new numbers for this?

Host: Benjamin Thompson

Well, Nick, in 2021, there were just 14 cases reported in humans, and that was from four countries in sub-Saharan Africa – Chad, Sudan, Angola and Cameroon. And for some context, that’s a drop from 27 cases in 2020 and a drop from over 3.5 million a year back in the 1980s. And so, this is a huge drop in this time period, and it’s the result of efforts by international organisations and governments. And I think what’s especially remarkable about this, Nick, is that there’s no recognised treatment or vaccine for guinea worm, so eradication campaigns have really focused on preventing transmission.

Host: Nick Petrić Howe

And how do you go about preventing transmission of this?

Host: Benjamin Thompson

Well, contaminated water here is really, really important for this disease. And it has quite a recognisable cycle, as I’ve laid out there as well. And this is what makes it relatively straightforward to detect. And in many ways, it’s old school epidemiology that’s done the business here. So, in Chad, where 7 of the cases were detected, field agents created a network to track contaminated water sources and prevent people from drinking from them and using pesticides to kill the larvae. And this approach has worked in other places as well, which is what is keeping these numbers so low. And you said there’s 14 cases in the last year.

Host: Nick Petrić Howe

Is there any effort to get it all the way down to zero?

Host: Benjamin Thompson

I mean, those efforts are continuing, Nick, absolutely, but it’s quite a tricky one, eradication. And it’s difficult because guinea worm doesn’t just infect humans. In Chad again there were 790 reported guinea worm cases in dogs last year, but animal cases were down 45% in 2021. So, moving in the right direction there, and the hope of course is that guinea worm can be eradicated, and it will join quite a short list of diseases that have been purposely eradicated in human history. Smallpox and rinderpest – which was a disease that affected cattle – are the only two so far. So, I really, really hope that in the not-too distant future we can come onto the Briefing chat and say that humanity’s got there.

Host: Nick Petrić Howe

Well, Ben, I look forward to that time where we come on and say this has been eradicated. But for now, listeners, if you want more on these stories and you want to know how you can sign up to the Nature Briefing to hear more science stories like these, then you can check out the show notes for some links.

Host: Benjamin Thompson

And that’s all for this week’s show. If you want to get in touch with us, you can reach us on Twitter – we’re @NaturePodcast. Or you can send us an email to podcast@nature.com. I’m Benjamin Thompson.

Host: Nick Petrić Howe

And I’m Nick Petrić Howe. Thanks for listening.