Humans and volcanoes

I was 10 years old when I first went to Pompeii, and it made an enormous impression on me. We looked around the archaeological site, which was incredible. Then, we surveyed the plaster of Paris casts, the voids left by people's bodies — people who were engulfed by the pyroclastic density currents that poured down from Vesuvius and buried Pompeii.

We have good accounts of the terror that followed the Krakatoa eruption. It was an enormous explosive eruption; it interacted with seawater as well, which made it even more explosive and noisier. It is supposed to be the loudest bang ever heard by humans, heard as far away as Singapore and Australia.

The 2010 eruption of Eyjafjallajökull closed much of northern European airspace for many weeks. Aircraft and volcanoes are not very compatible. Volcanic ash, if it gets into aircraft engines, can melt and clog up various parts of the mechanism. There are famous examples of aircraft flying by mistake through volcanic plumes or volcanic ash clouds and their engines stalling. Fortunately, there has never been a major air disaster, but it has come very close. The regulations in 2010 included a zero-tolerance policy to volcanic ash. With the Eyjafjallajökull plume, the weather patterns were such that it was blowing over northern Europe. It formed a layer in the atmosphere. Where it was at all times was difficult to track. The community of atmospheric scientists, volcanologists and the Met Office in the UK were doing their very best, but there was the zero-tolerance policy about the aircraft's ability to go through this plume in order to land at key airports, like London's Heathrow – very busy airports.

Volcanoes often do give us some warning that they are going to erupt, but there are many challenges related to it. We look for warnings such as changes in very small earthquakes or seismic signals. They are much smaller than the big earthquakes that make the news for destroying cities, but nonetheless, we can use the signals from around volcanoes to understand more about how the magma is moving inside the plumbing system. We can look at how deep the earthquakes are, for example, to see where the magma is.

It is still not perfect, but all these strands of evidence together can really help us. What is very challenging is when we don't have good monitoring. Many different parts of the world do not have the same resources, or the volcanoes are very remote, so we don't have very good monitoring networks on these volcanoes. In more modern times, satellites have started to play a really key role. We cannot do seismicity from space, but we can look at the way that volcanoes are changing from space using radar satellites. This has been incredibly powerful, because it has allowed us to build up more of a global picture of how volcanoes behave, rather than just looking at individual volcanoes one by one. I'm really hopeful that we will continue to do an ever better job at being able to predict whether a volcano is going to erupt or not. It is still a challenge to be able to say it is definitely going to erupt — or we think there is a high probability that it is going to erupt — in the next six months. However, that is not incredibly helpful if you are a hazard manager charged with monitoring the situation, because you cannot evacuate a city for six months. What you really need to know is whether it is going to erupt in the next two days, and that is much more challenging.

People live with volcanoes in many different ways, and sometimes it is by necessity. They are living in a place where the population is very constrained, they need to find land, and the cheapest land is near the volcano. It is not always necessarily a matter of choice, but there are also times where people choose to live near volcanoes for very good reasons.

Santorini in Greece is one of the volcanoes I have worked on a lot. It is an absolutely spectacular place. If you get the chance to go there and you have not been, then go. It is incredible. It has amazing cliffs, and they are stunning; to the naked, untrained eye they look striped with a variety of different colors in them.

What Santorini does as a volcanic system is build itself up, so the Kameni islands are currently building up — the last eruption was in 1950 — and they build up in lava flow after lava flow and volcanic domes. It builds up an edifice. At some stage, the edifice gets big enough to stop future eruptions, and a large amount of magma can build up under the system. Then it has these absolutely enormous explosive eruptions, and they devastate the islands and empty out the Earth's shallow crust. Afterward, they leave collapses, called calderas — enormous craters — and that is what created the bay at Santorini. The last of such highly explosive eruptions was what is sometimes called the Minoan eruption, as it coincided with the Minoan civilization in the area of Crete and Santorini, in the late Bronze Age. There were Minoan settlements; there were what are sometimes called the Pompeii of Santorini at Akrotiri, which is being partially excavated now, and it is a Minoan settlement that was buried in the late Bronze Age eruption. What is interesting is we have not found any bodies in this settlement. We have also found very few valuable items. That tells us the inhabitants received warnings, which they heeded. We think there were small explosions that scattered some fine layers of ash over the island before the really big eruption happened. The hypothesis is that the Minoans fled, possibly back to Crete, which was the center of their civilization, and escaped with their belongings and their lives before the really destructive force of the eruption set in.

An enormous explosive eruption will happen again in Santorini's future, but all the evidence at the moment points to the fact that it is in one of these building phases, with many small eruptions every few decades. The last one was in 1950, so there will be another eruption of Santorini; we do not quite know when. It shows unrest from time to time, so there will be another.

If we look in the geological record, what we see is species diversity. The number of species that we see evidence for in the geological record is not constant through geological time. We go through periods of very large-scale species diversity, and then we go through these big contractions where lots and lots of species die out all at once. We call these mass extinction events. There are many small contractions in the number of species in the geological record, but we often refer to the Big Five mass extinction events.

Each of the most recent three coincide with something called a large igneous province. A large igneous province is an enormous outpouring of largely basaltic lavas onto the surface of the planet, and it happens over about a million years. It is triggered by an enormous hot plume of material coming up, possibly from as deep as the Earth's core-mantle boundary, and gradually convecting its way up very slowly, until it gets to the surface. It then causes a large-scale melting of the mantle, which drives this million years of heightened volcanic activity. We have evidence for large igneous provinces — from the Deccan Traps, the Central Atlantic Magmatic Province and the Siberian Traps — coinciding with all three of those mass extinction events. With the Cretaceous, there is the Chicxulub impactor hitting the planet near what is now Mexico, so that is happening as well. With the other two, we do not have any evidence of a meteor or an impactor hitting. We think that the large igneous provinces play a really key role in triggering the mass environmental change that contributes to the mass extinction event.

The messages that volcanoes send us are manifold. One of them is really about the immense power that our planet has. Within that is a message of our own insignificance.