The magma that fuels volcanic activity is formed in the upper part of the Earth’s mantle as a result of the partial dissolution of peridotite rocks and then rushes upward by fragmenting the rocks of the Earth’s crust. Sometimes it gets stuck and then tries to climb back up. There are different signs that help predict. In recent weeks, many people have predicted that spectacular volcanic activity would begin on Iceland’s Reykjanes Peninsula by the end of the year – meanwhile, Ulaun volcano erupted with great force in the Papua New Guinea archipelago, and Etna erupted again at the end of November. In the last case, the situation changed almost from one moment to the next, and a violent volcanic eruption began.
How predictable are volcanic eruptions?
In an area where there has been no volcanic activity for centuries, with no visible volcano, it is not easy to predict when and where the ground will break open. But it is also worth noting that even in the case of an active volcano, it is not easy to determine when the nature of the volcanic activity changes and when a quiet eruption that attracts tourists turns into a serious and larger volcanic event. The events of the past few weeks faithfully reflect all of this. Although the tools needed for prediction have greatly improved, and changes in the shape of the Earth’s surface can now be detected with millimeter precision, and the path of magma can be deduced from signs of earthquakes, the big question remains: Will it happen? Magma erupts to the surface, and if so, when and how exactly?
On Iceland’s Reykjanes Peninsula, by early November, magma had risen to the surface more than 10 centimeters near one of the island’s biggest tourist attractions, the Blue Lagoon. Then it pushed sideways into an area of rocky weakness, which caused the upper crust to crack to the point of expanding by more than a meter and sinking by a metre. This also affected the quiet oceanside town of Grindavik, with the ground cracking in streets, parks and under houses, in some places creating fissures more than 20 meters deep. The nearly 800-year-old peaceful environment of the Reykjanes Peninsula has changed dramatically. According to model calculations, several hundred million cubic meters of magma rose into the Earth’s crust and spread to a depth of 2-3 kilometers. Forecasts predicted large-scale volcanic activity. By the end of the month, the chance of an outbreak had decreased significantly. Is this now an ugly failure for volcanologists, who were previously anticipating a major eruption? The fact is that the future, especially the near future, is difficult and almost impossible to predict accurately in the presence of such a complex system.
It is not easy for magma to reach the surface, and it is a miracle that it sometimes happens. The ground does not open up on its own, so molten rock can easily escape. Magma forms at a depth of 40-80 km, where it can rise when its quantity is already such that the buoyant force resulting from its lower density than its surroundings exerts sufficient pressure to break up the rocky body above it. This continues to the lower part of the Earth’s crust, but there are already rocks of lower density, so the buoyancy disappears. New physical processes are needed so that the magma can break down the rock body further.
In Iceland, on the Reykjanes Peninsula, the Earth’s crust is not very thick, about 10-12 kilometers (for comparison: in Hungary, the Earth’s crust is 25-28 kilometers thick). However, the crustal rocks in Iceland have the same composition as the magma that wants to rise, and they are also massive basalt, so it is not easy to break through. Despite this, the magma almost reached the surface, losing only a few hundred meters in places. Although the upper rock body was already fragmented in many places, the buoyancy resulting from the physical properties of the magma was no longer sufficient for the final step.
Failure of magma or failure of volcanologists?
None of them: That’s how the Earth works! Volcanic activity is a fairly rare event, there are much more cases of movement in the Earth’s crust. The magma is present at a depth of a few kilometers, moves a little, gives signals, and then calms down. This is how volcanoes work: they fill once, twice, several times, but they rarely send magma to the surface. If professionals are preparing for an outbreak, warning of the possibility, but then it doesn’t happen, it’s not a good idea to see it as a blind alarm, a failure, or an unnecessary panic.
They constantly monitored events, and when they saw the time was right, they proposed closing Iceland’s tourist attractions, evacuating the small town, closing roads, evaluating observations and data day by day, and based on this, the results of the model calculation informed residents what to expect. They did what they could using the tools of science and knowledge they acquired and communicated it in a way that even ordinary people could understand.
But there is always an element of uncertainty in models. Now, the 15 km horizontal spread of magma has helped it cool more forcefully, reducing its movement. In the end, it failed to emerge to the surface, but the experience of the activity of the Krafla volcano in Iceland, which occurred between 1975 and 1984, also shows: that there are such events, which are quickly followed by other events that lead to such events. Volcanic eruption. The current situation is also the same: we can still expect a volcanic eruption on the Reykjanes Peninsula in the future, perhaps for many years. Peace has ended after hundreds of years, and unfortunately life in the Grindavik settlement will never be the same again.
Etna volcano eruption on the evening of December 1, 2023 Photo: Giuseppe Tonzozo/Telex
Meanwhile in Italy
Meanwhile, in mid-November, after a short period of dormancy, Etna also began to show signs of life. Among the summit craters, the southeastern crater became active again and began operating unusually for more than two weeks. Between short bursts of lava fireworks, sometimes accompanied by a large explosion sound effect, 60-80 minutes passed without anything happening. The clock can be roughly adjusted according to frequent volcanic eruptions. The last time a similar event occurred was from May to June 2017, when about 60 short Stromboli-type eruptions followed one another. This was the case then, and the eruption was quiet for several months. However, this type of eruption has another possible consequence: the nature of the eruption can suddenly change, in which case a large amount of gas-rich magma erupts, resulting in an eruption of a lava fountain hundreds of meters high and a cloud of volcanic ash reaching a height of several kilometers. . This eruption mechanism is well known, and the main question is always when exactly it occurs. This often cannot be known for certain until a few tens of minutes before the violent explosion begins. Volcanologists at the Etna Observatory are already well aware of the signs of this, and taking into account the specific wind direction, they can warn people living near the volcano of the expected danger.
Volcanic forecasts have improved a lot in recent decades. This requires very sensitive instruments, but also the knowledge that specialists gain from the results of research work carried out in dormant periods or in other volcanic areas. However, it must also be accepted that the future can only be predicted with a certain probability, meaning that even an opportunity with a low probability may occur, but a predicted event with a high probability may not occur either. However, you should always prepare for the worst, this provides the most protection and this is what science can provide.
(The author is a volcanologist, Corresponding Member of the Hungarian Academy of Sciences, Director of the Institute, University Professor, and Head of a Research Group; ELTE TTK Institute of Geography and Earth Sciences, Department of Geology and Geochemistry, Hungarian Academy of Sciences – ELTE Volcanology Research Group)
