Cosmic rays can alert you to an impending volcanic eruption. How is this possible?

Every second, thousands of invisible subatomic particles fly through your body. Scientists have just found that these particles can be used to monitor what is happening inside volcanoes. In this way, you can even create an early warning system for an impending eruption.

These particles are muons, the stream of which is constantly bombarding every place on Earth. These particles, traveling at a speed close to the speed of light, will pass through almost everything, because they do not interact in any special way with the nuclei of the medium in which they are located. As a result, muons reaching the Earth’s surface penetrate it even for several hundred meters. The particles themselves are almost indistinguishable from electrons. The exception is mass: muons have 207 times the mass of an electron.

Where do such particles come from? Cosmic rays consisting of protons and the nuclei of light atoms, hitting the Earth’s surroundings, collide with the nuclei of atoms that make up the upper layers of the atmosphere. As a result of such a collision, risers. On their way to the Earth’s surface, the pions decompose into muons, and it is the muon flux that can be measured already on the Earth’s surface.

To peer inside the volcano, scientists check how many muons hitting the volcano’s slope are able to pass through it and exit from the other side. As they fly through different parts of the volcano, the muons will collide with caves, chambers, magma, and rocks. Each of these layers has a different density. The denser the matter through which a muon passes, the faster it slows down and leads to disintegration. If we set up detectors on the slope of a volcano, we will see – like in an X-ray of a broken leg – where more muons pass through the volcano, and where there are fewer of them. This will create a two-dimensional image. However, if more such detectors were set up around the volcano, a three-dimensional image of its interior could be created to determine where the voids are, where the rock is thicker, and where the magma accumulates.

The above technique, mionography, has recently been used to study the internal structure of two Japanese (Sakurajima and Mt Asama) and three Italian volcanoes.

As scientists argue in the latest scientific article published in the Proceedings of the Royal Society, muons can be used not only to study the internal structure of volcanoes but also to monitor the movement of magma inside them, so that it will be possible to monitor the risk of a potential eruption.

If the detector noticed that something had changed near the top of the volcano, where a lot of muons had passed through it, it could mean that something is getting in the way of the muon stream. This, in turn, may mean that where there has been no magma before, it has started to accumulate. This may already be a clear signal of an impending eruption.

Prior knowledge of an impending eruption may allow the regional authorities to order an evacuation early enough, which in turn may significantly improve the safety of residents living in the immediate vicinity of volcanoes all over the Earth.