Magical Muons and Magma Movement

Volcanoes can threaten public safety, water supplies, land, and contribute to temporary climate changes (U.S. Geological Survey, 2018). Canada primarily has volcanic areas in British Columbia and Yukon, but is also exposed to volcanoes along the United States border that may erupt again in the future (Government of Canada, 2020). Volcanoes, therefore, pose a threat to Canadians due to their proximity to cities and vital resources, particularly if there is late detection of the eruption (Government of Canada, 2020). While there are ways to predict volcanic activity, such as GPS and seismic networks and the observation of gas emissions, many of these methods have shortcomings, such as blind spots or delivering warnings close to the volcanic event (Leone et al., 2021). Volcanic muography is an alternative technique that images muons and can provide a system producing numerous warning signs of volcanic activity farther in advance, and is estimated to increase prediction effectiveness by 75%(Leone et al., 2021). In addition, this technology could allow scientists to track changes and movements of magma (Nagamine et al., 1995).

Muons are elementary particles similar to electrons and were proven to exist in 1937 (Street and Stevenson, 1937). The primary differences between electrons and muons are their masses, which is over 100 times that of an electron, and muons’ superior ability to reach and penetrate the ground, as seen in Figure 1 (Street and Stevenson, 1937; Adam, 2021). Muons are formed at great heights in the atmosphere where cosmic rays enter the atmosphere and collide with the atomic nuclei of the various gases present in the air. This crash causes pions, another type of subatomic particle, to form and almost instantaneously decay into muons (Adam, 2021).

Figure 1: The formation of primary and secondary particles, the production of secondary particles, is caused by the primary particles’ interactions with nuclei in the atmosphere. Only muons and neutrinos are able to penetrate the ground (Zhang et al., 2020)

Muography operates based on the physical properties of muons as they pass through matter. As muons pass through matter, they lose energy; the more dense the matter in which they are passing through, the more energy is lost (Adam, 2021). When a significant amount of energy from the muon is lost, the muon particle decays into a different subatomic particle, such as an electron (Adam, 2021). Muography uses detectors to track the number of muons that pass through a specified volume; this can give insight into the density of the inner constitution of the observed volume; this setup can be seen in Figure 2 (Leone et al., 2021). Detectors must be put below the volume that is to be observed as muons originate from the atmosphere (Adam, 2021). The tracked muons are then compared to the number of muons that would be observed in the sky revealing which parts of the volcano are dense and which are more vacuous (Adam, 2021).

Figure 2: The set up for recording muography images through the detection and tracking of muons coming from cosmic rays. The detector is below the volume that is to be detected. The energy of the recorded muons are compared with the expected values to create an image. (Gibney, 2018)

Muography has been used for various aspects of monitoring volcanic activity. For example, muography allowed scientists to analyze features of the mountain post-eruption. In a study of Mt. Asama in Japan, muography images found that there was a dense region within the mountain, this is shown in Figure 3 (Tanaka et al., 2007). The region was identified as the lava mound formed in the last eruption based on its recorded shape and positioning within the mountain (Tanaka et al., 2007). Additionally, muography has made it feasible for one to observe magma moving through the volcano’s conduit by targeting the mountain’s summit (Tanaka, 2019).

Figure 3: A muography image, blue shaded colours represent low-density regions while red shaded regions represent high-density areas. The higher arrow shows a high-density neighbourhood and was determined to be a lava mound based on its shape. A low-density area is directly below it, shown by the lower arrow and designating magma’s suggested pathway (Tanaka, 2007; Tanaka, 2019).

Muography detectors can provide helpful information during the initial stages of a volcanic eruption and for monitoring and analyzing the features of the mountain post-eruption (Tanaka et al., 2009). Thus, muography has essential applications allowing for more preparation and protection of public safety and vital resources against volcanic eruptions.


Adam, D., 2021. Core Concept: Muography offers a new way to see inside a multitude of objects. Proceedings of the National Academy of Sciences, 118(14), p.e2104652118.

Gibney, E., 2018. Muons: the little-known particles helping to probe the impenetrable. Nature, 557(7707), pp.620–621.

Government of Canada, 2020. Where are Canada’s volcanoes? [online] Canada. Available at: [Accessed 16 Nov. 2021].

Leone, G., Tanaka, H.K.M., Holma, M., Kuusiniemi, P., Varga, D., Oláh, L., Presti, D.L., Gallo, G., Monaco, C., Ferlito, C., Bonanno, G., Romeo, G., Thompson, L., Sumiya, K., Steigerwald, S. and Joutsenvaara, J., 2021. Muography as a new complementary tool in monitoring volcanic hazard: implications for early warning systems. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 477(2255), p.20210320.

Nagamine, K., Iwasaki, M., Shimomura, K. and Ishida, K., 1995. Method of probing inner-structure of geophysical substance with the horizontal cosmic-ray muons and possible application to volcanic eruption prediction. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 356(2–3), pp.585–595.

Street, J. and Stevenson, E., 1937. New Evidence for the Existence of a Particle of Mass Intermediate Between the Proton and Electron. Physical Review, 52(9), pp.1003–1004.

Tanaka, H., Nakano, T., Takahashi, S., Yoshida, J., Takeo, M., Oikawa, J., Ohminato, T., Aoki, Y., Koyama, E. and Tsuji, H., 2007. High resolution imaging in the inhomogeneous crust with cosmic-ray muon radiography: The density structure below the volcanic crater floor of Mt. Asama, Japan. Earth and Planetary Science Letters, 263(1–2), pp.104–113.

Tanaka, H.K.M., 2019. Japanese volcanoes visualized with muography. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 377(2137), p.20180142.

U.S. Geological Survey, 2018. Which U.S. volcanoes pose a threat? [online] Available at: [Accessed 16 Nov. 2021].

Zhang, Z.-X., Enqvist, T., Holma, M. and Kuusiniemi, P., 2020. Muography and Its Potential Applications to Mining and Rock Engineering. Rock Mechanics and Rock Engineering, 53(11), pp.4893–4907.

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