Tonga’s massive undersea volcanic eruption was also detected using cosmic particle radiation — University of Oulu spinoff company involved in developing the method

Over the years, measurement and calculation technology based on muons generated by cosmic radiation has been developed at the University of Oulu. Such technology is suitable for geological land and bedrock studies. Experimental development work began at Pyhäsalmi mine (Callio Lab). Based on this research work, Muon Solutions Oy, a spinoff company of the University of Oulu, has been established. Marko Holma, Chief Executive Officer of the company, also works part-time at Kerttu Saalasti Institute.
Hunga Tonga Google Earthissa

Muography (1), i.e., density imaging using muons, can be used in extractive industries (2-3), groundwater applications (4) and forecasting volcanic activity (5-7). According to a recent study, muography is also suitable for detecting tsunami waves.

Technologies based on the detection of muons generated by cosmic particle radiation used and developed by Muon Solutions can be divided into two categories: density imaging by muons (muography) (1-7) and underwater positioning by muons (muometry) (8-10).

“Our research suggests that muography equipment can detect a tsunami already at the point when a dangerous wave is just approaching the coast, though this is only possible if a muographic measurement system is installed on or below the seabed. In the latter case, a tunnel is needed. Overall, it’s good to remember that a tsunami can arise in several different ways. The four most common are a submarine earthquake, a submarine volcanic eruption, a large landslide into the ocean and a tsunami wave caused by a major storm,” Marko Holma says.

The fact that muography is also suitable as a “tsunami warning system” became evident in Muon Solutions’ collaboration with the University of Tokyo. One of such collaborative projects relates to the observations of a muographic measuring station located below Tokyo Bay (11). The latest significant result is the detection of the tsunami generated by the huge submarine volcanic eruption of Hunga Tonga on 15 January 2022 near Tonga, almost 8000 km away from the HKMSDD system in Japan (13). The system’s English name is “Hyper Kilometric Submarine Deep Detector” (HKMSDD) and it is installed in a road tunnel below Tokyo Bay (11).

Due to the volcanic eruption of Hunga Tonga, waves up to 15 m high were broken into the shores of the outer islands of Tonga (14). Due to the enormous size of the Pacific, the tsunami caused by the eruption reached different parts of the coasts at different times. The first tsunami reached the Gulf of Tokyo about 8 hours later. The sound wave caused by the eruption was also observed at different times in different locations, but in any case as far away as about 10,000 km away in Alaska.

The HKMSDD measurement station in Tokyo Bay has been built to detect numbers of muons generated by cosmic radiation in terms of time, that is, it monitors the so-called muon flux. Detection occurs after muons have passed through the medium being monitored. In the current case, muons allow to see the altitude of seawater, as well as changes in the average density of the atmosphere. Detection is based on the fact that otherwise statistically stable muon flux changes as the average density between the observational devices and the upper part of the atmosphere (the place where muons emerge) changes. The greater the thickness or bulk density of the volume under consideration, the fewer muons arrive at the measuring instrument, since some of the muons lose energy and stop before reaching the measuring instrument. On its statistical principles, muography resembles X-ray imaging.

According to an observation by the HKMSDD measurement station in the Tokyo Bay, the wave height deviation generated by the Tonga eruption was about 20 cm. The observation is important because it shows the measurement of cosmic muon radiation allows the construction of a tsunami warning system independent of other measurement methods user for measuring the heights of water bodies, even globally. Building an independent tsunami warning system will help scientists and authorities get an even more accurate snapshot of the arrival of a potential tsunami, which in turn is important in making decisions about evacuations of people in coastal areas.

“Detection of tsunamis as early and as reliably as possible allows for the construction of life-saving warning systems. In addition to detecting tsunami waves generated by a volcanic eruption at HKMSDD measuring stations, they can also detect tsunamis generated by earthquakes, unusual high tidal waves, and so-called meteotsunamis (meteorological tsunamis). Meteotsunamis are generated by storms such as major tropic cyclones. However, the actual eruption of the volcano cannot be observed with this system. For that we need muon telescopes installed at the base of the actual volcano (10),” Marko Holma says.

Photo: Eric Gaba – Wikimedia Commons user: Sting

For more information:

Project Geologist, Kerttu Saalasti Institute, University of Oulu

Chief Executive Officer, Muon Solutions Oy Ltd

Marko Holma

+358 (0) 46 920 8781

+358 (0) 40 836 4317


1) Holma, M., Aittola, M., Enqvist, T., Jalas, P., Joutsenvaara, J., Kuusiniemi, P., Loo, K. & Virkajärvi, A., 2019. Uusi menetelmä: Myonigrafian soveltaminen maa- ja kallioperän suhteellisten tiheysvaihteluiden kartoittamisessa. Materia 2/2019, 54-56. (

2) Zhang, Z.-X., Enqvist, T., Holma, M. & Kuusiniemi, P., 2020. Muography and its potential applications to mining and rock engineering. Rock Mechanics and Rock Engineering 53, 4893–4907. doi:10.1007/s00603-020-02199-9. (

3) Holma, M.J., Zhang, Z.-X., Kuusiniemi, P., Loo, K. & Enqvist, T., 2021. Future Prospects of Muography for Geological Research and Geotechnical and Mining Engineering. AGU Books. doi:10.1002/9781119722748.ch15. (painossa)

4) Kurikka-lehti, 14.10.2021. Kosmista säteilyäkin mitataan pohjavesitutkimuksessa.

5) Leone, G., Tanaka, H.K.M., Holma, M., Kuusiniemi, P., Varga, D., Oláh, L., Lo Presti, D., Gallo, G., Monaco, C., Ferlito, C., Bonanno, G., Romeo, G., Thompson, L., Sumiya, K., Steigerwald, S. & 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 447(2255). doi:10.1098/rspa.2021.0320. (

6) The New York Times, 10.11.2021 . How Do You See Inside a Volcano? Try a Storm of Cosmic Particles. (

7) Oulun yliopisto, 12.11.2021. Oulun yliopistosta ponnistava suomalainen startup-yritys mukana kehittämässä uutta menetelmää tulivuorien purkautumisen ennakoimiseen. (

8) Oulun yliopisto, 16.12.2021. Suomalaiset mukana kehittämässä uutta vedenalaista paikannusjärjestelmää. (

9) Yle, 16.12.2021. Suomalainen startup-yritys kutsuttiin kehittämään vedenalaista paikannusta, josta voi tulla uusi GPS – rahoittajana Yhdysvaltain laivasto. (

10) Helsingin Sanomat, 13.1.2022. Suunnistus sukelluksissa voi onnistua avaruudesta iskeytyvien myonien avulla, suomalaiset mukana kehittämässä laitteita.

11) Tanaka, H.K.M., Aichi, M., Bozza, C., Coniglione, R., Gluyas, J., Hayashi, N., Holma, M., Kamoshida, O., Kato, Y., Kin, T., Kuusiniemi, P., Leone, G. et al., 2021. First results of undersea muography with the Tokyo‑Bay Seafloor Hyper‑Kilometric Submarine Deep Detector. Sci Rep 11, 19485. doi:10.1038/s41598-021-98559-8. (

12) Wikipedia, luettu 23.1.2022. 2022 Hunga Tonga eruption and tsunami (

13) University of Tokyo, Research Bulletin, 15.1.2022. 日本時間)のフンガ・トンガ-フンガ・ハアパイ火山の噴火. (

14) Yle, 18.1.2022. Tongan tulivuorenpurkaus muistutti uhasta – voivatko Tyynenmeren saarivaltiot tuhoutua luonnonmullistuksessa? (

Last updated: 27.1.2022