The Matterhorn appears as an immovable, massive mountain that has towered over the landscape near Zermatt for thousands of years. A study just published in the journal “Earth and Planetary Science Letters” (https://doi.org/10.1016/j.epsl.2021.117295) now shows that this impression is wrong. An international research team has proven that the Matterhorn is instead constantly in motion, swaying gently back and forth about once every two seconds. This subtle vibration with normally imperceptible amplitudes is stimulated by seismic energy in the Earth originating from the world’s oceans, earthquakes, as well as human activity.
"The movements of the underground cause every object to vibrate, which we fortunately cannot feel, but detect with sensitive measuring instruments," emphasises Donat Fäh from the Swiss Seismological Service at ETH Zurich. These so-called natural frequencies depend primarily on the geometry of the object and its material properties. The phenomenon is also observed in bridges, high-rise buildings, and now even mountains. "We wanted to know whether such resonant vibrations can also be detected on a large mountain like the Matterhorn," says Samuel Weber, who carried out the study during a postdoctoral period at the Technical University of Munich (TUM) and is now working at the WSL Institute for Snow and Avalanche Research SLF. He emphasizes that the interdisciplinary collaboration between researchers at the Swiss Seismological Service at ETH Zurich, the Institute for Computer Engineering and Communication Networks at ETH Zurich, and the Geohazards Research Group at the University of Utah (USA) was particularly important for success of this project.
High alpine measuring devices
For the study, the scientists installed several seismometers on the Matterhorn, including one directly on the summit at 4,470 meters above sea level and another in the Solvay bivouac, an emergency shelter on the northeast ridge, better known as Hörnligrat. Another measuring station at the foot of the mountain served as a reference. Extensive past experience from Jan Beutel (ETH Zurich / University of Innsbruck) and Samuel Weber installing equipment for measuring rock movements in high mountains made deployment of the measurement network possible. The data are automatically transmitted to the Swiss Seismological Service.
The seismometers recorded all movements of the mountain at high resolution, from which the team could derive the frequency and direction of resonance. The measurements show that the Matterhorn oscillates roughly in a north-south direction at a frequency of 0.42 Hertz, and in an east-west direction at a second, similar frequency (see animation). In turn, by speeding up these ambient vibration measurements 80 times, the team was able to make the vibration landscape of the Matterhorn audible to the human ear, translating the resonant frequencies into audible tones.
