(ORDO NEWS) — From a human perspective, mountains look stoic and still, massive symbols of calm endurance and stillness.
But new research shows that mountains are in fact constantly in motion, swaying gently as seismic rhythms ripple through the ground they rest on.
A recent study published in the journal Earth and Planetary Science Letters reports that the Matterhorn, one of the most famous mountains on the planet, constantly vibrates about once every 2 seconds due to ambient seismic energy resulting from earthquakes and ocean waves around the world.
“It’s kind of a real mountain song,” said Geoffrey Moore, a geologist at the University of Utah and senior author of the study. “It just hums with this energy, and it’s very low frequency; we can’t feel it, we can’t hear it. It’s the tone of the Earth.”
Recording of “Song of the Mountain”
Every object “wants” to vibrate at certain frequencies depending on its shape and what it is made of (this property is known as resonance).
Notable examples are forks and wine glasses; when the energy of the resonant frequency hits the object, it vibrates more strongly. Moore and his colleagues suggested that mountains, like tall buildings, bridges, and other large structures, also vibrate at a predictable resonance based on their topographic shape.
But unlike the world of civil engineering, where you can check which frequencies are resonant by placing large shakers on a structure or waiting for cars to drive over them, it would be impractical to excite something as big as a mountain.
Instead, Moore and his international team of colleagues attempted to measure the impact of surrounding seismic activity on perhaps one of the world’s most extreme mountains, the Matterhorn.
Located on the border of Italy and Switzerland in the Alps, the pyramid-shaped Matterhorn is the most photographed mountain in the world. It rises to a height of nearly 4,500 meters (15,000 feet) and its four faces face the cardinal directions.
The researchers took a helicopter up the Matterhorn to install a single solar-powered seismometer the size of a “big coffee cup” on top.
Another was placed under the floorboards of a hut a few hundred meters below the summit, and a third was placed at the foot of the mountain as a reference, said Samuel Weber, a researcher at the Institute for Snow and Avalanche Research in Switzerland and lead author of the study.
Seismometers continuously recorded movements and allowed the team to determine the frequency and direction of the resonance.
The movements are small, on the order of nanometers at baseline, to millimeters during an earthquake, Moore said. “But it’s very real. It always happens.”
Measurements showed that the Matterhorn constantly oscillates in the north-south direction at a frequency of 0.42 hertz, or a little less than once every 2 seconds, and in the east-west direction at a similar frequency.
By comparing the movement at the top of the mountain with measurements from a reference seismometer at its base, the researchers found that the top moves much more strongly than the base.
“It was pretty amazing that we measured the movement at the top, which was 14 times stronger than near the mountain,” Weber said.
The researchers also took measurements on the Grosser Mithen, a similarly shaped (though smaller) Swiss mountain, and found a similar resonance.
“I just think it’s a smart combination of site selection, which is so iconic, and careful instrument placement,” said David Wald, a USGS seismologist who was not involved in the study. Choosing a smooth mountain like the Matterhorn also eliminated soil and sediment issues that would have added another layer of complexity when measuring movement.”
The basic vibrations of mountains like the Matterhorn are caused by the hum of seismic energy.
“A lot comes from earthquakes rumbling all over the world, and very distant earthquakes are capable of spreading energy and low frequencies,” Moore says. “They’re just constantly ringing all over the world.”
But the data also points to another, unexpected source: the oceans.
Ocean waves moving along the seafloor create a continuous background of seismic vibrations, known as microseisms, that can be measured around the world, Moore said. Interestingly, microseisms have a frequency similar to the Matterhorn resonance.
“What was interesting was that there was… some kind of connection between the world’s oceans and the excitation of this mountain,” Moore said.
The research has practical implications in understanding how earthquakes can affect steep mountains, where landslides and avalanches are a constant concern.
But it also allows you to re-evaluate the Matterhorn and all the other mountains, which in their own way sway to the music hidden deep underground.
“You come to one of these mountains with the thought that you are trying to capture something hidden, something new and unknown,” says Moore. “It’s actually a lot of fun because it makes you sit back and think about grief in a different way.”
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