The muffled noises emitted by certain mountains before an avalanche are usually due to the fracturing of snow and rocks under the effect of accumulated stress. These sounds can be a sign of imminent instability, potentially announcing the occurrence of an avalanche.
Mountains are in perpetual motion, even if it’s not obvious. At the heart of the rocky massif, the layers of snow and ice accumulated exert an enormous pressure on the underlying rocks. In response, the rocky crust deforms slightly, cracks, or subtly slips along existing faults. These micro-movements sometimes generate subdued vibrations, much like when you slowly bend a wooden stick that ends up creaking just before it breaks. Another important player is the water infiltrated into the crevices of the rock, which, by freezing and thawing regularly, also exerts internal tensions responsible for these deep creaks. These muted sounds actually reflect the internal activity of the mountain, which often precedes the triggering of an avalanche.
Before an avalanche, the accumulated snow begins to endure significant mechanical forces. This pressure causes the layers of snow to compact and deform slightly. As the slope accumulates snow, microscopic cracks appear between the different layers, weakening the entire structure. This phenomenon is called the formation of weak layers. Gradually, these tiny cracks widen due to accumulation and temperature changes, creating internal tensions. When a weak layer eventually breaks abruptly, it triggers a rapid and noisy mechanical phenomenon known as a slab fracture. It is precisely this sudden rupture, preceded by those small cracking and internal friction noises, that generates the famous muffled sounds sometimes signaling an imminent avalanche.
When the layers of accumulated snow begin to slide slightly against the ground or against each other, friction naturally generates vibrations. These vibrations often manifest as dull sounds or rumblings that seem to come from afar. It's somewhat like rubbing two rough surfaces together: the energy released by this friction creates small sound waves that we perceive as low noises. The snow and rocks, under the pressure of the unstable snowpack, undergo these small repeated movements, gradually amplifying the audible sounds. The greater the friction increases with the weight and internal tensions within the snowpack, the more pronounced and alarming the noises become just before an avalanche occurs.
The muffled sounds emitted by a mountain travel differently depending on the rock structure: cracks, faults, or the porosity of the rocks shape their path and modify their intensity. In dense and homogeneous rock, sounds travel quickly and far, whereas in fractured or porous rock, they will be absorbed, weakened, or distorted. Certain types of rock, such as very compact granite, act almost like a natural speaker, effectively transmitting very deep sounds to the outside. Variations in sound propagation often indicate the presence of fractures or internal tensions, useful clues for anticipating a potential avalanche.
Often, the louder the dull noise generated by the mountain is intense, the greater the tension accumulated in the snow and the lower layers. A notable increase in the intensity or frequency of dull sounds generally indicates that the layers of snow are sliding or deforming further, signaling a critical instability. In other words, it's a bit like a natural sound alert: if the noises become louder, closer together, or sharper, it is often a sign of a high risk of an imminent avalanche. But beware, a complete absence of noise is not necessarily reassuring either—some avalanches are triggered without warning by obvious acoustic signs.
In Switzerland, scientists are using ultra-sensitive microphones placed on the mountainsides to detect subtle sound changes that may indicate a possible avalanche.
Low-frequency sounds travel more easily through solid mediums such as rock or ice, which explains why the precursor sounds of an avalanche are often heard as deep rumblings rather than high-pitched noises.
Some species of wild animals, such as ibex or chamois, sometimes show a reaction of stress or flight before avalanches, likely in response to the vibrations or sounds emitted by the mountain.
Some avalanches can reach speeds of up to 300 km/h, making them one of the fastest and most difficult natural phenomena to predict.
If you are in the mountains and hear dull or unusual noises coming from the slopes, it is essential to immediately leave the exposed area and head towards safe and protected locations. Do not hesitate to notify the relevant local authorities.
Here is the translation: "Animals, especially wild ones, are generally more sensitive to certain sound frequencies. They can sense or hear these vibrations much earlier than humans, which sometimes explains their unusual behaviors before avalanches."
Apart from the muffled sounds, some visible signs include a sudden and localized settling of the snowpack, the presence of visible cracks on the snow surface, and recent light avalanches in the surrounding area.
Yes, thanks to acoustic sensors and seismographs installed at various strategic points, researchers can analyze and measure the sounds and vibrations emitted by the mountains in order to assess the risk of triggering an avalanche with some anticipation.
No, the dull noises do not systematically precede every avalanche. They may be absent or imperceptible, depending on the geological and meteorological conditions as well as the structure of the snow and rock.
No one has answered this quiz yet, be the first!' :-)
Question 1/5
