How can we explain the regular, muffled noise emanating from extinct volcanoes?

Have you ever wondered what that muffled sound that seems to emanate from certain extinct volcanoes is all about? No, it’s not a herd of elephants marching under the mountain while you sleep, nor is it a resentful gorilla repeating “I’m here!” to scare you. No, there’s a scientific explanation, and it’s as fascinating as it is surprising! In fact, this mysterious sound, as regular as your fridge alarm when it malfunctions, is the result of a natural orchestra of geological and physical phenomena. From subterranean vibrations resonating in the cooled rocky bowels of the volcano, to the residual activity of lazy volcanic gases still dancing beneath our feet, a whole little world stirs in the shadows.
The phenomenon isn’t just a random noise; it’s a kind of geological rhythmic drum set playing in a tempo that’s often predictable, linked to how rock and magma behave after thousands of years of explosive tranquility. By connecting this enigma to nearby seismic activity, the natural resonance of cavities within the mountain, and even the slight degassing that persists, we are finally beginning to decipher this sonic code. So, ready for a dive into the little-known world of volcanic monitoring on the scale of a supposedly dormant volcano? Why does an extinct volcano still make a “thumping” sound? An extinct volcano should be the geological equivalent of a forgotten microwave, right? Well, no. These mountains, even without displaying molten lava or a spectacular eruption, often maintain a certain internal activity. The famous regular thumping sound isn’t just an auditory hallucination caused by hours spent in nature: it is actually a manifestation of subterranean vibrations.

These vibrations are generated by several factors, including: Geological resonance Cavities and fractures in the rock. Slow and continuous degassing of volcanic gas pockets that have never completely disappeared.

The movement and contraction of the underlying cooled magma, which, despite its name, remains sensitive to temperature and pressure.

• Low seismic activity even in the absence of visible eruptions. Imagine a quartz crystal that vibrates when you rub it, but a hundred thousand times larger, and embedded in rock that responds with a deep, resonant sound. The slow fracturing and pressure changes inside create a natural resonating chamber effect. This is what transforms these micro-tremors into an audible rumble, a kind of playful song of the mountains. This song, with its regular frequency, has piqued the curiosity of volcanologists for decades. And today, thanks to next-generation volcanic monitoring equipment, we can identify these sounds as a valuable indicator of the internal state of extinct volcanoes. Discover the possible causes of the regular rumbling noise emanating from extinct volcanoes and understand the geological phenomena behind this mysterious sound.
• What are the physical causes of these rumbling vibrations? To understand why an extinct volcano emits a rumbling noise, we must delve into the heart of rock and gas physics. What is sometimes called “the breath of the sleeper” is not simply wind in the trees, but a multifactorial phenomenon resulting from very precise interactions beneath the surface. Here are several concrete physical causes:
• Thermal contraction of cooled magma: Magma that has cooled never truly ceases its internal activity. Under the effect of temperature variations, the solid rock contracts and expands slightly, creating microfractures and vibrations. Continuous degassing:
• Buried pockets of volcanic gas still release bubbles of air or carbon dioxide, which slowly rise through fissures. This movement creates a low, almost regular rumble, a bit like an old soda that still fizzes even if you shook it yesterday. Resonance in fracture networks: All these cavities carved out by erosion, tectonic activity, or past explosions can act as resonating chambers. When vibrations travel through these natural tunnels, they amplify the initial rumble.

Low but continuous seismic activity: Even if the volcano is no longer erupting, it remains subject to micro-tremors often imperceptible to the naked eye but transformed into audible rumblings through sensitive instruments. These phenomena, combined, form a kind of geological symphony that the most attentive human ears (or ultra-sophisticated microphones) can capture. Moreover, this regular sound frequency has been used by some researchers to detect subtle changes in the internal state of volcanoes, which could one day help to better predict their awakening—or lack thereof.

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A concrete example: The sound survey of volcanoes in the French Massif Central

In the Massif Central, where many volcanoes have been extinct for millennia, researchers equipped with ultrasensitive sensors detected a low, regular noise. This discovery led them to reconsider the notion of complete extinction, because the instruments show that volcanic gases continue to escape slowly, and that local geological resonance prolongs this sound phenomenon. So, even tired volcanoes can have a voice!

1. https://www.youtube.com/watch?v=a9USh0GiCPc Volcanic monitoring: the key to deciphering these mysterious noises
2. Did you think extinct volcanoes were just big, silent mounds? Think again! Volcanologists now use ultra-precise volcanic monitoring techniques to capture and analyze these regular, muffled sounds. Sensors, microphones, seismic activity measuring devices—everything is fair game to scan this incomprehensible symphony and extract valuable information. This monitoring allows us to: Detect the slightest abnormal seismic activity that sometimes precedes a reactivation.
3. Distinguish between the sounds caused by normal degassing and those heralding an awakening. Monitor local geological resonance and identify structural changes in the mountain.
4. Catalog the frequencies of these muffled vibrations to create a kind of “sound map” specific to each volcano. Thanks to these technologies, we now know that these rocks, which we thought had breathed their last, are still quietly singing, telling their millennia-old story. Which is quite reassuring: it’s not time to wake up yet, but a bit like a purring cat, it shows that there is indeed life below. This continuous monitoring, especially in 2025, is even crucial to prevent any explosive surprises, given that some so-called “extinct” volcanoes may not be completely dormant.

https://www.youtube.com/watch?v=ELuWNDTbUu0

How to distinguish the muffled rumble of an extinct volcano from other natural phenomena?

Have you ever heard the

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muffled rumble

of an extinct volcano and wondered if it was a distant thunderstorm or a massive power outage? Good question. Nature loves to make music, and not always the best kind. To tell the difference, look for these criteria: The sound is regular and repetitive, not a random crash like thunder (which is more explosive, more instantaneous). It is often localized precisely around the mountain, unlike the rustling of the wind or animals.

• The noise sometimes accompanies weak seismic activity detected in the area, which is a scientific clue. The volcanic gases that are released, often invisible but detectable with instruments, confirm the presence of an internal source of the sound. It is not accompanied by any meteorological phenomenon, which helps to distinguish it from atmospheric noises like thunder or a storm.
• When you put all this together, you become an expert in recognizing muffled volcanic sounds, and you can impress people at parties. Imagine the scene: “Yes, it wasn’t a ghost train, but clearly a vibration related to the cooled magma and geological resonance.” You’ll be a real conversation starter! 🔊 Characteristic
• 🌩️ Thunder 🌋 Volcanic rumble 🌬️ Wind or thunderstorm
• Regularity

Random

Regular

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Variable

Sound duration Short, bursts Long and continuous

• Variable Origin Atmospheric
• Internal geological source
• Atmospheric
• Associated earthquake
• Often no

Yes, low seismic activity

No	Why is it making noise when the volcano is supposed to be extinct?	The word “extinct” applied to volcanoes is a bit like saying a computer is off when it’s still plugged in and emitting a little light. In volcanic jargon, an	extinct volcano
is supposed to have no more likely eruptions in the near future, but that doesn’t mean internal activity has ceased. In fact, volcanoes often retain some volcanic gases, or even some cooled magma, with which they play hide-and-seek in their depths, producing that regular, muffled noise that we sometimes hear.	It’s a bit like restaurants that close but leave a few employees to clean and tidy the kitchen: the former active arena isn’t completely empty. Internal physical and chemical processes continue on a small scale, with:	Slow movements of rock under pressure	Gradual, rather than immediate, cooling of the magma
Intermittent release of gas, such as		degassing	Sometimes, this noise is welcome news for the locals, who have a good excuse to claim that their mountain prefers to purr softly rather than spew fire. You can almost imagine the volcano saying, “I’m just on pause, don’t worry.”
Can an extinct volcano awaken?	Yes, some so-called extinct volcanoes can become active again, although this is rare. That’s why volcanic monitoring continues, even on these volcanoes, to watch for any signs of awakening.	Can you hear this muffled noise with the naked ear?	This noise is often very faint and difficult to perceive without specialized sensors. However, sometimes, in very calm conditions, attentive observers can perceive this rumbling.
Is the noise associated with a risk of eruption?	Not necessarily. This noise can be a sign of residual internal activity but does not predict an imminent eruption.	How do scientists choose where to install their sensors?	They target areas with low but regular seismic activity or anomalies in volcanic gas emissions, often in conjunction with historical and geological data.

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Does degassing fully explain the noise?

No, it is a phenomenon combined with geological resonance and the vibrations of the cooled magma, which complicates the origin of the noise.