Noise Explained: Exploring the Acoustic Phenomena of Flowing Lava

A years before I experienced my first eruption, I asked my friend who is geologist: what is the sound of flowing lava? He answered: “it is like you are breaking the glass non stop”. Since then, I have been obsessed with the urge to record that. Flowing lava, a phenomenon often associated with raw power and geological change, presents a unique auditory experience. In this article I would like to examine the question: WHY does the sound of flowing lava often resemble that of shattering glass? Through an objective lens, we will explore the physical and environmental factors that contribute to this intriguing sonic resemblance. I am a musicologist, I need to complicate simple things and explain them 🙂

The sound of lava, from its initial deep rumblings to the sharp crackles as it flows, is a complex interaction of geology and physics. Understanding why this molten rock produces sounds similar to breaking glass involves delving into its dynamic properties and the conditions under which it moves.

Cracking and Popping: The Sound of Expansion and Fracture

As lava surfaces, it produces a series of cracking and popping sounds. These are caused by the thermal expansion and subsequent fracturing of materials in the lava’s path. The heat from the lava causes materials to expand unevenly and rapidly, resulting in a sound akin to glass breaking.

The sound produced by different types of lava can vary mainly due to their viscosity and the way they flow. Here are some examples:

Basalt lavas: These are thin and fluid, so when flowing they may sound like flowing water or a turbulent stream. Because they cool and solidify quickly, they may also produce cracking and cracking sounds.

Andesitic and dacite lavas: Have higher viscosity, which can lead to louder and more dramatic sounds. As they flow and cool, they may make louder cracking and cracking noises, as well as rumbling sounds resulting from gases accumulating and rapidly releasing.

Rhyolite lavas: These are the most viscous, which can cause violent explosions. The sound of these eruptions can be loud and explosive, resembling explosions or thunder.

Interactions with Water: A volcano spewing lava upon contact with water may produce loud steam explosion sounds, as well as hissing and whistling sounds resulting from the rapid evaporation of water.

It is worth noting that these sounds are not only the result of the lava movement itself, but also of accompanying phenomena, such as gas explosions, rock cracks, as well as interactions with the environment, such as water and the atmosphere.

The Hiss of Escaping Gases

When gases trapped in the lava get out, they make different hissing and sizzling noises, kind of like the sound you hear when steam is let out of something under pressure. How loud or strong these sounds are depends on how much and what kind of gases are coming out of the hot, melted rock.

Thermal Expansion:

When hot lava moves, it heats up and expands itself and whatever it touches. This quick growing can make things crack and break, making noises like glass breaking. How much noise it makes depends on how much hotter the lava is compared to the area around it.

Environmental Interactions:

The noises lava makes also change depending on what it’s moving over. For example, when lava goes into water, it creates a lot of steam and loud hissing sounds, which is different from the quieter sounds it makes when it flows over dry ground. The place where the lava is affects the kinds of noises it makes, showing how it changes things around it. Like the moss which the volcanic eruption in July 2023 was burning around the crater.

I am a field recordist deeply obsessed with geology, volcanoes especially. To capture the sound of lava I sacrificed a lots of time, strength, countless hikes up to the volcano, sleepless night. I don’t regret anything. To this day, the sound of flowing lava is the most beautiful one I have heard – maybe because it is so rare?