MIT explains what makes fresh snow crack when you walk on it
Researchers from the Massachusetts Institute of Technology have shed light on the crisp, distinctive sound produced by fresh snow underfoot. This explanation was reported by Live Science, highlighting a long standing question in snow science.
Even though snow has been studied for decades, the moment of crunch as it is compressed has puzzled scientists. New findings from MIT point to how the inner structure of snow responds under stress, creating that familiar crackle we hear with every step.
According to Craig Carter, a professor of materials science at MIT, the crack happens when thousands of microcrystals fail at once. The snow is not a simple solid but a complex network. Each snowflake links with neighboring crystals, forming bridges that hold the layer together. When weight is applied, these connections break in a coordinated way, releasing energy as sound waves that travel through the snow and into the air.
Snow forms when water droplets freeze around tiny particles such as dust or pollen. As more flakes accumulate, the individual crystals bond, creating a lattice. This network acts like a fragile scaffold. When you step on fresh snow, thousands of microcontacts fail in a rapid sequence. The resulting impacts send vibrations through the packed lattice, which we hear as the crunch. The temperature plays a notable role: colder conditions tend to produce louder crackles because the crystals are drier and stiffer, while slightly warmer, moister snow can dampen some of the movement and reduce the volume of the sound. In near zero temperatures a thin film of moisture can still be present, shaping how the cracks propagate and what we perceive as the crackling noise.
There is a parallel in another natural material. Wet sand also exhibits a similar structure where grains are bonded and then released under load, producing a squeak or crack as the grains separate. This analogy helps illustrate how small granular contacts can translate mechanical stress into audible sound across different materials. The same idea underpins how snow behaves as it bears weight, with microcontacts breaking and reforming as the surface shifts under pressure.
Past research has emphasized the role of the snowpack as a dynamic, evolving system. The balance of crystal bonds, the amount of trapped air, and the presence of moisture all influence how the snow responds to stress. When the surface becomes compacted by footsteps or wind, the internal network rearranges, altering both its mechanical properties and the sound produced. This insight helps illuminate how snow cover persists in various climates and conditions around the world, including Canada and the United States, where snow is a prominent seasonal feature. Researchers continue to refine models of snow mechanics to better predict behavior under different temperatures and loading scenarios. The work underscores that even everyday sounds like crunching snow arise from a finely balanced microstructure that responds to small, rapid changes in its environment. It is a reminder that seemingly simple experiences can reflect intricate physical processes beneath our feet. These findings come from a combination of laboratory experiments and real-world observations, illustrating how the acts of formation, bonding, and breaking of tiny crystals culminate in the everyday sensation and sound of walking on fresh snow.
In summary, the classic crunch of fresh snow arises from a cascade of microcrystal failures within a carefully arranged lattice. The collective breaking of millions of intercrystal bonds releases energy as acoustic waves, giving rise to the audible crack. Temperature and moisture content modulate this process, shaping how crisp or muted the sound becomes. This explanation aligns with broader principles of granular physics, where small-scale contact events govern large-scale macroscopic behavior. From the quietest winter mornings to the heaviest snowfalls, the sound of snow underfoot reflects the hidden order of its ice crystal network. Attribution: MIT researchers as cited by Live Science