Science has explained why snow is white and why snowflakes come in various strange shapes. However, the reason why snow crunches softly underfoot is something that few people know.
Walking through a winter wonderland can evoke magical feelings with its fresh air, the stunning white scenery, and the soft crunching sound beneath your feet.
While science has clarified many aspects of snow, such as how snowflakes acquire their unique shapes and why snow appears white, very few scientists have investigated why this powder creates such a pleasant crunching sound when we walk on it.
There are several factors that cause snow to crunch under your feet.
To fully understand the cause of this delightful crunching sound, we need to know how snow forms. For snow to fall, the air must have enough moisture and a temperature at or below 0 degrees Celsius.
Snow forms when water droplets freeze onto a particle, such as a dust particle or a pollen grain. Generally, snow will begin to accumulate on the ground if the surface temperature is at least 5 degrees Celsius; otherwise, the snowflakes that land will start to melt immediately.
Once there is enough snow covering the ground, the magic happens, and we can hear a “symphony” of crunching sounds with each step we take.
So, what creates that sound?
Professor W. Craig Carter, a material science expert at the Massachusetts Institute of Technology, explains that each step on the snow causes many tiny things to break simultaneously.
He likens this process to running a fingertip across the teeth of a comb. Imagine something much smaller than a comb, with thousands of such tiny things “breaking” at once.
The complex structure of snow is the main factor that creates sound when stepped on. Professor Carter elaborates: “It is essential for the snowflakes to gather and touch each other, similar to ice cubes in a freezer. If you place them in a bowl of ice water, they will stick together, and this sticking process is known as sintering.”
Sintering occurs when “necks” of ice form between ice crystals, connecting them like a thick necklace. The snowflakes adhere to each other but are not tightly bound, so when you step on them, a series of these connecting “necks” break simultaneously.
Temperature also plays a role in this. When the temperature is just below 0 degrees Celsius, the ice crystals are coated with a liquid-like layer, making them slippery. You won’t hear any noise because these particles slide past each other without breaking. However, as the temperature drops further and sintering occurs, the brittleness of the snowflakes increases.
Snow isn’t the only thing that crunches underfoot; wet sand does too. Sand particles also stick together like snowflakes. Since silica dissolves only slightly in water, when two sand grains barely touch, it’s an ideal moment for the formation of bonds that will break underfoot.
