The snow crunch

I was walking in snowy Manchester yesterday and was astonished by how loud the crunching underfoot was. The snow has been on the ground for a couple of days, and the compacted snow on the pavements seems to have reached the optimal consistency for making loud crunching sounds.
Why does snow make a crunching sound when you walk on it? There doesn’t appear to be any research into this surprisingly! But a lot is known about crispy foods; biscuits, deep fried batter or even fruit. Some food researchers even use the sound of snow crunching as a way of describing what they mean by crispy food: “’Crispy’ [fruit] was associated with a sound like walking on snow …” [1]

Magnified snow crystals
Magnified snow crystals {3}

What makes food crispy is air trapped inside a brittle framework, where the structure can fracture and disintegrate rapidly [2]. Snow is ice with lots of air. When lightly compacted by foot fall, the snow forms firm but brittle structures, including a thin crust on-top, which can break rapidly and create the distinctive crunch sound.
[1] Laurence Fillion, David Kilcast, “Consumer perception of crispness and crunchiness in fruits and vegetables,” Food Quality and Preference 13 23–29 (2002).
[2] Garmt Dijksterhuis, Hannemieke Luyten, Rene de Wijk, Jos Mojet, “A new sensory vocabulary for crisp and crunchy dry model foods,” Food Quality and Preference 18 37–50 (2007).

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