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 …” 
What makes food crispy is air trapped inside a brittle framework, where the structure can fracture and disintegrate rapidly . 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.
 Laurence Fillion, David Kilcast, “Consumer perception of crispness and crunchiness in fruits and vegetables,” Food Quality and Preference 13 23–29 (2002).
 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).