When snow melts does its volume decrease or increase?

The volume of the snow decreases. This had happened because the snow is made up or comprised of water (H2O) and oxygen (O). When the snow starts melting, the air inside the snow discharges into the atmosphere and the water turn out to be a puddle on the ground. 

a pan containing water is placed in a positio n where it is exposed to a 10 mile per hour wind. the pan contains a uniform depth of 1.27 cm of water, is quite wide, and has a length of 2.44 m in the wind direction. the water in the pan is at a constant temperature of 15.5 °c.