cold and the surface of the basin 12 is frozen the water underneath the surface is liquid and remains at a sufficient temperature to heat and start fluidising the snow the water injected into the compacted snow therefore allows initial fluidisation the snow is then chopped and mixed by chopping and mixing means 2 comprising a plurality of chopping and mixing devices 2 arranged horizontally and parallel each chopping and mixing device 2 comprises a plurality of discs with toothed periphery and or with fingers or projections in the form of blades 2 a tilted in relation to the vertical in a regularly spaced and parallel arrangement and mounted around and along a horizontal shaft 2 b able to be set in rotation by a motor 2 c the rotating toothed discs and or blades 2 a create the triple technical effect of chopping mixing and forced downward movement of the compacted snow to a lower part 1 c of the reservoir arranged below the chopping and mixing means 2 in the lower part 1 c the side walls of the first reservoir are of pyramidal of funneled shape at this level the compacted snow has been partly fluidised and is in the form of a mixture any pieces of ice contained therein have been crushed and any blocks of highly compacted snow have been chopped the chopped mixed snow is also subjected to water injection treatment by second lower water spray nozzles 3 b arranged underneath the chopping and mixing devices 2.