Humans are aware that during molecular changes, rapid expansion can and does occur. Explosions are such a situation. Subatomic particles bound closely to the nucleus of atoms go on the move, and bump each other during this activity, so the exploding mass as a whole requires more space. There is pressure outward. But explosions seem to be accompanied by heat, where the formation of ice crystals seems to be due to the lack of heat. So why would ice crystals expand, requiring greater space than the liquid state just before? Gaze at a drop of water and the same water molecules represented as fluffy snow. Snow, as the weary crews that plow roads in winter are painfully aware, takes up so very much more space. Several feet of snow, when melting in the winter, end up representing only a few inches of rainwater.
Heat is composed of several subatomic particles that act as a lubricant for molecular motion, where atoms change their position with respect to one another. Thus, as is well known by humans, hot metal or rock can become liquid. The lack of heat particles creates a situation at a certain point where atoms are pressed against each other, and a different drama ensues. Just as within explosions, where subatomic particles on the move require more space than in the prior, pre-explosive state, just so the near proximity of other atoms can create this need for more space. The loss of heat does not necessarily accompany this expansion, as the processes are separate though often occur simultaneously. In the case of ice formation, there is a steady lose of heat during the freezing process, however, so to some degree one might call the formation of ice a controlled explosion.
What occurs at the point that freezing water turns to ice is that subatomic particles trapped within each water particle are encouraged to move into areas formerly occupied by heat. Like children under a teacher's thumb while at their desks, when the teachers are elsewhere, they scamper out into the halls to play. They no longer bump into heat particles flowing between atoms when the normal course of their movement within the water atoms brings them to the periphery. Just as in an explosion, where the rearrangement of particles at the atomic level requires more space, just so the quiet explosion that freezing water represents requires more space. The water atoms are now increasingly sharing subatomic particles, which move to the periphery of an atom and loop through and around other atoms before returning. Thus the atoms become bound to each other by the wash of this motion, and become static ice!