I think it may be a physical change, because both sides of the pond are connected by ice, and the force generated by ice is concentrated in this narrow place, so it is impossible for ice to be formed by squeezing on both sides (rolling on both sides as soon as it is formed in the middle). You can observe for yourself. If it is very thick, it will produce a protrusion in the middle, which is more common in the north.

Another situation is that water flows in this narrow place and it is not easy to freeze.