Why do flowing rivers freeze?

The reason why the flowing river freezes:

When water turns into ice, the movement of water molecules can't break the hydrogen bond, which plays a major role. It combines water molecules together to form a regular spatial structure. In the crystal lattice, four hydrogen atoms are located at the vertex of the regular tetrahedron, and one oxygen atom is located at the center of the tetrahedron.

In this way, the gap between molecules becomes larger and remains unchanged, so the volume of water becomes larger when it forms ice; In water, the movement of molecules can not only break the hydrogen bond between water molecules, but also prevent frequent collisions between molecules caused by violent movement of molecules, and molecules can slide and cross each other, thus filling the gaps with each other and increasing the volume.

Generally speaking, the river will freeze below zero.

Extended data:

There are two situations in which rivers freeze. One is to start from the shore, first form shore ice, develop towards the center of the river, and gradually merge into an ice bridge, and the width of the ice bridge is expanded, so that the whole river surface is completely frozen. Another is that after flowing ice forms an ice dam in a narrow or shallow river, it quickly freezes between ice cubes and between ice cubes and river banks, and expands upward against the water flow, freezing the whole river surface.

When the temperature rises in spring, the ice in the river begins to melt, and the decomposed ice flows down with the river, and the river is opened. However, not all river ice is thawed in such a gentle way, so that the river can be unblocked, and sometimes it thaws quickly, especially when the temperature rises sharply or the water level rises sharply, and large pieces of ice surge down, which is easy to cause freezing.

Baidu Encyclopedia-Ice under the River