A layer of ice forms on the surface of a pond during freezing weather because of the unique density behavior of water as it cools. Water reaches its maximum density at about 4°C. As water cools below this temperature, it becomes less dense and rises to the surface. When the top layer of water cools to 0°C, it freezes, forming ice that is less dense than liquid water. This ice floats on the surface, forming a layer that insulates the water below and prevents the pond from freezing solid. This phenomenon is due to water’s molecular structure and its hexagonal crystalline formation when it turns to ice, which takes up more space and reduces its density compared to liquid water.
