When a liquid is heated, its volume increases, and density decreases with the rise in temperature. Exceptions are observed in the case of water for a certain range of temperatures. When heated from 0°C to 4°C, the volume of water decreases, and the density increases. Above 4°C, the volume of water increases again with the increase in temperature.
Hence, the water has a maximum density and a minimum volume at 4°C. Also, on cooling from 4°C to 0°C, the volume of water increases instead of decreasing. This exceptional behavior of water in respect of expansion within the range of 0°C to 4°C is called Anomalous Expansion of Water.
Effects of Anomalous Expansion of Water:
Due to the Anomalous Expansion of Water, fishes, and various living creatures can survive under frozen lakes, rivers, or seas. In cold countries, with the fall in atmospheric temperature, the upper surfaces of lakes, seas, and various ponds gradually cool. The water on the upper surface, then being denser and heavier moves down. Water below it being comparatively warmer and lighter moves up. This convection process in water continues until the density of the water in the lower part becomes maximum. The temperature of the upper surface decreases further below 4°C.