Usually only a small section of the pipe actually freezes but once it does, no water can flow. Water expands as it freezes (10% in volume); the expansion starts by increasing in length along the pipe. If the freezing zone is small and the length of the pipe is straight and long, the likelihood of bursting is small. If the pipe has bends in it, the ice that forms is less likely to expand away from the cold zone. In this instance, a section of water in the pipe can become trapped. When this trapped water starts to freeze the pressure in that section increases; once the pressure gets too high the pipe will split open(burst). It is important to know that although the pipe has burst at this time, there will not be any water leakage until the pipe actually thaws out and the water starts to flow again.