This column is provided as a public service by the Geophysical Institute, University of Alaska Fairbanks, in cooperation with the UAF research community. T. Neil Davis is a seismologist at the institute. One of the quirks of fate is that frozen water pipes typically burst at locations where freezing last occurs. Thus an insulated portion of an otherwise poorly insulated pipe is likely to be the place where the pipe breaks. As everyone knows, the freezing of water causes the material to expand.
Ice occupies a greater volume than does the water it formed from.
While the expansion of water as it freezes is the underlying cause of bursting pipes and bent buckets, the actual deformation or breakage of the water container results from a secondary consequence of the expansion, namely hydraulic pressure in that part of the water last to freeze . A series of experiments described by John Houk in the Summer 1974 issue of the Northern Engineer illustrates the role of hydraulic pressure rather well. A water-filled metal bucket set on a block of styrofoam ends up with a bulged bottom created by the hydraulic pressure in the last water to freeze, in this case, at the bottom of the bucket. Yet if the styrofoam is placed on the top of the bucket, no bulging occurs because the last water to freeze is near the top surface where there is no metal to be bent. In other experiments, Mr. Houk wrapped insulation around short sections of otherwise exposed pipe filled with water.