Explaining and exploiting a winter worry
Every spring, farmers in frigid climes reap an irksome harvest of rocks in their fields. Driven up by ice and water, once-buried boulders emerge during winter with enough force to crack roads and foundations, dismaying engineers and homeowners as well.
Though researchers have proposed many theories to explain this "frost heave," the mechanism has remained unclear. Now, a physicist has come up with seven brief equations that strongly support one explanation, suggesting ways to both limit the damage and harness the underlying force.
Every frozen substance has a thin coating of melted liquid, even when the surrounding temperature is below its melting point, notes J. Gregory Dash of the University of Washington in Seattle. His calculations, described in the Dec. 22 SCIENCE, indicate that when one part of an ice chunk is colder than another, the temperature difference sets up a suction, drawing the liquid toward the colder region.
If the ice lies within a wet, spongy environment such as soil, the suction pulls in outlying liquid as well. If the ice also lies under a rock, the drawn-in water takes up enough space that it forces the rock upward to make room, Dash calculates.
The new equations apply to any …