After more than a week of warm days and cold nights, the Colorado Piedmont lakes have been especially noisy. The sharp pops, high-pitched whines and mellow, kettle drum sounds are produced by the surface ice as it contracts, expands and vibrates. As one might expect, the symphony is most pronounced during the morning and evening hours, when the ambient temperature is most rapidly changing.
Anyone who has used ice-cube trays or forgot to retrieve a can of soda from the freezer knows that water expands when it freezes. In fact, it increases in volume by 9%, exerting tremendous pressure on its container. Affected by other factors as well, including currents, water depth, the age of the ice, snow cover and fish activity, lake ice is often in a state of flux, characterized by fractures, compression, scraping, heaving and splintering, among other pressure induced phenomena. The various noises are the result of pressure release, producing a sudden thunder clap or sending more subtle vibrations through the ice sheets. While this "booming" does not necessarily portend danger for those who ski, hunt or fish on the ice, it certainly makes most of us wary, especially after an extended period of mild weather.
In many ways, the physics of lake ice mimics that of plate tectonics. While the latter is driven by the opening and closing of oceans (induced by heat transfer within the mantle), the rearrangement of lake ice occurs in response to the freeze-thaw cycle. In both cases, solidified segments (crust or ice) are subjected to rifting, compression and lateral friction, producing zones of uplift, thinning, faulting and overthrust. And though the process of plate tectonics is far more gradual than the gyrations of lake ice, the periods of pressure augmentation far exceed the brief but dramatic rupture events (booming and earthquakes).
