Uudelleenjähmettyminen

Uudelleenjähmettyminen, also known as regelation in English, is a phenomenon observed in ice. It occurs when ice is subjected to pressure, causing it to temporarily melt at a lower temperature than its normal freezing point. When the pressure is removed, the water refreezes. This process is crucial for phenomena like ice skating, where the pressure of the skate blades on the ice causes a thin layer of water, reducing friction and allowing smooth gliding.

The scientific explanation for uudelleenjähmettyminen lies in the thermodynamic properties of ice. At standard atmospheric pressure, ice melts at 0 degrees Celsius. However, under increased pressure, the melting point of ice decreases. This is because the solid phase (ice) is less dense than the liquid phase (water). Increasing pressure favors the denser phase, which is water, thus lowering the temperature at which melting can occur.

When the pressure is relieved, the water's melting point rises back to 0 degrees Celsius. If the surrounding temperature is at or below 0 degrees Celsius, the water will rapidly refreeze. This cycle of melting under pressure and refreezing when pressure is removed is the essence of uudelleenjähmettyminen. While most commonly associated with ice, the principle can apply to other substances with similar solid-liquid density relationships, though it is most evident and practically significant with water ice.