Regelation and Pressure Melting

The phenomenon described—where ice melts under pressure and then refreezes once the pressure is removed—is called Regelation.

The Mechanism of Regelation

Pressure Melting: Water is one of the few substances that expands upon freezing, meaning its solid phase (ice) is less dense than its liquid phase (water). According to thermodynamics (the Clausius-Clapeyron relation), for substances that contract on melting (like ice), an increase in pressure lowers the melting point.
The Wire's Action: When a thin wire with weights attached is placed over a block of ice, the high pressure exerted by the wire on the ice surface directly beneath it causes the ice to melt locally, forming a thin layer of water.
Refreezing: The wire then sinks into the water layer. Once the wire has passed, the pressure on the water immediately above the wire is released. Since the melting point returns to normal (above the ambient temperature of the ice), the water immediately refreezes, leaving the block of ice intact without a split.

This process is responsible for the movement of glaciers and is essential for the formation of snowballs.

The other options describe phase changes: **Condensation** (gas to liquid), **Fusion** (solid to liquid, or melting), and **Sublimation** (solid to gas).

The phenomenon is specifically known as Regelation.

Physics Set 3

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