Regelation in Physics:
Regelation is defined as the melting of ice under the application of pressure and resolidification of the molten ice on withdrawal of the pressure.
When two pieces of ice at 0°C are pressed together, the melting point at the surfaces in contact falls below 0°C. But the temperature of ice remains 0°C, So ice melts at the junction. As the necessary latent heat is drawn from the ice itself, the temperature of the contact surface and of the molten ice falls below 0°C.
On the release of pressure, the melting point rises to 0°C again. Water at the surface of contact, being at a temperature lower than 0°C, freezes and the two pieces stick together to form a single piece of ice. This process of resolidification of water into ice is known as regelation.