What is regelation?
Why is it observed?

Explanation

i. The phenomenon in which the ice converts to liquid due to applied pressure and then re- converts to ice once the pressure is removed is called regelation.
ii. a. Due to applied pressure, melting point of ice is lowered below `0^(@)C`.
b. As a result, ice gets converted into water at ` 0^(@) C`.
c. When the applied pressure is removed, the melting point is restored to `0^(@)C` and water gets re-converted into ice.