Regelation - the melting of ice under pressure and its refreezing when the pressure is relieved. If two blocks of ice are squeezed together, their contacting surfaces will melt, for pressure lowers the melting point of ice. When the pressure is removed, the melting point rises back to normal and the water between the two blocks freezes.
The melting of ice under pressure makes skating possible. Ice melts under skates and forms a film of water on which the skater slides. In extremely cold weather, when the weight of the skater is not enough to melt the ice, skating is impossible.
Snowballs are formed by the regelation of particles of snow. Regelation explains why glaciers flow like rivers.
