When two ice pieces are pressed together the pressure between the ice blocks increases. We know that as the pressure increases, the melting point decreases. Therefore the ice at the joint melts and forms water. When the pressure is released the melting point increases and the water layer solidifies and unites the two pieces into a single piece. This is called regelation. Regelation is the phenomenon of melting under pressure and freezing again when the pressure is reduced. Many sources state that regelation can be demonstrated by looping a fine wire around a block of ice, with a heavy weight attached to it. For most substances, increasing the pressure when a system is in equilibrium between liquid and solid phases will increase the phase transition temperature. Water is one of a few special substances for which the pressure lowers the temperature of transition. The basic reason is that water actually expands when it goes from the liquid to solid phase.