The Collaborative International Dictionary
Regelation \Re`ge*la"tion\ (-l?"sh?n), n. [Pref. re- + L. gelatio a freezing.] (Physics) The act or process of freezing anew, or together,as two pieces of ice.
Note: Two pieces of ice at (or even) 32? Fahrenheit, with
moist surfaces, placed in contact, freeze together to a
rigid mass. This is called regelation.
--Faraday.
Wiktionary
n. The fusion of two pieces of ice by pressure (which lowers its freezing point)
Wikipedia
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. The pressure exerted on the ice slowly melts it locally, permitting the wire to pass through the entire block. The wire's track will refill as soon as pressure is relieved, so the ice block will remain solid even after wire passes completely through. This experiment is possible for ice at −10 °C or cooler, and while essentially valid, the details of the process by which the wire passes through the ice are complex. The phenomenon works best with high thermal conductivity materials such as copper, since latent heat of fusion from the top side needs to be transferred to the lower side to supply latent heat of melting.
If 1 mm diameter wire is used, over an ice cube 50 mm wide, the area the force is exerted on is 50 mm. This is 50×10 m.
Force (in newtons) equals pressure (in pascals) multiplied by area (in square metres).
If at least 500 atm (50 MPa) is required to melt the ice, a force of (50×10 Pa)(50×10 m) = 2500 N is required, a force roughly equal to the weight of 250 kg on Earth.
Regelation was discovered by Michael Faraday. Regelation occurs only for substances, such as ice, that have the property of expanding upon freezing, for the melting points of those substances decrease with increasing external pressure. The melting point of ice falls by 0.0072 °C for each additional atm of pressure applied. For example, a pressure of 500 atmospheres is needed for ice to melt at −4 °C.