# Regelation

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## What is Regelation?

Regelation is a phenomenon in which the freezing point of water is lowered by the application of pressure. Regelation is defined as the phenomenon in which at below 0°C temperature, on the application of pressure the ice melts to water and on the removal of pressure refreezes back to ice. It is demonstrated by the process of compressing the ice under pressure and turning it into the water, and when the pressure is removed it solidifies again. That's why the refreezing of water derived from the melting of ice under pressure when the pressure is relieved. Meaning that as a liquid changes into solid when heat and pressure are released, freezing is almost always an exothermic process. Glaciers act as a source of a river due to regelation.

### Examples of Regelation

Here are a few examples:

1. Glaciers act as a source of the river due to regelation. The mass of the glacier exerts pressure on the lower surface, which lowers the melting point of the ice at its base. This results in the melting of ice and propels the glacier to slide over the liquid. Under appropriate conditions, liquid water flows from the base of the glacier to lower altitudes when the temperature of the air is above the freezing point of water.

2. Preparation of an ice ball: The ice slab is shredded into pieces and the shredded pieces are pressurized around the tip of a stick to prepare the ice ball. If two small pieces of ice are taken and pressed against each other, they stick to each other.

3. Glaciers act as a source of a river due to regelation.

4. Skating is possible on snow due to the formation of water only for the regelation. Water is formed due to the increase of pressure and it serves as a lubricant.

### Regelation of Ice

Using a metallic wire by performing an experiment on an ice slab the regelation of ice can be better understood. The procedure of the experiment is as follows:

1. Take a slab of ice.

2. Take a wire and fix two blocks, say 5 kg each, at its ends.

3. Put the wire over the slab.

4. If you observe, you can see that the wire passes through the ice slab.

5. Due to the fact that just below the wire, ice melts at a lower temperature, this happens due to an increase in pressure.

6. Water above the wire freezes again when the wire has passed.

7. Thus the wire passes through the slab and the slab doesn't split. This process of refreezing is called regelation.

Here, the melting point of the ice becomes lower than 0°C due to the applied pressure. This implies that at 0°C ice is converted into water and as soon as the pressure is removed the melting point is restored back to 0°C and the water is converted back to ice again.

Skating is possible on snow due to the formation of water only for the regelation. Water is formed due to the increase of pressure and it serves as a lubricant.

### Fun Facts

1. Microscopy, Astrid Döppenschmitt, and Hans-Jürgen Butt, (These all are research works) measured the thickness of the liquid-like layer on ice using atomic force which is roughly 32 nm at −1°C, and 11 nm at −10°C, in 1998.

2. For normal crystalline ice, its melting point is far below,  there will be some relaxation of the atoms near the surface. Near its melting point, the simulations of ice show that there is significant melting of the surface layers rather than a symmetric relaxation of atom positions. Evidence for a liquid layer on the surface of ice is being provided by Nuclear magnetic resonance.

3. The surface melting can account for the low coefficient of friction of ice, as experienced by skaters, ease of compaction of ice, high adhesion of ice surfaces.

4. A glacier can exert a sufficient amount of pressure on its lower surface to lower the melting point of its ice. It allows it to move from a higher elevation to a lower elevation with the melting of the ice at the glacier's base. at lower elevations when the temperature of the air is above the freezing point of water the Liquid water may flow from the base of a glacier.

5. Glaciers act as a source of a river due to regelation.