Regelation

Regelation is the phenomenon where ice melts into water under pressure and refreezes back into ice when the pressure is removed, even when the temperature is below 0°C.

• When pressure is applied to ice, its melting point decreases below 0°C, causing it to melt into water.
• Once the pressure is removed, the melting point returns to 0°C, and the water refreezes into ice.
• This happens because freezing is an exothermic process, meaning heat is released when a liquid turns into a solid.

1. Glacier Movement: The mass of the glacier exerts pressure on the lower layers, reducing the melting point. This causes melting at the base, allowing the glacier to slide over the melted water. When the pressure decreases, the water refreezes, making glaciers a continuous source of rivers.
2. Formation of Ice Balls: When shredded ice is pressed together, it melts slightly due to pressure. Once the pressure is removed, it refreezes, forming a solid ice ball.
3. Ice Sticking Together: If two small ice pieces are pressed against each other, they stick together. This is because the pressure causes localised melting, and when the pressure is released, the melted water refreezes, bonding the pieces together.
4. Skating on Ice: Skating is possible due to regelation. The pressure of the skate blade melts the ice, creating a thin layer of water that acts as a lubricant, reducing friction and allowing smooth movement.

1. Aim: To demonstrate the phenomenon of regelation, where ice melts under pressure and refreezes when pressure is removed.

2. Requirements: a small ice slab, a thin metallic wire, two identical weights, and a stand.

3. Procedure

• Place a slab of ice on a stand.
• Take a thin metal wire and pass it over the ice slab.
• Attach equal weights to both ends of the wire so that it presses down on the ice.
• Observe the wire gradually cutting through the ice.
• Notice that after the wire passes through, the ice remains unbroken.

Regelation

4. Conclusion

The wire applies pressure on the ice, lowering its melting point, causing it to melt beneath the wire. As the wire moves downward, the pressure is removed, and the water refreezes back into ice, leaving the slab intact. This confirms that regelation allows ice to melt under pressure and refreeze once the pressure is removed.