Regelation occurs when a material melts under pressure and refreezes when the pressure is reduced. The pressure from the immense weight of a glacier causes liquid water to form, over which the glacier can slide. You can demonstrate regelation on a much smaller scale using an ice cube. Attach heavy weights to each end of a fine wire. Place the wire over a block of ice. The weight of the wire will produce localized melting. Eventually the wire will pass through he ice. The ice won't be cut because the water will refreeze behind the wire as it passes.
More About Regelation | Why Ice Floats