Two real mechanisms, honestly compared. A common myth says a skater's weight, concentrated over the narrow blade, presses hard enough to melt the ice by pressure alone. The exact Clausius–Clapeyron relation is computed here:
ΔT_m = T_m·Δv/L_f · ΔP
Δv = v_water − v_ice ≈ −9.05×10⁻⁵ m³/kg
L_f = 334,000 J/kg, T_m = 273.15 K
Even at hundreds of atmospheres of real skate-blade pressure, this shifts the melting point by only hundredths to a few tenths of a degree.
The dominant real effect is frictional flash heating: sliding dissipates power q = μ·P·v at the contact, and because the contact patch is narrow and fast-moving (high Péclet number), a Jaeger-style moving-heat-source estimate ΔT ≈ q/(1.13·k_ice)·√(L_c·α_ice/v) gives a local temperature rise of several degrees — far more than pressure alone. Once the surface reaches the (slightly lowered) local melting point, the leftover heat forms a thin lubricating meltwater film — shown here as the blue band under the blade, exaggerated in thickness for visibility, with a fading trail behind it as it refreezes (faster on colder ice). The illustrative constant mapping excess heat to film thickness is a simplification; the underlying energy balance and the dominance of friction over pressure are the real physics being shown.