Pressure melting point

The pressure melting point is nearly a constant 0 °C at pressures above the triple point at 611.7 Pa, where water can exist in only the solid or liquid phases, through atmospheric pressure (100 kPa) until about 10 MPa.

[1] Glaciers are subject to geothermal heat flux from below and atmospheric warming or cooling from above.

As the pressure increases with depth in a glacier from the weight of the ice above, the pressure melting point of ice decreases within bounds, as shown in the diagram.

[2] In static equilibrium conditions, this would be the highest level where water can exist in a glacier.

It would also be the level of the base of an ice shelf, or the ice-water interface of a subglacial lake.

In this log-lin pressure-temperature phase diagram of water , the pressure melting point for a given pressure lies along the black line rising from the solid/liquid/vapour triple point along the 0 °C vertical line.