The pressure melting point of ice is the temperature at which ice melts at a given pressure. The pressure melting point is nearly a constant 0
°C at pressures above the
triple point
In thermodynamics, the triple point of a substance is the temperature and pressure at which the three Phase (matter), phases (gas, liquid, and solid) of that substance coexist in thermodynamic equilibrium.. It is that temperature and pressure at ...
at 611.7
Pa—where ice, water, and water vapour coexist in equilibrium—through atmospheric pressure (100
kPa) until about 10
MPa. With increasing pressure above 10 MPa, the pressure melting point decreases to a minimum of −21.9 °C at 209.9 MPa. Thereafter, the pressure melting point rises rapidly with pressure, passing back through 0 °C at 632.4 MPa.
Pressure melting point in glaciers
Glaciers
A glacier (; or ) is a persistent body of dense ice, a form of rock, that is constantly moving downhill under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires ...
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. The level where ice can start melting is where the pressure melting point equals the actual temperature.
In static equilibrium conditions, this would be the highest level where water can exist in a
glacier
A glacier (; or ) is a persistent body of dense ice, a form of rock, that is constantly moving downhill under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires ...
. It would also be the level of the base of an
ice shelf, or the ice-water interface of a
subglacial lake.
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References
Glaciology
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