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
The degree Celsius is the unit of temperature on the Celsius scale (originally known as the centigrade scale outside Sweden), one of two temperature scales used in the International System of Units (SI), the other being the Kelvin scale. The ...
at pressures above the
triple point
In thermodynamics, the triple point of a substance is the temperature and pressure at which the three phases (gas, liquid, and solid) of that substance coexist in thermodynamic equilibrium.. It is that temperature and pressure at which the subli ...
at 611.7
Pa, where water can exist in only the solid or liquid phases, 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 (; ) is a persistent body of dense ice that is constantly moving under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires distinguishing features, such as ...
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. It would also be the level of the base of an
ice shelf, or the ice-water interface of a
subglacial lake.
[
]
References
Glaciology
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