The specific enthalpy difference between two phases of a substance at the same temperature. The latent heat of vaporization is the water vapor specific enthalpy minus the liquid water specific enthalp
y. When the temperature of a system of dry air and water vapor is lowered to the dewpoint and water vapor condenses, the enthalpy released by the vapor heats the air-vapor-liquid system, reducing or eliminating the rate of temperature reduction. Similarly, when liquid water evaporates, the system must provide enthalpy to the vapor by cooling. The latent heat of fusion is the specific enthalpy of water minus that of ice and the latent heat of sublimation is the specific enthalpy of water vapor minus that of ice. The latent heats of vaporization, fusion, and sublimation of water at 0C are, respectively, L_v = 2.501 * 10^6 J/kg L_f = 3.337 * 10^5 J/kg L_s = 2.834 * 10^6 J/kg It is common to see an expression like "release of latent heat." In other thermodynamic terms in this glossary, such expressions are avoided in favor of others using enthalpy and temperature, which are measurable quantities.
A polynya that forms from strong winds in a persistent direction that push the ice away from a barrier (the coast, fast ice, a grounded iceberg, or an ice shelf).
Lateral moraines are piles of loose unsorted rocks along the side margins of the glacier. The rocks may be pushed there by the moving ice or dumped from the glacier's rounded surface. As glaciers melt
, their remaining load of rocks is distributed in several ways. Rocks may be dropped in place by the melting ice; they may be rolled to the ice margins, or they may be deposited by meltwater streams. Collectively, these deposits are called 'glacial drift'. 'Till' refers to the debris deposited directly by the glacier. Rock debris rolls off the glacier edges and builds piles of loose unconsolidated rocks called 'glacier moraine'. 'Lateral moraines' form along the side of a glacier and curl into a 'terminal moraine' at the glacier's downvalley end. Drift and moraines are valuable to geologists because they outline the boundaries of past glaciations.
A sediment ridge, located on a glacier's surface adjacent to the valley walls, extending down glacier to the terminus. It forms by the accumulation of rock material falling onto the glacier from the v
alley wall, rather than by water deposition. Debris deposited along the side of a glacier, comprising both rockfall debris from above and debris ground up by ice-marginal processes.