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Definition:
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The spatially averaged altitude of the equilibrium line. The ELA may be determined by direct visual observation, but is generally determined, in the context of mass-balance measurements, by fitting a curve to data representing surface mass balance as a function of altitude (see mass-balance profile). This is often an idealization, because the equilibrium line tends to span a range of altitudes. Many approximations of the ELA have been suggested; the glaciation level and the mid-range altitude are examples. The ELA is understood to be the Annual ELA unless it is qualified as the transient ELA.
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