Coordinate: firn area, firn field

[pbuttigieg]

Term	Def	Source
Firn area	The zone of the glacier where the summer surface is underlain by firn instead of glacier ice. Changes in extent of the firn area, and thickness of the firn, complicate mass-balance calculations by the geodetic method since Sorge's law no longer applies. The firn area is not the same as the accumulation zone.	Cogley et al. IACS-UNESCO Glacier Mass Balance 2011
Firn field	1.An area of firn that is not part of a glacier. 2.Same as accumulation area.	AMS - glossary of meteorology

[Garybc]

Interesting phrase in ENVO definition " metamorphic transition" - different pressure and temperature condition from which the snow (?)/top layer? was formed.