DEFINICIONES DE GLACIAR

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Referencias recopiladas por Andrés Rivera

Glacier: A mass of ice that originates on land, usually having an area larger than one tenth of a square kilometer; many believe that a glacier must show some type of movement; others believe that a glacier can show evidence of past or present movement.

“Se llama glaciar o ventisquero o aun Helero (las tres palabras son sinónimas y, desde 1935, aceptadas por la Academia Española), toda masa de hielo perenne, formada por acumulación de nieve, cualquiera sean sus dimensiones y su forma. Cuando el glaciar adquiere cierto espesor, fluye bajo su propio peso hacia las alturas inferiores”.

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Considerando lo señalado por Post and others, (1971), esta definición se complica porque: 
1. Incluso la nieve invernal o estacional muestra propiedades de flujo 
2. Pueden existir masas de hielo perenne de dimensiones importantes, pero que no evidencian propiedades de flujo 
3. Glaciares anteriormente activos pueden estancarse y cesan de mostrar evidencias de flujo 
4. Acumulaciones de hielo perenne alimentado por avalanchas desde glaciares activos colgantes, frecuentemente muestran poco movimiento. 

An extensive body of land ice which exhibits evidence of down slope movement under the influence of gravity and which forms from the recrystallization of firn.

A glacier is defined as an aggregated snow and ice body located on land and which continuously flows down slope by gravity.

Glacier is any large mass of perennial ice that originates on land by the recrystallization of snow or other forms of solid precipitation and that shows evidence of past or present flow. A glacier occupying an extensive tract of relatively level land and exhibiting flow from the centre outward is commonly called an ice sheet.

A large mass of ice resting on or adjacent to a land surface, and typically showing movement.

A mass of ice and snow which deforms and flows under its own weight if sufficiently thick.

A glacier is a collection of contiguous complete flow lines through snow and ice that persists on the Earth’s surface for more than one year.

A mass of land ice which flows downhill under gravity (through internal deformation and/or sliding at the base) and is constrained by internal  stress and friction at the base and sides. A glacier is maintained by accumulation of snow at high altitudes, balanced by melting at low altitudes or discharge into the sea.

They have decided upon the following definition of a “glacier” for the purposes of GLIMS. Note that the definition is tailored to remote sensing, and thus does not involve motion of ice.

A glacier consists of a body of ice and snow that is observed at the end of the melt season, or, in the case of tropical glaciers, after transient snow melts. This includes, at a minimum, all tributaries and connected feeders that contribute ice to the main glacier, plus all debris covered ice. Excluded is all exposed ground, including nunataks. An ice shelf ice downstream of the grounding zone of two or more glaciers that is floating on ocean water shall be considered as a separate glacier.

The following consequences and observations must be kept in mind:

1. Ice fields above the bergschrund (Rimaya en español) that are connected to the glacier shall be considered part of the glacier, because they contribute snow (through avalanches) and ice (through creep flow) to the glacier.

2. A tributary in a glacier system that has historically been treated (and named) as a separate glacier should, within the GLIMS framework, be included as part of the glacier into which it flows. The name field for the glacier should be populated with all relevant names of tributaries.

3. Any steep rock walls that avalanche snow onto a glacier but do not retain snow themselves are NOT included as part of the glacier.

4. A stagnant ice mass still in contact with a glacier is part of the glacier, even if it supports an old growth forest.

5. If no flow takes place between separate parts of a continuous ice mass, they should, in general, be treated as separate units, separated at the topographic divide. 

6. All debris covered parts of the glacier must be included.

7. It is possible that an ice body that is detached from another may still contribute mass to the latter through ice avalanches, or it may no longer do so. It is practically impossible to tell which is the case from a single satellite image. Therefore, within GLIMS, adjacent but detached ice areas should, in general, be considered as different “glaciers”, regardless of whether they contribute mass to the main glacier through snow or ice avalanches. However, at the analyst's discretion, detached ice masses may be included as parts of one glacier. This is similar to the situation described in 5 above. If the pieces are analyzed separately later, each piece should be given a new GLIMS ID, the old one being used as the “parent ice mass” ID for all the pieces.

8. What about the lower parts of lateral snowfields, whose extent varies from year to year? Map only at the end of the ablation period, preferably in a year without snow outside of the glaciers, to exclude seasonal snow. Then map everything that is connected to the glacier. If snowfields are identifiable, they should be disconnected from the main glacier. For hydrological purposes they can be included in the GLIMS Glacier Database under a separate GLIMS glacier ID, but they must be marked as a snowfield. Lateral glacier outlines that might be hidden by seasonal snow or by avalanches should be labelled as preliminary, or even the entire glacier can be excluded. Ice avalanche cones below a glacier terminus (dry calving) are not a part of the glacier.

Jeffrey S. Kargel of the University of Arizona Department of Hydrology and Water Resources. Suggested the following definition within GLIMS: 

A surficial, perennial mass of snow and ice with a minimum area of 1 km², incorporating any amount of rock debris, air, and water, which exhibits strong morphological evidence of flow under the force of gravity. 

Jeff added: This definition does not indicate anything about minimum glacier size, and it would include rock glaciers.  I am struggling a bit with this definition as regards flowing lowland permafrost or gelifluction lobes of types that probably none of us would feel comfortable calling a glacier.  My guess is that there is a full continuum of landforms produced by multiple discrete processes occurring in different ratios, and some of them all of us would call glaciers, some (like lobes of slowly deforming lowland permafrost) none of us would call glaciers, and some (like rock glaciers) we would have differences of opinion.  I don't think any one definition is going to satisfy everybody. 

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