Unpack: Firn line/firn edge/firn limit/equilibrium line

[pbuttigieg]

Lots to unpack and deconvolute here.. @brandonnodnarb to chime in...

[brandonnodnarb]

definitions from Glossary of Geology:

firn (a) Wetted snow that has survived one summer without being transformed into ice. Firn becomes glacier ice when interconnecting air passages between grains are sealed off (Paterson, 1994). The term has also been defined, although rarely, on the basis of certain physical properties, such as density. Syn: névé; firn snow. (b) A geographic term applied to the accumulation area or upper region of a glacier. This usage is being supplanted by firn field, or by névé (in Great Britain). Etymol: German, adjective meaning "old, of last year". Sp: nevero.

firn line Commonly used as a synonym for equilibrium line. This is not preferred, however, as firn from previous years may be exposed in the upper part of the ablation area. The lower boundary of the firn may then be significantly lower in elevation than the equilibrium line. The preferred synonym is firn limit.

firn edge The boundary on a glacier between glacier ice and firn during the ablation season.

firn limit see firn line

equilibrium line A line on a glacier where the specific net balance is zero. The boundary between the ablation area and the accumulation area. At the end of the melt season, snow or superimposed ice from the previous winter persists above the equilibrium line. Below it, there may be bare glacier ice or either firn or superimposed ice, or both, from a preceding balance year. Cf: climatic snowline; snowline; firn line. Less preferred synonym: equilibrium limit.

[charlesvardeman]

One observation. Equilibrium usually implies that there are rates associated with the process and that those (perhaps forward and backwards) rates are balanced.

[Garybc]

I seem to notice that the firn line is not 1 dimensional, It has an upper and lower line and seems to be more of a small zone.

[pbuttigieg]

I seem to notice that the firn line is not 1 dimensional, It has an upper and lower line and seems to be more of a small zone.

@Garybc, yes, perhaps ENVO's tree line ecotone can provide an example of a transitional line. We do have "envrionmental zone" semantics too, to reference immaterial sites where stuff (like transitions) can happen. Looking at the defs above, this seems more appropriate as fiat boundaries appear to be involved.

[Garybc]

Pier,

Thanks for the timely update on this topic. I do like the idea of leveraging a (3D)"zone" concept of which an "environmentl" zone would yield many useful sub-types. We already have "accumulation zone etc." In addition existing vocabularies like firn line (Commonly used as a synonym for equilibrium line.) and firn edge get defined in relation the relevant zone. Following the geometry all zones may have lines and edges. Seems useful as a first approximation to be tested by science cases and attempts to align to other vocabularies.

Gary Berg-Cross Ph.D. Independent Consultant Potomac, MD 240-426-0770

On Mon, Apr 9, 2018 at 6:04 AM, Pier Luigi Buttigieg < notifications@github.com> wrote:

I seem to notice that the firn line is not 1 dimensional, It has an upper and lower line and seems to be more of a small zone.

@Garybc https://github.com/Garybc, yes, perhaps ENVO's tree line http://purl.obolibrary.org/obo/ENVO_01000953 ecotone can provide an example of a transitional line. We do have "envrionmental zone" semantics too, to reference immaterial sites where stuff (like transitions) can happen. Looking at the defs above, this seems more appropriate as fiat boundaries appear to be involved.

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[pbuttigieg]

Following the geometry all zones may have lines and edges. Seems useful as a first approximation

Yes, but I think it's wise to stick to the idea that all lines and edges - unless they are data artifacts - are expanded in 3D if we're concerned with environmental entities. Otherwise it feels like geospatial semantics, which is of course fine, but we should be aware of any switches here.

I'll encode these classes in ENVO for a point of reference for others hacking this...

[Garybc]

Pier et al,

GBC>> Following the geometry all zones may have lines and edges. Seems useful as>>a first approximation

PLB>Yes, but I think it's wise to stick to the idea that all lines and edges - unless they are data artifacts - are expanded in 3D if we're concerned with environmental entities. Otherwise it feels like geospatial semantics, which is of course fine, but we should be aware of any >switches here.

Yes, it may be useful to think of these as slices in a 3D objects....But, (slap me if I am getting too pedantic) there may be a practical issue of granularity here and some widths, say, are so small that a dimension is collapsed. Looking down on a zone we may, at this high level of granularity, use a line construct to say what is in or out of a zone.

Gary Berg-Cross 240-426-0770

On Mon, Apr 9, 2018 at 10:59 AM, Pier Luigi Buttigieg < notifications@github.com> wrote:

Following the geometry all zones may have lines and edges. Seems useful as a first approximation

Yes, but I think it's wise to stick to the idea that all lines and edges - unless they are data artifacts - are expanded in 3D if we're concerned with environmental entities. Otherwise it feels like geospatial semantics, which is of course fine, but we should be aware of any switches here.

I'll encode these classes in ENVO for a point of reference for others hacking this...

[pbuttigieg]

Some attempts in ENVO under the following PURLs (not yet live, still in the editors' version of the ontology, available here, but will be released soon):

http://purl.obolibrary.org/obo/ENVO_01001347 # glacial equlibrium line http://purl.obolibrary.org/obo/ENVO_03000037 # glacial ice ablation zone http://purl.obolibrary.org/obo/ENVO_01001352 # glacial ice accumulation zone

The subclass axioms and synonym lists on these classes capture quite a lot of the above. I've dbxreffed this thread and the geology glossary @brandonnodnarb mentioned in ENVO:01001347.

Hacky screenshot of the immediate neighbourhood looks like this:

There are some redundancies in the axioms, but I'm preserving these until things settle down.