new classes: firn / firn-ice transition / névé-firn transition / related terms

[kaiiam]

Hey @pbuttigieg let us also revise our definition of firn. Currently we have:

Ice which is an intermediate between snow and glacial ice and which is formed by the compaction and recrystalisation of snow melted from névé.

Your concerns with this were:

This definition isn't clear on what firn actually is. The definitions need to focus on the properties of the material rather than what it derives from or how long it's been around. Assume you have a mass of some material presented to you with no information on where it came from or how old it is. All you can use are its qualities to determine what it is.

The definition from Encyclopedia of Snow, Ice and Glaciers, google book version is:

Compacted snow that has survived at least one melt season in a temperate glacier, or in a Polar Region compacted snow that underlies fresh snow, if any, and has undergone some metamorphism.

We could define firn as:

Compact, densely packed granular snow containing interconnected gaseous pores, which underlies fresh snow and has undergone some metamorphic transition from névé.
We could add as a note:

Thus we also need to add the term: firn-ice transition

A material transformation process in which firn transitions to water-ice.

And we could possible add the term névé-firn transition

A material transformation process in which névé transitions to firn.

Thus we also need more terms:
nivation wiki:

A material transformation process occurring due to a mass wasting process or by cycles of freezing and thawing in which fresh snow is compacted into firn or névé, which occurs in a snow patch.

snow patch wiki

A site of snow and firn accumulation, residing upon a material surface for prolonged time interval.

possible subclasses of snow patch:

seasonal snow patch:

A snow patch which undergoes melting during the late summer.

perennial snow patch

A snow patch which persists for at least two consecutive years.

[pbuttigieg]

firn

Compact, densely packed granular snow containing interconnected gaseous pores, which underlies fresh snow and has undergone some metamorphic transition from névé.

This is better, focused more on the material's attributes. "Metamorphic" transition needs to be more clear. So firn =

Granular snow which contains a proportion of fused granules formed through melting and re-thawing while being compacted by the weight of overlying material and which contains interconnected gaseous pores.

I removed fresh snow because, as your nivation def suggests, the compaction may be caused by multiple masses.

You can move this part to a comment:

and has undergone some metamorphic transition from névé.

névé-firn-ice transitions

Thus we also need to add the term: firn-ice transition
A material transformation process in which firn transitions to water-ice.

I agree, this should be added, but the actual mechanics of the process should be described in more detail. Something discussing the full fusing of granules into a continuous matrix of ice. @kaiiam mentioned polycrystalline --> porous mass

And we could possible add the term névé-firn transition
A material transformation process in which névé transitions to firn.

As above, focus on the changes to the properties of the material.

nivation:
A material transformation process occurring due to a mass wasting process or by cycles of freezing and thawing in which fresh snow is compacted into firn or névé, which occurs in a snow patch.

This is interesting as it reveals multiple paths to firn and névé which we can link to mass wasting and use to generalise the def. Again, a good example why focusing on the physical properties is more stable than the formation processes at times.

Also, is the snow patch needed here? I think it's clear that snow must be present to be compacted.

snow patch

snow patch
A site of snow and firn accumulation, residing upon a material surface for prolonged time interval.

This sounds iffy: I'm sure some would not expect or require firn in a snow patches, just because of the label. You can expand this to be unambiguous and say accumulation of snow, névé, and firn with a broad synonym snow patch.

Also, the 'prolonged' interval is problematic. What is this time? It may be better to focus on what happens within this time pocket, i.e. compaction/melt/refreezing.

possible subclasses of snow patch:

seasonal snow patch:
A snow patch which undergoes melting during the late summer.

So the lifetime of this snow patch ends in the warm season right? We could generalise this by some rephrasing here: "A snow patch which forms during ... and melts away during ..."

perennial snow patch

A snow patch which persists for at least two consecutive years.

I dislike these because of arbitrary time intervals, however, if this is a stable community definition (e.g. like climate being tropospheric weather integrated over ~30 years), then we can go with it.

[kaiiam]

Hey @pbuttigieg thanks for your quick response,

I've added/updated several terms to my envo fork pull request pending.

I updated firn, as discussed here

névé-firn-ice transitions

perhaps we can define firn-ice transition as:

A material transformation process in which firn a packed granular snow material containing interconnected porous, gaseous spaces, transitions to a polycrystalline solid ice containing individual gas bubbles.

Perhaps we define névé-firn transition def as:

A material process in which névé snow has been sufficiently compressed forcing individual ice crystals to bind together and force out trapped gaseous pockets, resulting in the transition to firn ice.

I've added nivation with the following definition:

A material transformation process occurring due to a mass wasting process, or by cycles of freezing and thawing in which fresh snow is compacted into firn or névé.

editors note: Link to mass wasting process.

snow patch terms:

Any thoughts on these terms?

snow patch
I'm a little unclear on your comment are you saying that there should be a class like snow accumulation,

def = An accumulation of snow, névé, and or firn.

which would have has a broad synonym snow patch?

Finally what about these terms:

seasonal snow patch

A snow patch which forms during the cold winter season and melts away during the warmer spring or summer seasons.

perennial snow patch

A snow patch which persists within a longer temporal scale then a seasonal snow patch.

Are these definitions better?

[pbuttigieg]

névé-firn-ice transitions

perhaps we can define firn-ice transition as:

A material transformation process in which firn a packed granular snow material containing interconnected porous, gaseous spaces, transitions to a polycrystalline solid ice containing individual gas bubbles.

Tweaks:

A material transformation process during which the granules constituting firn, and their interstitial gases, transition into a polycrystalline solid ice with trapped gas bubbles.

Can we say why this happens? That is, is it always due to (partial melting)-refreezing-compaction?

We've previously imported granular from PATO, please use that in your axioms. Also, please add an issue to the PATO repo requesting polycrystalline configuration as a new class somewhere near crystal configuration. We can then use it to create crystallite in the material branch (as a defined class) and add+axiomatise polycrystalline ice.

Perhaps we define névé-firn transition def as:

A material process in which névé snow has been sufficiently compressed forcing individual ice crystals to bind together and force out trapped gaseous pockets, resulting in the transition to firn ice.

Try:

A material transformation process during which the ice crystals constituting névé are compressed into granules and some interstitial gas is forced out, resulting in the formation of firn.

Avoid terms like "sufficiently" if possible - try to identify the criteria for sufficiency instead.

Was it not compression and partial melting and refreezing?
Also: is firm really considered "ice" yet / névé still considered snow? Not sure if there's a definitive answer there, perhaps we should add a comment saying this is a fuzzy boundary.

I've added nivation with the following definition:

A material transformation process occurring due to a mass wasting process, or by cycles of freezing and thawing in which fresh snow is compacted into firn or névé.
editors note: Link to mass wasting process.

Some rephrasing:

A material transformation process during which compaction or cycles of freezing and thawing result in the fusing of ice crystals and expulsion of interstitial gases in fresh snow, forming névé or firn.

The link to mass wasting isn't wrong, but it may be too specific - one doesn't need a mass wasting process to cause compression (anything with mass, such as research and logistics vehicles, can do the same). We can create a subclass mass wasting induced nivation if needed.

Do we have something like compaction process?

snow patch terms:

snow patch
I'm a little unclear on your comment are you saying that there should be a class like snow accumulation,

def = An accumulation of snow, névé, and or firn.
which would have has a broad synonym snow patch?

Of snow patches, I noted:

You can expand this to be unambiguous and say accumulation of snow, névé, and firn with a broad synonym snow patch.

I was suggesting the class label should be accumulation of snow, névé, and firn rather than snow patch. On reflection, however, as firn and névé are typically considered subclasses of snow, we can stick to the snow patch label with the definition An accumulation of freshly fallen, powdery snow, névé, and/or firn. The 'and/or` bit is necessary, as some snow patches may not have all three.

Investigate some writings on metamorphosis so we get the terminology right and mention the key processes. "Sintering" should be in there as should "snowpack".

seasonal snow patch

A snow patch which forms during the cold winter season and melts away during the warmer spring or summer seasons.

perennial snow patch

A snow patch which persists within a longer temporal scale then a seasonal snow patch.
Are these definitions better?

Yes, minor tweaks:

seasonal snow patch =def. A snow patch which forms during a season of cold weather and melts away during the warmer seasons.

`perennial snow patch =def. A snow patch which persists across one or more seasonal cycles.`

Note that there's some debate on how to do this best - both are just snow patches. When we axiomatise, we should created a class seasonal melting process and assert that the seasonal snow patch participates in this while the perennial snow patch does not. Good chance to get #253 done too.

[pbuttigieg]

PS: This section on Wikipedia has some interesting avalanche terms to help with mass wasting processes relevant to compaction in snowy regions. Snow drift etc are also good classes to have:

There are four main mechanisms for movement of deposited snow: drifting of unsintered snow, avalanches of accumulated snow on steep slopes, snowmelt during thaw conditions, and the movement of glaciers after snow has persisted for multiple years and metamorphosed into glacier ice.

[kaiiam]

@pbuttigieg snow patch and metamorphosis concerns to be addressed in #487