Unpack: "equilibrium line" and "snow line"

[pbuttigieg]

According to our definitions here, EL is a fiat boundary formed by averaging.

However, as @sjskhalsa points out, this is often proxied by the physical SL.

It would be interesting to form a design pattern around these sorts of fiat and material entities...

[Garybc]

What competency Qs do we want to ask of an EL that the improved model might serve? The makeup of the SL in an EL "zone"?

[Garybc]

If we take the Fiat Object from BFO as a starting point we might be saying that GlacierX is an instance of a material object and has a fiat object part (Equilibrium line) such that for all times t, if GlacierX exists at t then there is is a EL and EL is demarcated from the remainder of GlacierX by a two-dimensional continuant fiat boundary.
But it seems to me we want to say more than this. This Equilibrium line is a geographic or location concept with a boundary and it is defined in relation to accumulation and ablation zones. We might say it plays a role of dividing or separating these - The boundary between the ablation area and the accumulation area. We also seem to have to appeal to this idea of "net balance" and "mass-balance" which defines this line on a glacier where the specific net mass balance is zero.
And there is some a physical feature like a snow line associated with it.

[sjskhalsa]

yes, EL is a boundary. SL is used as proxy because it can be detected visually or spectrally. But SL is not the same, and if you get into unpacking it, you have to bring in the concepts like firn line, superimposed ice zone. From Paterson 1981, The Physics of Glaciers:

[Garybc]

SJ, Interesting "unpacked" details. I get the impression that these feature on a feature concepts like EL and SL cannot be adequately dealt with unless we take some time, like season or "end of the summer" qualifier in the diagram, (and perhaps event-actions) into account. So we always have an EL, but where it is changes by seasonal time as does all the other zones that help define it. Do you think we may need to unpack the processes that affect the zones beyond the accumulation and abrasion labels and the sub-types? Gary Berg-Cross

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On Thu, May 10, 2018 at 5:33 AM Siri Jodha S Khalsa < ***@***.***> wrote: yes, EL is a boundary. SL is used as proxy because it can be detected visually or spectrally. But SL is not the same, and if you get into unpacking it, you have to bring in the concepts like firn line, superimposed ice zone. From Paterson 1981, The Physics of Glaciers: [image: fig9 6] <https://user-images.githubusercontent.com/10770264/39863063-d868df9c-5445-11e8-9f83-0d2a70a0da82.gif> — You are receiving this because you commented. Reply to this email directly, view it on GitHub <#3 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AJDIImuw0j7LDfeClKJed18TlJwonmNPks5txAldgaJpZM4R235G> .