[GLIMS] Special rock glaciers

Tue May 5 19:18:39 MDT 2020

Frank, thanks. First, before getting to your points, Bruce responded that not many of the parameters that are identified in my PDF are visible and measurable from space. So it;s more of a ground-based view of what rock glaciers are a a glacier context. But now to your points: Yes, more parameters (environmental ones as well as attributes of the rock glaciers) can be defined. I actually think that it doesn't break down in terms of response to climate. It's a matter of ice and debris, their thermophysical properties and supply rate and mass balance (rock throughput and ice thrroughput)...  these are all straight-up responses to climate and changes in climate and any other changes, such as in rock supply (which can be connected to climate). It also has to do with the maturity of the landforms, e.g., whether enough time has elapsed since the feature's origin to attain a dynamic equilibrium-- so there is the glacier response time (and this includes rock glacier response time). Rock glaciers commonly occupy cirques that were glaciated in the Pleistocene or at various points in the Holocene and up to the LIA. Some have not has enough time to grow to be in equilibrium with present climate, so they can still be growing. It;s not thet they obey different thermodynamic laws than "ice glaciers." It;s that there configuration of debris and ice is different, they often rest more in shadows that often-bigger ice glaciers, they get more debris than typical ice glaciers by direct rock falls, they get more avalanche (mixed with rock) nourishment relative to direct snowfall (which typically is zero in terms of direct snow annual mass balance), the importance of freezing rain is sometimes greater relative to ice glaciers, and so on. The various rates are in different balances or dynamic states. But the similarities are that all of these processes are shared by ice glaciers, but in deiffering relative rates, and some are negligible. And some processes, like sublimation, are less for rock glaciers than ice glaciers. So we think of them as being very different. But they just occupy different niches of these parameter diagrams (multidimensional space), but all in a continuum sense. I don;t think anything breaks down. Our patience and agreement can break down. But the same physics and same processes are happening to rock glaciers and ice glaciers. Our image of the differs. Our human time scale relative to the hydrological and climatic timescales differ. Those are human perception issues, not any absolutely profound difference in ice glaciers versus rock glaciers. They are different, just as clean-ice and debris-covered glaciers are different; but physics stays the same. The dominating processes differ. And so there are useful aspects of calling a rock glacier by that name, a debris-cpvered glacier and debris-free glacier by those names, polythermal, temperate, and polar type glacier by those names. And it can be helpful to model them separately, for example, zeroing out some processes (such as annual snow mass balance for rock glaciers, and instead just talk part of the snow melt and percolate it and refreeze it into the rock.  In terms of response to climate, it's just a continuum of the  debris-free to debris covered to rock glacier, and hypsometry ranging from a high-elevation (relative to any classically defined ELA) to entirely-below-ELA (like Crater Glacier).

In other words, there should exist a possibility to reach a Unified Theory of all these landform types. There is nothing spooky about any of it (I am not implying that you said so... you didn't). I like rock glaciers because they exist in a different climatic niche than ice glaciers. But it's still all a geomorphological continuum.

And I agree that there is an extremely useful set of purposes to mark rock glaciers as such. (Same for debris covered and clean ice,,, different purposes can favor filtering that the different names allow

In terms of the troublesome continuum... anybody looking at rock glaciers has observed some that have an icier upper part that resembles a glacier accumulation zone. Usually a very small one, and it is probably in most cases avalanche fed. But otherwise, they look like rock glaciers, and you wouldn't assign an ELA to it normally. But these, I warrant, are a part of the continuum from the endmember idealized perfect rock glacier (which also exist and in no way have anything resembling a snow accumulation zone) and heavily debris covered and avalanche-fed ice glaciers. The differences start to blur, because it is all continuum.  So something that IS satellite observable is the presence or absence of a snow accumulation area if one exists for what otherwise is generally seen as a rock glaciers. There are examples of those. I guess the only actionable aspect of this whole long thing is to stay alert to possible snow accumulation zones on some rock glaciers (and then map them). In some regions they might not exist. But I see them in Alaska. I get the feeing that possibly some of the trans-Atlantic dichotomy in rock glacier treatments is that possibly Alps and western U.S. rock glaciers tend toward slightly different parts of the continuum, with Alps rock glaciers being mainly idealized endmembers tucked in the corners of the diagrams I sent. (I'm guessing.)

My main message is that I like the idea of including rock glaciers in the GLIMS database, as has been done for several years, and we should keep doing that.

Okay, redwood trees... I have to think about that! 😉 Yes, long-growing rock glaciers.

--Jeff

________________________________
From: Frank Paul <frank.paul at geo.uzh.ch>
Sent: Wednesday, May 6, 2020 12:23 AM
To: Jeffrey Kargel <jeffreyskargel at hotmail.com>
Cc: GLIMS Mailing List <glims at nsidc.org>
Subject: Re: [GLIMS] Special rock glaciers

Hi Jeff

Although I agree to disagree (as you know), I like your slides! You can create additional triangles for criteria such as 'temperature', 'ice contents', 'flow velocities', or 'water release' to stay in the picture of a continuum by the range of physical properties. All fine! However, in my opinion things break down when it comes to criteria such as 'response to climate change' (advance/retreat) or mass balance (gain/loss). And this is actually what 'we' currently measure and model. As (active) rock glaciers can only advance and gain mass (i.e. grow over time), they do not fit into currently available schemes to model their response to climate change (or their mass balance). One might even say they are doing the opposite, i.e. advance and gain mass under higher temperatures.

In other words, it is not just an issue of maybe similar physical or geomorphological properties (and being special end-members of a continuum), but it is a simple yes/no thing (e.g. glaciers have an ELA, rock glaciers do not). Hence, to not confuse related computations, there must be a possibility to deselect their polygons in a database. In my opinion they are thus not a special class of mammals (dogs or babies), but belong more to the plants (maybe Redwood Trees that also need hundreds of years to properly grow up? ;)

All the best, Frank

On May 5, 2020, at 11:56 PM, Jeffrey Kargel wrote:

Dear GLIMS folks,
I am not sure whether this attachment will go through to the GLIMS list. I prepared this
to address an issue that has arisen many times in GLIMS discussions over the past 20 years, including at today's GLIMS/RGI virtual meeting. A question was raised "Is a rock glacier a type of glacier?" There are different views, and as of today's meeting it became
much more of an academic point, as it was reconfirmed that rock glaciers will be included
in the GLIMS database. (This is as it has been for quite a few years, but the matter keeps coming up).
This presentation gives my views on the matter, and it also provides a schematic concept
that can be put to use. Maybe not now in the GLIMS database, but whenever the detailed
dynamical characteristics and rock-ice composition of glaciers comes up in research.
Cheers,
Jeff Kargel

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