[CRYOLIST] When is a glacier no longer a glacier?

Bruce RAUP braup at nsidc.org
Thu Aug 16 08:30:16 PDT 2018


Hi all,

>From the GLIMS (Global Land Ice Measurements from Space) and remote sensing
point of view, I have a different and purely practical approach:  If a body
of ice has been mapped as a glacier (and is, e.g., in the GLIMS Glacier
Database), then as it shrinks, I would track it until it is no longer
identifiable in imagery.  Within our database, it would still be considered
a "glacier", though in reality it might more properly be called
a "remnant".  Examples are the little ice caps on Ellesmere Island at 64.16
W longitude, 81.96 N latitude, for which we have nine outlines spanning 58
years, ranging in area from 7.5 km2 down to 0.09 km2.

People frequently ask questions such as, "When will such-and-such glaciers
be gone?", or "What are examples of glaciers that are now gone?"  These
questions imply a mindset that, at least in this era of warming and rapid
glacier shrinkage, the life cycle of a glacier extends to its
disappearance, not simply to when it stops moving significantly.

Cheers,
Bruce


2018-08-14, 17:35:  Jiskoot, Hester wrote:

> 
> Dear Allen and others,
> 
> 
> When does a glacier cease to be?
> 
>  
> 
> From Principles of Glacier Mechanics (Hooke, 2005):
> 
> “As humans, one way in which we try to organize knowledge and enhance communication is by classifying objects into neat compartments, each with its own label. The
> natural world persistently upsets these schemes by presenting us with particular items that fit neither in one such pigeonhole nor the next, but rather have
> characteristics of both, for continua are the rule rather than the exception. This is as true of glaciers as it is of other natural systems.”
> 
>  
> 
> Yet, to a glacier there may be:
> 
> A minimum thickness limit: Pure ice needs to have a minimum thickness of ~30 m to deform and flow.
> 
> Minimum area limits: <0.1 km2 (USGS, 2018); <0.01 km2 (Pelto, 2008); <0.005 km2 (Huss and Fischer, 2016).
> 
>  
> 
> The book Glacier Ice (Post and LaChapelle, 1971/2000), has a beautifully written paragraph (p. 12) about when a retreating glacier ceases to be one. In summary, a
> glacier needs to have: True glacier ice, some ice flow, and to the geologist some specific geomorphological features.
> 
> 
> Serrano et al. (2011) is about a glacier changing into an ice patch in the Spanish Pyrenees, attempts to quantify the difference between a true glacier and an ice
> patch and provides some good background literature.
> 
>  
> 
> References:
> 
> Hooke, R.L. (2005). Principles of glacier mechanics. Cambridge University Press.
> 
> Huss, M., & Fischer, M. (2016). Sensitivity of very small glaciers in the Swiss Alps to future climate change. Frontiers in Earth Science, 4, 34.
> 
> Pelto, M.S. (2008). Impact of climate change on North Cascade alpine glaciers, and alpine runoff. Northwest Science, 82(1), 65-75.
> 
> Post, A., & LaChapelle, E.R. (2000). Glacier ice. University of Washington Press and the IGS.
> 
> Serrano, E., González‐trueba, J.J., Sanjosé, J.J., & Del Rio, L.M. (2011). Ice patch origin, evolution and dynamics in a temperate high mountain environment: the Jou
> Negro, Picos de Europa (NW Spain). Geografiska Annaler: Series A, Physical Geography, 93(2), 57-70.
> 
> USGS (2018) https://www.usgs.gov/faqs/there-a-size-criterion-a-glacier?qt-news_science_products=0#qt-news_science_products
> 
> 
> Cheers, Hester
> 
> 
> ______________________________________________________________________________________________________________________________________________________________________
> 
> Dr. Hester Jiskoot
> Associate Professor of Physical Geography & Glaciology
> Department of Geography
> University of Lethbridge
> Lethbridge, Alberta, T1K 3M4, Canada
> 
> phone: + 1 403 329 2739
> office: AWESB WE-2050
> email: hester.jiskoot at uleth.ca
> web: http://people.uleth.ca/~hester.jiskoot
> 
> Associate Chief Editor: International Glaciological Society: Journal of Glaciology
> Associate Editor: Journal of Geophysical Research - Earth Surface 
> Fellow: Royal Canadian Geographical Society 
> 
> ______________________________________________________________________________________________________________________________________________________________________
> 
> 
> 
> ______________________________________________________________________________________________________________________________________________________________________
> From: CRYOLIST <cryolist-bounces at lists.cryolist.org> on behalf of Andrew Fountain <andrew at pdx.edu>
> Sent: August 14, 2018 15:51
> To: Allen Pope
> Cc: cryolist
> Subject: Re: [CRYOLIST] When is a glacier no longer a glacier?  
> I have always preferred Mark Meier's definition of a glacier. Simple, straight foward, memorable,
> A glacier is a mass of perennial ice or snow that moves.
> 
> Andrew
> 
> On Tue, Aug 14, 2018 at 2:47 PM, Allen Pope <apope00 at gmail.com> wrote:
>       Dear Cryolist,
> I recently saw this documentary advertised (https://www.notokmovie.com/) about the Icelandic (former) glacier of Okjökull, and it is partly premised on being
> the first glacier in Iceland to lose its formal title of glacier. (We are going to do a screening in north Iceland, too, at the end of next week. You know, if
> you happen to be around Dalvík next Friday night...)
> 
> This documentary uses a definition of size and thickness, and therefore not currently able to flow any more, to be stripped of its title.
> 
> BUT, the Glossary of Glacier Mass Balance and Related Terms defines a glacier as "A perennial mass of ice, and possibly firn and snow, originating on the land
> surface by the recrystallization of snow or other forms of solid precipitation and showing evidence of past or present flow. ", and it would seem that Ok, from
> its patterning, could be argued to show evidence of past flow, I think?
> 
> So - what does Cryolist think? When does a glacier become not a glacier? Are there other examples of this being claimed/stated? Or any literature on this? I
> know this may seem a bit pedantic, but it is a claim that can and has clearly drive some headlines and will be happening increasingly in the future.
> 
> Best,
> Allen
> --
> about.me/allenpope
> twitter.com/PopePolar
> 
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> 
> 
> 
> --
> Andrew G. Fountain
> 
> Department of Geology
> Department of Geography
> 
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> ------------------------                 --------------------------
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>

-- 
Bruce H. RAUP
National Snow and Ice Data Center
University of Colorado
449 UCB,  Boulder, CO 80309
Phone:  303-492-8814
http://cires.colorado.edu/~braup/
GLIMS:  http://www.glims.org


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