/ Shrinking glaciers - chamonix area

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pneame 10 Oct 2019

Some interesting aerial comparisons of the Mer de Glace, the Bossons et al and the Glacier d'Argentiere 

https://www.theguardian.com/environment/2019/oct/10/shrinking-glaciers-mont-blanc-from-the-air-100-years-on

Nothing new, really, but sobering nevertheless. I can still vividly recall bopping along the path to the Mer de Glace in the mid-90s, based on my recollection from the mid 70s (and, of course, ignoring the signs) and being shocked as it disappeared.... and suddenly realising that the folks putting signs up may have known a thing or two. 

kathrync 10 Oct 2019
In reply to pneame:

I was there this summer for the first time since 2007 and was horrified by how much everything had receded - Bossons in particular.  I think the most sobering thing is the signs noting the glacier level in previous years on the stairs that go up to the Montenvers bubble.  Standing at the sign that showed the level closest to my last visit (2005, I think) and looking at how far below the glacier is now was very sobering. 

Doug 10 Oct 2019
In reply to kathrync:

I didn't visit Chamonix in summer between 1980 and 2007 & was amazed at the difference. I think it was the changes to the Bossons glacier which most shocked me

jon 10 Oct 2019
In reply to pneame:

That's a pretty neat presentation. Interestingly though, there's not so much difference high up on the mountains - looking at the long rock buttresses that drop down from Tacul and Maudit and also those on Mont Blanc itself, they're very similar in that there's no more rock exposed now than 100 years ago.  This seems to imply that the reservoir of ice is less diminished than we thought...? But surely that can't be so?

ianstevens 10 Oct 2019
In reply to jon:

> That's a pretty neat presentation. Interestingly though, there's not so much difference high up on the mountains - looking at the long rock buttresses that drop down from Tacul and Maudit and also those on Mont Blanc itself, they're very similar in that there's no more rock exposed now than 100 years ago.  This seems to imply that the reservoir of ice is less diminished than we thought...? But surely that can't be so?

Partly you can't tell because of the scale, and partly because most of the changes are going on in the lower elevations. To simplify somewhat, a glacier "in balance" (i.e. neither gaining nor losing mass) can be theoretically split into two halves. An upper, accumulation zone, where mass is primality gained, and a lower ablation zone, where mass is primarily lost. Mass gained in the accumulation area flows downhill to the ablation area, where it is lost. This is of course complicated by seasonality but it averages out over the year so we can discard it for now. 

However ELAs (the imaginary line between the accumulation and ablation zone where mass is neither lost nor gained) are rising with climate change - meaning that ablation areas become bigger than accumulation areas. The accumulation area no longer gains enough mass to feed the ablation area with the same amount ice that is being lost. In terms of the entire glacier, ablation > accumulation and the glacier shrinks. However this is primarily observed where mass is being lost, the ablation zone, in the lower portion of the glacier. So glacier's lose mass, but little visual change occurs in the upper portion of the glacier, which is still gaining mass, primarily via snowfall (remember, accumulation zone) despite the net loss of mass.

Hopefully this makes sense - it's late in the day and I may have explained it badly. TL;DR: most mass loss occurs at lower altitudes, upper altitudes generally don't lose much mass.

(If you have more glaciology questions please ask, for info I have a PhD in it and am more than happy to explain things)

Post edited at 22:09
Toby_W 10 Oct 2019
In reply to pneame:

I was flying over bits of Norway we’d climbed the other day on google maps and was also rather sobered by the large expanses of rock where there was once ice.  I’m sad to say it had more of an impact seeing it somewhere i’d been.

Cheers

Toby

rif 10 Oct 2019
In reply to jon:

I see what you mean in the Bossons photo pair, but there are big differences high up in the other two pairs. What used to be classic snow/ice north faces, climbable in summer, have either shrunk into small icefields connected by goulottes (Argentiere NFs, Jorasses) or disappeared completely (Charmoz). Some small steep glaciers coming off the lower peaks have also shrunk drastically, by thinning as well as snout retreat (e.g. Nantillons and the one that descends from the Rochefort arete). In some cases what was a continuous steep glacier is breaking up into isolated parts that pass mass from upper to lower part only by serac fall, and in some places what was a tributary to a large glacier is becoming uncoupled.  

Incidentally my recollection of summer conditions 50ish years ago is much more like the 1919 photos, which fits with much other evidence about the increasing pace of global warming. 

Rob F

Misha 10 Oct 2019
In reply to ianstevens:

That’s a very clear explanation, thanks. 

Robert Durran 11 Oct 2019
In reply to jon:

> That's a pretty neat presentation. Interestingly though, there's not so much difference high up on the mountains - looking at the long rock buttresses that drop down from Tacul and Maudit and also those on Mont Blanc itself, they're very similar in that there's no more rock exposed now than 100 years ago.  This seems to imply that the reservoir of ice is less diminished than we thought...? But surely that can't be so?

Does that not reflect the fact that raising temperatures 5C from,say -10C to -5C does not result in extra melting, whereas from -2C to 3C does? (I know that is a simplification, but you do need to have temperatures above zero for melting to take place.

rif 11 Oct 2019
In reply to Robert Durran:

Net radiation, even at subzero temperatures, is a substantial part of the surface energy balance. And there's a positive feedback as the ELA rises: more ice is exposed, and glacier ice reflects a lot less solar radiation than snow.

ianstevens 11 Oct 2019
In reply to rif:

> Net radiation, even at subzero temperatures, is a substantial part of the surface energy balance. And there's a positive feedback as the ELA rises: more ice is exposed, and glacier ice reflects a lot less solar radiation than snow.

Yes, but SWR (the main radiative component, all from the sun) isn’t really changing to any noticeable degree. Thermal fluxes, related to air temperature (amongst other things) are so these are more relevant to consider on a glacier scale with regards to CC response. LWR fluxes will also increase - the primary source of this is from the surrounding land radiating heat energy to glacier surfaces. 
 

You’re right that there is some increased SWR receipt associated with retreating snow lines and albedo. FYI dirty snow (which is basically any snow on the surface in the summer) has an albedo of around 0.5, and glacier ice between 0.2-0.5 depending primarily on the amount of debris on it. Also worth noting that debris flux to a laying ice is generally increasing in the alps as retreat exposes unconsolidated sediments on the margins of the glacier, which end up on the surface. This is all really as a result of rising ELAs, occurring predominant from increasing annual average air temps.

Another interesting thing to consider is the role of response time - even if CC stopped this second most alpine glaciers would continue to shrink as they’re out of equilibrium with the current climate - IIRC glaciers in the alps take decades to adjust to mass balance changes.

pneame 11 Oct 2019
In reply to ianstevens:

Great explanation - one thing I've always wondered: you see a lot of "x, y, z glaciers are retreating but a and b are advancing" in the press. I've always assumed that this is a typical lack of understanding as I'd thought that glaciers that suddenly advanced are doing so because the subglacial lubrication (melt water) has increased and the advance will quickly (in glacial terms) be followed by rapid retreat. 

Is this correct?

I'm minded of the huge river(s) that now run down the Mer de Glace before disappearing down a hole. I don't recall seeing these at all in the early 70s and could blithely wander around anywhere on the dry part of the glacier. 

The other huge change was the appearance of a large medial moraine....

1
pneame 11 Oct 2019
In reply to Toby_W:

A visit to Uppsala a couple decades ago brought to my awareness another interesting phenomenon that is happening in Scandinavia - the land is slowly rising as it bounces back from the loss of the glacial ice sheets. There were some viking mounds that used to be pretty close to the sea; the sea is now miles away. 

https://en.wikipedia.org/wiki/Post-glacial_rebound

It's huge in arctic Canada, it would appear!

Post edited at 15:07
Doug 11 Oct 2019
In reply to pneame:

happening in Scotland as well, but more slowly  (meanwhile England is sinking)

ianstevens 12 Oct 2019
In reply to pneame:

Ah yes. This is a little more complex than it first seems, and is more to do with glacier flow processes than changes to mass balance. Firstly, it’s important to distinguish the two - and advance just means the the glacier takes up a greater area, and is not necessarily linked with a change in ice volume. Although it can be. We’ll start off with that situation.

Go back to our glacier above that’s in balance (i.e. ablation = accumulation, with no net change in balance). Mass is transferred from the accumulation to the ablation zone via flow, which is always occurring. Glaciers flow in two ways - by deformation of the ice itself (slow) and by sliding across the bed, which is speed up by meltwater lubrication (faster) - what your thinking of. A good analogy is that of a conveyor belt, moving mass from high to low altitudes where it is respectively gained and lost.


If we increase the accumulation in this system, so that the glacier has a net mass gain, the glacier will eventually get larger, in terms of both area. The terminus (or snout) of the glacier will advance, and the glacier will probably get a bit thicker. This is one way a glacier can advance, and is related to mass gain. This is happening virtually nowhere under the present climate.

Another mechanism glaciers can advance is by a process called surging, which is entirely related to flow rather than to mass balance. This doesn’t happen to all glaciers and we don’t really know why - surge-type glaciers are most common in Svalbard and Alaska/west Canada. What happens with these is that they have two distinct flow states - one of quiescence, or slower flow, and a surge phase with fast flow. Periodicity of these vary between individual glaciers. To pick an example, variegated glacier in Alaska has a quiescence phase of 10-20 yeas, and usually surges for about 6-18 months. Then repeat. The relevance of this to your question is that during a surge, glaciers often advance with regards to the terminus - the area increases and the terminus will move down valley. This is due to the increased flow rate rather than a gain in mass - and is what is commonly occurring in the contemporary climate when advances are referred to.

There are some hypothesised links with water at the bed and surging. Essentially the process of surging is the creation of an unstable system, where in the quiescence phase mass is accumulated at high altitudes on the glacier  in a reservoir. At some point a threshold in the system is crossed, and this ice is rapidly advected down glacier during the surge phase. One hypothesised mechanism is a switch in bed conditions. In Svalbard and Alaska (where surge-type glaciers are common) most glaciers are polythermal, and at high altitudes are  probably cold based with little to no basal meltwater. This means ice in the accumulation zone can only flow via internal deformation (the slow way) and accumulated faster than it is advected to the ablation zone. Once enough ice builds up, thickening the glacier, the pressure at the bed increases allowing water to melt (with enough pressure you can get liquid water at sub zero temperatures). The presence of liquid water at the bed, coupled with the lack of an efficient drainage mechanism* results in a film of water at the bed - ideal sliding lubricant. This increases the speed of the glacier, resulting in a surge, and non-mass gain based advance. There are other surging hypotheses but I’m not up on the literature enough to provide a simple explanation right now.
 

Hopefully, in a long winded way, this answers your question? Maybe an UKC glaciology AMA is needed! 
 

*A lot of glaciers will have an efficient channelised system at the bed for removing water. However this needs water supply over multiple melt seasons to develop - opening subglacial channels is a pressure battle between water and ice deforming down. In the case of the accumulation area of a surge type arctic glacier, there won’t be any form of subglacial channel so water is distributed in a thin film across the entire bed. This is a very inefficient way of removing water from the subglacial system. Coupled with the distributed nature of a thin film of water at the bed, it makes for a very good lubricant to speed up flow.

ianstevens 12 Oct 2019
In reply to pneame:

The surface rivers you describe are common in the ablation zone, and is how water is removed from the ice surface. The flow into holes (moulins, to use the technical term) into the en- and sub- glacial channel networks. These ultimately come out the terminus into the pro-glacial river and into the river in the main Cham valley.

The supra-glacial (surface) channel network is nothing new - they’re ubiquitous in ablation zones. However, with CC ELAs are rising as are ablation zones with regard to their altitude. I’d suspect that in the 70s not a lot of melt was occurring on the bit of the MdG people went on (i.e from the ladders up) whereas now it is (ELAs rising remember). This is visually apparent with a more developed supraglacial network. Anecdotally I’ve noticed this too - and you also get a lot more algae around 2500m in the alps than you did 7/8 years ago when I first started going - which is a sure indicator of increase liquid water availability.

Apologies if there are typos in these, I’m doing it on my phone on a train!

pneame 12 Oct 2019
In reply to ianstevens:

I think my knowledge of glaciology has just jumped 10-fold! Thanks, Ian. 

Previously, my knowledge was based largely on (1) a friend of mine, Dave Collins, who was a glaciologist and (2) a fantastic 2 week trip as an apprentice glaciologist with Dave during which we skied when the weather let us, collected samples (not so often it was onerous) and festered (pretty literally) in the power station tunnels just downstream from the snout of the Gornergletscher. 

https://www.ukclimbing.com/photos/dbpage.php?id=277017

https://www.ukclimbing.com/photos/dbpage.php?id=277018

I presume the increased algae acts as a feedback loop to increase ice melting by reducing its albedo?

Ah, I see "yes" - https://www.frontiersin.org/articles/10.3389/fmicb.2019.00524/full

And I'm very impressed at you typing all that on a phone!

ianstevens 12 Oct 2019
In reply to pneame:

Your more than welcome! Sounds like you had a fun trip back then. Any recollection of what the samples were for?

Good find on that algae paper - one of the good recent ones. In a very timely fashion, Bristol Uni (and others) have recently (yesterday) been awarded a big fat grant to investigate algae on Greenland for the next six years. A big and exciting step for glacial microbiology for sure!

RE: phone typing - it was a long train journey and I’m young enough that I’m a native to writing on a phone  

Post edited at 22:23
philipivan 13 Oct 2019
In reply to pneame:

A friend's site (if anyone is interested in glaciers) 

http://www.antarcticglaciers.org

WVRox 13 Oct 2019
In reply to ianstevens:

A friend in the years just post uni was doing a PHd I Geography/Glaciology - he spent weeks in the summers of ‘82 and ‘83 taking readings and measuring the temperature of the meltwater on the Bossons.......while his mates who had less foresight than him relentlessly took the piss of course! You lot mark my effin words......ahead if his time! Mind, he broke some of his thermometers early on, and the only ones he could find in Cham were in a Boots type shop - they hard 2 marks on the scale ‘baby’s bath is too hot’ and ‘baby’s bath is ready’!

pneame 13 Oct 2019
In reply to philipivan:

> A friend's site (if anyone is interested in glaciers) 

Very comprehensive!

pneame 13 Oct 2019
In reply to ianstevens:

> Sounds like you had a fun trip back then. Any recollection of what the samples were for?

Most of the work on-site was done by what we called "the milking machine" which sampled the outflow from the terminus twice a day. At the end of the trip Dave and I did a run down the gornergletscher where Dave measured the pH and/or conductivity in the upper parts of the glacier. Neither of us were in great shape - Dave had spent the night breathing mould from the roof of the hut we stayed in and was feeling rather nauseous and I pranged on ice as soon as we started skiing, putting my right arm out of action. Many jokes about Napoleon as I wandered around with it tucked into my shirt. 

On the last afternoon we harvested the milking machine - filtering the liter of water from each sample  to obtain samples of glacial sediment and putting samples in little bottles. By far the hardest tasks on the trip was carrying the milking machine back down the moraine in the coldest conditions of the trip. The second hardest task was trying to get suitable for civilization in the toilets at Tasch station. 

Here's one of his papers - https://www.tandfonline.com/doi/abs/10.1080/00040851.1979.12004139

All this, like so much research, would be much, much easier and more comprehensive these days. 


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