Support the Arctic Sea Ice Forum and Blog

Author Topic: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland  (Read 821342 times)

werther

  • Grease ice
  • Posts: 727
    • View Profile
  • Liked: 11
  • Likes Given: 0
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1550 on: May 22, 2016, 11:48:38 AM »
Impressive!

Thanks Espen, you are our 'raven eye'.

nukefix

  • Frazil ice
  • Posts: 462
    • View Profile
  • Liked: 9
  • Likes Given: 1
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1551 on: May 22, 2016, 12:35:26 PM »
Wow that pretty much guarantees a new record retreat by the end-of-summer....interesting to see how far the retreat will go and whether it will recover during the winter.

johnm33

  • Nilas ice
  • Posts: 1318
    • View Profile
  • Liked: 109
  • Likes Given: 49
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1552 on: May 22, 2016, 04:28:37 PM »
Wow, thanks Espen,  three days of big tides to go, and at last some serious movement at the other end too http://www.lookr.com/lookout/1310041325-Ilulissat

Wipneus

  • Citizen scientist
  • Young ice
  • Posts: 4025
    • View Profile
    • Arctische Pinguin
  • Liked: 689
  • Likes Given: 0
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1553 on: May 23, 2016, 05:59:52 PM »
2016-05-22, R068 is in. Some parts cloudy, the calving fronts are affected but still visible. Uploaded as S2A_R068_V20160522T151915.22WEB.B04.tiff.
« Last Edit: May 23, 2016, 06:32:29 PM by Wipneus »

Wipneus

  • Citizen scientist
  • Young ice
  • Posts: 4025
    • View Profile
    • Arctische Pinguin
  • Liked: 689
  • Likes Given: 0
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1554 on: May 23, 2016, 06:22:02 PM »
R068 (relative orbit nr 68) has no recent cloud free samples, to make perfect animations with.

Melting is literary everywhere. Here is a detail of the elbow in natural color. 

notjonathon

  • New ice
  • Posts: 47
    • View Profile
  • Liked: 0
  • Likes Given: 0
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1555 on: May 24, 2016, 01:01:39 AM »
Wipneus--

Do you know where all this melt water is going? Will it refreeze in place, drain through the ice or carve channels to flow downhill? In some of the earlier pics, we do see water draining from higher ponds to lower ones, but do any of these make their way to the sea?

Wipneus

  • Citizen scientist
  • Young ice
  • Posts: 4025
    • View Profile
    • Arctische Pinguin
  • Liked: 689
  • Likes Given: 0
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1556 on: May 24, 2016, 09:00:36 AM »
Wipneus--

Do you know where all this melt water is going? Will it refreeze in place, drain through the ice or carve channels to flow downhill? In some of the earlier pics, we do see water draining from higher ponds to lower ones, but do any of these make their way to the sea?

I am hardly the one to ask this, but my understanding is that all of this happens, including refreezing at the end of the season.  Melt pond draining will leads to liquid water between the ice and the bedrock, then act as a lubricant speeding up the glacier.

Attached a detail, chosen at random: it is all over the image, showing the "explosion" of melting that happened in a weeks time.

Laurent

  • Young ice
  • Posts: 2536
    • View Profile
  • Liked: 6
  • Likes Given: 26
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1557 on: May 24, 2016, 10:36:32 AM »
I don't know the answer either but I think we are at a point where the melting goes to the sea straight (or following the pleats that are on the edge of Greenland, that does not appear on this picture but you can see the lines the melt ponds follow) or taking a much longer course goes in the inner Greenland before exiting through Jakobshavn (for this part). The arrow is where I think the melting front of Jakobshavn is (in the middle of the two lines).
« Last Edit: May 24, 2016, 10:44:12 AM by Laurent »

oren

  • Young ice
  • Posts: 4710
    • View Profile
  • Liked: 1041
  • Likes Given: 1343
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1558 on: May 24, 2016, 12:24:44 PM »
It seems all these melt lakes came a bit early this year, but I have no data to back this up

oren

  • Young ice
  • Posts: 4710
    • View Profile
  • Liked: 1041
  • Likes Given: 1343
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1559 on: May 24, 2016, 12:29:12 PM »
Browsing this forum last year has the first post where melt lakes are visible at mid-July. Not a proof though.

johnm33

  • Nilas ice
  • Posts: 1318
    • View Profile
  • Liked: 109
  • Likes Given: 49
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1560 on: May 24, 2016, 02:52:45 PM »
"Will it refreeze in place, drain through the ice or carve channels to flow downhill?" Wipneus is right, it's worth taking a look at this link, it shows the deep channel which is probably now connected to the tides, the steepness/depth of the ice, and not just for Jakobshavn.
 http://nholschuh.com/glaciers.html

Wipneus

  • Citizen scientist
  • Young ice
  • Posts: 4025
    • View Profile
    • Arctische Pinguin
  • Liked: 689
  • Likes Given: 0
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1561 on: May 24, 2016, 03:44:30 PM »
Browsing this forum last year has the first post where melt lakes are visible at mid-July. Not a proof though.

Browsing USGS EarthExplorer for Landsat 8 browse quality images of the Jacobshavn calving front. Comparing the latest image 2016/05/23: LC80070122016144LGN00 with those from 2015 gives these results:

2015/06/20 LC80090112015171LGN00 is the first browse image with extensive melt ponds, just not extensive as the one from 2016.
2015/06/27 LC80100112015178LGN00 the melting has greatly increased and is at least as extensive as the current one.

About one month ahead of 2015 is no exaggeration.



P-maker

  • Frazil ice
  • Posts: 248
    • View Profile
  • Liked: 23
  • Likes Given: 0
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1562 on: May 24, 2016, 05:16:37 PM »
Wipneus:

Quote
About one month ahead of 2015 is no exaggeration.

I remember doing fieldwork in these tracts during mid-May in the 1980ies. In those days it was -18 deg C and a fierce wind came off the ice-sheet.

I can hardly believe my own eyes, when I see this "Waterland" nowadays.

Did I just sound like an old crank there?

A-Team

  • Young ice
  • Posts: 2523
    • View Profile
  • Liked: 327
  • Likes Given: 23
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1563 on: May 24, 2016, 11:51:27 PM »
Quote
do we see water draining from higher ponds to lower ones, but do any of these make their way to the sea?
There have no surface streams in the satellite record that make their way on the surface to the sea at Jakobshavn or any marine terminating Greenland glacier at its latitude and above. The situation is quite different for land-terminating glaciers to the south. Some of these streams carve melt tunnels underground before emerging on land as conventional braided glacial streams. This has been validated with fluorescent dyes and immersible probes.

It is generally believed that for the northern glaciers, along the lines of what Wipneus described, that copious amounts of water makes its way to the interface of bedrock/till and bottom ice, eventually emerging at the base of the calving front as powerful jets that erode caverns that eventual help undermine the front.

There is direct sonar observations of this for several West Greenland glaciers. However there is no direct data one way or another for this at Jakobshavn -- it's too hard to get instruments up to the calving front.

While Jakobshavn has a very large drainage basin in the topographic sense, it's unclear how much of the annual precip and melt in that basin finds its way to the sea via the calving front within a year or two. A lot will get refrozen in place.
« Last Edit: May 25, 2016, 03:23:14 AM by A-Team »

notjonathon

  • New ice
  • Posts: 47
    • View Profile
  • Liked: 0
  • Likes Given: 0
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1564 on: May 25, 2016, 02:01:38 AM »
Great responses, thanks.

If this phenomenon is repeated all over Greenland (and I realize that each glacier has its own individual topography), what are the chances of catastrophic failures? Is gradual melt, though probably at increasing rates, more likely?

To a retired liberal arts academic like me, this begins to sound a bit like a modernist vs. postmodernist argument, but systems that can withstand one shock cannot always withstand two. In the recent Kumamoto earthquake, there were two large temblors a day apart. Many buildings that survived the first quake with no apparent damage collapsed during the second. Might the sub-ice channels that undermine the calving front (per A-Team, above) be undermining the stability of the entire glacier?

Adam Ash

  • Frazil ice
  • Posts: 308
    • View Profile
    • The 100 metre line
  • Liked: 9
  • Likes Given: 20
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1565 on: May 25, 2016, 05:34:13 AM »
Interesting...

A-Team '...copious amounts of water makes its way to the interface of bedrock/till and bottom ice, eventually emerging at the base of the calving front as powerful jets'

A significant effect of these copious amounts of water is that to flow they must be above freezing temperature.  Thus these sub-surface flows will be shifting substantial amounts of heat into the base of the glacier ice.  This (I imagine) must be leading to a general rise in the glacier ice temperature, with corresponding weakening of the ice structure. 

In extremis this could lead to increased risk of phase change and sudden outrush of the affected former ice mass.  So we could have what looks like a nice slab of a substantial volume of grounded ice making no contribution to SLR today which could convert into a vast swimming pool with ice blocks bobbing in it all heading for the coast tomorrow.

A-Team

  • Young ice
  • Posts: 2523
    • View Profile
  • Liked: 327
  • Likes Given: 23
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1566 on: May 25, 2016, 05:51:55 AM »
Indeed why can Austfonna Glacier in Svalbard make a dramatic surge (documented on another forum by Wipneus) but not West Greenland glaciers?

http://forum.arctic-sea-ice.net/index.php/topic,1325.msg62909.html#msg62909

https://en.wikipedia.org/wiki/Surge_%28glacier%29 (surge theory list)

Glacier surge: Austfonna, Svalbard (satellite image timelapse)


Glacier-surge mechanisms promoted by a hydro-thermodynamic feedback to summer melt
T Dunse et  al
http://www.the-cryosphere.net/9/197/2015/tc-9-197-2015.html

Quote
Here we present continuous GPS measurements and satellite synthetic-aperture-radar-based velocity maps from Basin-3, the largest drainage basin of the Austfonna ice cap, Svalbard. Our observations demonstrate strong links between surface-melt and multiannual ice-flow acceleration.

We identify a hydro-thermodynamic feedback that successively mobilizes stagnant ice regions, initially frozen to their bed, thereby facilitating fast basal motion over an expanding area. By autumn 2012, successive destabilization of the marine terminus escalated in a surge of Basin-3. The resulting iceberg discharge of 4.2 Gt/yr over the period April 2012 to May 2013 triples the calving loss from the entire ice cap. The related sea-level rise contribution amounts to 7.2 Gt/yr.

This rate matches the annual ice-mass loss from the entire Svalbard archipelago over the period 2003–2008, highlighting the importance of dynamic mass loss for glacier mass balance and sea-level rise. The active role of surface melt, i.e. external forcing, contrasts with previous views of glacier surges as purely internal dynamic instabilities.

Given sustained climatic warming and rising significance of surface melt, we propose a potential impact of the hydro-thermodynamic feedback on the future stability of ice-sheet regions, namely at the presence of a cold-based marginal ice plug that restricts fast drainage of inland ice. The possibility of large-scale dynamic instabilities such as the partial disintegration of ice sheets is acknowledged but not quantified in global projections of sea-level rise."

We propose a hydro-thermodynamic feedback mechanism triggered by surface melt reaching a growing fraction of the glacier bed. Intrusion of surface melt to the glacier bed provides an efficient heat source through cryo-hydrologic warm- ing, facilitating a thermal switch from cold to temperate basal conditions, permitting for basal motion. Initiation of hydraulic lubrication, along with rising pore-water pressure within subglacial sediments, further enhances basal motion, eventually destabilizing the overlying ice.

Given continued climatic warming and increasing surface melt, we hypothesize that the hydro-thermodynamic feedback may gain significance in other glaciated areas, including the ice sheets. In light of recent record melt and rising equilibrium line altitude [ELA separates ablation zone from higher altitude accumulation zone] of the Greenland Ice Sheet, the proposed mechanism has the potential to lead to a long-term enhancement of outlet glacier discharge and calving loss, as earlier proposed by Phillips 2013 (http://onlinelibrary.wiley.com/doi/10.1002/jgrf.20079/full).

Our expectation contrasts with recent studies that indicate limited effects of surface-melt-induced acceleration on the future net mass balance of the Greenland Ice Sheet (Nick et al., 2013; Shannon et al., 2013).
« Last Edit: May 25, 2016, 04:05:41 PM by A-Team »

Tealight

  • Frazil ice
  • Posts: 431
    • View Profile
    • CryosphereComputing
  • Liked: 134
  • Likes Given: 14
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1567 on: May 25, 2016, 01:02:48 PM »
There have no surface streams in the satellite record that make their way on the surface to the sea at Jakobshavn or any marine terminating Greenland glacier at its latitude and above.

I agree the surface is just too broken up to support any kind of stream. In one area north of the main channel melt ponds could drain into their own small basin about 100-400m below sea level, but I don't know if they really do.

Click on the image to see my first gif animation showing bedrock elevation for Jakobshavn.

A-Team

  • Young ice
  • Posts: 2523
    • View Profile
  • Liked: 327
  • Likes Given: 23
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1568 on: May 25, 2016, 04:42:06 PM »
Nice! Note sub-glacial water can and will flow uphill depending on effective pressure differences (ie overlying ice thickness). You might enjoy:

Considering thermal-viscous collapse of the Greenland ice sheet
W Colgan et al
http://onlinelibrary.wiley.com/doi/10.1002/2015EF000301/full

Quote
We explore potential changes in Greenland ice sheet form and flow associated with increasing ice temperatures and relaxing effective ice viscosities. We define “thermal-viscous collapse” as a transition from the polythermal ice sheet temperature distribution characteristic of the Holocene to temperate ice at the pressure melting point and associated lower viscosities. The conceptual model of thermal-viscous collapse we present is dependent on: (1) sufficient energy available in future meltwater runoff, (2) routing of meltwater to the bed of the ice sheet interior, and (3) efficient energy transfer from meltwater to the ice...

It looks like the 22 May 16 Sentinel 2A that Wipneus uploaded, while it has some cloud issues, is still clear enough to animate the calving front. What we are looking for, not really expecting to find yet, is acceleration attributable to the anomalous melt this year.

Two issues here:

-- Jakobshavn accelerates in the spring even with average weather and its velocity is affected by many other factors so how could May velocity changes be specifically attributed to this season's early/extra surface melt?

-- The melt, it appears to me, is sharpening crevasse and other surface features, which is normally advantageous for recognizability and accurate measurement of displacement but now is happening too fast on the time scale of consecutive cloud-free scenes with RO68 geometry, ie even rather distinctive features disappear between takes.

Here animations can help but the outcome is less than ideal in the fastest region of the channel because of too many clouds, illumination angle changing with date, intrinsic contrast variability, too few frames and melt changes on the surface.

2016 03 23 S2A_R068_V 20160323T151927.22WEB.B04 day 083
2016 04 02 S2A_R068_V 20160402T151928.22WEB.B04 day 123 +40
2016 05 22 S2A_R068_V 20160522T151915.22WEB.B04 day 143 +20 +60
« Last Edit: May 25, 2016, 11:56:27 PM by A-Team »

sidd

  • First-year ice
  • Posts: 5294
    • View Profile
  • Liked: 585
  • Likes Given: 0
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1569 on: May 25, 2016, 09:55:03 PM »
Thanks for the Colgan reference. I have a feeling that cryo-hydrologic warming and thermal viscocity feedback will be ... interesting.

"Indeed, the potential deformational velocity gradients stemming from the periphery of the
ice sheet warming to pressure melting point temperature before the interior of the ice sheet would
likely challenge the continuum mechanics of ice, facilitating an inland propagation of fracturing and
crevassing"

Just one of the thought provoking points in the paper.

A-Team

  • Young ice
  • Posts: 2523
    • View Profile
  • Liked: 327
  • Likes Given: 23
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1570 on: May 26, 2016, 12:54:34 AM »
Quote
'the interior of the ice sheet may not be able to respond fast enough to deformation at the warming periphery, which amounts to a breakdown of continuum mechanics used in ice sheet models and translates to rapid inland propagation of fractures and crevasses.' [paraphrased]

sidd has pulled out a key idea from the paper here. Indeed this may be what is happening at Jakobshavn already, as in the unprecedented calving event of 15 Aug 15. The earlier massive acceleration may have left its mark as massive mechanical deformation of the interior of the periphery which, being brittle, lead to deep fracturing inland from the calving front, not to mention massive interior release of heat.

A calving event at the front end removes buttressing propping up the interior, so is followed by a cascade of events, each removing a bit more buttressing on what is left, with the effect over a day or so of removing a kilometer and more of ice to the east.

Was this just a one-off event that consumed legacy fractures left from a one-off acceleration, or is this the new normal for the calving mode? We shall find out by the end of August 2016. Two such events is one too many.

-=-=-=-=-=-=-=-

Explanatory note #1: continuum mechanics in ice sheet models is a small corner of academic physics developed in 19th century primarily by Cauchy and resurrected in glacial applications as invariants of tensor calculus by the 1950's. As the name suggests, crevasse and fracture (rips and tears) are not accommodated within this plastic deformation framework. Decent enough account up at https://en.wikipedia.org/wiki/Continuum_mechanics

Explanatory note #2: people on these forums, sometimes with very sketchy competence in mathematical physics, often invoke exotic collapse mechanisms such as state changes, phase changes, bifurcations, Thom catastrophe theory, Lorenz strange attractors, butterflies flapping their wings in Brazil, fractial dimensions, dark energy and so forth.

Colgan et al are not doing this. There is no need to. If you invoke exotic explanations within academic science, you will simply be patted on the head and pointed to Occam's razor (keep it simple, 1347 AD) or Laplace saying (in 1812) extraordinary proposals require extraordinary evidence. In other words, the burden of proof is on you so spare us until you have it.
« Last Edit: May 26, 2016, 03:31:23 PM by A-Team »

sidd

  • First-year ice
  • Posts: 5294
    • View Profile
  • Liked: 585
  • Likes Given: 0
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1571 on: May 26, 2016, 05:52:39 AM »
"A calving event at the front end removes buttressing propping up the interior, so is followed by a cascade of events, each removing a bit more buttressing on what is left, with the effect over a day or so of removing a kilometer and more of ice ..."

Precisely. This ties into Bassis cliff collapse/hydrofracture mechanism. I keep coming back to rubble pile flows, grain size, volumes above flotation, sandhills with phase change, differential sticking, and deformable beds to keep it interesting. Not so easy. Colgan has done a good job, but so much more remains.

sidd

  • First-year ice
  • Posts: 5294
    • View Profile
  • Liked: 585
  • Likes Given: 0
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1572 on: May 26, 2016, 06:26:52 AM »
Colgan:

"Ultimately, it is the tremendous difference between the latent heat of fusion of water (3.34 × 10 5 J/kg) and the specific heat capacity of ice (2.01 × 10 3 J/kg/K), which means even a trace meltwater volume can act as a potent heat source in the ice sheet energy equation. One kilogram of refreezing meltwater releases sufficient energy to warm 100 kg of ice by ∼1.6 K, corresponding to a decrease in effective viscosity of ∼11% [Paterson, 1994]."

That refreeze is a titanic transfer of heat. How titanic ?

"As stated above, a year 2100 meltwater runoff anomaly of 700 Gt/a is equivalent to a latent energy anomaly of 2.34 × 10^20 J/a, which is more than an order of magnitude greater than the energy delivery rate required for partial thermal-viscous collapse over four centuries."

Gt/a is gigaton per annum. Recall that Greenland mass loss in 2012 was 474 Gt, and Enderlin et seq. establish that SMB (aka melt) is now dominant. So how much sticks around and dont run off to sea ?
No good guess yet, but some.

"In the virtually flat interior of the Greenland ice sheet, bedrock slope often exceeds 11 times surface slope (Figure 4). In the best-surveyed regions of the ice sheet, with the least uncertainty in bed topography, equipotential theory suggests widespread areas where englacial and subglacial water flow is primarily governed by bedrock topography. Given that the interior bed of the ice sheet is depressed below sea level, meltwater introduced to the subglacial network sufficiently far inland should theoretically exhibit a tendency to flow to bedrock sink points in the ice sheet interior. Such reverse drainage and collection behavior has been modeled for smaller ice caps [Flowers et al., 2005]. Recent observations of discrete refrozen basal ice masses confirm that subglacial water can be routed inland toward relatively cold sink points in the ice sheet interior where it refreezes [Bell et al., 2014]. Although considerable uncertainty exists in the precise origin of this refrozen water (i.e., whether surface meltwater, basal meltwater, or ocean water), these observations suggest that nontrivial reverse drainage and interior refreezing do occur under contemporary climate."

One other thing that doesnt seem to figure in ice models is the steepening of the edges of Greenland (lower melts quicker)

"Observed increases in crevasse extent likely stem from a combination of: (1) thinning and steepening of the ablation area, which increases tensile stress while decreasing lithostatic stress, ..."

Will have to reread.

sidd

A-Team

  • Young ice
  • Posts: 2523
    • View Profile
  • Liked: 327
  • Likes Given: 23
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1573 on: May 26, 2016, 04:49:01 PM »
Quote
steepening of the edges of Greenland (lower melts quicker) .. increases in crevasse extent from steepening of the ablation area, which increases tensile stress while decreasing lithostatic stress
Right. We don't consider the vertical dimension here that often, like the drunk looking for his car keys under the streetlight -- the flat nadar views from S1A, S2A and Landsat.

Landsat might as well go home, there's hardly been any Jakobshavn imagery this spring. The 'lake district' to the south was mostly clear however on May 23rd. It is fairly well confined to lower elevations. The first image below contrasts it with the Google Earth base image used by USGS at EarthExplorer, which I chased down to 24 June 2011 using the somewhat dodgy timeline feature within GE. Some of the lakes appear to reoccur at the same sites.

The high resolution zooms show WorldView-1 satellite images of 01 June 2010 of the melt area at the upstream bend that wipneus featured above in S2A imagery. The topography and drainage seem not to have changed very much.

nukefix

  • Frazil ice
  • Posts: 462
    • View Profile
  • Liked: 9
  • Likes Given: 1
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1574 on: May 26, 2016, 05:15:01 PM »
Speaking of non-continuum fracturing upstream, what are the strange features between the arrows on this S-1a IW-image from 21.5.2015? I hope we can catch an optical shot soon..

edit: 10m pixel size in auto UTM-zone
« Last Edit: May 26, 2016, 05:33:47 PM by nukefix »

Wipneus

  • Citizen scientist
  • Young ice
  • Posts: 4025
    • View Profile
    • Arctische Pinguin
  • Liked: 689
  • Likes Given: 0
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1575 on: May 26, 2016, 06:01:50 PM »
Speaking of non-continuum fracturing upstream, what are the strange features between the arrows on this S-1a IW-image from 21.5.2015? I hope we can catch an optical shot soon..

edit: 10m pixel size in auto UTM-zone

Melt ponds and streams.

Thanks for that projection. It made the alignment real easy.

johnm33

  • Nilas ice
  • Posts: 1318
    • View Profile
  • Liked: 109
  • Likes Given: 49
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1576 on: May 26, 2016, 10:07:19 PM »
" what are the strange features between the arrows"
I was going through last August where I found the following image. Is it possible that tidal waters have reached that 1500m trough? and is that a slump shown from the top just right of centre pushing through the main flow?

[ http://forum.arctic-sea-ice.net/index.php/topic,154.msg60970.html#msg60970]

Anyone wanting to familiarise themselves with whats happening /about to happen could do a lot worse than read this page and the one before and after
http://forum.arctic-sea-ice.net/index.php/topic,154.msg60651.html#msg60651
« Last Edit: May 26, 2016, 11:07:10 PM by johnm33 »

Adam Ash

  • Frazil ice
  • Posts: 308
    • View Profile
    • The 100 metre line
  • Liked: 9
  • Likes Given: 20
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1577 on: May 27, 2016, 10:06:59 AM »
At one of the crests in the bed there should be a crevasse field with cracks aligned normal to the flow direction. 

If the tensile strength of the ice is high, then the distance between crevasses would be long, while as the tensile strength reduces (aka the ice temperature increases) I would expect the distance between crevasses at the same section to reduce, until eventually there is just a shuffling mass of mush with little tensile strength left.

Is there any evidence of this effect (if real) in the images?  It could be a useful way to get a proxy for change in ice strength / temperature.

A-Team

  • Young ice
  • Posts: 2523
    • View Profile
  • Liked: 327
  • Likes Given: 23
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1578 on: May 27, 2016, 06:05:17 PM »
Here is that crevasse field at higher resolution from a mid-August 2010 1 m WorldView-1 ... click to enlarge. It covers the same area that nfix and wipneus are discussing above. At google earth itself, the original colors clearly show blue water accumulating in the eastern crevasses. This area was animated a couple hundred posts ago using a Landsat-8 time series.

Adam Ash

  • Frazil ice
  • Posts: 308
    • View Profile
    • The 100 metre line
  • Liked: 9
  • Likes Given: 20
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1579 on: May 29, 2016, 07:38:42 AM »
Thanks A-Team!  I don't think I can pursue my hypothesis very far among that jumble! 

A-Team

  • Young ice
  • Posts: 2523
    • View Profile
  • Liked: 327
  • Likes Given: 23
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1580 on: May 31, 2016, 02:15:40 PM »
Here is the end of May calving front, nothing remarkable about its position. Some very large bergs are visible down the fjord, stable and suitable for helicopter samping. The best 'action' seems to be with tributary inflows in the northeast corner .. a 3x enlargement (5m) of Landsat LC80080112016151LGN00 is shown but we await the next S2A for better interpretability.
« Last Edit: May 31, 2016, 02:33:15 PM by A-Team »

Shared Humanity

  • Young ice
  • Posts: 4097
    • View Profile
  • Liked: 500
  • Likes Given: 55
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1581 on: May 31, 2016, 02:35:19 PM »
Both of those bergs seem to have a very curious feature. At the same distance from the top of each berg, there is a wide band of ice that seems to be quite a bit thinner (melted) or less mass than on both the portion above it and below it. This is much more visible on the berg on the lower left but it seems to be present on the second as well.

Any ideas?

A-Team

  • Young ice
  • Posts: 2523
    • View Profile
  • Liked: 327
  • Likes Given: 23
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1582 on: May 31, 2016, 02:49:18 PM »
Quote
Any information in berg shapes?
On these, we don't know which way either berg rolled at the time(s) of calving -- bottom out is more common but top out is not unusual, so we don't know for sure whether what we see represents the interior or exterior of the calving front. In previous events where the calving was filmed, a concave surface like the upper berg is the interior face. (Concavity is expected on the inner face from the nature of the fracturing process.)

In terms of ice stream surface or bedrock scraping bottom, in one previous case we could see embedded till that established the bottom. Here that is either not present, not evident, or on another fragment. These bergs should persist for weeks, until the next S2A color 10 m, which would help resolve this.

Wipneus

  • Citizen scientist
  • Young ice
  • Posts: 4025
    • View Profile
    • Arctische Pinguin
  • Liked: 689
  • Likes Given: 0
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1583 on: May 31, 2016, 03:10:31 PM »
Quote
we await the next S2A for better interpretability.

2016/5/25 ( R111) seems to be fallen in a crack or so (see screen shot of R111 slices).

next:
2016/5/29 ( R025) is available on ESA (7.25GB), but not amazon (300 MB) cloud storage yet. Overall cloudiness 58%.

Wipneus

  • Citizen scientist
  • Young ice
  • Posts: 4025
    • View Profile
    • Arctische Pinguin
  • Liked: 689
  • Likes Given: 0
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1584 on: June 01, 2016, 06:11:14 PM »
2016/5/29 ( R025) is now on amazon cloud storage. Some clouds but probably useful.
Uploaded S2A_R025_V20160529T150918.22WEB.B04.tiff .
« Last Edit: June 01, 2016, 06:48:14 PM by Wipneus »

A-Team

  • Young ice
  • Posts: 2523
    • View Profile
  • Liked: 327
  • Likes Given: 23
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1585 on: June 02, 2016, 12:20:04 AM »
Floes are peeling away from the line of frozen melange in the calving bay. The second image shows at 2 m the big bergs we looked at earlier in Landsat -- lots of detail is available in Sentinel 2A just in a single 10 m band.

The large berg might be well worth doing in 2 m full color if the Maestro can find a free moment. There seem to be fine grooves across the main grooves, more apparent in 'unionjack' indexed color. This suggests the mid-interior ice of the calving front is not homogenous (as modeled) but instead has a substructure reflected in the surface of larger calved bergs. See #1590 though for brittle fracture processes that could also leave their mark
« Last Edit: June 02, 2016, 05:03:05 PM by A-Team »

A-Team

  • Young ice
  • Posts: 2523
    • View Profile
  • Liked: 327
  • Likes Given: 23
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1586 on: June 02, 2016, 12:30:59 PM »
The 5 m Sentinel 2A animation shows the NE corner of the south branch over the three starred dates with clear weather. These are each a month apart. The movement, diagonal to the SW, is steady at 2.7 m/d or 973 km/yr in the upper right corner or about 1/17 as fast as the main channel at its fastest. It varies substantially in magnitude and slightly in direction across the scene.

The RGB color made from the three grayscale frames suggests several wave groups of different periodicities and orientations.

2015 10 22 S2A_R025_V 20151022WEB.B04.tiff
2016 03 30 S2A_R025_V 20160330WEB.B04.tiff*
2016 04 09 S2A_R025_V 20160409WEB.B04.tiff
2016 04 19 S2A_R025_V 20160419WEB.B04.tiff
2016 04 29 S2A_R025_V 20160429WEB.B04.tiff*
2016 05 29 S2A_R025_V 20160529WEB.B04.tiff*

Wipneus

  • Citizen scientist
  • Young ice
  • Posts: 4025
    • View Profile
    • Arctische Pinguin
  • Liked: 689
  • Likes Given: 0
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1587 on: June 02, 2016, 01:15:52 PM »

The large berg might be well worth doing in 2 m full color if the Maestro can find a free moment.

My attempt is attached. All editing in 16bits in ImageMagick: cropping, scaling and stretching the values between 0 and 100%

Timothy Astin

  • New ice
  • Posts: 50
    • View Profile
  • Liked: 0
  • Likes Given: 0
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1588 on: June 02, 2016, 04:50:14 PM »
Those large bergs are showing some of the typical features of fracture faces (as seen also in rocks, glass, ceramics, flint knapping etc.). Often people distinguish the broad categories of "ripples" and "hackles" on such faces.

"Ripples" form parallel to the propogating fracture tip. They are thought to be associated with slower periods of fracture propogation, including (but not exclusively) during sub-critical crack growth.
"Hackles" form roughly at right angles to the fracture tip and so indicate the direction of fracture growth. They are formed most prominently during critical fracture growth, that is during rapid failure.

The faces have strongest ripples to the lower right, and strongest hackles to the upper left. So I infer fractures that intiated at the lower right, grow relatively slowly, and then failed rapidly to the upper left.

As berg fractures likely develop from surface crevasses, the top of the bergs is to the lower right.  The bergs show that crevasses slowly deepen, before reaching a critical state when there is rapid failure and berg calving.

A-team, Wipneus, I appreciate all the observations, data processing, and thoughts you and others post. It all goes to stimulate the grey matter.

A-Team

  • Young ice
  • Posts: 2523
    • View Profile
  • Liked: 327
  • Likes Given: 23
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1589 on: June 02, 2016, 05:58:02 PM »
Quote
All editing in 16bits in ImageMagick
Came out rather nice. Grooves are better.
Quote
seen also in rocks, glass, ceramics, flint knapping
This seems very applicable to brittle ice, including perhaps the slower propagation features in the middle where the ice is believed colder. The larger berg is ~960 m long, nearly full height (though an accurate ice thickness at the current calving front is wanting).

The 50 m grid below over wipneus' image allows an estimate of initial crevasse depth and thickness (via mean freeboard). This berg looks like a bowl so where is the water splashed in from the calving event? There may be drains at the bottom and/or top. The flat gray surfaces could be refrozen water but the color seems wrong.

I re-located the sapphire calving event discussion at #1019 et seq. This references the May 2-14 calving event filmed by Ruben Wernberg-Poulsen on an AirZafari flight. We will never have that information quality or detail for the current bergs under consideration. These bergs are important to sample because there are no prospects for ever drilling ice cores into Jakobshavn.

« Last Edit: June 02, 2016, 10:12:47 PM by A-Team »

TenneyNaumer

  • New ice
  • Posts: 75
    • View Profile
    • Climate Change: The Next Generation
  • Liked: 1
  • Likes Given: 10
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1590 on: June 05, 2016, 05:41:01 AM »
Sure wish there was a high res sentinel image of what is going on down the south branch:

http://ocean.dmi.dk/arctic/images/MODIS/Disko/20160604s01a.ASAR.jpg

A-Team

  • Young ice
  • Posts: 2523
    • View Profile
  • Liked: 327
  • Likes Given: 23
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1591 on: June 09, 2016, 03:22:24 PM »
Quote
wish there was a high res sentinel image of what is going on
Following the calving season has been difficult this spring because of impenetrable clouds affecting S2A and Landsat-8 and irregular scheduling of IW-grade S1A images. However a couple of Landsat's did come in, oddly for consecutive days (June 5th and 6th).

The first of these (LC80822332016157LGN00) is the more interesting as path,row = 08,223 images have a very low sun angle (8.7º, 45º NW azimuth) and can only be taken around the summer solstice. The result is long shadows that can be used to determine landscape topography.

The berg we have been tracking casts a 507 m long shadow indicating a peak of 77.6 m above sea level. This only puts a weak upper bound on berg thickness; a full model of above-ground ice would be needed to get at the underwater portion and even then keel depth would remain unknown until the berg grounds on the Illulisat shoal of known bathymetry.

The animation of consecutive days shows active calving (retreat) matched by rapid forward glacier motion (advance), with no net retreat and nothing unusual about calving front position for this date. The dramatic early melt features have all but disappeared. Thus we have no clues on how the season will end up.

S1A's from June 5, 7, and 8 have been posted at the AWS hub but not yet tifs at the Wipneus site. The 8th looks clear and the resolution/color are better. It is an R025, part of a series favorable for slow velocity determinations.

There is another large berg much nearer the calving front. It does not have the bowl shape suitable for an ice camp (staff roped into an idlying helicopter).
« Last Edit: June 09, 2016, 03:44:29 PM by A-Team »

Wipneus

  • Citizen scientist
  • Young ice
  • Posts: 4025
    • View Profile
    • Arctische Pinguin
  • Liked: 689
  • Likes Given: 0
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1592 on: June 09, 2016, 07:07:12 PM »
R025 2016-06-08 is in. Nice few clouds. S2A_R025_V20160608T150916.22WEB.B04.tiff has been uploaded.
« Last Edit: June 09, 2016, 07:59:18 PM by Wipneus »

Wipneus

  • Citizen scientist
  • Young ice
  • Posts: 4025
    • View Profile
    • Arctische Pinguin
  • Liked: 689
  • Likes Given: 0
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1593 on: June 09, 2016, 07:21:03 PM »
A-Teams ice berg seen by S2A in nat color.

Wipneus

  • Citizen scientist
  • Young ice
  • Posts: 4025
    • View Profile
    • Arctische Pinguin
  • Liked: 689
  • Likes Given: 0
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1594 on: June 13, 2016, 07:08:34 AM »
2016/6/11 -  R068 is in. Cloudy, but calving fronts visible. Uploaded S2A_R068_V20160611T151937.22WEB.B04.tiff  .
« Last Edit: June 13, 2016, 07:57:33 AM by Wipneus »

Adam Ash

  • Frazil ice
  • Posts: 308
    • View Profile
    • The 100 metre line
  • Liked: 9
  • Likes Given: 20
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1595 on: June 13, 2016, 01:19:16 PM »
While not wishing for the worst, I am somewhat surprised (and relieved) that Jakobshavn Isbrae has chewed out as little an embayment east of the coastal islands after trying so hard for so long.

Eventually I guess the calving fronts of JI and its neighbouring ice streams north and south will withdraw to the point where they meet, at which point the encouragement for the ice cap to slide off into the surrounding ocean will be somewhat greater than it is today. 


I wonder when...

Shared Humanity

  • Young ice
  • Posts: 4097
    • View Profile
  • Liked: 500
  • Likes Given: 55
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1596 on: June 13, 2016, 02:50:49 PM »
The near 100% surface melt and melt lakes are amazing to look at.

oren

  • Young ice
  • Posts: 4710
    • View Profile
  • Liked: 1041
  • Likes Given: 1343
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1597 on: June 13, 2016, 05:46:38 PM »
The near 100% surface melt and melt lakes are amazing to look at.
Yes!

Anne

  • Grease ice
  • Posts: 527
    • View Profile
  • Liked: 8
  • Likes Given: 2
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1598 on: June 13, 2016, 06:30:51 PM »
Bed geometry revealed by Operation Ice Bridge

'Huge ancient river basin may help explain the location, size and velocity of Jakobshavn Isbræ' - Bristol University press release Link

Palaeofluvial landscape inheritance for Jakobshavn Isbrae catchment, Greenland
Authors: M. A. Cooper, K. Michaelides, M. J. Siegert, J. L. Bamber

Abstract

Subglacial topography exerts strong controls on glacier dynamics, influencing the orientation and velocity of ice flow, as well as modulating the distribution of basal waters and sediment. Bed geometry can also provide a long-term record of geomorphic processes, allowing insight into landscape evolution, the origin of which may pre-date ice sheet inception. Here, we present evidence from ice-penetrating radar data for a large dendritic drainage network, radiating inland from Jakobshavn Isbræ, Greenland's largest outlet glacier. The size of the drainage basin is ∼ 450,000 km2 and accounts for about 20% of the total land area of Greenland. Topographic and basin morphometric analyses of an isostatically uplifted (ice-free) bedrock topography suggests that this catchment pre-dates ice sheet initiation and has likely been instrumental in controlling the location and form of the Jakobshavn ice stream, and ice flow from the deep interior to the margin, now and over several glacial cycles.
http://onlinelibrary.wiley.com/doi/10.1002/2016GL069458/full



Wipneus

  • Citizen scientist
  • Young ice
  • Posts: 4025
    • View Profile
    • Arctische Pinguin
  • Liked: 689
  • Likes Given: 0
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1599 on: June 15, 2016, 11:20:19 AM »
2016/6/14 ( R111) is in. Patched with clouds, but some of the calving front visible. S2A_R111_V20160614T152913.22WEB.B04.tiff uploaded.

Cropping to a fairly large subimage gives a rather nice picture of bright sunny ice with patchy clouds. You will have to click the picture for the full resolution (10m/pix) image.