Close

what massive Greenland iceberg calving looks like from the air

Sometime May, 2014 AirZafari (+299 55 28 19) 13 year old guest photographer Ruben Wernberg-Poulsen captured a new perspective on massive Greenland glacier calving.  In addition to the massive scale of the event seen clearly from the air, I think we’ve never seen that basal ice so clearly and so graphically from this birds eye perspective.

The video is from none other than the site than that which  grabbed headlines as the world’s fastest glacier calved a giant area (12.4 sq km) and retreated (at least temporarily) to a new record minimum between 14 and 16 August, 2015 [1].

A rough dimension of the 2014 iceberg in the aerial video suggests a volume of ~180 million cubic meters of ice. If spread out over the Washington DC Mall from the Capitol steps to the Washington Monument (1.8 km x 0.4 km), this ice  would have a depth (~375 m) more than twice the 169 m height of the Washington Monument.

cliff

Sapphire blue basal ice

Extreme pressure from 500-900 m ice overburden plus extreme strain due to friction between the glacier and its bed, strain heating, all seem to compress air bubbles straining the white ice into denser blue ice. Else, likely pressure melting, possible freeze-on of melt water or sea water may also be at play to produce the curious sapphire blue basal ice on display in this extremely large iceberg calving event.

basal_ice

Commentary on the 12 sq km event 14 to 16 August, 2015 [1]

It’s impressive to see the Jakobshavn glacier retreat further, to a new record position upstream.
I wouldn’t say it’s the largest calving event to occur. The glacier lost a larger area between 2002 and 2004, a floating ice shelf. What’s different now: the ice is grounded or near floatation.
There is an interesting interplay to consider; accelerated forward motion of ice given loss of internal flow resistance on calving that will move the ice front forward quickly to replace the void. So, in not many days, the calving front may be back to the position as in the before image.
The calving front position represents the dynamic interplay between calving, producing front migration upstream and forward flow. Hypotherically, that dynamic could be in balance; no net front position change over time. Or the front could be in imbalance with retreat upstream as is the case in point.
This and most other Greenland glaciers are thinning (vertically), having the effect of un-grounding the ice from the bed at the glacier front. As this is a flooded, underwater system, these glaciers have because of buoyancy forces, what is called ‘marine instability’, allowing the glacier to retreat more quickly as they have fronts near or at floatation. Recent West Antarctic Ice Sheet glacier retreat (e.g. Rignot and others, 2014) suffers from the same marine instability.
This is an inherently unstable system given that the bed of the glacier is underwater several 10s of km upstream.
In this Greenland case, there is an upstream reverse bed slope, the bed gets deeper upstream at some point, not far from where the calving front has retreated to now. Further retreat upstream can be to deeper ice. This is unstable, so an even further retreat will occur given likely continued thinning.
A negative feedback here, something to dampen that instability, is an increase of ice flooding into the void from the sides of the flow, re-jamming it up a bit (regaining internal flow resistance), like partially recorking the flow.
There is a titanic struggle here between accelerated flow [due to loss of flow resistance from calving] and ice flooding into the void, partially re-jamming it up. Given likely continued thinning*, the winner is the loser, of more ice.
* from likely increased surface melting, likely increasing ocean temperatures. However, from year to year (the weather of climate), we may have a cold year that reverses this activity, leading to a short term advance, amid a longer term retreat observed at this an other Greenland glaciers in the past decade.

follow @Climate_ice and Prof. Jason Box science on Facebook

Works Cited

  • [1] massive calving event captured by the Arctic Sea Ice Blog.
  • Rignot, E., J. Mouginot, M. Morlighem, H. Seroussi, and B. Scheuchl (2014), Widespread, rapid grounding line retreat of Pine Island, Thwaites, Smith, and Kohler glaciers, West Antarctica, from 1992 to 2011, Geophys. Res. Lett., 41, 3502–3509, doi:10.1002/2014GL060140.

Acknowledgements

Thanks Ruben Wernberg-Poulsen for capturing and sharing the video with World of Greenland. Thanks to Malik Milfeldt for the tip.

Structure from Motion (SfM)

from K. Mankoff …A newish class of algorithms that have been classified under the name “structure from motion” or SfM. While these algorithms have been in use in the robotics / computer science / other domain for over a decade (Microsoft released an implementation titled “PhotoSynth” several years ago), they have not yet been widely used in the Earth Science domain. This is changing.

Three papers have come out in the past few months introducing SfM to Earth Scientists, providing case studies:

http://dx.doi.org/10.1002/esp.3366
http://dx.doi.org/10.1016/j.geomorph.2012.08.021
http://dx.doi.org/10.1029/2011JF002289

from Adam Steer …

1. It is possible to make 3D models using photographs using freely
available software (eg SfM toolkit, bundler, CMVS, PMVS), but packages
like Photoscan (mentioned by Matt) are vastly easier to use and
contain already the tools required to geolocate your point cloud, and
do some error analysis. I’ve built both an implementation of
bundler/CMVS/PMVS in Ubuntu Linux, attempted to install and run
SfMtoolkit in Windows 7, and managed to get my hands on Photoscan for
Linux. I don’t use bundler-> CMVS or SfMtoolkit anymore. One key
reason is that I can give photoscan apriori image coordinates for use
in its bundle adjustment, and get some ideas about predicted vs
adjusted camera positions (error). The other is that I don’t have to
chase *nix libraries for every new build.

2. On the down side, SfM algorithms struggle a little on ice, since
they rely on inhomogeneous imagery to work with. It is very easy to
make models of say, Antarctic stations. It is not very easy to make
great models of sea ice unless there are lots of features and the
light is good. Mountain glaciers or snowpacks on sunny days, however,
should provide great subjects!

EIS comes to Geografisk Institut, Københavns Universitet

During an invited lunchtime presentation, I will begin the process of assembling a team of students to analyze Greenland EIS data.

Title Extreme Ice Survey lapse cameras measure Greenland glacier changes

Abstract Beginning in 2007, the Extreme Ice Survey (EIS) installed 12 cameras beside 7 of the largest West Greenland glaciers. By 2009 EIS had captured extremely dynamic images that, especially when animated, teach us a tremendous amount ice-climate interaction and motion dynamics. In 2010, we published a scientific article[1] documenting a technique deriving glacier motion from single camera views. In this process, we developed and documented the software. By 2011, 3 new EIS rigs were installed by GEUS glaciology field workers at 3 new sites. Today, we stand ready to tap into the archive of photos, to apply our software and expand what we do. Let’s assemble a team of students to analyze the data with the help of Jason Box and James Balog. We’ve been only scratching the surface of the tip of the iceberg. Discoveries are within reach and include the possibility of more Greenland field work. We just have to take the next steps.

[1]  Ahn, Y. and J.E. Box, 2010: Glacier velocities from time lapse photos: technique development and first results from the Extreme Ice Survey (EIS) in Greenland, J. Glaciol., 56(198), 723-734. PDF