Steensby Glacier Calving Event and Retreat, Northern Greenland

Steensby Glacier flows north from the Greenland Ice Sheet into the Arctic Ocean between Petermann Glacier to the west and Ryder Glacier to the east. The glacier terminates 100 km up the twisting Sankt George Fjord from the ocean after flowing 60 km down the twisting valley from the ice sheet. This distance and the fact that the fjord empties into the Arctic Ocean would suggest it is less easily reached by warming ocean water to melt the floating glacier tongue. The glacier has a thin floating ice tongue like Petermann Glacier at the terminus with a thickness of 75-105 m. The terminus as a result has a low velocity and would not accelerate and retreat via the same mechanism of backforce reduction that has led to retreat of almost all marine terminating outlet glaciers that do not have large floating ice tongues. The snowline was noted as 800 m in the 1970-1980′s, has in recent years been 1000 meters (Pelto, 2010). With the warm weather the past two summers it has seemed inevitable that Ryder and Steensby Glacier would have a terminus response. Steensby had last been observed in retreat back in 1947 (Ahnert, 1962). From 1947 to 1976 and since 1976 has changed little. On my return from glacier field work I checked the MODIS daily imagery from 8/15 and saw nothing. This glacier seemed a particularly likely culprit for retreat this summer because the terminus area is such a melange of ice as seen in the 2006 Landsat image (M),and as Ahnert had observed, the crack that created the icebergs is likely the same one visible in 2006, blue arrows. In the invaluable blog Arctic Sea Ice run by Neven, the calving event was noted by commenters on Aug. 24th Sphaerica, Twemoran and Espen Olsen. This is what makes the blog so valuable many of the participants are actively examining daily satellite imagery making interesting observations, and as a glaciologist this proves to be remarkably valuable and interesting resource time and again.

Here we first look at MODIS images of Steensby Glacier from 8/2010, 8/2011, and 2012. The 2012 images are from 8/12, 8/15 , 8/23 and 8/24, with the crack first appearing in the 8/15 and open water appearing on 8/23 and widening by 8/24. The icebergs approximate maximum dimensions are 4 km by 6 km. The last image is a terminus closeup.
Melting has been significant in northern Greenland for three straight summers. In 2010 the first image the melt area is below 1000 meters at the head of the Steensby Glacier outlet denoted by red arrows, this is a typical pattern of the last few years (P=Petermann, R=Ryder, S=Steensby). In 2012 the area of extensive melt has expanded from a zone around the head of the valley of Steensby and Ryder Glacier near 1000 m in July (blue arrows) to a wide zone extending all the way from Steensby to Ryder Glacier in August. Unlike Petermann Glacier, Steensby Glacier does not have a deep connection to the ice sheet as indicated by bedrock maps of the glacier from Bamber et al. (2011). The glacier is much narrower, thinner at the grounding line and its velocity is much less, volume wise the Steensby Glacier just lacks the importance in terms of influence on the larger ice sheet that Petermann Glacier has.

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23 thoughts on “Steensby Glacier Calving Event and Retreat, Northern Greenland

  1. Nice one. I think the sill depth (shallowest connection of fjord to ocean) at the mouth of the fjord determines, if this glacier has access to heat from the Atlantic layer in the Arctic Ocean. The sill depth of Petermann Fjord is somewhere between 350 to 450 meter allowing the warmer (and saltier) Atlantic waters from nares Strait to enter. These waters enter Nares Strait from the Arctic Ocean in the north as they are blocked to enter from the south by a 220 meter sill in Kane Basin. I am not aware of anyone having actually taken measurements of bottom depth, sill depth, temperature, or salinity inside the fjord to tell one way or the other. NASA’s IceBridge project may have data, though.

    • And what do you know of the sill depth here, or for that matter the difference in water characteristics at depths of 250-500 meters where the glacier base is after the grounding line?

    • Is it possible that halo siphoning could have the effect of drawing the warm waters over the sill, and if so would the additional melt channeling out of the fjord enhance this action.

      Terry

      • Mauri

        Social engagements fill my day, but i will get back tonight to try and explain my thought processes. It doesn’t seem to me to matter what the sill height is (as long as it’s sufficient), but more the velocity of the out flowing fresh, cold layer.

        Terry

      • Possibly (probably?) I’m asking a sophomoric question, but:

        My understanding of the Halo Siphon effect is that it’s similar to the gyre effect that one would expect behind a rock in a fast flowing stream – except that it’s vertical.

        Just as a canoeist finds himself sucked upstream when downstream from a rock if the current is sufficient, I’m assuming that as the out flow in a fjord increases due to increased runoff, the deep warm brine being sucked over the sill would increase proportionally. The glacier terminating upstream would be further undercut by this influx increasing the likelihood of a calving event.

        A fjord without a sill (if such exists) wouldn’t experience this so the incoming (Atlantic?) waters and wouldn’t be any warmer than what would be found at a similar depth in open waters.

        If I’m whistling up the wrong tree I’d appreciate being set straight.

        Thanks
        Terry

      • I am a glaciologist not an oceanopgrapher, but this does not sound plausible. Flow into and out of fjords is regulated by density and the stratification that develops. This is wher Andreas Muenchow at Icy Seas is an expert.

  2. Pingback: Steensby Gletscher Sheds 10 km^2 Ice Island | Icy Seas

  3. Mauri

    Thanks for the plug for Neven’s blog. As one of the amateurs posting there it’s nice when our efforts are recognized.

    Terry

  4. Mauri,

    I was not aware of the the earlier reports on the Steensby Bræ, but thanks anyway.
    RE: Zachariae, are you aware of the split of the tongue at Zachariae, it is not a real calving since the front of the tongue did not move at all?

    • Zachariae is calving heavily in the 8/19 imagery, and the main front is now isolated from the northeast floating section, is that your point. There is a large rift in the Nioghalvfjerdsbrae (79N) and is not really new.

  5. Don’t know if you take requests/answer questions but I do have one about Zachariae.

    An old Byrd Institute blog had a nice summary and animation of Zachriae’s retreat from 2002 thru 2008.

    http://bprc.osu.edu/MODIS/?p=32

    And this nice Modis shot from last week shows that the retreat has continued and in fact it has retreated all the way back to the southern tip of the island that separates Zachariae and 79N.

    http://rapidfire.sci.gsfc.nasa.gov/imagery/subsets/?subset=Arctic_r02c03.2012233.terra.250m

    My question is what is the fast area of ice just east of the calving area of Zachariae? Was it once the tongue of Zachariae and now is orphaned by the retreat of Zachariae or is it more accurately an ice shelf?

    Zachariae is almost certainly the second biggest loser in Greenland after Petermann but I assume given it’s relative inaccessibility it doesn’t get much study. Any conjecture as to why it’s retreating so fast especially when it’s nearest neighbor (79N) isn’t?

    • I have been waiting for two years for a more appreciable terminus change from Zachariae to focus on it. It is certainly along with 79N a very important glacier in terms of tapping the interior of the GIS along with Petermann and Jakobshavn the most important. The retreat has not been that fast in my mind. This separation must be what Espen meant by the split. I will pull up some Landsat imagery to illustrate the point in the next day.

      • Jøkelbugt/ Zachariae:
        Last time we saw a similar situation in the area, was 2003-4, in the meantime fast ice reestablished itself, but with this seasons change of general rules I think we have seen the last of “stubborn” fast ice if the current “trend” continues next season. The only reason the “fast ice” island is still there is because of the very shallow water of Jøkelbugt at the Belgium Bank with Tobias Ø and the large numbers of reefs in the area. The ice in the “Jøkelbugt Lagoon”, is showing a tremendous willingness to get out, and this will eventually have an impact on the behaviors of both Zachariae and 79. The same situation is very similar around Station Nord and Prinsesse Margrethe Ø, so this season we may see the end of fast ice inn all of Greenland, except from some mixed fast ice / glacier areas.

  6. Yahoo! I feel like one of those amateur astronomers who discovers a comet or an asteroid.

    Except comets and asteroids don’t melt.

    [Dang it. I need to buy a telescope.]

    • Just keep using the MODIS scope as you do. Unlike comets or asteroid which already exist, discoveries like on Steensby do not until the moment exist.

  7. Jøkelbugt:

    My “studies” show, although limited to the sat-age from year 2000.
    In the early 2000s, culminating in 2003 the sea in front of Jøkelbugt was relatively sea ice free. September 24 th 2003 :Only the area behind Norske Ø and Isle de France, was was covered with some melange kind of ice as seen on this Modis image:
    http://rapidfire.sci.gsfc.nasa.gov/cgi-bin/imagery/single.cgi?image=crefl1_143.A2003267164500-2003267165000.500m.jpg

    The tongue of 79 was then larger especially the northern branch up the Fjord, and the separation of the Zachariae tongue only just started.
    The separation of the tongue seems to be complete by now.

    Since 2003 until this season the extend of ice in the area went up down, and the situation looked like a “recovery”, until this season were the last off shore “fast” ice, probably will be forced to move.
    With the new regime in the Polar Sea I doubt we will see the grounded fast ice again, for a while, since sea ice with keels are becoming more rare. What influence the missing sea ice in front of these 2 giant glaciers will have will be interesting to study in future seasons.

  8. Pingback: Zachariæ Isstrøm Further Retreat, NE Greenland « From a Glaciers Perspective

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