Greenland Glacier: back or forth?

Researchers survey movements of the Jakobshavn Isbrae Glacier

Jakobshavn Isbrae from Space © NASA
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Jakobshavn Isbrae on the west coast of Greenland is one of the fastest and most productive glaciers in the world. Every year it produces icebergs in the total volume of about 35 cubic kilometers; the most prominent of them is said to have rammed the "Titanic" in 1912. Four researchers from the TU Dresden are now embarking on a new expedition designed to determine more precisely the spatial-temporal movement patterns of the glacier using on-site photogrammetric measurements.

Recent evidence suggests that the retreat of the ten-kilometer-wide ice front is temporarily stagnant after the glacier has shrunk dramatically in the last three years. The scientists now want to gather evidence. Prof. Hans-Gerd Maas, Director of the Institute for Photogrammetry and Remote Sensing at the TU Dresden, and Prof. Reinhard Dietrich, Professor for Theoretical and Physical Geodesy and also Chairman of the German Commission for the International Polar Year, will work together with two PhD students for several weeks capture the movement of ice with high-resolution digital cameras for a long time.

Measurement with 4, 000 individual points

Simply the speed measurement is not. Since the huge glacier, which belongs to the UNESCO World Natural Heritage since 2004, is itself impassable, so that no measuring points can be placed on prominent points, Hans-Gerd Maas and his colleagues must analyze the flow movements of the glacier from the edge via photogrammetric images and supplementary geodetic measurements, The photogrammetric evaluation of the images based on 4, 000 centimeter-tracked individual points on the glacier surface, which a digital camera with a sensor format of 39 megapixels takes every 15 minutes, are hampered by the extremely rugged topography of the glacier surface and the shadow of the ice walls.

Day after day, gigantic amounts of ice crackle and grumble past the camera, which is positioned on a side elevation of the glacier fjord about one to two kilometers away from the ice, until they crash into the sea with a soft crash. With the measurements of their first expedition in 2004, the Dresden researchers were able to detect for the first time a vertical lifting movement of the glacier tongue in the tidal cycle by about two meters. Obviously, the front part of the glacier floated on the fjord.

Speed ​​has risen sharply in recent years

After all, since 1893, measurement results for the movement of the glacier are available; thereafter, the speed of the glacier remained approximately constant at twenty meters per day for 100 years, but during the last few years it increased almost abruptly to last forty meters per day. The Jakobshavn Glacier produces up to 35 cubic kilometers of ice per year; converted this amount corresponds to ten times the water consumption of the whole of Germany. display

However, the glacier now seems to shrink less, possibly due to topographical causes: the part of its tongue, which lay on the ten-kilometer-wide Kangia Fjord, is almost completely broken off. The rest of the glacier is on the mainland, behind the so-called "grounding line". Here the tides can no longer rattle the glacier tongue - the broad one

Jakobshavn Isbrae therefore breaks up more slowly.

From the 8th of July on, the researchers will be on site for several weeks and - completely cut off from civilization - will, in addition to the ongoing measurements, finally spend some more time reading the scientific articles to have. In addition to the Jacobshavn Isbrae, the method of photogrammetric determination of the flow behavior is also applied to two glaciers located further north. If it turns out that the speed of the glacier has actually decreased again, Prof. Maas wants to teach his colleagues something special: a twelve-year-old Irish whiskey with a few pieces of one hundred thousand years Greenish ice ...

(Technical University Dresden, 04.07.2007 - NPO)