Mittivakkat
| Mittivakkat | ||
|---|---|---|
 Mittivakkat Glacier from the southwest (August 2016) |
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| location | Ammassalik Ø ( Greenland ) | |
| Type | Ice cap / valley glacier | |
| length | 7.4 km (2015) | |
| surface | 15.8 km² (2014) | |
| Exposure | Southwest ( main tongue ) | |
| Altitude range | 880 m - 160 m (2013) | |
| Tilt | ⌀ 5.6 ° (10%) | |
| width | ⌀ 1.5 km | |
| Ice thickness | ⌀ 90 m (2014) | |
| Ice volume | 1.44 km³ (2014) | |
| Coordinates | 65 ° 41 '24 " N , 37 ° 50' 24" W | |
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| drainage | Sermilik and Tasiilaq fjords , Irmingersee | |
Mittivakkat (East Greenlandic for sponges , West Greenlandic Milluakkat or, according to the old spelling, Mitdluagkat ) is a 973 m high nunatak and the unofficial name of a glacier on the Ammassalik Island in southeastern Greenland, almost 100 kilometers south of the Arctic Circle . The ice mass, first geodetically measured in 1933, is considered to be the most studied glacier in Greenland that is not related to the Greenland Ice Sheet . The starting point for glaciological , climatological and geomorphological research activities is the nearby Sermilik station operated by the University of Copenhagen .
Location and surroundings
The Mittivakkat glacier extends as a local ice cap in the western part of Ammassalik Ø, on which Tasiilaq is located around twelve kilometers away . The glacial environment is defined by steep mountains and deeply cut valleys. The highest point near the glacier is Vegas Fjeld at 1084 meters. The glacier mostly drains in a south-westerly direction to the Sermilik fjord , but it also has smaller tongues draining to the south and east ( Tasiilaq ). Research bases in the vicinity are the Sermilik station, located directly by the sea (around an hour's walk to the glacier) and the Nunatak station ( 515 m ) in all-roof construction .
The eponymous Nunatak Mittivakkat ( 973 m ) rises above the glacier as Nunatak. Like the surrounding mountains, it is made of Proterozoic gneiss and forms a wall around 100 meters high to the west. Instead of a summit cross, there is an Inussuk on the southwest summit .
A popular multi-day trekking route , most of which is not marked, encircles the glacier over a relatively large area. Numerous glacial lakes are passed, which are also fed by the meltwater of the Mittivakkat. The inspection of the crevice-rich glacier surface itself is done almost exclusively by scientific staff and students.
glaciology
| Mittivakkat | |
|---|---|
 Nunatak over the glacier |
|
| height | 973 m |
| location | Ammassalik Ø ( Greenland ) |
| Dominance | 2.3 km → Elevation on the eastern edge of the glacier |
| Notch height | 200 m ↓ ice divide |
| Coordinates | 65 ° 43 ′ 14 " N , 37 ° 46 ′ 24" W. |
| Type | Nunatak |
| rock | Gneiss |
| Age of the rock | Proterozoic |
The Mittivakkat glacier is a temperature-controlled valley glacier , the surface temperature of which is around 0 ° C as an annual mean. The ice cap forms several tongues , with the main direction of flow being southwest. The ice divide was at around 880 meters in 2013, the lower edge of the glacier with the glacier gate at a good 160 meters above sea level. The length of the main tongue from the ice divide to the glacier front is about 7.4 kilometers. While the accumulation area remains mostly snow-covered over the summer, the ablation area is characterized by numerous superficial drainage channels, mills and crevices. This results in an extremely rough glacier surface, which makes an ascent quite difficult. Large parts of the main tongue appear “dirty” due to the sediments carried along , which has a corresponding effect on the albedo .
Between 1986 and 2011 the mean specific mass balance was −0.97 ± 0.75 meters of water equivalent . During this time, the average ice thickness decreased by 15% and the volume by 30%. From measurements of the mass balance using the glaciological method on the ice surface, one can conclude that the vertical expansion of the glacier seems to compensate a not inconsiderable part of the losses, in the lower part 60% are compensated in this way, in the upper 25%. The mean speed of the glacier on the surface decreased by 30% during this period, which is most likely due to the change in glacier dynamics due to the decrease in thickness .
Climatic basics
Climate measurements have only been carried out on the Mittivakkat Glacier since the 1990s, which is why the station in Tasiilaq, twelve kilometers away, is used if long-term data is required. There the average annual temperature is -1.4 ° C. The average annual precipitation is 866 mm, of which 722 mm falls as snow in winter.
The main wind directions are NNW and NW. Piteqqat with speeds of well over 100 km / h arise over the inland ice and are among the strongest winds measured worldwide. They have a significant impact on the distribution of snow on Ammassalik Island. Measurements of the snowpack base temperature at 165 m in the winter of 1994/95 resulted in values of around −5 ° C, which, together with the mean air temperature, is an indication of the occurrence of permafrost .
Research history
Knud Rasmussen's seventh and last Thule expedition took him to the Ammassalik region in 1932/33. The latest technologies, including an improved photo theodolite and aerial photography via seaplane, were used for the mapping . The geologist Keld Milthers (1907–1960) was given the task of investigating the glaciers and their relationship to the respective landforms. In the summer of 1933, he explored five of the 15 regional glaciers in more detail by making photo documentation of their tongues. He provided four of them with level sticks that were supposed to measure the ablation , including an ice sheet in the southwest of Ammassalik Island. Milthers referred to the previously unnamed glacier in his field book after the central Nunatak as Midtluagkat . In contrast to the Greenlandic authorities, the geographers Larsen (1959) and Fristrup (1960) adopted the name, which has since established itself in specialist literature and also appears on tourist maps. In the meantime, the East Greenland spelling Mittivakkat is almost exclusively used.
In 2009, researchers at the University of Copenhagen discovered the base plates of his theodolite recordings with the help of Milthers' field book, which enabled a comparative reconstruction of the photos for the first time. One of these was created as part of a Milthers commemorative expedition that led to the original recording locations in 2010. In this way, a horizontal retreat of the glacier of 1283 meters in the period 1933-2010 could be determined. He also succeeded in reconstructing the ablation rate for the summer of 1933 based on his records.
Web links
- The Sermilik Scientific Research Station (English)
Remarks
- ↑ The Nunatak measures 973 or 931 meters, depending on the map. A GPS measurement carried out on July 28, 2016 in high pressure weather confirmed the first value. In addition, the measuring point varies in the available map material; either the front (southern) or the rear (around 500 meters northeast) summit is inscribed as Mittivakkat or Mitdluagkat .
Individual evidence
- ↑ a b c d USGS satellite image via Google Earth , taken on July 8, 2015
- ↑ a b c Jacob C. Yde et al .: Volume measurements of Mittivakkat Gletscher, southeast Greenland. In: Journal of Glaciology , Vol. 60, No. 224 (2014), pp. 1199–1207 (English), doi: 10.3189 / 2014JoG14J047 .
- ↑ Sebastian H. Mernild et al .: Identification of snow ablation rate, ELA, AAR, and net mass balance using transient snowline variations on two Arctic glaciers. In: Journal of Glaciology . Vol. 59, No. 216 (2013), pp. 649-659 (English), doi: 10.3189 / 2013JoG12J221 .
- ↑ a b c Anders A. Bjørk, LM Kruse & PB Michaelsen: Brief communication: Getting Greenland's glaciers right - a new data set of all official Greenlandic glacier names . In: The Cryosphere 9 (2015), pp. 2215-2218 (English), doi: 10.5194 / tc-9-2215-2015 .
- ↑ a b c Sebastian H. Mernild et al .: Thinning and slowdown of Greenland's Mittivakkat Glacier. In: The Cryosphere Discussions 6 (2012), pp. 4387-4415 (English), doi: 10.5194 / tcd-6-2005-2012 .
- ↑ Hasse Højmark Andersen et al .: Hiking routes in East Greenland. Ammassalik / Tasiilaq . Committee on Walking Tourism in Greenland. Copenhagen 1995, p. 13, ISBN 87-985364-2-7 .
- ↑ Danish Meteorological Institute. Quoted in: Hanne Christiansen et al. (1999)
- ↑ Hanne H. Christiansen, Andrew S. Murray, Vagn Mejdahl & Ole Humlum: Luminescence dating of Holocene geomorphic activity on Ammassalik Island, SE Greenland. In: Quaternary Geochronology 18 (1999), pp. 191-205 (English), doi: 10.1016 / S0277-3791 (98) 00052-3 .
- ↑ PH Jensen: Piteraq . Atuakkiorfik 1990. Quoted in: Hanne Christiansen et al. (1999)
- ↑ W. Haeberli (1973): The base temperature of the winter snowpack as a possible indicator for the spread of permafrost in the Alps . Journal of Glacier Science and Glaciology, IX. Quoted in: Hanne Christiansen et al. (1999)
- ↑ a b Bent Hasholt, Dirk van As & Niels Tvis Knudsen: Historical ablation rates on south-east Greenland glaciers Measured in the 1933 hot summer . In: Polar Research 2016, p. 1, doi: 10.3402 / polar.v35.28858 .