Recent Glacier Melt in the Inner Himalayas
University of Göttingen, Institute of Geography, Department of Geography and High Mountain Geomorphology, Goldschmidtstraße
5, 37077 Göttingen, hachenb1@gwdg.de
Hermann Achenbach
5, 37077 Göttingen, hachenb1@gwdg.de
Hermann Achenbach
Figure 1: Research area
In 2007 and 2008, I undertook two research expeditions to 25 glaciers located in High Valleys north of the Annapurna- and Dhaulagiri Himalayas (figure 1).
Due to their poor accessibility many of the studied ice streams have not yet been scientificaly investigated. The 1-8 km long glaciers here are similar to those in South- and Central Tibet. Caused by the rain shadow of the Higher Himalayas they are of subcontinental type, what means they are cold glaciers, which get 500 to 1000 mm precipitation per year. Most of the precipitation fals during the monsoon season from June to September. In contrast to many huge and debris covered ice streams in the Higher Himalayas (e. g. Khumbu- and Kangchenjunga Himalayas) or in the Karakoram, which very often show a delayed response to climate signals, I expected that the smaller and mostly debris free glaciers in the Inner Himalayas are quite sensitive to changes in temperature or precipitation.
In the vicinity of the today's tongue ends I mapped the morphological features and took sediment samples from morainic material and meltwater accumulations. Al glacier forefields are bordered by great lateral moraines indicating the .Little IceAge.-maximum (AD 1600-1800) ( in figure 2). Compared to this ice cover, which was probably the most extensive during historical times (<~1700BP) today's glaciated area in the research section is decreased by 35%.
Due to their poor accessibility many of the studied ice streams have not yet been scientificaly investigated. The 1-8 km long glaciers here are similar to those in South- and Central Tibet. Caused by the rain shadow of the Higher Himalayas they are of subcontinental type, what means they are cold glaciers, which get 500 to 1000 mm precipitation per year. Most of the precipitation fals during the monsoon season from June to September. In contrast to many huge and debris covered ice streams in the Higher Himalayas (e. g. Khumbu- and Kangchenjunga Himalayas) or in the Karakoram, which very often show a delayed response to climate signals, I expected that the smaller and mostly debris free glaciers in the Inner Himalayas are quite sensitive to changes in temperature or precipitation.
In the vicinity of the today's tongue ends I mapped the morphological features and took sediment samples from morainic material and meltwater accumulations. Al glacier forefields are bordered by great lateral moraines indicating the .Little IceAge.-maximum (AD 1600-1800) ( in figure 2). Compared to this ice cover, which was probably the most extensive during historical times (<~1700BP) today's glaciated area in the research section is decreased by 35%.
Figure 2: Glaciers in the Hong de Himal
(photo:H.Achenbach)
From 1960 to 1980 some mountaineers and scientists took pictures of several glaciers that were also examined on my expeditions figure3a .Thus,I had the possibility to compare the conditions in those days with the situation in 2007 and 2008. This comparison showed, that in the last 30 to 50 years almost all (with the exception of one) glacier tongues melted back. The maximum length reduction from 1974 to 2007 was measured for the Mukut Glacier (figure 1 and figure 3). It was 400 m. Highly likely this ice melt is caused by a strong increase in temperature, that started in Nepal around 1975 (Shresthaetal.1999).
From 1960 to 1980 some mountaineers and scientists took pictures of several glaciers that were also examined on my expeditions figure3a .Thus,I had the possibility to compare the conditions in those days with the situation in 2007 and 2008. This comparison showed, that in the last 30 to 50 years almost all (with the exception of one) glacier tongues melted back. The maximum length reduction from 1974 to 2007 was measured for the Mukut Glacier (figure 1 and figure 3). It was 400 m. Highly likely this ice melt is caused by a strong increase in temperature, that started in Nepal around 1975 (Shresthaetal.1999).
Figure 3: Mukut Glacier
In Nepal and Southern Tibet the warming trend of the last century was interrupted by a slight temperature drop (maximum temperature decrease of 0,3° K) that started around 1940/50 Shrestha et al. 1999). As can be seen on above mentioned pictures, this colder period (from ~1940/50 to ~1975) caused a glacier stage in the 1970s. In almost all visited forefields the position of the lateral- and terminal moraines, which is some decameters beside or in front of the glacier snouts today, indicates the ice margin positions during that time ( in figure 3b). That means they were built up by a stagnant ice front or anadvance in the1970s(figure3a)
In contrast to relatively thick tongues and steep ice fronts during a slight advance/stagnation in the 1970s the today's glacier retreat is due to very flat glacier termini (figure 3b). According to Shresthaet al. (1999) in Nepal the warming after the 1970s was 0,06-0,12°K/yr. If the temperature keeps rising the glacier retreat will continue in the next decades.
The consistent retreat of the investigated glaciers after the Little Ice Age.-maximum as well as their synchronous behaviour to the short time temperature drop in the last century indicate that those small and mostly debris free glaciers react synchronously and relatively directly to climate changes. Thus they are very good indicators for climate signals.
In contrast to relatively thick tongues and steep ice fronts during a slight advance/stagnation in the 1970s the today's glacier retreat is due to very flat glacier termini (figure 3b). According to Shresthaet al. (1999) in Nepal the warming after the 1970s was 0,06-0,12°K/yr. If the temperature keeps rising the glacier retreat will continue in the next decades.
The consistent retreat of the investigated glaciers after the Little Ice Age.-maximum as well as their synchronous behaviour to the short time temperature drop in the last century indicate that those small and mostly debris free glaciers react synchronously and relatively directly to climate changes. Thus they are very good indicators for climate signals.
References
Achenbach, H. (2011): Historische und rezente Gletscherstandsschwankungen in den Einzugsgebieten des Cha Lungpa (Mukut-, Hongde- und Tongu-Himalaja sowie Tach Garbo Lungpa), des Khangsar Khola (Annapurna N-Abdachung) und des Kone Khola (Muktinath-, Purkhung- und Chulu-Himalaja, Dissertation, Universität Göttingen, 260 S. (electronic version: http://webdoc.sub.gwdg.de/diss/2011/achenbach/) Nakawo, M.: Glacier studies in a greater context: the shrinkage of summeraccumulation glaciers in Asia and a consideration of human life downstream. In: http://mri.scnatweb.ch/index2.php?option=com_docman&t ask=doc_view&gid=287&Itemid=20 ( Access: 22.06.2010), S. 1-39. Shrestha, A.B., Wake C.P., Mayewski, P.A. and Dibb, J.E, (1999): Maximum temperature trends in the Himalaya and its vicinity: An analysis based on temperature records from Nepal for the period 197194. In: J. of Climate, 12, 2775-2786.
Achenbach, H. (2011): Historische und rezente Gletscherstandsschwankungen in den Einzugsgebieten des Cha Lungpa (Mukut-, Hongde- und Tongu-Himalaja sowie Tach Garbo Lungpa), des Khangsar Khola (Annapurna N-Abdachung) und des Kone Khola (Muktinath-, Purkhung- und Chulu-Himalaja, Dissertation, Universität Göttingen, 260 S. (electronic version: http://webdoc.sub.gwdg.de/diss/2011/achenbach/) Nakawo, M.: Glacier studies in a greater context: the shrinkage of summeraccumulation glaciers in Asia and a consideration of human life downstream. In: http://mri.scnatweb.ch/index2.php?option=com_docman&t ask=doc_view&gid=287&Itemid=20 ( Access: 22.06.2010), S. 1-39. Shrestha, A.B., Wake C.P., Mayewski, P.A. and Dibb, J.E, (1999): Maximum temperature trends in the Himalaya and its vicinity: An analysis based on temperature records from Nepal for the period 197194. In: J. of Climate, 12, 2775-2786.