Glaciers are represented by the flowing movement of a thick mass of ice and form as a result of the compaction or recrystallization of snow. Glaciers occur in areas whose climate favours the seasonal accumulation of snow in greater volumes than seasonal ablation. Here the seasonal accumulation of snow outpaces seasonal ablation that occurs due to loss of snow from melting, calving, evaporation and/or wind erosion. Glaciers can thus be found in Polar and Alpine Regions where temperatures can be substantially low and significant precipitation in the form of snow also can occur. Glacial landforms are formed as a result of erosion that occurs during glacial advances and also deposition that occurs during glacial retreat (Goff, 2016).
The state of a glacier is measured according to the difference between accumulation and ablation of a glacier, and is known as the Mass Balance of the glacier. When the accumulation is greater than ablation, the glacier is said to have a positive mass balance and when ablation is greater than accumulation, the glacier is said to have a negative mass balance. The measurement indicated as mass balance is useful in identifying glacial advance or glacial retreat and its mechanisms can help in making concurrent estimates about the health of a glacier.
However, although glacial progress in the contemporary time can be ascertained with the help of mass balance measurements, the study of glacial landforms such as moraine boulders, sediment deposits, etc and organic matter within sites of present and past glacial activity can help us in understanding glaciations in geological time in the past. Studying glacial activity in the past can help us in better understanding glacial landforms and their various influences on geomorphology and their relation to and interaction with past climatic conditions. In utilizing glacial landforms in studying past climate, the studies of fjords in the Svalbard archipelago in the Arctic for example were utilized by the National Centre for Antarctic and Ocean Research (NCAOR), in reconstructing past climate variability at different timescales (NCAOR, Undated). Such can be invaluable tools in understanding the effects of climatic variability.
Glacial Landforms in the Himalaya
There are however, many issues in the study of the geological past of Himalayan glaciers that pose difficulties in forming comprehensive conclusions on the timing and extent of glaciations and responses in terms of climate and hydrology in the Himalaya. Other than issues around the political and logistical inaccessibility of the Himalaya, estimating former glaciation extent is also hindered by difficulties in the mapping of glacial landforms. The principal difficulty in this respect is the difficulty of finding organic material that would allow radiocarbon dating that could allow researchers to make temporal estimates. As such radiocarbon dating, for one, is mostly limited to dating organic material from the wetter parts of the Himalayas, and second, it is mostly restricted to dating the Holocene period. New techniques however, are emerging such as optically stimulated luminescence (OSL) and terrestrial cosmogenic nuclide (TCN) surface exposure dating. While OSL dating allows for temporal estimates for sediments, TCN dating can be used for glacially eroded surfaces and moraine boulders (Owen, 2016).
Undoubtably the glacial landforms have played an important part in shaping the periglacial geomorphology of the areas around the higher Himalaya. Additionally, the glacier catchments contribute to the hydrological system of the Ganges, the Brahmaputra and the Indus river basins by the melting of snow in the Himalayas, as well as by the melting of Himalayan glaciers, such as the melting of the Gangotri glacier for the Ganges river basin for instance. Annual snowmelt provides between 10 to more than 30 per cent of water for the 10 major river basins that originate in the Hindu Kush Himalayas for instance (ICIMOD, 2018). The melting of snow in the Himalaya is representative of a change in climatic systems in the Himalayas from an earlier colder period to the contemporary period which is comparatively warmer.
Kulkarni et al. (2017) recently published a study in an International Journal which reports that low altitude glaciers in the Himalaya are at particular risk of receding as compared to those at higher altitudes. He comments that glaciers might not vanish altogether in the Himalayas in the very near future although the smaller ones might be significantly affected. He estimates that in the Chandra basin of Himachal Pradesh alone, a 67 per cent of the loss in water volume was contributed by low altitude glaciers in the past 3 decades while higher altitude glaciers contributed to 19 per cent of the water loss. It is also extrapolated that regions fed by low altitude glaciers might experience water scarcity because of a rapid run off (Chauhan, 2017). Contrary to popular perception that connects glacial retreat with recent global warming, glaciers in the Himalaya have been in constant retreat since observations began in the mid-Nineteenth century (Raina, 2009).
More extensive glaciation is observed in the western Himalayas as they are present in higher latitudes than the eastern Himalayas. In the cooler Pleistocene era, the regions of what are now Kashmir and Ladakh were covered with very large glaciers. Pleistocene moraine deposits have formed gorges as deep as 100 m in these regions. As an example of Pleistocene moraine deposits, in the north eastern slope of the Pir Panjal Range, glacial material has completely covered the bedrock due to glaciation during the Pleistocene era. At an altitude of between 3000 to 3300 m, this glacial matter is in the form of sorted ground moraines and at a higher altitude of between 3300 and 3600 m, the glacial matter is in the form of unsorted lateral moraines. At a distance of about 600 m from active moraines and live ice are located the older moraine deposits which were found to be covered with vegetation, especially juniper and birch forests and grasses (Vohra, 2012). Active moraines however, are largely devoid of plant cover.
Observations of Pleistocene glaciation suggest that glaciers might have come down to an altitude of about 600 m above sea level during the era. There is also evidence that the eastern Himalayas had more extensive glaciations during the Pleistocene era than in current times. The northern regions of Bhutan and Sikkim have mountains that bear many old moraines that are located several kilometres from the smaller present-day glaciers. The ice cover in these regions might have been much thicker in the past as evidenced by material possibly derived from higher mountains deposited on hills composed of older moraine deposits that are several meters above the surrounding areas (Vohra, 2012). The study of glacial landforms can thus contribute to a greater understanding of past events in earlier eras. These in turn can help in understanding how climatic shifts can influence the geomorphology of regions in the Himalayas.
Rowan (2016) has described how the expansion of glaciers in the Himalaya occurred between 1400 AD and 1900 AD due to northern hemisphere cooling, which is also sometimes called the little ice age. Conclusions on these glacial expansions were based on the study of the position and appearance of moraines and were found to be similar to little ice age advances in Europe. Moraine building can thus offer a guide for instance about past climatic environments and shifts and how they could have influenced the geomorphology of the Earth. Rowan was able to determine how colder northern hemisphere air temperatures that were sustained due to increased precipitation as a result of air circulation patterns resulted in the expansion of Himalayan glaciers on the basis of studying glacial landforms.
Glacial landforms and the climate are co-dependent, and any difference in temperatures, air circulation patterns, precipitation and so on can massively impact the advance or retreat of glaciers. Glacial activity can in turn impact the surrounding landscape, as in how water can be stored in the form of ice in glaciers thus impacting local or regional hydrology, in the forms of landforms carved out by glaciers, in the issues of accessibility caused due to changes in glacial activity and so on. It can be said that glaciers and glacial landforms are sensitive barometers of a changing climate, in that even small differences in precipitation and temperature for instance can result in palpable changes in glacial mass balance. With many accessibility issues arising in the case of many glaciers and glacial landforms, more resources must be devoted to the studies and measurements of glaciers if we are to keep track of global warming. The study of past climatic changes can in turn be conducted with the help of dating the glacial landforms using modern techniques, providing thus invaluable insights into the impacts of past climate change.