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The sudden surging of glaciers is not related to climatic fluctuations, and surges can take place even at times when glaciers retreat.
It should be emphasized that the problem of climate change is extremely difficult to understand, and it has still not been possible to know what factors in the past decades—natural or anthropogenic—have caused the warming.

The Earth’s climate undergoes fluctuations and for the past thousand years has experienced periods of warming and cooling. In the seventeenth century, severe and long-standing winters, known as the Little Ice Age, recurred in the south of Europe. One can see frozen channels and snow-covered Holland in the paintings of famous Flemish artists.

Little Ice Age

The cold epoch ended in the middle of the nineteenth century and the climate began to warm in the last century and a half, quicker in the first half especially in the Polar regions. In the decade starting 1920, average annual temperatures in the Arctic had risen by 2° to 4°C, along with frequent cyclonic activity in the northern latitudes. Glaciers retreated in mountains almost everywhere: By 1950, glacier area shrunk by 25 per cent in Switzerland and by 15 per cent in the Caucasus. Although mountain glaciers sporadically advanced in the 1920s and 1960s, these cold periods were short and limited in scope and, by 2000, the steady rise in temperature became global.

Global warming has caused serious concern and has been the subject of discussions amongst scientists and decision makers. The UN Intergovernmental Panel on Climate Change (IPCC) assessment reports verify that surface air temperatures are rising. Undoubtedly, this warming is one of the factors for faster melting of mountain glaciers and ice sheets, with the exception of the Antarctic ice sheet that stores about 90 per cent of global ice. And studies of the Antarctic ice sheet over the past 50 years show that, not withstanding measurement errors, the ice mass did not diminish, which demonstrates its stability. However, the slow rise in sea levels caused by thermal expansion of oceanic water and by the melting of the Greenland ice sheet and other polar and mountain glaciers is of great importance to coastal populations.

Against this background of climate change, I will try to explain how glaciers become unstable, or surge into surrounding areas threatening human populations, and how to monitor against such surges.

Special Class of
Surging Glaciers

On occasion, individual glaciers advance quickly against a general shortening of glaciation—the term for a glacier’s growth and maturity. For instance, in 1963, the glacier Medvezhiy, “awoke” and surged down the western slope of the Academia Nauk mountain range, the highest of the Pamirs in Central Asia. The glacier’s usual velocity had been 200-400 metres per year, no more than 1 metre per day. But in April 1963, its velocity suddenly shot up by a hundredfold, and it surged down the valley at 100 metres a day. Within a month, Medvezhiy’s tongue measured almost 2 kilometres (km) as it split a valley into two, forming an 8-metre-deep lake. The lake’s pressure eventually fractured the ice coffer dam and soon water flooded the Vanch River at 1000 cubic metres per second, ferrying large chunks of ice and stone. (Fig. 2)

Medvezhiy’s surge lent impetus to a study of surging glaciers in the former Soviet Union. Starting in 1963, a special expedition regularly explored the glacier, recording thorough observations which formed the basis for predicting the next surge. Following several surveys of Medvezhiy, it was possible to predict the time and scale of the next surge, which happened in the summer of 1973. It was the first-ever scientific prediction of a glacial calamity. A few months later, in the spring of 1973, Medvezhiy again began to advance. Within two months its tongue lengthened 1.8 km and lapped up the remains of its surge 10 years ago. The glacier again dammed the tributary in the valley, and a lake again welled up behind the glacial barrier, which broke twice, flooding the surroundings with a discharge of 1000 cubic metres per second.

Since the 1960s and 1970s, studies of surging glaciers, particularly of Medvezhiy, painted a scientific picture of the structure and nature of glaciers. It was found that a glacier repeated its surge in almost equal time intervals provided that external conditions did not change. Yet even under similar geographic conditions, different glaciers reacted differently. Medvezhiy surged every 9-17 years. According to indirect data and local sightings, the glacier advanced in 1937 and 1951, while direct observations noted surges in 1963, 1972, and 1989.

The sudden surging of glaciers is not related to climatic fluctuations, and surges can take place even at times when glaciers retreat. This is the usual behaviour of some glaciers and can not be evidence of an impending surge. A time interval between the start of a surge and its end is called a pulsation and, in fact, periodic pulsations arise due to instability within the glacier. The frictional force at the glacier’s bed breaks the ice. Hundreds of surging glaciers are now known in many glacial regions, with the largest numbers in Alaska, Iceland, the Spitsbergen—the largest island of the Svalbard archipelago in the Arctic Ocean—as well as in the mountains of Central Asia and in the Pamirs.

A glacier’s pulsation consists of two main stages: a surge and a regeneration. During a surge, a glacier releases accumulated tension from its preceding stage of regeneration. The glacier splits, its velocity shoots up, and ice mass from the top of the glacier is displaced into its middle and lower zones. As this happens, the glacier’s upper and lower zones come closer, forcing the glacier’s tongue to lengthen. At the end of a surge, the regeneration begins when ice accumulates in the upper pulsating zone, while the front end of the activated area gradually moves.

But there is an unsolved question: what is the difference between a “normal” and a surging glacier, and can a normal glacier turn into a surging one? In any case, as mentioned earlier, a glacier’s activation does not always result in a surge. But the glacier’s movement does disrupt the structure and regime of the glacier as a whole: as ice accelerates, cracks appear in it that are filled with stone and new morainic deposits.

Causes and mechanisms of glacier surges

Generally, a glacier surges when narrow mountain valleys or morainic cover holds back the discharge of ice, creating instability. Unfortunately, direct observations of a change in the movement of a glacier at the onset of a surge are still very rare, and the causes for surges are not yet clear. At present, some hypotheses are being proposed in an attempt to explain the mechanism of surges.

A glacier’s velocity increases abruptly either due to intensification of forces that drive it (mainly gravity) or a more problematic cause is the weakening friction inside the glacier and on the mountain bed. Both these processes are connected. The flow of ice increases suddenly after overcoming a threshold load, which happens as a result of accumulation of ice over the years in the glacier’s reservoir.