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[degrees] to 4[degrees]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 glaciers 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 glaciers 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)
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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. …