by Kenneth Hewitt, Cold Regions Research Centre, Wilfrid Laurier University, Ontario, Canada
Between 1994 and 1996 catastrophic movement of the 15.5-kilometer-long Chiring Glacier in northern Pakistan transferred 1-1.5 km3 of ice from its upper two thirds to its lower third, and into the main Panmah Glacier, of which it is a tributary. By October 1996, a lobe of Chiring ice some 3.2 km2 in area had entered and compressed the main glacier, which was severely disturbed for 3 kilometers above and 5 kilometers below the junction of the glaciers (see Figure 1). Ice streams and on-ice moraines--accumulations of rock carried by glaciers--were pushed into a series of looped or "tear-drop" forms that are common to surging glaciers. Despite an observational record back to 1856, it was not previously realized that changes in the Chiring Glacier involve surging.
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| Figure 1. The junction of the Chiring with the main glacier in October 1996. showing the results of the surge. The view looks southwest from above Skinmang Camp. The heavily crevassed chiring ice still reflects disturbance by the surge. A lobe of Chiring ice has compressed and overridden the main glacier and created looped or "tear-drop" forms in its ice streams. Arrows in the left, near-ground identify "trim-lines" of stagnant ice left by the passage of the surge. Here, the Chiring is roughly 1 kilometer wide, and the main glacier is 2.5 kilometers wide. |
Surges are relatively short-lived episodes in which ice movement suddenly increases significantly, mainly because of rapid sliding at the base or bed of the glacier. One or more pulses of sharply accelerating flow also move down the glacier accompanied by a rise and severe crevassing of the ice surface. Surge events can last from a few months to several years. While some surges advance the outer margin of the glacier several kilometers in a few months, others dissipate before reaching the outer margin, especially those of tributary glaciers such as the Chiring. But even when a surge has subsided, the ice it contributes can lead to glacier advance later.
Surges can be serious hazards in populated areas, engulfing occupied land, generating sudden floods, or disrupting local communications below and across glaciers. They tend to recur in cycles, but seem unrelated to normal patterns of advance and retreat. In regions with many surging glaciers, such as the Karakoram Himalaya, surges complicate the normally sensitive relationship between glaciers and climate.
The Karakoram lies immediately north of the western part of the greater Himalaya and is the highest of the southwest central Asian mountain systems. It has the largest concentration of glaciers on mainland Asia and outside high latitudes, with 8 glaciers over 50 kilometers long and more than 20 over 30 kilometers. The perennial snow and ice cover, which exceeds 16,000 km2, comprises a huge fresh water store in a generally arid, drought-prone region. Glacial meltwaters make a major contribution to the flow of the Indus and Yarkand Rivers and to the livelihood of some 130 million people.
In the last 100 years, 26 sudden, rapid advances involving 17 glaciers have been reported in the Karakoram region. Another 12 glaciers have features associated with surge behavior (see Figure 2).
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| Figure 2. Location map of the Karakoram Himalaya, its glacier cover, and known or suspected surging glaciers. Click photo for enlarged view |
In its lower 5 kilometers, the glacier was much thicker than in 1992, burying the former outwash plain--and our October 1992 base campsite--under 110-150 meters of ice! Deep crevasses sliced directly across the central regions, 20-40 meters apart, giving way in narrow lateral zones to crevasses angled sharply down glacier (see Figure 1). By late 1996, however, the active ice was well below the full height of the surge.
At the head of the Chiring is the New Mustagh Pass (5,800 meters), an ancient route to central Asia. The discovery that Chiring is a surging glacier gives a new slant to an old debate about the role of glacier fluctuations in historic closings of this and other glacier passes to inner Asia. Maps, drawings, and photographs from 1856, 1861, 1929, and 1937 show the lower Chiring was easily crossed by travelers. Although altitude and bad weather posed problems, the upper glacier also offered a relatively straightforward traverse to the pass. In 1887, however, a British explorer, Francis Younghusband, coming from the Chinese side, found the pass closed. After crossing by another route, he attempted to ascend the Chiring but found it impassable because of "... an immense ice-slip on to the glacier and gigantic blocks of ice... tumbled about on top of one another...". His descriptions accord with the effects of a surge and strongly suggest that the Chiring last surged in 1885-87, giving a surge cycle of about 110 years. Other evidence suggests that the Chiring is not the only surging tributary of Panmah. Satellite imagery and earlier expedition reports show the Drenmang, immediately upstream, has surged twice this century. Major changes in the Maedan between 1856 and 1861 indicate a surge, and this glacier had advanced 1.5 kilometers between 1993 and 1996 (see Figure 3).
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| Figure 3. Panmah Glacier basin showing the topography, main ice streams, and extent of surge activity of the Chiring by October 1996 (The base map after the unpublished Shipton-Royal Geographical Society (R. G. S.) map, 1939, held in the R. G. S. map library, and Landsat imagery.) Click photo for enlarged view |
Surges raise special and partly unresolved questions for glaciologists, including the conditions that initiate surging, problems of fast glacier flow, and whether deposits left by surges can be used to identify their role in the history of glaciation. Surges occur in some small ice caps, a wide range of valley glaciers from high-altitude to tidewater locations, and from polar to subtropical and maritime to midcontinental areas. No specific or general, environmental or glaciological parameters appear uniquely identified with surging. None seem to explain why surging does not occur in most glaciated regions, including the American cordilleras, from northern British Columbia to central Argentina, and the European Alps.
Whatever the controlling factors and exact mechanisms, the key to surging lies in conditions that periodically promote instability at the glacier bed. Yet, a highly uneven geography and large numbers in just a few regions suggest that special combinations of conditions promote or suppress surging. The kinds of evidence available from the Karakoram are of broadest interest in relation to this line of inquiry and in comparison to the better-known examples. The Karakoram surging glaciers lie at much higher elevations than those of the Alaska-Yukon ranges, Svalbard, or Iceland, and are generally much steeper. They have an extreme continental location comparable to the nearby Pamir examples, and subtropical latitudes similar to those of Andean Argentina. The upper elevation limits of surging activity generally occur in the accumulation zones between 5,000 and 7,000 meters above sea level and some 2,000-3,000 meters above the termini. The enormous extent, steepness, and elevation range of rock walls surrounding the glaciers may be the most distinctive aspect of the environment and these ice masses.
Many Karakoram glaciers, and all of those known to surge, are fed by avalanches. The upper parts of these glaciers are subject to all-season avalanching. Moreover, the zone of highest precipitation lies between 5,000 and 7,000 meters. The avalanches also carry more abundant snowfall directly to the glaciers, where much of it accumulates below the regional snow and firn limits. Avalanche nourishment raises special questions of glacier mass balance and gives the ice a much heavier debris content.
Most of the snow descends from the coldest perennial ice climate zone and accumulates directly as dense, avalanched snow at lower altitudes in summer and winter, suggesting that there may be complex thermal layering. Meanwhile, relatively dirty ice contributes to significantly higher melting rates in the upper and middle melting zones, while a buildup of thick glacial debris on top of the glacier tends to suppress melting in the lower melting zone. One model of surging relies on the presence of sediment under the glacier. Where the bed is unfrozen, the more abundant debris in avalanche-derived ice could contribute to this. Enormous ramps of glacial debris develop and build outward beside and beneath the melting zones of the avalanche-fed glaciers--but many are not known to surge. The geology of the Karakorm is extremely complex and diverse, and most surging glaciers cross two or more major formations. No specific and distinctive relationship of surging to the underlying rocks is yet apparent. There are no volcanoes, but hot springs are widespread across the region and some scientists have suggested that they, or the higher geothermal heat flow they imply, could be a factor in surges. As with the Panmah-Chiring relation, main glaciers that do not surge are much longer, of gentler slope, and wider than their surging tributaries.
The new evidence reported here shifts the balance of interest in surges toward those of tributary glaciers, over half the known Karakoram examples. Moreover, five confirmed, and three other possible, tributary surges have occurred in the past decade (see Figure 2). Whether this number reflects exceptional activity or improved observation, it raises new questions for interpreting glacier fluctuations and their relations to climate change.
The Karakoram is of unusual interest and perhaps sensitive to climate change to an unusual degree because its glaciers lie within the variable influence of three major weather systems: the "sub-Mediterranean" regime of mainly winter, westerly storms; the summer monsoon; and the Tibetan Plateau anticyclone. Winter storms are the main source of glacier nourishment at present. However, nearly one-third of the high-elevation snow accumulation we measured occurs in summer. It has been argued that general patterns of glacier advance and retreat in the region relate to changing vigor of the monsoons. The possibility of such large shifts in the atmospheric sources and seasonal occurrence of glacier nourishment does not seem to arise in other regions with surging glaciers, whose relation to the larger climatic shifts, remains unresolved.
| A Few Words From the Author | |
I am currently acting director of the Cold Regions Research Centre, which I helped found 10 years ago, and Professor of Geography at Wilfrid Laurier University, Waterloo, Ontario, Canada. I have also taught at the Universities of Toronto, Ontario, and Rutgers, New Jersey. I received an M.A. from the University of Cambridge and a Ph.D. from the University of London. My research focuses on high mountain regions, especially the Karakoram Himalaya, and on environmental risks and disasters involving, especially, extreme natural events. I=ve spent eleven field seasons in the Karakoram, five in the Canadian Rocky Mountains, and made short-term investigations in the European Alps, mountains around the Eastern Mediterranean, and the Andes. |
A fascination with mountains and opportunities for travel and mountaineering started me off. I had not expected to do well enough academically to go into research or find employment that would turn this into a vocation! I did want to teach and, thanks to some excellent mentors and colleagues, I was fortunate to get the opportunity to combine that with research on places and topics that interested me most. The mountaineer Eric Shipton, who had explored the high glacier basins of the Karakoram in the 1930s--including Panmah--first suggested I might find the region worth investigating. Eventually, a planned mountain adventure turned into a hard year of field research on a Karakoram glacier, the basis of a doctoral dissertation. My work has been increasingly influenced by the realization that many of the world's high mountain peoples and environments are in serious trouble. Modern developments from mountain tourism to climate change raise unusual problems of ethical, let alone sustainable use, for concerned researchers no less than in resource extraction and for indigenous peoples. This has led me to a growing concern with the scope and forms of human activities than are adversely affecting high mountain environments and the vulnerability to their inhabitants to natural disaster. |