Glacier Fluctuations and Hazards

Abstract

discussion of the types of hazards associated with climatically led oscillations in populated areas and their timing. The threat from such glaciers has diminished but not disappeared with the recession of the last century. The impact of the more dramatic oscillations of surging glaciers and those with floating tongues has been limited by their restricted spatial distribution. Increased penetration of economic development into hitherto remote mountain regions and escalation of the numbers of people involved in sports such as skiing and mountaineering increase glacier hazard. Any future change in climate towards the conditions obtaining in the Little Ice Age would now involve greater risk from hazard than existed in former centuries. A more probable change in climate is rising temperature caused by more carbon dioxide in the atmosphere resulting in rising sea levels and perhaps surging of the Antarctic icesheet. IT IS ONLY AT PARTICULAR TIMES and in particular places that glaciers have offered any threat. Most of them are concentrated in remote places far from habitation. From the utilitarian point of view their main importance is as water storage sources, especially for power generation. In the last few decades they have come to provide an increasing number of people with opportunities to climb, ski or just admire, usually but not always from a safe distance. Glaciers are, however, rarely static for very long. As they respond sensitively to climate, and climate is not constant, so glaciers expand and shrink, extend and retract, and some of the physical adjustments involved may present high risk situations if glaciers are near populated areas or if they are near dams, railways and other such engineering structures. Glacier hazards are, it may be suggested, strongly localized in time and place. They are most severe in those instances where the glaciers are associated with active volcanoes near plate boundaries. Glaciers on every continent expanded during the Little Ice Age. During this period, mean annual temperatures were of the order of 1-2?C cooler than they are today and snowlines were as much as 200 or 300 metres lower. The climatic shifts involved were sufficient to cause valley glaciers to thicken and lengthen by a matter of two or three kilometres. The Little Ice Age was not a period of uniform climate but one during which groups of years with short cool summers, late springs and early autumns occurred more frequently than they have in the last 130 years or so. Glaciers at first advanced rather swiftly to reach unwontedly forward positions; then, their fronts oscillated to and fro leaving in many cases a sequence of moraines; and finally, since the late nineteenth century, they have retreated once more. The Little Ice Age in Europe is best known where literate communities living near the glaciers have left a mass of documents, some of them remarkably precise, which make it possible to sort out the sequence of events and some of their consequences. Even here, however, information is incomplete; we know, for instance little of the course of events in northern Scandinavia. In the European Alps valley glaciers advanced rapidly between 1580 and 1600 and remained enlarged, though not constant in either size or terminal position, until the mid-nineteenth century. In southern Scandinavia and in Iceland there are no clear records of advance before the late