A range of environmental and social dimensions of disasters occur in or are affected by the mountain cryosphere (MC). Core areas have glaciers and permafrost, intensive freeze-thaw, and seasonally abundant melt waters. A variety of cryospheric hazards is involved, their dangers magnified by steep, high, and rugged terrain. Some unique threats are snow or ice avalanches and glacial lake outburst floods. These highlight the classic alpine zones, but cryospheric hazards occur in more extensive parts of mountain ecosystems, affecting greater populations and more varied settings. Recently, habitat threats have become identified with global climate warming: receding glaciers, declining snowfall, and degrading permafrost. Particularly dangerous prospects arise with changing hazards in the populous mid-latitude and tropical high mountains. Six modern calamities briefly introduce the kinds of dangers and human contexts engaged. Disaster style and scope differs between events confined to the MC, others in which it is only a part or is a source of dangerous processes that descend into surrounding lowlands. The MC is also affected by non-cryospheric hazards, notably earthquake and volcanism. In human terms, the MC shares many disaster risk issues with other regions. Economy and land use, poverty or gender, for instance, are critical aspects of exposure and protections, or lack of them. This situates disaster risk within human ecological and adaptive relations to the predicaments of cold and steepland terrain. A great diversity of habitats and cultures is recognized. “Verticality” offers a unifying theme; characterizing the MC through ways in which life forms, ecosystems, and human settlement adjust to altitudinal zones, to upslope transitions, and the downslope cascades of moisture and geomorphic processes. These also give special importance to multi-hazard chains and long-runout processes including floods. Traditional mountain cultures exploit proximity and seasonality of different resources in the vertical, and avoidance of steepland dangers. This underscores sustainability and changing risk for the many surviving agro-pastoral and village economies and the special predicaments of indigenous cultures. Certain common stereotypes, such as remoteness or fragility of mountain habitats, require caution. They tend to overemphasize environmental determinism and underestimate social factors. Nor should they lead to neglect of wealthier, modernized areas, which also benefit most from geophysical research, dedicated agencies, and expert systems. However, modern developments now affect nearly all MC regions, bringing expanding dangers as well as benefits. Threats related to road networks are discussed, from mining and other large-scale resource extraction. Disaster losses and responses are also being rapidly transformed by urbanization. More broadly, highland–lowland relations can uniquely affect disaster risk, as do transboundary issues and initiatives in the mountains stemming from metropolitan centers. Anthropogenic climate warming generates dangers for mountain peoples but originates mainly from lowland activities. The extent of armed conflict affecting the MC is exceptional. Conflicts affect all aspects of human security. In the mountains as most other places, disaster risk reduction (DRR) policies have tended to favor emergency response. A human ecological approach emphasizes the need to pursue avoidance strategies, precautionary and capacity-building measures. Fundamental humanitarian concerns are essential in such an approach, and point to the importance of good governance and ethics.
This is an advance summary of a forthcoming article in the Oxford Research Encyclopedia of Natural Hazard Science. Please check back later for the full article.
Rock avalanches are very large (> 1 million cubic meters) landslides from rock slopes, which can travel much farther across the landscape than smaller events; the larger the avalanche, the greater the excess travel distance. Rock avalanches first became prominent in Switzerland in the 1800s, when the Elm and Goldau events killed people a surprisingly long way from the origin of the landslide; these events first posed the “long-runout rock-avalanche” problem. In essence, the long runout of these events appears to require low friction beneath and within the moving rock mass in order to explain their extremely long deposits; but in spite of recently intense research, this low friction still lacks a generally accepted explanation. Large collapses of volcano edifices can also generate rock avalanches that travel very long distances, albeit with a different runout-volume relationship to that of non-volcanic events. Compounding the puzzle is the presence of long-runout deposits not just on land, but also beneath the sea and on the surfaces of Mars and the Moon.
Numerous studies of rock avalanches have yielded some consistencies of material and behavior, for example, that little or no mixing of material occurs within the moving debris mass during runout; that the deposit material beneath a meter-scale surface layer is pervasively and intensely fragmented, with fragments down to sub-micron size; that many of these fragments are themselves agglomerates of even finer particles; that throughout the travel of a rock avalanche, large volumes of fine dust are produced; that rock avalanche surfaces are typically hummocky at a range of scales; and that there are definite trends in plots of runout distance against volume from rock avalanches in different environments.
Since rock avalanches can travel tens of kilometers from their source, they pose severe, if low-probability, direct hazards to societal assets in mountain valleys. Compounding this is their effect in the triggering of extensive and long-duration geomorphic hazard cascades.
Although large rock avalanches are rare, magnitude-frequency studies show that the proportion of total volume involved in large events is greater than the proportion in small events, so that a large proportion of the total sediment generated in mountains by uplift and denudation originates in large rock avalanches. Consequently, large rock avalanches exert a significant influence on mountain geomorphology by, for example, blocking rivers and forming landslide dams; these either fail, causing large dambreak floods and intense, long-duration aggradation episodes to propagate down river systems; or remain intact to infill with sediment and form large valley flats. Rock avalanches that fall onto glaciers often result in large terminal moraines being formed as debris accumulates at the glacier terminus, and these moraines may have no relation to any climatic change. In addition, misinterpretation of rock avalanche deposits as moraines can cause serious underestimation of hazard risk and misinterpretation of paleoclimate; for example, a deposit 28 km long in Kyrgyzstan was originally thought to be of glacial origin, but it is now known to be a rock avalanche caused by coseismic failure of a mountain slope.
Rock avalanche runout behavior poses truly fundamental scientific questions, and rock avalanches have important effects on a wide range of geomorphic processes. Better understanding of these awesome events is crucial for both geoscientific progress and for reducing impacts of future disasters.
Avalanches have long been a natural threat to humans in mountainous areas. At the end of the Middle Ages, the population in Europe experienced significant growth, leading to an intensive exploitation of upper valleys. At almost the same time, Europe’s climate cooled down considerably and severe winters became more common. In the Alps, several villages were partly destroyed by avalanches, forcing inhabitants to develop the first mitigation strategies against the threat. By the late 19th century, the development of central administrations led to the creation of national forestry departments in each alpine country, principally to tackle the dangers posed by avalanches. As a result, forest engineers conceived not only the science of avalanches but also the first large-scale techniques to alleviate avalanche risks (such as reforestation). However, with the steady growth of transport, industry, tourism, and urbanization in high-altitude areas, these earlier measures soon reached their limits. A new impetus was then given to better forecasting avalanche activity and predicting the destructive potential of extreme avalanches. Avalanche zoning, snowfall forecasts, avalanche-dynamics models, and new protection systems for the protection of structures and inhabitants have become increasingly more common since World War II.
With the advent of personal computers and the increasing sophistication of computational resources, it has become easier to predict the behavior of avalanches and protect threatened areas accordingly. The success of this research and the protection policies implemented since World War II are reflected in the drastic reduction in the number of disasters affecting dwellings in the Alps (most deaths by avalanche now occur during recreational activities). Significant progress has been made since the 1980s, leading to a better understanding of avalanche behavior and the mediation of associated risks. Yet we should not assume that this progress is steady or that our capacity to control such hazards is more advanced than it was two decades ago. Efforts to predict avalanches contrast with work in other sciences such as meteorology, for which forecasts have become increasingly more reliable with advancements in computational power. Explaining the difference is simple: in meteorology, the material is air, a substance whose behavior is well known. The main difficulty lies in the computation of enormous volumes of air encountering various flow and temperature conditions. For avalanches, the material is snow, a subtle mixture of water (in different forms) and air, whose behavior is remarkably complex. Modern models of avalanche dynamics are able to predict this behavior with varying degrees of success.