Glacier retreat is considered to be one of the most obvious manifestations of recent and ongoing climate change in the majority of glacierized alpine and high-latitude regions throughout the world. Glacier retreat itself is both directly and indirectly connected to the various interrelated geomorphological/hydrological processes and changes in hydrological regimes. Various types of slope movements and the formation and evolution of lakes are observed in recently deglaciated areas. These are most commonly glacial lakes (ice-dammed, bedrock-dammed, or moraine-dammed lakes).
“Glacial lake outburst flood” (GLOF) is a phrase used to describe a sudden release of a significant amount of water retained in a glacial lake, irrespective of the cause. GLOFs are characterized by extreme peak discharges, often several times in excess of the maximum discharges of hydrometeorologically induced floods, with an exceptional erosion/transport potential; therefore, they can turn into flow-type movements (e.g., GLOF-induced debris flows). Some of the Late Pleistocene lake outburst floods are ranked among the largest reconstructed floods, with peak discharges of up to 107 m3/s and significant continental-scale geomorphic impacts. They are also considered capable of influencing global climate by releasing extremely high amounts of cold freshwater into the ocean. Lake outburst floods associated with recent (i.e., post-Little Ice Age) glacier retreat have become a widely studied topic from the perspective of the hazards and risks they pose to human society, and the possibility that they are driven by anthropogenic climate change.
Despite apparent regional differences in triggers (causes) and subsequent mechanisms of lake outburst floods, rapid slope movement into lakes, producing displacement waves leading to dam overtopping and eventually dam failure, is documented most frequently, being directly (ice avalanche) and indirectly (slope movement in recently deglaciated areas) related to glacial activity and glacier retreat. Glacier retreat and the occurrence of GLOFs are, therefore, closely tied, because glacier retreat is connected to: (a) the formation of new, and the evolution of existing, lakes; and (b) triggers of lake outburst floods (slope movements).
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.
Lukas U. Arenson and Matthias Jakob
Mountain environments, home to about 12% of the global population and covering nearly a quarter of the global land surface, create hazardous conditions for various infrastructures. The economic and ecologic importance of these environments for tourism, transportation, hydropower generation, or natural resource extraction requires that direct and indirect interactions between infrastructures and geohazards be evaluated. Construction of infrastructure in mountain permafrost environments can change the ground thermal regime, affect gravity-driven processes, impact the strength of ice-rich foundations, or result in permafrost aggradation via natural convection. The severity of impact, and whether permafrost will degrade or aggrade in response to the construction, is a function of numerous parameters including climate change, which needs to be considered when evaluating the changes in existing or formation of new geohazards. The main challenge relates to the uncertainties associated with the projections of medium- (decadal) and long-term (century-scale) climate change. A fundamental understanding of the various processes at play and a good knowledge of the foundation conditions is required to ascertain that infrastructure in permafrost environment functions as intended. Many of the tools required for identifying geohazards in the periglacial and appropriate risk management strategies are already available.