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Article

Wilfried Haeberli and Fabian Drenkhan

Continued retreat and disappearance of glaciers cause fundamental changes in cold mountain ranges and new landscapes to develop, and the consequences can reach far beyond the still ice-covered areas. A key element is the formation of numerous new lakes where overdeepened parts of glacier beds become exposed. With the first model results from the Swiss Alps around 2010 of distributed glacier thicknesses over entire mountain regions, the derivation of glacier beds as potential future surface topographies became possible. Since then, climate-, water-, and hazard-related quantitative research about future lakes in deglaciating mountains all over the world rapidly evolved. Currently growing and potential future open water bodies are part of new environments in marked imbalance. The surrounding steep icy slopes and peaks are affected by glacial debuttressing and permafrost degradation, with associated long-term stability reduction. This makes the new lakes potential sources of far-reaching floods or debris flows, and they represent serious multipliers of hazards and risks to down-valley humans and their infrastructure. Such hazard and risk aspects are also of primary importance where the lakes potentially connect with hydropower production, freshwater supply, tourism, cultural values, and landscape protection. Planning for sustainable adaptation strategies optimally starts from the anticipation in space and time of possible lake formation in glacier-covered areas by numerical modeling combined with analyses of ice-morphological indications. In a second step, hazards and risks related to worst-case scenarios of possible impact and flood waves must be assessed. These results then define the range of possibilities for use and management of future lakes. Careful weighing of both potential synergies and conflicts is necessary. In some cases, multipurpose projects may open viable avenues for combining solutions related to technical challenges, safety requirements, funding problems, and societal acceptance. Successful implementation of adaptive projects requires early integration of technical-scientific and local knowledge, including the needs and interests of local users and decision makers, into comprehensive, participatory, and long-term planning. A key question is the handling of risks from extreme events with disastrous damage potential and low but increasing probability of occurrence. As future landscapes and lakes develop rapidly and are of considerable socioeconomic and political interest, they present often difficult and complex situations for which solutions must be found soon. Related transdisciplinary work will need to adequately address the sociocultural, economic, and political aspects.

Article

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).