Hazardous geomorphic processes in the extratropical Andes with a focus on glacial lake outburst floods

<p>This study examines hazardous processes and events originating from glacier and permafrost areas in the extratropical Andes (Andes of Chile and Argentina) in order to document their frequency, magnitude, dynamics and their geomorphic and societal impacts. Ice-avalanches and rock-falls from permafrost areas, lahars from ice-capped volcanoes and glacial lake outburst floods (GLOFs) have occurred in the extratropical Andes causing ~200 human deaths in the Twentieth Century. However, data about these events is scarce and has not been studied systematically. Thus, a better knowledge of glacier and permafrost hazards in the extratropical Andes is required to better prepare for threats emerging from a rapidly evolving cryosphere. I carried out a regional-scale review of hazardous processes and events originating in glacier and permafrost areas in the extratropical Andes. This review, developed by means of a bibliographic analysis and the interpretation of satellite images, shows that multi-phase mass movements involving glaciers and permafrost and lahars have caused damage to communities in the extratropical Andes. However, it is noted that GLOFs are one the most common and far reaching hazards and that GLOFs in this region include some of the most voluminous GLOFs in historical time on Earth. Furthermore, GLOF hazard is likely to increase in the future in response to glacier retreat and lake development. To gain insight into the dynamics of GLOFs I create a regional-scale inventory of glacier lakes and associated hazards in the Baker Basin, a 20500 km2 glaciated basin in the Chilean Patagonia. I also simulate and reconstruct moraine- and ice- dammed lake failures in the extratropical Andes using numerical and empirical models. More than 100 GLOFs have occurred in the extratropical Andes since the Eighteenth Century and at least 16 moraine-dammed lakes have produced GLOFs. In the extratropical Andes most of the failed moraine-dammed lakes were in contact with retreating glaciers and had moderate (> 8°) to steep (>15°) outlet slopes. Ice-dammed lakes also produced GLOFs in the extratropical Andes, damaging communities and highlighting the need for a better understanding of the GLOF dynamics and hazards. Thus, I reconstruct and model GLOFs that occurred in maritime western Patagonia (Engaño Valley) and the high-arid Andes (Manflas Valley) to characterise the GLOF dynamics in these contrasting environments. Hydraulic modelling and geomorphologic analysis shows that the Engaño River GLOF (46º S) behaved as a Newtonian flow and incorporated tree trunks, from the gently sloping and heavily-forested valley, which increased the GLOF damaging capacity. In contrast, the Manflas GLOF (28º S) descended from a steep valley behaving as a sediment-laden flow, which was capable of moving boulder-size rocks dozens of kilometres from the GLOF source. In both events lack of awareness of the GLOF hazard and a lack of territorial planning accentuated the GLOF damage. These GLOF reconstructions highlight both the difficulties in modelling sediment-laden flows over long distances, and the utility of empirical debris-flow models for regional-scale hazard analysis. This thesis synthesises and increases our knowledge about the distribution, frequency, magnitude and dynamics of hazardous processes that have occurred in glacier and permafrost areas in the extratropical Andes. This knowledge forms a basis for future assessments of glacier and permafrost related hazards in the Chilean and Argentinean Andes and helps inform strategies and policies to face hazardous geomorphologic and hydrological processes emerging from a rapidly evolving cryosphere.</p>

Hazardous geomorphic processes in the extratropical Andes with a focus on glacial lake outburst floods

<p>This study examines hazardous processes and events originating from glacier and permafrost areas in the extratropical Andes (Andes of Chile and Argentina) in order to document their frequency, magnitude, dynamics and their geomorphic and societal impacts. Ice-avalanches and rock-falls from permafrost areas, lahars from ice-capped volcanoes and glacial lake outburst floods (GLOFs) have occurred in the extratropical Andes causing ~200 human deaths in the Twentieth Century. However, data about these events is scarce and has not been studied systematically. Thus, a better knowledge of glacier and permafrost hazards in the extratropical Andes is required to better prepare for threats emerging from a rapidly evolving cryosphere. I carried out a regional-scale review of hazardous processes and events originating in glacier and permafrost areas in the extratropical Andes. This review, developed by means of a bibliographic analysis and the interpretation of satellite images, shows that multi-phase mass movements involving glaciers and permafrost and lahars have caused damage to communities in the extratropical Andes. However, it is noted that GLOFs are one the most common and far reaching hazards and that GLOFs in this region include some of the most voluminous GLOFs in historical time on Earth. Furthermore, GLOF hazard is likely to increase in the future in response to glacier retreat and lake development. To gain insight into the dynamics of GLOFs I create a regional-scale inventory of glacier lakes and associated hazards in the Baker Basin, a 20500 km2 glaciated basin in the Chilean Patagonia. I also simulate and reconstruct moraine- and ice- dammed lake failures in the extratropical Andes using numerical and empirical models. More than 100 GLOFs have occurred in the extratropical Andes since the Eighteenth Century and at least 16 moraine-dammed lakes have produced GLOFs. In the extratropical Andes most of the failed moraine-dammed lakes were in contact with retreating glaciers and had moderate (> 8°) to steep (>15°) outlet slopes. Ice-dammed lakes also produced GLOFs in the extratropical Andes, damaging communities and highlighting the need for a better understanding of the GLOF dynamics and hazards. Thus, I reconstruct and model GLOFs that occurred in maritime western Patagonia (Engaño Valley) and the high-arid Andes (Manflas Valley) to characterise the GLOF dynamics in these contrasting environments. Hydraulic modelling and geomorphologic analysis shows that the Engaño River GLOF (46º S) behaved as a Newtonian flow and incorporated tree trunks, from the gently sloping and heavily-forested valley, which increased the GLOF damaging capacity. In contrast, the Manflas GLOF (28º S) descended from a steep valley behaving as a sediment-laden flow, which was capable of moving boulder-size rocks dozens of kilometres from the GLOF source. In both events lack of awareness of the GLOF hazard and a lack of territorial planning accentuated the GLOF damage. These GLOF reconstructions highlight both the difficulties in modelling sediment-laden flows over long distances, and the utility of empirical debris-flow models for regional-scale hazard analysis. This thesis synthesises and increases our knowledge about the distribution, frequency, magnitude and dynamics of hazardous processes that have occurred in glacier and permafrost areas in the extratropical Andes. This knowledge forms a basis for future assessments of glacier and permafrost related hazards in the Chilean and Argentinean Andes and helps inform strategies and policies to face hazardous geomorphologic and hydrological processes emerging from a rapidly evolving cryosphere.</p>

Glacial lake outburst floods enhance benthic microbial productivity in perennially ice-covered Lake Untersee (East Antarctica)

Benthic ecosystems of perennially ice-covered lakes in Antarctica are highly sensitive to climate-driven changes. Lake Untersee has been in hydrological steady-state for several hundred years with a high pH water column and extremely low levels of dissolved inorganic carbon. Here, we show that glacial lake outburst floods can replenish carbon dioxide-depleted lakes with carbon, enhancing phototrophic activity of the benthic ecosystem. In 2019, a glacial lake outburst flood brought 17.5 million m3 of water to Lake Untersee, the most substantial reported increase for any surface lake in Antarctica. High-resolution grain-size and carbon isotope analyses of microbial mats suggest that glacial lake outburst floods have occurred periodically over the Holocene and help explain the complex patterns of carbon cycling and sequestration observed in the lake. Our findings suggest that periodic flooding events may provide biological stimuli to other carbon dioxide-depleted Antarctic ecosystems and perhaps even icy lakes on early Mars.

Climate Change and Possible Impacts on Travel and Tourism Sector

Nepal is a diverse country with lowlands of Terai to the highest mountains attracting many tourists and visitors to make visits. So, the tourism in Nepal is primarily nature-based as tourists are mostly attracted by the spectacular landscapes, majestic mountains, glaciers, lakes, rivers and biodiversity across its diverse ecological gradient. Mountaineering, trekking, whitewater rafting and jungle safari tours are the main forms of nature-based tourism activities in our country. Climate change is affecting Nepal in a number of ways and the travel and tourism sector cannot remain untouched. Various studies on climate change shows increased weather uncertainties and extremities resulting into long dry period and intense rain during monsoon leading to increased water induced disasters like floods, inundation, landslides, cloudburst floods, and glacial lake outburst floods (GLOFs) which are projected to continue in future as well. This has affected natural landscapes, and Himalayas influencing every walk of life and livelihood options. Though the impacts of climate change can be observed in the whole world, poor country like Nepal is likely to suffer most due to limited resources to cope with and adapt to the effects of climate change. In this paper, an effort has been made to review the impact of climate change on the travel and tourism sector in Nepal through the study of previous literatures on climate changes.

Observed and simulated winter temperature over Gurudongmar area, North Sikkim, India

The global warming and its impact on the cryosphere is a matter of serious concern. The Sikkim and the Eastern Himalaya are a canvas of vivid landscapes and of different climate zones. The study of cryosphere needs more attention on long term climatic trends of surface air temperature. The Gurudongmar area is very much important because this area is surrounded by glaciers and as well as cold desert and TsoLhamo Lake nearby. The Gurudongmar lake (located at an altitude of 17,800 ft) has been studied by several researchers in the context of Glacial Lake Outburst Floods (GLOFs) and reported a high risk lake which is being largely affected by global warming and climate change. The present study is aimed to investigate the trend of temperature in recent past and in future time periods over the study area of Sikkim. The observed and model’s simulated gridded temperature data is considered to inkling of rising trend in winter months of December-January-February (DJF) over the study area. An increase in temperature is found for the future time period. This can be linked to the increasing hazard risk and change in local cryosphere environment.

Central Himalayan rivers record the topographic signature of erosion by glacial lake outburst floods

In steep landscapes, river incision sets the pace of landscape evolution. Transport of coarse sediment controls incision by evacuating material delivered to river channels by landslides. However, large landslide-derived boulders that impede bedrock erosion are immobile even in major runoff-driven floods. Glacial lake outburst floods (GLOFs) mobilize these boulders and drive incision, yet their role in regional-scale erosion is poorly understood, largely because of their rarity. Here, we find a topographic signature consistent with widespread GLOF erosion in the Nepal Himalaya. In rivers with glaciated headwaters that generate GLOFs, valleys stay narrow and relatively free of sediment, with bedrock often exposed to erosion. In turn, tributaries to these valleys are steep, allowing less efficient erosional regimes to keep pace with GLOF-driven incision. Where GLOFs are less frequent, valleys are more alluviated and incision stalls. Our results suggest the extent of headwater glaciation may play an important role in erosion of Himalayan river valleys and deserves more attention in future work.