A global assessment of the societal impacts of glacier outburst floods

Glacier outburst floods are sudden releases of large amounts of water from a glacier. They are a pervasive natural hazard worldwide. They have an association with climate primarily via glacier mass balance and their impacts on society partly depend on population pressure and land use. Given the ongoing changes in climate and land use and population distributions there is therefore an urgent need to discriminate the spatio-temporal patterning of glacier outburst floods and their impacts. This study presents data compiled from 20 countries and comprising 1348 glacier floods spanning 10 centuries. Societal impacts were assessed using a relative damage index based on recorded deaths, evacuations, and property and infrastructure destruction and disruption. These floods originated from 332 sites; 70% were from ice-dammed lakes and 36% had recorded societal impact. The number of floods recorded has apparently reduced since the mid-1990s in all major world regions. Two thirds of sites that have produced > 5 floods (n = 32) have floods occurring progressively earlier in the year. Glacier floods have directly caused at least: 7 deaths in Iceland, 393 deaths in the European Alps, 5745 deaths in South America and 6300 deaths in central Asia. Peru, Nepal and India have experienced fewer floods yet higher levels of damage. One in five sites in the European Alps has produced floods that have damaged farmland, destroyed homes and damaged bridges; 10% of sites in South America have produced glacier floods that have killed people and damaged infrastructure; 15% of sites in central Asia have produced floods that have inundated farmland, destroyed homes, damaged roads and damaged infrastructure. Overall, Bhutan and Nepal have the greatest national-level economic consequences of glacier flood impacts. We recommend that accurate, full and standardised monitoring, recording and reporting of glacier floods is essential if spatio-temporal patterns in glacier flood occurrence, magnitude and societal impact are to be better understood. We note that future modelling of the global impact of glacier floods cannot assume that the same trends will continue and will need to consider combining land-use change with probability distributions of geomorphological responses to climate change and to human activity

A review of glacier outburst floods in Iceland and Greenland with a megafloods perspective

The very largest glacier outburst floods have been termed ‘megafloods’ given their volume and peak discharge. That definition might be revised because those floods have become understood due to their distinctive and pervasive landscape impacts. At least three floods in Iceland can be categorized as megafloods since they produced impressive bedrock canyons and giant fluvially-transported boulders. Glacier lake outburst floods (GLOFs) in Greenland might also have megaflood-type attributes given the enormous lake volumes drained. We therefore here present the first review of glacier outburst floods in Greenland: sites Isvand, Russell Glacier, Kuannersuit Glacier, Lake Tininnilik, two unnamed lakes near Amitsulooq Ice Cap, and Iluliallup Tasersua, Base Camp Lake, Lake Hullett, Qorlortorssup Tasia, Imaersartoq, Tordensø, North Midternæs and an outlet glacier of the A. P. Olsen Ice Cap. Overall, megaflood-type landscape impacts in Iceland tend to be best-preserved and most easily identified inland although there has also been extensive offshore sedimentation. There are very few reported impacts of glacier outburst floods in Greenland. In Greenland ice-dam failure causes frequent flooding compared to the volcanically-triggered floods in Iceland and this combined with the proximity of the Greenland glacier lakes to the coast means that most proglacial channels in Greenland are flood-hardened and most landscape impact is likely to be offshore in estuaries and fjords. Future floods with megaflood-type attributes will occur in Iceland induced by volcanic activity. In Greenland they will be induced by extreme weather and rapid ice melt. Any potential landscape impact of these future floods remains open to question

Toward Numerical Modeling of Interactions Between Ice-Marginal Proglacial Lakes and Glaciers

Global climate change is evidently manifest in disappearing mountain glaciers and receding and thinning ice sheet margins. Concern about contemporaneous proglacial lake development has spurred an emerging area of research seeking to quantitatively understand lake - glacier interactions. This perspectives article identifies spatio-temporal disparity between the coverage of field data, remote sensing observations and numerical modelling efforts. Throughout, an overview of the physical effects of ice-marginal lakes on glaciers and on ice sheet margins is provided, drawing evidence together from very recent and high-impact studies of both modern glaciology and of the Quaternary record. We identify and discuss six challenges for numerical modelling of lake - glacier interactions, namely that there are meltwater exchanges between glaciers and ice-marginal lakes, lake bathymetry and glacier bed topography are often unknown, lake - glacier interactions affect the longitudinal stress regime of glaciers, lake water temperature affects glacier melting but is very poorly constrained, the interactions persist with considerable spatio-temporal variability and with boundary migration, and data for model parameterisation and validation is extremely scarce. Overall, we contend that numerical modelling is a key frontier in the cryospheric sciences to deliver process understanding of lake - glacier interactions

Complex circular subsidence structures in tephra deposited on large blocks of ice: Varða tuff cone, Öræfajökull, Iceland

Several broadly circular structures up to 16 m in diameter, into which higher strata have sagged and locally collapsed, are present in a tephra outcrop on southwest Öræfajökull, southern Iceland. The tephra was sourced in a nearby basaltic tuff cone at Varða. The structures have not previously been described in tuff cones, and they probably formed by the melting out of large buried blocks of ice emplaced during a preceding jökulhlaup that may have been triggered by a subglacial eruption within the Öræfajökull ice cap. They are named ice-melt subsidence structures, and they are analogous to kettle holes that are commonly found in proglacial sandurs and some lahars sourced in ice-clad volcanoes. The internal structure is better exposed in the Varða examples because of an absence of fluvial infilling and reworking, and erosion of the outcrop to reveal the deeper geometry. The ice-melt subsidence structures at Varða are a proxy for buried ice. They are the only known evidence for a subglacial eruption and associated jökulhlaup that created the ice blocks. The recognition of such structures elsewhere will be useful in reconstructing more complete regional volcanic histories as well as for identifying ice-proximal settings during palaeoenvironmental investigations

Deglaciation and proglacial lakes

Glaciers and ice sheets are important constituents of the Earth's land surface. Current worldwide retreat of glaciers has implications for the environment and for civilisation. There are a range of geomorphic changes occurring in cold environments and it is anticipated that these will be accentuated as a consequence of climate change. In particular, the number and size of proglacial lakes is currently increasing as a result of deglaciation and their significance for the physical environment and for society is becoming increasingly apparent. This article provides an overview of the major interdependent relationships between climate change, glaciers and proglacial lake development. In particular, it describes the key processes and impacts associated with proglacial lake evolution with reference to examples drawn from the European Alps, North America, the Himalayas, the Andes, Greenland, New Zealand and Iceland

Deglaciation controls on sediment yield: Towards capturing spatio-temporal variability

Accelerated glacier and ice sheet retreat and thinning in recent decades has profound consequences for catchment sediment supply with attendant repercussions for nutrient cycling, carbon fluxes and natural resource management. This paper evaluates the impacts of deglaciation on sediment yields from glaciated, deglaciating and recently-deglaciated catchments. It summarises the key characteristics of sediment yields from glaciated catchments to be that they span five orders of magnitude, vary with latitude and are greatest in high-relief and tectonically-active regions. We review the available quantitative data on sediment yields from glaciated catchments and we comment extensively on spatio-temporal variability to understand global to local and inter- and intra-catchment controls. Significant gaps in the available sediment yield data and also in our knowledge of sediment sources, pathways and sinks are identified. We constrain a set of novel approaches by which these gaps could be addressed. In particular, we suggest that the opportunities presented by emerging datasets and analytical methods enabling landcover changes, Digital Elevation Model (DEM) change detection, analyses of connectivity and analyses of sediment plumes are exciting and these approaches should become practical tools for understanding intra- and inter-catchment sediment yields from deglaciating landscapes. We showcase preliminary studies utilising these datasets and they are used to formulate hypotheses designed to stimulate further research