Glacial Processes References Revision

Stuart et al., 2003

• Ground-penetrating radar profiles were used to collect data on an englacial channel system for cold-glacier austere Brøggerbreen, Svalbard

• The size of conduits varied from a large semicircular channel at 5m wide to a vertically elongated 2.5m channel close to the outlet as well as variations in the depth of water in the channel from 14 to 90% of channel height 

• Results of dye-tracing experiments combined with the low channel gradient of less than 2 degrees suggests that there is significant ponding along the channel; radar reflections were useful in determining the depth, dimensions and water content of these englacial watercourses

• This channel geometry was probably formed during a period of increased crevassing from the Little Ice Age, these channel dimensions were sourced from direct descent into the moulin to verify these interpretations through glacio-speleology

Samimi & Marshall, 2017

• Meltwater refreezing and storage in the superglacial snowpack can reduce and delay meltwater runoff from glaciers, but the effect of these processes are often uncertain for temperate alpine glaciers

• The temperature and meltwater content in the upper 50cm of the supraglacial snowpack of Haig Glacier was measured using thermistorics and Time Domain Reflectometry (TDR) probes and supplemented by automatic weather station data 

• These methods found strong diurnal cycles in snow water content through the summer melt season with subsurface refreezing only significant in May, after this overnight freezing was restricted to only a thin surface layer of the snowpack; here diurnal variation in supraglacial hydrology were revealed showing high levels of water stored in the daytime contrasting with minimum levels overnight 

• Overnight decreases in water content after May were associated with meltwater percolation and drainage; overall there was a negligible meltwater retention in the snow on a daily basis

Hock & Hooke, 1993

• During the 1989 melt season, 10 tracer experiments were conducted to investigate the seasonal, diurnal and spatial variations in the englacial drainage system of Storglaciarien, Sweden where dye was injected into moulins and its concentration and discharge monitored at the glacier terminus 

• Transit velocities ranged from 0.07 to 0.29 m/s, implying that drainage was initially taking place through a well-defined conduit system as part of a multi-branched aborescent network of wide, low passages; this dispersivity declined during the early part of the meltseason to reflect structural changes in conduits including a decrease in braiding and increase in size before the final configuration was reached in early August

• The conduits were found to be full of water during periods of higher daily discharge with water pressure exceeding atmospheric pressure

• Overall, variation in tracer return curves and dispersivity on a diurnal time scale reflect changes in the degree of braiding as lower divides are drowned between channels and discharge increases

Fountain et al., 2005

• The prevailing hypothesis explains that water flow through the body of a glacier takes place in a network of tubular conduits; however, video images from 48 boreholes drilled into Storglaciӓren, Sweden, shows that the hydrological system  is instead dominated by fractures converting water at slow speeds at all depths

• Fractures provide the main pathways for surface water to reach deep within the glacier whereas conduits only form in special circumstances

• These fractures are useful in explaining the evolution of the englacial water flow system, seasonal regeneration and in understanding the collapse of ice shelves and hydraulic connection between the surface and bed of an ice sheet

• Findings from this study expose claims to universality within englacial theory and instead provide evidence for spatial variation between and within glaciers

Benn & Evans, 2010

• The production, storage and transport of water has a profound influence on glacier behaviour as water contributes to glacial erosion, debris transport and deposition as a direct agent; water released from glaciers also present benefits and hazards for human populations through cultivating valleys for agriculture, hydroelectricity and flooding

• The contrasting permeabilities of snow and ice mean that supraglacial drainage systems on snow-covered surfaces and bare ice are very different; on snow the water readily percolates through pore spaces until it reaches the freezing point, this kind of drainage becomes more efficient over time as rills and surface channels form; for ice surfaces the meltwater cannot percolate as the ice is impermeable so much run off the surface in sheet flows or channels 

• The englacial drainage system conveys surface meltwater to the bed of glaciers, for many years models of englacial drainage were based on the theoretical model developed by Shreve in 1972 but this did not provide a realistic picture of actual drainage as they show no tendency to follow theoretical potential gradients and do not behave as predicted

• Insights into the character of englacial drainage systems have been developed through video imaging of boreholes, ice cores, glacio-spelology and surface geophysical surveys that reveal important insights to challenge assumptions of conduits being semicircular without variation, that these dominate water flow and into their seasonal, diurnal and geographical variation

• Subglacial channels may be incised into the ice or cut into the glacier bed, they develop through creep closure leading to the development of branches drainage systems that can fluctuate in response to diurnal and weather related variations in melting; these channels cannot always be assumed to be semicircular but instead have complex forms, travel in many directions and are subject to strong seasonal variation

Miles et al., 2020

• The hydrological characteristics of debris-covered glaciers are known to be fundamentally different from those of clean-ice glaciers, this influences the timing and magnitude of meltwater discharge to impact communities who rely on this for sanitation, irrigation and hydropower 

• The rugged surface of debris-covered glaciers means supraglacial systems are likely to involve channels and ponds as well as unknown pathways; englacial conduits are frequently abandoned and reactivated as water supply changes, new lines of permeability are exploited and drainage captured as well as being subject to the seasonal influence of monsoons that reorganise these systems rapidly

• This study used dye tests on debris-covered Khumbu Glacier in Nepal to infer the existence of a channelised subglacial drainage system that discharge large volumes of heavily debris-laden water during the melt season

• It was inferred that the subglacial system increased in efficiency and interconnection throughout the melt season; this channelised system was revealed but there was no evidence found for the evolution of the system from, or returning to, cavities showing greater spatial variability in subglacial drainage systems around the world

Church et al., 2020

• Between 2012 and 2019 repeated GPR surveys were carried out over an active englacial conduit network within the ablation area of temperate Rhonegletscher in Switzerland, this showed that during the summer melt seasons there are active, water-filled, sediment transporting englacial conduit networks 

• The surveys provided evidence that the conduits were up to 20m wide and formed by hydraulic fracturing 

• During the winter, the englacial conduit no longer transports water and became physically closed or very thin to produce, following the melt season this reactivated in the exact same position

• This highlights the importance of observations in testing englacial hydrology theory to allow it to capture greater spatial and temporal variability

Campbell et al., 2006

• Dye tracing was conducted in the 2004 melt season at Haut Glacier d’Arolla, Switzerland, to better understand the role of the supraglacial snowpack in mediating the delivery of meltwater produced by the snowpack surface to the rest of the glacier with implications for proglacial forms and subglacial water pressure

• Observations show the complexity of flow patterns to yield average flow rates for percolation through the snowpack of between 0.13 and 0.49 m/h with an increase in percolation rates over the course of the melt season in the efficiency of which the snowpack transmits water 

• The reason for an increase in percolation rates over the course of the melt season is attributed from the progression of the snowpack from an initial cold, impermeable surface to a warmer, better connected layer facilitating more rapid percolation by the end of the melt season and proving that the dampening effect of the snowpack varies seasonally  

• Snow permeability in this study was found to be significantly lower than previous studies, showing a need for improved research on snowpack hydrology

Willis et al., 2012

• Digital elevation models of the surface and bed of a glacier can be used to calculate the subglacial hydraulic potential and infer drainage system structures, a distributed degree day model is also used to calculate the spatial distribution of melt on the glacial surface to impact water flux beneath the glacier

• Comparisons of 78 dye tracing tests over 33 injection sites as well as measures of water discharge suggest that the temporally and spatially averaged steady state water pressure beneath the glacier were around 70% over ice burden meaning k equalled 0.7 in the hydraulic potential equation for subglacial hydrology

• This shows that the main drainage network of the eastern half of the glacier consists of hydraulically efficient systems of broad, low channels and the smaller drainage system on the west consists of hydraulically ineffective distributed systems with very broad low channels showing how the subglacial drainage system can vary within an individual glacier

Fountain & Walder, 1998

• It is important to understand water movement through glaciers to understand glacier dynamics, glacier-induced floods and predict runoff

• Firn can influence the supraglacial drainage system as when it is porous and permeable the flux of water to the glacier interior varies slowly due to the firn temporarily storing water and smoothing out variations in supply through the dampening effect; however, in the firn-free ablation zone the flux of water depends directly on the rate of surface melt or precipitation

• In the englacial drainage system the water moves from the surface to the bed through a network of steep conduits that deliver water to the bed, in the accumulation zone these are steady state features that convey water delivered via firn so are usually full of water and pressurized; in the ablation area they are only pressurised near times of daily flow or during storms 

• The subglacial drainage system can be made up of many distinct elements from a branching network of channels to a more extensive network of nonarborescent channels converting water slowly and poorly connected; the arborescent channel largely collapses during the winter but reforms in the spring as the bed disabilities cavities in the non-arborescent network 

• The volume of water stored by glaciers varies diurnally and seasonally with daily fluctuations of up to 20-30 mm; most water storage is likely to occur englacially and if this is abruptly released it can lead to catastrophic flooding

• This shows that there are great variations in the hydrology of an individual glacier between the accumulation and ablation zone

Cuffey & Paterson, 2010

• The hydrological system of glaciers can be broken down into three main categories; the supraglacial, englacial and subglacial systems that examine the movement of water on the surface of the ice, within the ice, and at the glacier bed

• Within each of these categories, there is a plethora of theories on how runoff, transportation and drainage systems are characterised; these often first come from widely accelerated theoretical analyses of hydrological processes that are then tested, critiqued and improved through the observations and the application of empirical data

• Observations are collected from the field in a number of water including drilling boreholes into ice, ice core examination, dye testing and glacio-speleology that can be combined with remote sensing methods including ground-penetrating radar (GPR) analyses

• There remains a need to continue to develop observation techniques and combine them in innovative ways to fill gaps in knowledge on glacier systems

UNESCO World Water Assessment Programme, 2025

• In March of 2025, the UN World Water Development Report found that the 2 billion people worldwide who depend on glacier meltwater for sanitation, irrigation and water security were set to face ‘severe’ consequences to their livelihoods as glaciers continue to melt as a result of anthropogenic climate change

• This impact is exacerbated as glacier melt has a profound effect on glacier hydrology by changing the volumes and timings of runoff leading to glacier behaviours changing and impacts to humans being altered

• Glacier hydrology theory is key to predicting the extent of these changes and ensuring appropriate measures are taken to reduce risks to populations that rely on glaciers to support their lifestyles

Zoet & Iverson, 2020

• The slip of marine-terminating ice sheets over beds of deformable till is responsible for most of the contribution of the West Antarctic Ice Sheet to sea level rise; flow models require a law that relates slip resistance, velocity and water pressure at the bed formed through the use of ring-shear devices

• Steady-state slip resistance increases with slip velocity due to sliding across the bed; however, above a certain threshold velocity the sliding becomes too fast the till begins to deform and resistance stops increasing as it reaches Coulomb strength; this shift from ice sliding to till deformation motivates the formation of a generalised slip law for glacier-flow models that combine the processes of hard-bed sliding and bed deformation

• Rapid slip occurs where ice is at the pressure melting point and rests on unlithified, water-saturated till made from a mixture of mud, sand and larger particles that can shear and weaken when the sliding rate increases above resistance and the flow of ice transitions to plasticity

• Experiments with hard beds provide an incomplete description of soft bed slip behaviour and do not take into account where the transition to bed deformation occurs when the drag from the ice flow causes them to flow and mobilises the bed; this shows that the classical mechanisms of glacier sliding over rigid beds and till deformation mechanics act collectively to shape the basal-slip relation where glaciers rest on deformable sediment

Benn & Evans, 2010

• Glacier flow transfers ice from accumulation areas where ice is lost by melting and calving, this is important as the mechanisms of glacier flow impact the response of the cryosphere to climate change, sea level rise and landscape change, transportation and deposition; there has been an increase in knowledge on glacier motion but there remain questions on controls of flow rates including temperature, debris control, bed roughness and water pressure due to data being very difficult to obtain

• Stress is a measure of how hard a material is being compressed, strain measures the deformation as a result of stress; the relationship between the two is termed rheology and is important in understanding glacier dynamics

• The deformation of ice in response to stress can occur by creep defined as a deformation resulting from movement within or between individual ice crystals, this occurs as ice is a thick, viscous fluid thats flow is described by Glen’s Flow Law stating that the strain rate of ice is determined by a temperature dependent constant of ice hardness multiplied by the effective shear stress raised to an exponent generally accepted to equal 3 showing that ice is highly sensitive to its environment and can transition from flowing very slowly at low temperatures and stresses to flowing very fast in opposing conditions 

• Ice creep can occur differently in practice to the values calculated using Glen’s Flow Law as factors other than temperature can influence the creep rate including the size and orientation of crystals, impurities and water content; within a glacier deformation also occurs at different rates as the basal ice is under higher stress due to the weight of the ice above it and a steeper slope meaning it can deform faster; inner grain boundary processes allow deformation to impact the whole glacier and creep as a polycrystalline entity

• Ice sliding refers to the slip between a glacier and its bed, this is limited by the resistance of bumps on the bed forming frictional drag meaning the ice must flow past obstacles through regelation and enhanced ice creep in which water plays a key role to reduce bed roughness by submerging bumps and increasing driving forces

• Many glaciers are underlain by unlithified sediment or poorly consolidated sedimentary rock that deforms in response to stress imposed by the overlying ice; the rheology of subglacial till can be reduced by increased sliding speeds and high water pressure in diurnal cycles

Rignot et al., 2011

• Data from satellite radars of the Antarctic Ice Sheet between 2007 and 2009 emphasize the importance of basal-slip dominated tributary flow over deformation dominated ice sheet flow with implications for the prediction of ice evolution

• Ice velocity ranged from a few cm/year near divides to a few km/year on fast-moving glaciers and floating ice shelves showing much spatial variation especially in tributary flow

• Bedrock topography has a clear impact on the flow pattern of ice, here patterned enhance flow initiates at low speeds and includes a major basal slip component due to the presence of subglacial valleys that channelise thicker ice to generate more friction, heat and melt water for lubrication to allow basal slip to become a key component of ice motion in Antarctica at the flanks of ice divides

• This challenges the view of the Antarctic ice sheet becoming dominated by internal deformation as basal slip in tributaries instead dominates; this is likely not unique to Antarctica but instead a common feature of ice sheets that can be applied to other cryospheric environments to model ice sheet dynamics in response to a warming climate

Millstein et al., 2022

• Ice viscosity is often described by a simple but largest untested and uncalibrated relation to Glen’s Flow Law where the rate of deformation is proportional to stress raised to the power of n, commonly assumed to be 3 but observations and experiments support a range of possible values

• In fast flowing areas of Antarctic ice shelves observations prove that the viscous flow of ice is better captured by an exponent of approximately 4.1 to show that viscosity and flow rate are more sensitive to changes in stress than most ice-flow models allow for

• There is a need to improve projections of future glacier change by calibrating Glen’s Flow Law and challenging the assumption of the flow-law exponent as 3 everywhere; further analyses should be conducted to refute this universality and improve projections of future glacier change, sea-level rise and response to climate forcings challenging common assumptions of the flow law

Boulton & Hindmarsh, 1987

• Experiments beneath Breidamerkurjökull in Iceland have led to the development of flow laws for subglacial till that relate strain rate to shear stress and effective pressure

• Water pressure in the till areas are less than ice pressures which may lead to the infiltration of ice into the sediment to inhibit sliding at the base; although theories of subglacial deformation predict stable states at the ice-bed interface, it is likely that unsteady behaviour of this type may be the form of glaciers flowing over unlithified sediment beds

• Natural variability in subglacial sediment beds leads to the development of drumlins on the glacier bed to form piping and tunnels drawing down subglacial water pressures to prevent unstable deformation

• This is an interaction that leads to an anomalous behaviour and draws attention to the many uncertainties that remain around the controls on flow rates of ice

Clarke, 2005

• The thermal conditions at the ice-bed interface (melting ot non melting) and the mechanical properties of the glacial substrate (soft or hard) determine which processes can be activated in terms of ice flow, the warm-soft case supports the greatest variety of processes and is the most important for fast-flow dynamics and the mobilisation of subglacial sediment 

• Subglacial processes determine the large-scale behaviour of glaciers and ice sheets, but there is a large knowledge gap on these interactions; West Antarctica’s ice streams show how there is a transformation from fast and slow flowing ice with defined margins suggesting a spatial switch 

• Beneath warm-based glaciers water exists at the bed and the pressure of this water influences the degree of frictional interaction between the glacier and the bed and the strength of the sediment; beneath fast-flowing West Antarctic streams the water pressure is very close to the ice flotation pressure allowing streams to virtually float on subglacial water and move very fast

• The main processes that enable sliding are regelation, enhanced creep and cavitation and these depend on the size and spacing of the bed roughness obstacles; regelation is most effective when the size is small and enhanced creep when the size is large allowing different sliding processes to dominate in different bed conditions; the mechanical properties of the substrate as deforming or non-deforming are also key in how sliding occurs

• Cold-warm switches can occur as a result of thermal processes which can enable basal sliding for hard bedded glaciers and sediment deformation for softbedded glaciers; the transition from slow to fast flow across margins is evidence of a spatial switch in subglacial processes such as a shift in subglacial drainage morphology

• The balance of processes of ice creep, hard-bed and soft-bed sliding is determined primarily by the thermal conditions at the ice-bed interface, water pressure the mechanical properties of the substrate

Cuffey & Paterson, 2010

• Ice behaves a thick viscous fluid that slowly and continuously deforms under applied stress through creep calculated through Glen’s Flow Law

• The ability of ice to flow in this manner is directly linked to its structure, as snow is compacted it undergoes a transition through wet-snow to firn and then glacial ice and in this process air, water and debris become trapped to result in a complex final assemblage; as a result the ice behaves as a thick, viscous fluid undergoing deformation characterised as intermediate between a Newtonian viscous and perfectly plastic material

• Glacial ice is polycrystalline, made up of many individual crystals and grains that work together to determine bulk creep behaviour of ice

• Ice creep happens most easily when stress is high (above 200kPa), strain is high (material deforms quickly), temperature is low and there are coarse grains; the activation energy for ice creep is accepted at around 10 degrees

Cuffey & Paterson, 2010

• The problem of measuring hard-bed sliding lies in explaining how ice moves past mumps on the glacier bed

• The first mechanism for this is regelation, a process assuming the ice is at the pressure melting point; when the ice encounters a bump in the bed, it initially becomes highly pressurised due to experiencing resistance to its flow, this pressure lowers the melting point of the ice, as a result melt begins, once melted the pressure gradient forces the water to move away from the high-pressure zone by flowing around the bump; on the downstream side, the pressure returns to a lower level and the melting point increases, allowing the meltwater to refreeze to solid ice; this process is more effective for small bumps less than 1 meter in length

• For larger bumps enhanced creep is more effective in facilitating sliding; here the ice experiences resistance from an obstacle, this increases the stress experienced by viscous ice; according to Glen’s Flow Law, the increase in stress leads to an increased rate of deformation, allowing the ice to creep around the obstacle and continue to slide

• These processes of sliding can lead to cavity formation on the downstream side of bumps, when these bumps become very large and the leeside pressure is very low ice is unable to refreeze to the bed immediately and instead forms a meltwater filled cavity that enlarges as the ice slides and reduces the frictional strength of the bed allowing for basal slip to accelerate

• On a soft-bed, sliding involves the deformation of a thin layer of substrate; here the adhesive strength of the substrate limits the forces by which the bed resists the movement of ice; the more readily the substrate deforms, the smaller the resisting forces and the faster the slip as a result of a ‘well lubricated’ bed

Minchew & Joughin, 2020

• A slip law for deformable sediments has been proposed that is similar to laws derived for rigid beds and therefore supports a universal slip law to improve projections of ice sheet contributions to sea level

• Irrespective of hard or soft beds, glaciers have roughness features that influence drag and where water can act as a lubricant; where water is highly pressurised cavities can form downstream of bumps to decouple the ice from the bed showing how total drag varies based on water pressure and the rate of slip at the bed

• Zoet and Iverson derive a simple slip law where form drag dominates when the bed is rigid and ice flows around rocks and skin friction when the bed deforms with the transition controlled when the sediment reaches its yield strength

• This slip law was formed for deformable beds but also relates to rigid beds as form drag initially occurs around roughness features the transition to plasticity occurs at faster slip rates as a result of cavity formation reducing ice-bed contact

• Despite differences in physical mechanisms the two models have the same parameters and therefore a universal law could be applied and could model slip without needing prior knowledge of if the bed is rigid or deforming, this would help reduce uncertainties in sea level projections

• These forms are similar as initially sliding is limited due to resistance, but at a certain point (Coulomb strength or cavity formation) the sliding rate increases above resistance allowing for a transition of the flow of ice to plasticity at high velocities

Alley et al., 1986

• Evidence for bed deformation as a mechanism of ice flow has been found in West Antarctica at the Whillans Ice Stream

• Here, seismic observations reveal that the ice stream rests on a layer of unconsolidated sediment between 5 and 6 meters thick; the deformation of this till as a result of applied shear stress has been proven to be the primary mechanism by which the ice stream flows 

• Since this study, many more have been carried out to clarify the importance of the process and better understand how it functions leading to the formation of a soft-bed sliding slip law and universal glacier slip law

Goldsby & Kohlstedt, 2001

• Studies of the Antarctic ice shelves and other relevant observations suggest that the rate of ice creep is more sensitive to changes in stress than most current models account for

• This provides a case for reevaluating Glen’s Flow Law (especially the exponent n of shear stress) and reconstructing models of glaciers in the future

Srestha et al., 2023

• As glaciers recede and surrounding slopes become increasingly unstable, GLOF events are expected to increase; between 1833 and 2022 there were 697 individual GLOFs documented in High Mountain Asia with nearly 7000 fatalities

• High Mountain Asia has the largest expanse of glacial ice between the two poles and has around 30,000 glacial lakes but these have been retreating and losing mass since the 1960s leading to the formation and rapid expansion of glacial lakes, a trend expected to create new hotspots of hazardous lakes with implications for GLOF hazards and risk

• Processes identified as direct or indirect triggers include slope movements such as rockfalls, avalanches or landslides into lakes to form overtipping waves as well as intense rainfall or ice melt leading to an increase in water levels that strain dams; these then cause fatalities as well as damaging infrastructure and farmlands as developments grown in downstream areas to increase risk

• There is a peak in GLOFs seasonally where westerlies bring South Asian monsoons to show that regional precipitation is an important driver of outburst flooding in the region

• The hazard of a GLOF is closely associated with moraine stability which is linked to the history of glacier retreat with areas of recent permafrost change likely to be more susceptible to mass movement

• Distributed datasets on infrastructure, population and ecosystems would allow for assessments on impacts and vulnerabilities when coupled with potential paths and remotely sensed vegetation data; this would allow for estimates of local economic and ecological impacts to form hazard zonation maps

Miner et al., 2020

• In the Mount Everest Region risks arise from a natural and anthropogenic changes to the biological system leading to diverse risks to ecosystems, human health, geology and climbing conditions; as high mountain glaciers worldwide decrease in extent and volume there are significant consequences to water availability, hazards such as outburst floods and slope failure, ecosystems and socioeconomic futures

• There are risks of seismic hazards, landslides and avalanches as well as rockslides that become more frequent as glaciers melt away from headwalls and expose steep unstable rock faces

• Rain events can trigger flooding, often this water can be contaminated by chemicals, pesticides and anthropogenic metals meaning that drinking water sourced from snow and ice melt poses a risk to human health; climbers can also lead pathogenic organisms in meltwater

• These risks are diverse and constantly changing so much be monitored in order to inform proper adaptation and mitigation of risks to tourism and local populations

Worni et al., 2014

• Many recent GLOF events involve process chains where mass movement impacts glacial lakes to trigger dambreaches and cause outburst floods; the effects of climate change and increased instability of high mountain slopes pose a threat as they may exacerbate process chains 

• GLOF events compromise a series of cascading processes that should be modelled to improve our understanding and assessment of future hazards as new glacial lakes form and slopes destabilise

• The initiation of process chains can differ e.g. rock fall, precipitation, upstream GLOF but they typically begin with an impulse-wave generation, dam overtopping and breaching and then lake emptying and flood propagation

• The stability of dams depends on their geometry, internal structure, material properties and particle size/distribution; once they are overtopped they initiate dam erosion that continually increases hydraulic forces to enlarge the breach in an irreversible process leading to the emptying of the lake

Sherpa et al., 2019

• GLOFs are among the most serious cryospheric hazards for mountain communities and people’s perceptions of cryospheric risks can influence their actions, beliefs and responses to hazards; there has been a positive correlation found between perceptions of risk and livelihood sources of tourism and spatial proximity to glacial lakes

• There is much uncertainty and confusion related to GLOF risks often stemming from a disconnect in how scientific information is communicated to local communities, how policies are formed and awareness campaigns; there is a need to form a sustainable partnership of scientists, policymakers and local communities to improve cryospheric risk management 

• Only in recent years have social and humanistic perspectives on GLOFs emerged, but there is a need for an interdisciplinary approach to capturing the natural-social interactions of cryospheric hazards and appreciating that people's risk perceptions are shaped by direct personal experiences and second hand information, this perception influence how a person may act in the event of a hazard

• Rapid onset hazards have a perceived higher risk; local perception was also influenced by source of livelihood, age, prior experience and geography with younger people more likely to perceive a risk alongside those who support their livelihoods with tourism, those with prior experience of the hazard and living closer to lakes

Bajracharya et al., 2007

• Information on the extent and possible impact of GLOFs can be used for designing early warning systems and implementing management plans for lakes such as Imja Lake which is the largest and most dangerous in the Sagarmatha region

• Flooding occurs due to the breaking down of moraine dams leading to flash floods and debris flow downstream, pressures are increasing due to increased populations and tourism in mountain areas causing people to settle in areas highly exposed to natural hazards and trekking routes often leading through unsafe areas in floodways

• The most vulnerable areas were identified as settlements with agricultural land along river banks with scattered housing in vulnerable zones; around 5.8km of trails were judged as highly vulnerable due to running through flood plains

• Vulnerability maps generated through hydrodynamic modelling provide a systematic basis for identifying vulnerable populations, infrastructure and agricultural land and this can be used to develop management plans

Emmer, 2017

• Glacier retreat is connected to interrelated geomorphological processes and changes in hydrological regimes

• GLOFs are characterised by extreme peak discharges, exceptional erosion and transport potential and pose risks to human society potentially driven by anthropogenic climate change

• Despite regional differences in triggers and mechanisms, GLOFs are closely tied to the formation and evolution of new lakes and triggers

Salerno et al., 2017

• From the 1950s to 1990s there has been an overall decrease in glacier area as a result of temperature and precipitation variation, this is important as ice masses in the Himalayas constitute a water resource assuring the survival of around 500 million people in the area 

• The glaciers of the Sagarmatha national park are nearly all debris-covered, a characteristic that alters exchanges between ice and the atmosphere with the debris cover gradually increasing towards the lower part of the glacier ablation zone

Cenderelli & Wohl, 2001

• GLOFS can dramatically modify channels and valleys in the regions they affect by eroding, transporting and depositing large quantities of sediment for tends of km along flood routes

• GLOF discharges in the Mount Everest region were 7-60x greater than seasonal high flow flood discharges, with the greatest discharge occurring nearest to the moraines and declining downstream

Benn et al., 2012

• Superglacial debris cover can alter rates and spatial patterns of melting, this can be associated with the formation of moraine-dammed lakes that pose a risk of GLOFs as downwasting allows for supraglacial lake hollows to extend

• The probability of a flood is a function of lake volume, the geometry and structure of the dam and possible trigger mechanisms; these events can then lead to a loss of life, dwellings, infrastructure and farmland

• A major factor in determining GLOF potential is the hydraulic gradient across the moraine dam influencing its susceptibility to seepage as well as trigger mechanisms that can cause waves to overtop and erode moraine dams to initiate positive feedback loops of discharge and erosion

• At risk sites there is a need to continue to monitor the complex webs of factors that contribute to the occurrence of GLOF hazards through in situ and remote sensing techniques, predictions of GLOF impact should be based on a scientific basis and have clear criteria for prioritising mitigation efforts

Hambrey et al., 2008

• Many Himalayan glaciers are enclosed by Little Ice Age moraine complexes which impound lakes, these dams can attain heights of over 100 metres and are made up of poorly sorted mixtures of sand and gravel; behind the dams there are lakes several kilometers long 

• During a GLOF, discharges of up to 60x greater than normal flow have been reported with a particularly high impact in the upper 16km of flood routes and with further consequences up to 200km downstream

• At debris covered glaciers downwasting (or vertical thinning) combined with a progressive reduction in slope profile sees supraglacial debris thicken towards the snout, forming and adding to terminal moraine dams behind which lakes are fed by glacial melt and precipitation, and expand due to cliff calving

Zheng et al., 2024

• A GLOF occurred in June 2020 in Tibet with a peak discharge of 5602 cubic meters per second, the landslide triggering the GLOF was likely caused by heavy south Asian monsoon rainfall in the same month that led to dam overtopping and erosion

• There were no casualties but there was severe destruction to villages and infrastructure downstream mainly to buildings, roads, bridges and farmland; there was great erosion of the river valley and alteration of the channel

• As the event took place in the daytime, villagers were upstream collecting herbs and were able to observe the flood and inform downstream populations to evacuate, leading to no casualties in this event

Cuffey & Paterson, 2010

• A jokulhlaup is the sudden and rapid drainage of a glacier-dammed lake that can cause extensive flooding and pose a great hazard to populations downstream

• They can occur once per year or only every several years, the flood can start when the level gets very high and may stop before the lake has emptied

• These floods often occur due to melt and transport sediment that is deposited in broad outwash plains at the periphery of ice caps

Motschmann et al., 2020

• GLOFs and water scarcity are often assessed by separate methods and by separate research communities despite being intertwined and shaped by multi-dimensional natural and socioeconomic drivers

• GLOF threat increases at the same time as declining melt water supply changes in the hydrological regime resulting in changing water availability

• There is a need to form more comprehensive analysis of risks related to water resources by considering climate change within multi-dimensional drivers across different scales and complex climate sensitive mountain regions to include local perspectives on risk reduction, adaptation and water management

Washakh et al., 2019

• In Nepal, there is a further risk posed to river basins housing hydropower plants that are key to generating income, forming reliable power sources and alleviating poverty

• If these power plants are hit by high discharges, they may be damaged or destroyed, leading to socioeconomic decline throughout the region

• In light of these wide ranging risks associated with GLOF events, there is a clear need to provide comprehensive risk assessments of fragile water and energy systems

Kumupulainen, 2006

• Vulnerability refers to the susceptibility of people, communities or regions to natural or technological hazards through three key dimensions of economic, social and ecological vulnerability

• Risk = hazard potential x exposure x vulnerability; vulnerability can be measured in terms of economic damage potential (economies, communication networks, infrastructure, production, distribution, consumption etc.), social coping capacities (the poorest find it harder to reconstruct their lives after a hazard) or ecological (ecosystems response to shocks)

• Vulnerability is broadly defined as the potential for loss but can be understood, measured and mapped in different ways; in the future there is a need to continue to research hazard centred and region centred vulnerability

United Nations Office for Disaster Risk Reduction, 2017

• Hazard is defined as a dangerous phenomenon, substance, human activity or condition that may cause loss of life, injury or other health impacts, property damage, loss of livelihoods and services, social and economic disruption or environmental damage

• Risk = hazard potential x exposure x vulnerability; this combines the probability of an event and its negative consequences to calculate the potential loss of life, injury or destroyed or damaged assets which could occur to a system, society or community in a specific period

Ding et al., 2021

• The cryosphere is very sensitive to global warming, with elevated temperature rise in high latitude and latitude areas it is dramatically changing through ice sheets melting, glaciers retreating, permafrost degrading and snow cover extent decreasing

• The atmospheric cryosphere involves hazards of frost, hail, freeze rain and extreme winter events; the oceanic sea ice, icebergs, coastal erosion and sea level rise; the land glacial hazards, collapse, debris flow as well as heavy snowfall, avalanches, flooding and permafrost hazards that all have effects to human livelihoods, economic assemblages, ecosystems and infrastructure in varied manners

• Although the cryosphere is shrinking as a result of climate change, cryospheric hazards will likely increase in both frequency and severity in a warming climate

Elia et al., 2023

• There has been less attention paid to natural hazards occurring in cryospheric environments than those in mid-latitudes as a result of periglacial regions hosting smaller human populations and therefore understanding and modelling hazards is seen as less prominent of a concern; however, this is changing as global warming radically changes periglacial surface processes and geomorphological processes

• Degrading permafrost has led to regressive thaw slumps and active layer detachments as types of cryospheric slope failure hazards, their development negatively affects human settlements, infrastructure and ecosystems due to changes to sediment budgets and releases of methane and carbon dioxide as permafrost melts 

• As a result, data-driven models were formed in order to improve understanding of cryospheric dynamics, map the susceptibility to certain slope failures and quantify potential impacts 

• The modelling protocol was successfully able to map areas prone to land failure and summarise this into a multi-hazard susceptibility map for Northern Alaska that could be used to mitigate against damage to infrastructure and ecosystems, as well as highlighting the role of unconsolidated materials, temperatures and snow covers in the incidence of these hazards

• Models are limited in their transferability meaning there should be more efforts to map cryospheric multi-hazards in ways that can be helpful in tailoring local adaptation and mitigation strategies

Nicu et al., 2023

• The Svalbard Archipelago represents the northernmost place on Earth where cryospheric hazards including thaw slumps and thermo-erosion gullies could take place and develop due to climatic variations, as permafrost is very sensitive to warming there is a need for a deeper understanding of processes to foresee the dynamics of hazards and future global implications

• Permafrost thawing of internal ice within soils often leads to subsidence and slumps called thermokarst which threats ecosystems, infrastructures and cultural heritage sites alongside releasing GHGs into the atmosphere; in Svalbard thaw slumps and thermo-erosion gullies are of particular interest in the multi-hazard model to understand how they may occur in the same terrain and be mutually triggering 

• Multi-hazard assessment is part of Agenda 21 for Sustainable Development and is highlighted due to the combination of one or more hazards together being more threatening than one, this is especially applicable to cryospheric hazards where little knowledge exists on hazard dynamics

• Data driven models were used to form a multi-hazard susceptibility model of Northern Svalbard to these processes and revealed that different factors drove each, as well as identifying high-risk zones as an important tool for urban planning and risk management 

• This model was the first of its kind in high-Arctic environments and provides an important baseline for further studies of the changing landscape and developing quantifications of future risks to Arctic communities and ecosystems

Clague, 2013

• Glaciers are greatly impacted by climate change with their hazards amplified as a result, most Alpine glaciers reached their largest size near the end of the Little Ice Age but have all thinned and receded in response to warming in the Holocene

• Warming leads to glacier melt and sea level rise with the most catastrophic events predicted with changes to the Greenland and Antarctic Ice Sheets leading to widespread displacement of those living on shorelines and threats to coastal infrastructure

• The thinning and retreat of alpine glaciers have led to rock-slope failures due to declining stability of slopes, this debuttressing can be caused by glacier melt, freeze-thaw weathering and permafrost degradation; rock falls can pose hazards to climbers and tourists at increasing rates in the European Alps and similar areas

• Permafrost thaw and snow cover decline may also lead to an increased frequency of debris flows as a result of slope instability, ice avalanches may also occur as a result of changes to subglacial hydrology; streams may also be impacted due to changes in the delivery of water and sediments from glaciers

• There are theories that large scale deglaciation may be responsible for triggering seismicity or volcanism due to changing stresses on the lithosphere that may induce the upward movement of magma and trigger slipping

Smellie & Edwards, 2016 

• Many of the most significant volcanic disasters in history are directly linked with volcano-water interactions including Krakatoa 1883 and Nevado del Ruiz 1895

• Ice-drapped and fully subglacial volcanoes may erupt or flood at any time of year, whereas non-ice clad volcanoes depend more strongly on annual climate variations and seasonal cycles; these eruptions can cause a range of local, regional or global hazards depending on the factors of magma and eruptive environments 

• Lava flows can melt snow and ice to cause floods, interact explosively with meltwater and form lava termini that are high;y fractured and susceptible to gravity driven failure; this was seen in Eyjafallajokull 2010 to transform subglacial tunnels into open channelised lava flows; lava domes can also interact with glaciers snow and ice such as Mt St Helens 1980

• Ash production tends to be more fine and at greater volumes and temporal scales for glaciovolcanic eruptions to cause risks for aviation, deposition onto snow and ice causing melting, contaminating drinking water and blocking water sources

• Pyroclastic density currents can interact with meltwater to cause rapid melting produce lahars, this can be a direct driver of mass flows where water combined with volcanic debris travel fast down steep volcanic slopes to devastate local populations and infrastructures; these can also be indirectly triggered by longer-term volcanic heat release into snow/ice craters

• Avalanches and lightning can also be associated with glaciovolcanism; eruptions can also influence the climate with short-term cooling and long-term warming expected to be greater from glaciovolcanism due to eruption rates increasing and more greenhouse gases being released into the atmosphere

Oppenheimer, 2011

• Volcanoes can release ash, gases and aerosols that block sunlight and form short-term global cooling; this can be mitigated or negated by the release of GHGs during the eruption leading to long-term warming

• Sulphur emission is critical to producing strong climatic forcing, sulphur rich magmas have low sulphur solubility so very explosive eruptions tend to be silicic rather than basaltic; magmas must also be highly oxidising or highly reducing to have the highest sulphur emissions

• Eruptions must be explosive and intense enough to penetrate the stratosphere in order to stay aloft and have a significant effect on radiation

Naranjo et al., 1986

• The small Plinian eruption of Nevado del Ruiz ejected huge amounts of mixed tephra into the atmosphere, it caused small pyroclastic flows and surges of the glacier to melt 10% of the volcanoes ice cap leading to meltwater floods; these floods incorporated soils and loose sediments from the flanks into lahars that claimed at least 25,000 lives

• The dispersal of tephra was extensive with ash falls reported more than 400km NE of the volcano, pumice scorched vegetation

• Minor pyroclastic flows destroyed buildings and melted the glacier to form major lahars once mixed with eroded soils and deposits 

• On the east flank, two lahars combined to inundate the town of Armero at about 11pm, most of the population was killed in two to three waves of this lahar; on the western flank around 1000 people were killed in Chinchina

• The principle source of water for lahars was the glacier on the Ruiz volcano, it is likely the glacier surged and broke up during the eruption or released much subglacial meltwater being stored in tunnels and crevasses near the crater to release huge amounts of water for the formation of high fluidity lahars

Edwards et al., 2020

• The use of a spatial database on global glacierized volcanoes can be used to identity where land ice and volcanoes co-exist on Earth, this is useful for future studies aimed at hazard reduction, projections of dangerous volcanoes, paleoclimate reconstructions and continued monitoring

• There are 245 Holocene volcanoes with glacier ice within a radius meaning it is likely to impact or be impacted by volcanism, this can be either partially or fully covered by glaciers and they are mostly found in subduction zones

• Volcanism can be affected by glaciation from source to surface due to changes in overburden pressure, dyke formation, stress regime variability and further impacts to explosivity and characteristics of lava; conversely volcanic eruptions can impact the mass balance of glaciers, create topographies for accumulation, ash cover can expedite wasting, decrease albedo and be affected by magma, lahars and dome emplacement 

• Globally nearly 7 million people live within 30km of a glacierised volcano and almost 160 million people within 100km, meaning they could be impacted by lahars or disruption to water sources

• The most dangerous volcanoes on Earth can be identified through this database through comparisons of eruption history, ice volume and nearby populations

Huggel et al., 2017

• Colombia hosts important glacier-clad volcanoes and public and scientific attention has been focused on these since the 1985 Ruiz/Armero disaster but ice mass extent, volume and structure now changes as a result of atmospheric warming to see glaciers recede at the same time as populations grow in a number of communities around the volcano

• Despite this recession of glaciers, significant volumes of ice are still present and are likely to impose a hazard for potential volcano-ice interactions

• There remains considerable hazard potential from Nevados del Tolima and Huila; notably Nevado del Ruiz is assessed as retaining the conditions conducive to a repetition of events comparable to the 1985 lahars

• Integrated monitoring using seismic stations and remote sensing should be used to assess these changes as well as mitigation attempts including early warning systems and education campaigns

Barr et al., 2018

• Volcanic activity has notable impacts on glacier behaviour, it is important to document and quantify these in an attempt to predict future glacio-volanic behaviours and improve monitoring and mitigation of hazards including floods and lahars 

• The frequency and nature of volcano-glacier interactions are likely to change with time, meaning predictions of future importance is difficult but is being improved through advanced remotely sensed data and observations

• Direct impacts of volcanoes on glaciers include subglacial heating, subglacial dome growth, subglacial eruptions, lava flows, PCDs, supraglacial tephra deposition, floods and lahars etc. to impact the future stability of glaciers that can have wider impacts on ice sheet collapse and global sea level rise; indirect impacts occur through the impact of volcanoes on the climate (e.g. short-term cooling and long-term warming) to influence glacier response to the changing climate 

• Volcanic activity directly affects glacier behaviour due to glaciers being located on active volcanoes or due to interactions with glaciers in adjacent regions