Spatial variability in mass change of glaciers in the Everest region, central Himalaya, between 2000 and 2015

The mass balance of the majority of Himalayan glaciers is currently negative, and has been for several decades. Region wide averaging of mass change estimates has masked any catchment or glacier scale variability in glacier recession, thus the role of a number of glaciological processes in glacier wastage remains poorly understood. In this study, we quantify surface lowering and mass loss rates for the ablation areas of 32 glaciers in different catchments across the Everest region, and specifically examine the role of glacial lakes in glacier mass change. We then assess how future ice loss is likely to differ depending on glacier hypsometry. Spatially variable ice loss is observed within and between the Dudh Koshi and Tama Koshi catchments and glaciers that flow onto the Tibetan Plateau. Surface lowering rates on glaciers flowing onto the Tibetan Plateau are 54 and 19 % greater than those flowing southward into the Dudh Koshi and Tama Koshi catchments, respectively. Surface lowering rates of up to −3.78 ± 0.26 m a-1 occurred on some lacustrine terminating glaciers, although glaciers with small lakes showed rates of lowering comparable with those that terminate on land. We suggest that such a range reflects glacial lakes at different stages of development, and that rates of mass loss are likely to increase as glacial lakes expand and deep water calving begins to occur. Hypsometric data reveal a coincidence of the altitude of maximum surface lowering and the main glacier hypsometry in the Dudh Koshi catchment, thus a large volume of ice is readily available for melt. Should predicted CMIP5 RCP 4.5 scenario warming (0.9–2.3 °C by 2100) occur in the study area, 19–30, 17–50 and 14–37 % increases in the total glacierised area below the Equilibrium Line Altitude will occur in the Dudh Koshi and Tama Koshi catchments, and on the Tibetan Plateau. Comparison of our data with a conceptual model of Himalayan glacier shrinkage confirms the presence of three distinct process regimes, with all glaciers in our sample now in a state of accelerating mass loss and meltwater storage

Glacial Aerodynamic Roughness Estimates:Uncertainty, Sensitivity, and Precision in Field Measurements

Calculation of the sensible and latent heat (turbulent) fluxes is required in order to close the surface energy budget of glaciers and model glacial melt. The aerodynamic roughness length, z0, is a key parameter in the bulk approach to calculating sensible heat flux; yet, z0 is commonly considered simply as a tuning parameter or generalized between surfaces and over time. Spatially and temporally distributed observations of z0 over ice are rare. Both direct (from wind towers and sonic anemometers) and indirect (from microtopographic surveys) measurements of z0 are subject to sensitivities and uncertainties that are often unstated or overlooked. In this study, we present a quantitative evaluation of aerodynamic profile-based and microtopographic methods and their effect on z0 using data collected from Storglaciären and Sydöstra Kaskasatjäkkaglaciären, Tarfala Valley, Arctic Sweden. Aggressive data filters discard most of the wind tower data but still produce realistic z0 values of 1.9 mm and 2 mm. Despite uncertainty introduced by scale and resolution dependence, microtopographic methods produced estimates of z0 comparable to wind tower values and those found on similar surfaces. We conclude that (1) in the absence of direct turbulent flux measurements from sonic anemometers, the profile and microtopographic methods provide realistic z0 values, (2) both 2D and 3D microtopographic methods are dependent on scale, resolution, and the chosen detrending method, and (3) careful calibration of these parameters could enable glacier-wide investigations of z0 from remotely sensed data, including those increasingly available from satellite platforms

Spatio-temporal variability in geometry and geodetic mass balance of Jostedalsbreen ice cap, Norway

The Jostedalsbreen ice cap is mainland Europe's largest ice cap and accommodates 20% (458 km2 in 2019) of the total glacier area of mainland Norway. Jostedalsbreen and its meltwater contribute to global sea-level rise and to local water management, hydropower and tourism economies and livelihoods. In this study, we construct a digital terrain model (DTM) of the ice cap from 1966 aerial photographs, which by comparing to an airborne LiDAR DTM from 2020, we compute changes in surface elevation and geodetic mass balances. The area mapped in both surveys cover about 3/4 of the ice cap area and 49 of 82 glaciers. The measured glacier area has decreased from 363.4 km2 in 1966 to 332.9 km2 in 2019, i.e. a change of −30 km2 or −8.4% (−0.16% a−1), which is in line with the percentage reduction in area for Jostedalsbreen as a whole. The mean geodetic mass balance over the 49 glaciers was −0.15 ± 0.01 m w.e. a−1, however, large variability is evident between glaciers, e.g. Nigardsbreen (−0.05 m w.e. a−1), Austdalsbreen (−0.28 m w.e. a−1) and Tunsbergdalsbreen (−0.36 m w.e. a−1) confirming differences also found by the glaciological records for Nigardsbreen and Austdalsbreen

Heterogeneous water storage and thermal regime of supraglacial ponds on debris-covered glaciers

The water storage and energy transfer roles of supraglacial ponds are poorly constrained, yet they are thought to be important components of debris-covered glacier ablation budgets. We used an unmanned surface vessel (USV) to collect sonar depth measurements for 24 ponds to derive the first empirical relationship between their area and volume applicable to the size distribution of ponds commonly encountered on debris-covered glaciers. Additionally, we instrumented nine ponds with thermistors and three with pressure transducers, characterising their thermal regime and capturing three pond drainage events. The deepest and most irregularly-shaped ponds were those associated with ice cliffs, which were connected to the surface or englacial hydrology network (maximum depth = 45.6 m), whereas hydrologically-isolated ponds without ice cliffs were both more circular and shallower (maximum depth = 9.9 m). The englacial drainage of three ponds had the potential to melt ~100 ± 20 × 103 kg to ~470 ± 90 × 103 kg of glacier ice owing to the large volumes of stored water. Our observations of seasonal pond growth and drainage with their associated calculations of stored thermal energy have implications for glacier ice flow, the progressive enlargement and sudden collapse of englacial conduits, and the location of glacier ablation hot-spots where ponds and ice cliffs interact. Additionally, the evolutionary trajectory of these ponds controls large proglacial lake formation in deglaciating environments

Glaciovolcanic hydrothermal environments in Iceland and implications for their detection on Mars

Volcanism has been a dominant process on Mars, along with a pervasive global cryosphere. Therefore, the interaction between these two is considered likely. Terrestrial glaciovolcanism produces distinctive lithologies and alteration terrains, as well as hydrothermal environments that can be inhabited by microorganisms. Here, we provide a framework for identifying evidence of such glaciovolcanic environments during future Mars exploration, and provide a descriptive reference for active hydrothermal environments to be utilised for future astrobiological studies. Remote sensing data were combined with field observations and sample analysis that included X-ray diffraction, Raman spectroscopy, thin section petrography, scanning electron microscopy, electron dispersive spectrometer analysis, and dissolved water chemistry to characterise samples from two areas of basaltic glaciovolcanism: Askja and Kverkfjöll volcanoes in Iceland. The glaciovolcanic terrain between these volcanoes is characterised by subglacially-erupted fissure swarm ridges, which have since been modified by multiple glacial outburst floods. Active hydrothermal environments at Kverkfjöll include hot springs, anoxic pools, glacial meltwater lakes, and sulfur- and iron- depositing fumaroles, all situated within ice-bound geothermal fields. Temperatures range from 0 °C - 94.4 °C, and aqueous environments are acidic - neutral (pH 2 - 7.5) and sulfate-dominated. Mineralogy of sediments, mineral crusts, and secondary deposits within basalts suggest two types of hydrothermal alteration: a low-temperature ( 120 °C) assemblage signified by zeolite (heulandite) and quartz. These mineral assemblages are consistent with those identified at the Martian surface. In-situ and laboratory VNIR (440 – 1000 nm) reflectance spectra representative of Mars rover multispectral imaging show sediment spectral profiles to be influenced by Fe2 +/3 + - bearing minerals, regardless of their dominant bulk mineralogy. Characterising these terrestrial glaciovolcanic deposits can help identify similar processes on Mars, as well as identifying palaeoenvironments that may once have supported and preserved life

The long-term fate of permafrost peatlands under rapid climate warming

Permafrost peatlands contain globally important amounts of soil organic carbon, owing to cold conditions which suppress anaerobic decomposition. However, climate warming and permafrost thaw threaten the stability of this carbon store. The ultimate fate of permafrost peatlands and their carbon stores is unclear because of complex feedbacks between peat accumulation, hydrology and vegetation. Field monitoring campaigns only span the last few decades and therefore provide an incomplete picture of permafrost peatland response to recent rapid warming. Here we use a high-resolution palaeoecological approach to understand the longer-term response of peatlands in contrasting states of permafrost degradation to recent rapid warming. At all sites we identify a drying trend until the late-twentieth century; however, two sites subsequently experienced a rapid shift to wetter conditions as permafrost thawed in response to climatic warming, culminating in collapse of the peat domes. Commonalities between study sites lead us to propose a five-phase model for permafrost peatland response to climatic warming. This model suggests a shared ecohydrological trajectory towards a common end point: inundated Arctic fen. Although carbon accumulation is rapid in such sites, saturated soil conditions are likely to cause elevated methane emissions that have implications for climate-feedback mechanisms

Glacier thinning, recession and advance, and the associated evolution of a glacial lake between 1966 and 2021 at Austerdalsbreen, western Norway

The Jostedalsbreen is the largest ice cap in Norway and mainland Europe. Rapid retreat of many of its outlet glaciers since the 2000s has led to the formation of several glacial lakes. Processes causing the formation and expansion of glacial lakes and their interaction with a glacier and terminal moraine have not been widely addressed yet. In this study, we investigate the degradation of the front of the southeast-facing outlet glacier Austerdalsbreen. Based on a variety of remotely sensed data (UAV-based and airborne orthophotos and DEMs, satellite images), we analyze the coincident glacial and proglacial changes of Austerdalsbreen and quantify the evolution of this transition zone during the last decades. In particular, we focus on the short-term evolution of the glacial lake since 2010, we examine the context of a glacier advance in the 1990s, and we report long-term changes by utilizing 1960s imagery. We discuss the evolution and conditions of Austerdalsbreen compared to other outlet glaciers of Jostedalsbreen. Overall, the glacier terminus has experienced a recession in the last decades. The 1990s terminus advance was more restricted than at other nearby outlet glaciers due to glacier surface debris cover, which is a critical factor for the glacier and lake evolution. However, in the most recent period, since 2012, a distinct expansion of a glacial lake is quantifiable. Since the rates of glacier surface lowering also considerably increased since approximately 2017 and the glacier retreated since the beginning of the 2000s with a clear maximum length decrease in 2015, we interpret the recently formed glacial lake as a contributory factor of glacial changes

Testing the applicability of morphometric characterisation in discordant catchments to ancient landscapes: A case study from southern Africa

The ancient landscapes south of the Great Escarpment in southern Africa preserve large-scale geomorphological features despite their antiquity. This study applies and evaluates morphometric indices (such as hypsometry, long profile analysis, stream gradient index, and linear/areal catchment characteristics) to the Gouritz catchment, a large discordant catchment in the Western Cape. Spatial variation of morphometric indices were assessed across catchment (trunk rivers) and subcatchment scales. The hypsometric curve of the catchment is sinusoidal, and a range of curve profiles are evident at subcatchment scale. Hypsometric integrals do not correlate to catchment properties such as area, circularity, relief, and dissection; and stream length gradients do not follow expected patterns, with the highest values seen in the mid-catchment areas. Rock type variation is interpreted to be the key control on morphometric indices within the Gouritz catchment, especially hypsometry and stream length gradient. External controls, such as tectonics and climate, were likely diminished because of the long duration of catchment development in this location. While morphometric indices can be a useful procedure in the evaluation of landscape evolution, this study shows that care must be taken in the application of morphometric indices to constrain tectonic or climatic variation in ancient landscapes because of inherited tectonic structures and signal shredding. More widely, we consider that ancient landscapes offer a valuable insight into long-term environmental change, but refinements to geomorphometric approaches are needed

Structure from motion photogrammetry in physical geography

AbstractAccurate, precise and rapid acquisition of topographic data is fundamental to many sub-disciplines of physicalgeography. Technological developments over the past few decades have made fully distributed data sets ofcentimetric resolution and accuracy commonplace, yet the emergence of Structure from Motion (SfM) withMulti-View Stereo (MVS) in recent years has revolutionised three-dimensional topographic surveys inphysical geography by democratising data collection and processing. SfM-MVS originates from the fields ofcomputer vision and photogrammetry, requires minimal expensive equipment or specialist expertise and,under certain conditions, can produce point clouds of comparable quality to existing survey methods (e.g.Terrestrial Laser Scanning). Consequently, applications of SfM-MVS in physical geography have multipliedrapidly. There are many practical options available to physical geographers when planning a SfM-MVS survey(e.g. platforms, cameras, software), yet, many SfM-MVS end-users are uncertain as to the errors associatedwith each choice and, perhaps most fundamentally, the processes actually taking place as part of the SfM-MVSworkflow. This paper details the typical workflow applied by SfM-MVS software packages, reviews practicaldetails of implementing SfM-MVS, combines existing validation studies to assess practically achievable dataquality and reviews the range of applications of SfM-MVS in physical geography. The flexibility of the SfM-MVSapproach complicates attempts to validate SfM-MVS robustly as each individual validation study will use adifferent approach (e.g. platform, camera, georeferencing method, etc.). We highlight the need for greatertransparency in SfM-MVS processing and enhanced ability to adjust parameters that determine survey quality.Looking forwards, future prospects of SfM-MVS in physical geography are identified through discussion ofmore recent developments in the fields of image analysis and computer vision

Land cover changes across Greenland dominated by a doubling of vegetation in three decades

Land cover responses to climate change must be quantified for understanding Arctic climate, managing Arctic water resources, maintaining the health and livelihoods of Arctic societies and for sustainable economic development. This need is especially pressing in Greenland, where climate changes are amongst the most pronounced of anywhere in the Arctic. Ice loss from the Greenland Ice Sheet and from glaciers and ice caps has increased since the 1980s and consequently the proglacial parts of Greenland have expanded rapidly. Here we determine proglacial land cover changes at 30 m spatial resolution across Greenland during the last three decades. Besides the vastly decreased ice cover (− 28,707 km2 ± 9767 km2), we find a doubling in total areal coverage of vegetation (111% ± 13%), a quadrupling in wetlands coverage (380% ± 29%), increased meltwater (15% ± 15%), decreased bare bedrock (− 16% ± 4%) and increased coverage of fine unconsolidated sediment (4% ± 13%). We identify that land cover change is strongly associated with the difference in the number of positive degree days, especially above 6 °C between the 1980s and the present day. Contrastingly, absolute temperature increase has a negligible association with land cover change. We explain that these land cover changes represent local rapid and intense geomorphological activity that has profound consequences for land surface albedo, greenhouse gas emissions, landscape stability and sediment delivery, and biogeochemical processes