Mid-Term Monitoring of Glacier’s Variations with UAVs: The Example of the Belvedere Glacier

Recently, Unmanned Aerial Vehicles (UAV) have opened up unparalleled opportunities for alpine glacier monitoring, as they allow for reconstructing extensive and high-resolution 3D models. In order to evaluate annual ice flow velocities and volume variations, six yearly measurements were carried out between 2015 and 2020 on the debris-covered Belvedere Glacier (Anzasca Valley, Italian Alps) with low-cost fixed-wing UAVs and quadcopters. Every year, ground control points and check points were measured with GNSS. Images acquired from UAV were processed with Structure-from-Motion and Multi-View Stereo algorithms to build photogrammetric models, orthophotos and digital surface models, with decimetric accuracy. Annual glacier velocities were derived by combining manually-tracked features on orthophotos with GNSS measurements. Velocities ranging between 17 m y−1 and 22 my−1 were found in the central part of the glacier, whereas values between 2 m y−1 and 7 my−1 were found in the accumulation area and at the glacier terminus. Between 2 × 106 m3 and 3.5 × 106m3 of ice volume were lost every year. A pair of intra-year measurements (October 2017–July 2018) highlighted that winter and spring volume reduction was ∼1/4 of the average annual ice loss. The Belvedere monitoring activity proved that decimetric-accurate glacier models can be derived with low-cost UAVs and photogrammetry, limiting in-situ operations. Moreover, UAVs require minimal data acquisition costs and allow for great surveying flexibility, compared to traditional techniques. Information about annual flow velocities and ice volume variations of the Belvedere Glacier may have great value for further understanding glacier dynamics, compute mass balances, or it might be used as input for glacier flow modelling.

Contrasting surface velocities between lake- and land-terminating glaciers in the Himalayan region

Meltwater from Himalayan glaciers sustains the flow of rivers such as the Ganges and Brahmaputra on which over half a billion people depend for day-to-day needs. Upstream areas are likely to be affected substantially by climate change, and changes in the magnitude and timing of meltwater supply are expected to occur in coming decades. About 10 % of the Himalayan glacier population terminates into proglacial lakes, and such lake-terminating glaciers are known to exhibit higher-than-average total mass losses. However, relatively little is known about the mechanisms driving exacerbated ice loss from lake-terminating glaciers in the Himalaya. Here we examine a composite (2017–2019) glacier surface velocity dataset, derived from Sentinel 2 imagery, covering central and eastern Himalayan glaciers larger than 3 km2. We find that centre flow line velocities of lake-terminating glaciers (N = 70; umedian: 18.83 m yr−1; IQR – interquartile range – uncertainty estimate: 18.55–19.06 m yr−1) are on average more than double those of land-terminating glaciers (N = 249; umedian: 8.24 m yr−1; IQR uncertainty estimate: 8.17–8.35 m yr−1) and show substantially more heterogeneity than land-terminating glaciers around glacier termini. We attribute this large heterogeneity to the varying influence of lakes on glacier dynamics, resulting in differential rates of dynamic thinning, which causes about half of the lake-terminating glacier population to accelerate towards the glacier termini. Numerical ice-flow model experiments show that changes in the force balance at the glacier termini are likely to play a key role in accelerating the glacier flow at the front, with variations in basal friction only being of modest importance. The expansion of current glacial lakes and the formation of new meltwater bodies will influence the dynamics of an increasing number of Himalayan glaciers in the future, and these factors should be carefully considered in regional projections.

Glacier Speed-Up Events and Subglacial Hydrology on the Lower Franz Josef Glacier, New Zealand

<p>The contribution of glacier mass loss to future sea level rise is still poorly constrained (Lemke and others, 2007). One of the remaining unknowns is how water inputs influence glacier velocity. Short-term variations in glacier velocity occur when a water input exceeds the capacity of the subglacial drainage system, and the subglacial water pressure increases. Several studies (Van de Wal and others, 2008; Sundal and others, 2011) have suggested that high ice-flow velocities during these events are later offset by lower ice-flow velocities due to a more efficient subglacial drainage system. This study combines in-situ velocity measurements with a full Stokes glacier flowline model to understand the spatial and temporal variations in glacier flow on the lower Franz Josef Glacier, New Zealand. The Franz Josef Glacier experiences significant water inputs throughout the year (Anderson and others, 2006), and as a result, the subglacial drainage system is likely well-developed. In March 2011, measured ice-flow velocities increased by up to 75% above background values in response to rain events and by up to 32% in response to diurnal melt cycles. These speed-up events occurred at all survey locations across the lower glacier. Through flowline modelling, it is shown that the enhanced glacier flow can be explained by a spatially-uniform subglacial water pressure that increased during periods of heavy rain and glacier melt. From these results, it is suggested that temporary spikes in water inputs can cause glacier speed-up events, even when the subglacial hydrology system is well-developed (cf. Schoof, 2010). Future studies should focus on determining the contribution of glacier speed-up events to overall glacier motion.</p>

The Role of Climate and Bed Topography on the Evolution of the Tasman Glacier Since the Last Glacial Maximum

<p>Mountain glaciers respond to climatic changes by advancing or retreating, leaving behind a potentially powerful record of climate through moraine deposition. Estimates of past climate have been made based on the moraine record alone, using geometrical arguments; however, these methods necessarily ignore the effects of glacier dynamics and bed modification. Here, a one-dimensional coupled mass balance-flowline model is used to place constraints on the climate of the Late-glacial (13.5–11.6 kyr ago) and Last Glacial Maximum (LGM, 28 – 17.5 kyr ago) based on the well-mapped and -dated moraines at Tasman Glacier/Lake Pukaki, South Island, New Zealand. Due to the highly-dynamic nature of the system, distinct longitudinal bed profiles are considered for each of the glaciations modelled; the reconstructions show that terminal overdeepenings are likely present in all bed profiles, and hundreds of metres of sediment has been deposited in the glacier valley since the LGM. Using the coupled model and calculated bed topography, a 2.2°C temperature depression from the present is necessary to reproduce the Lateglacial ice extent, and 7.0°C is required for the early LGM, assuming presentday precipitation. The modelled Late-glacial ice extent is more sensitive to precipitation variability than that during the LGM, but the Tasman Glacier during both periods is primarily driven by temperature changes. While the Tasman Glacier shrank between the early and late LGM, modelling demonstrates that changes in bed topography due to erosion, transport and deposition of sediment are a major driver in reduction of glacier extent; a temperature increase of only 0.1°C is required to cause the transition between the two periods, which may be attributable to interannual, zero-trend climate variability. Thus, the consideration of the coupled glacier-sediment system is critical in accurately reconstructing past climate. Future work focusing on modelling this coupled system, such that the bed profile can evolve interactively with glacier flow, will be critical in better resolving transient events such as the early to late LGM transition.</p>

The Role of Climate and Bed Topography on the Evolution of the Tasman Glacier Since the Last Glacial Maximum

<p>Mountain glaciers respond to climatic changes by advancing or retreating, leaving behind a potentially powerful record of climate through moraine deposition. Estimates of past climate have been made based on the moraine record alone, using geometrical arguments; however, these methods necessarily ignore the effects of glacier dynamics and bed modification. Here, a one-dimensional coupled mass balance-flowline model is used to place constraints on the climate of the Late-glacial (13.5–11.6 kyr ago) and Last Glacial Maximum (LGM, 28 – 17.5 kyr ago) based on the well-mapped and -dated moraines at Tasman Glacier/Lake Pukaki, South Island, New Zealand. Due to the highly-dynamic nature of the system, distinct longitudinal bed profiles are considered for each of the glaciations modelled; the reconstructions show that terminal overdeepenings are likely present in all bed profiles, and hundreds of metres of sediment has been deposited in the glacier valley since the LGM. Using the coupled model and calculated bed topography, a 2.2°C temperature depression from the present is necessary to reproduce the Lateglacial ice extent, and 7.0°C is required for the early LGM, assuming presentday precipitation. The modelled Late-glacial ice extent is more sensitive to precipitation variability than that during the LGM, but the Tasman Glacier during both periods is primarily driven by temperature changes. While the Tasman Glacier shrank between the early and late LGM, modelling demonstrates that changes in bed topography due to erosion, transport and deposition of sediment are a major driver in reduction of glacier extent; a temperature increase of only 0.1°C is required to cause the transition between the two periods, which may be attributable to interannual, zero-trend climate variability. Thus, the consideration of the coupled glacier-sediment system is critical in accurately reconstructing past climate. Future work focusing on modelling this coupled system, such that the bed profile can evolve interactively with glacier flow, will be critical in better resolving transient events such as the early to late LGM transition.</p>

Glacier Speed-Up Events and Subglacial Hydrology on the Lower Franz Josef Glacier, New Zealand

<p>The contribution of glacier mass loss to future sea level rise is still poorly constrained (Lemke and others, 2007). One of the remaining unknowns is how water inputs influence glacier velocity. Short-term variations in glacier velocity occur when a water input exceeds the capacity of the subglacial drainage system, and the subglacial water pressure increases. Several studies (Van de Wal and others, 2008; Sundal and others, 2011) have suggested that high ice-flow velocities during these events are later offset by lower ice-flow velocities due to a more efficient subglacial drainage system. This study combines in-situ velocity measurements with a full Stokes glacier flowline model to understand the spatial and temporal variations in glacier flow on the lower Franz Josef Glacier, New Zealand. The Franz Josef Glacier experiences significant water inputs throughout the year (Anderson and others, 2006), and as a result, the subglacial drainage system is likely well-developed. In March 2011, measured ice-flow velocities increased by up to 75% above background values in response to rain events and by up to 32% in response to diurnal melt cycles. These speed-up events occurred at all survey locations across the lower glacier. Through flowline modelling, it is shown that the enhanced glacier flow can be explained by a spatially-uniform subglacial water pressure that increased during periods of heavy rain and glacier melt. From these results, it is suggested that temporary spikes in water inputs can cause glacier speed-up events, even when the subglacial hydrology system is well-developed (cf. Schoof, 2010). Future studies should focus on determining the contribution of glacier speed-up events to overall glacier motion.</p>

Elastic deformation plays a non-negligible role in Greenland’s outlet glacier flow

Future projections of global mean sea level change are uncertain, partly because of our limited understanding of the dynamics of Greenland’s outlet glaciers. Here we study Nioghalvfjerdsbræ, an outlet glacier of the Northeast Greenland Ice Stream that holds 1.1 m sea-level equivalent of ice. We use GPS observations and numerical modelling to investigate the role of tides as well as the elastic contribution to glacier flow. We find that ocean tides alter the basal lubrication of the glacier up to 10 km inland of the grounding line, and that their influence is best described by a viscoelastic rather than a viscous model. Further inland, sliding is the dominant mechanism of fast glacier motion, and the ice flow induces persistent elastic strain. We conclude that elastic deformation plays a role in glacier flow, particularly in areas of steep topographic changes and fast ice velocities.

Glacial processes and landforms

From 1965-2000 glacial geomorphology became increasingly specialised and developed significantly due to technological improvements, particularly in remote sensing, surveying and field-based glaciological process studies. The better understanding of basal thermal regimes in ice sheets and glaciers led to the development of concepts such as spatial and temporal migration of ice divides in dynamic ice sheets that could overprint subglacial landform assemblages, debris entrainment processes related to polythermal glacier systems, and glacier and ice sheet beds composed of cold and warm based mosaics. Process observations at the ice-bed interface led to the discovery of the third glacier flow mechanism, substrate deformation, which provided the impetus to reconstruct the genesis of subglacial bedforms such as drumlins and to evaluate the origins and potential flow law for till. Numerical evaluations of glacial erosion led to a better understanding of abrasion and quarrying as well as the erection of genetic models and erosion rates for larger scale features such as U-shaped valleys and cirques. Linkages were made between debris transport pathways and moraine construction in supraglacial environments, with the role of glacier structure being linked to specific landforms, such as medial, lateral, hummocky and ice-cored moraines as well as rock glaciers. Our appreciation of the erosional and depositional impacts of glacifluvial systems was enhanced significantly with the advent of process observations on the hydrology of modern glaciers as well as the final vindication of J.H. Bretz and his proposed jökulhlaup origins of the Channelled Scablands and the Missoula Floods. In addition to the increasing numbers of studies at modern glacier snouts, the embracing of sedimentology by glacial geomorphologists was to result in significant developments in understanding the process-form regimes of subglacial, marginal and proglacial landforms, particularly the recognition of landform continua and hybrids. Advances resulting from this included the recognition of different modes of moraine and glacitectonic thrust mass development, lithofacies models of the varied glacifluvial depositional environments, and the initial expansion of the sediments and depo-centres of glacimarine settings, the latter being the result of glacial research taking to submersibles and ice-strengthened ships for the first time. A similarly new frontier was the expansion of research on the increasingly higher resolution images returning from Mars, where extraterrestrial glaciations were recognised based on comparisons with Earth analogues. Holistic appreciations of glaciation signatures using landform assemblages were developed, initially as process-form models and later as glacial landsystems, providing an ever expanding set of templates for reconstructing palaeoglaciology in the wide variety of topographic and environmental settings, which also acknowledge spatial and temporal change in glacier and ice sheet systems.

Glacier Velocity Changes in the Himalayas in Relation to Ice Mass Balance

Glacier evolution with time provides important information about climate variability. Here, we investigated glacier velocity changes in the Himalayas and analysed the patterns of glacier flow. We collected 220 scenes of Landsat-7 panchromatic images between 1999 and 2000, and Sentinel-2 panchromatic images between 2017 and 2018, to calculate surface velocities of 36,722 glaciers during these two periods. We then derived velocity changes between 1999 and 2018 for the early winter period, based on which we performed a detailed analysis of motion of each individual glacier, and noted that the changes are spatially heterogeneous. Of all the glaciers, 32% have sped up, 24.5% have slowed down, and the rest 43.5% have remained stable. The amplitude of glacier slowdown, as a result of glacier mass loss, is significantly larger than that of speedup. At regional scales, we found that glacier surface velocity in winter has uniformly decreased in the western part of the Himalayas between 1999 and 2018, while increased in the eastern part; this contrasting difference may be associated with decadal changes in accumulation and/or melting under different climatic regimes. We also found that the overall trend of surface velocity exhibits seasonal variability: summer velocity changes are positively correlated with mass loss, i.e., velocity increases with increasing mass loss, whereas winter velocity changes show a negative correlation. Our study suggests that glacier velocity changes in the Himalayas are spatially and temporally heterogeneous, in agreement with studies that previously highlighted this trend, emphasising complex interactions between glacier dynamics and environmental forcing.