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.

Investigation of the Combined Effects of Rising Temperature and Pesticide Contamination on the Swimming Behaviour of Alpine Chironomids

Some pollutants can be transported through the atmosphere and travel medium–long distances to be deposited in glaciers at high altitude and latitude. The increase in the rate of glacier melting due to global warming can release these pollutants in alpine streams. This study investigated the combined effects of rising temperatures and chlorpyrifos (CPF) contamination on the swimming behaviour of alpine chironomids collected in a shrinking alpine glacier. We assessed the individual and interaction effects of rising temperatures (2–11 °C) and CPF concentrations (0–110 ng L−1) on the swimming behaviour of Diamesa zernyi (Chironomidae) larvae. Distance (mm) and speed (mm s−1) were recorded using a video-tracking system after 24–72 h of treatment. The two stressors caused different effects on distance and speed, with increasing temperature generally causing hyperactivity and CPF from hyperactivity to reduced mobility. Two interactions were detected between stressors when combined: (i) CPF superimposed the effect of temperature on both behavioural endpoints i.e., with 110 ng L−1 of CPF, at 11 °C, larvae moved less; (ii) warming (11 °C) magnified the negative effect of CPF: the smallest distance and slowest speed were recorded at the highest values of the two stressors after 72 h. Our results suggest that water contamination by CPF, even at sub-lethal concentrations, might increase the sensitivity of chironomids to warming, and vice versa, raising concerns about freshwater biodiversity conservation under climate change.

Reconciling the Apparent Absence of a Last Glacial Maximum Alpine Glacial Advance, Yukon Territory, Canada, through Cosmogenic Beryllium-10 and Carbon-14 Measurements

We present a new in situ produced cosmogenic beryllium-10 and carbon-14 nuclide chronology from two sets (outer and inner) of alpine glacier moraines from the Grey Hunter massif of southern Yukon Territory, Canada. The chronology potential of moraines deposited by alpine glaciers outside the limits of the Last Glacial Maximum (LGM) ice sheets potentially provide a less-ambiguous archive of mass balance, and hence climate than can be inferred from the extents of ice sheets themselves. Results for both nuclides are inconclusive for the outer moraines, with evidence for pre-LGM deposition (beryllium-10) and Holocene deposition (carbon-14). Beryllium-10 results from the inner moraine are suggestive of canonical LGM deposition, but with relatively high scatter. Conversely, in situ carbon-14 results from the inner moraines are tightly clustered and suggestive of terminal Younger Dryas deposition. We explore plausible scenarios leading to the observed differences between nuclides and find that the most parsimonious explanation for the outer moraines is that of pre-LGM deposition, but many of the sampled boulder surfaces were not exhumed from within the moraine until the Holocene. Our results thus imply that the inner and outer moraines sampled pre- and post-date the canonical LGM and that moraines dating to the LGM are lacking likely due to overriding by the subsequent Late Glacial/earliest Holocene advance.

Englacial hydrology of Annette Plateau, a temperate alpine glacier, Southern Alps, New Zealand

<p>The movement of water through temperate glaciers is important for understanding fundamental issues within glaciology. These include glacier induced floods, glacier dynamics and run-off prediction. Traditional englacial hydrology is thought to consist of interconnected tubular channels that merge down-glacier and drain through the glacier to the bed. However, englacial hydrology is much debated as the links between the glacier surface and bed are not well understood. Ground penetrating radar (GPR) is a geophysical tool that is well suited for studying glaciated areas. Recent ice coring attempts in New Zealand’s temperate alpine glaciers were not successful in coring to bedrock due to the interception of water at depth. This highlights the need for a better understanding of the englacial hydrology of temperate systems. This study investigates the englacial hydrology at Annette Plateau where on three occasions the interception of water has prevented successful coring to the glacier bed. Ground penetrating radar was used to conduct two high-resolution surveys on Annette Plateau in early spring 2011 and early summer 2011. Across-glacier profiles were acquired at 20 m spacing to enable tracking of englacial reflectors between profiles. Models of temperate englacial features were made to aid feature identification within radar profiles. Radar data is compared with density, stratigraphy and chemistry results from the 45 m ice core obtained at Annette Plateau in winter 2009. The early-summer survey indicates an increase in the glacier’s water content compared with the early-spring survey. Englacial reflectors show evidence of (a) spatially continuous englacial conduits, (b) the formation of a water table feature which shallows down glacier, and (c) detailed bedrock topography. Hydropotential surfaces, calculated for the water table and bedrock horizons, show the direction of water flow. Ice core chemistry shows a correlation between the depth of the water table and a significant hiatus indicated by tritium dating. We infer that an extensive water table has formed on an old melt surface where ice from approximately 1930-1991 has been removed. This water table responds to seasonal temperature changes and hydrological inputs.</p>

Englacial hydrology of Annette Plateau, a temperate alpine glacier, Southern Alps, New Zealand

<p>The movement of water through temperate glaciers is important for understanding fundamental issues within glaciology. These include glacier induced floods, glacier dynamics and run-off prediction. Traditional englacial hydrology is thought to consist of interconnected tubular channels that merge down-glacier and drain through the glacier to the bed. However, englacial hydrology is much debated as the links between the glacier surface and bed are not well understood. Ground penetrating radar (GPR) is a geophysical tool that is well suited for studying glaciated areas. Recent ice coring attempts in New Zealand’s temperate alpine glaciers were not successful in coring to bedrock due to the interception of water at depth. This highlights the need for a better understanding of the englacial hydrology of temperate systems. This study investigates the englacial hydrology at Annette Plateau where on three occasions the interception of water has prevented successful coring to the glacier bed. Ground penetrating radar was used to conduct two high-resolution surveys on Annette Plateau in early spring 2011 and early summer 2011. Across-glacier profiles were acquired at 20 m spacing to enable tracking of englacial reflectors between profiles. Models of temperate englacial features were made to aid feature identification within radar profiles. Radar data is compared with density, stratigraphy and chemistry results from the 45 m ice core obtained at Annette Plateau in winter 2009. The early-summer survey indicates an increase in the glacier’s water content compared with the early-spring survey. Englacial reflectors show evidence of (a) spatially continuous englacial conduits, (b) the formation of a water table feature which shallows down glacier, and (c) detailed bedrock topography. Hydropotential surfaces, calculated for the water table and bedrock horizons, show the direction of water flow. Ice core chemistry shows a correlation between the depth of the water table and a significant hiatus indicated by tritium dating. We infer that an extensive water table has formed on an old melt surface where ice from approximately 1930-1991 has been removed. This water table responds to seasonal temperature changes and hydrological inputs.</p>

Diurnal expansion and contraction of englacial fracture networks revealed by seismic shear wave splitting

Fractures contribute to bulk elastic anisotropy of many materials in the Earth. This includes glaciers and ice sheets, whose fracture state controls the routing of water to the base and thus large-scale ice flow. Here we use anisotropy-induced shear wave splitting to characterize ice structure and probe subsurface water drainage beneath a seismometer network on an Alpine glacier. Shear wave splitting observations reveal diurnal variations in S-wave anisotropy up to 3%. Our modelling shows that when elevated by surface melt, subglacial water pressures induce englacial hydrofractures whose volume amounts to 1-2 percent of the probed ice mass. While subglacial water pressures decrease, these fractures close and no fracture-induced anisotropy variations are observed in the absence of meltwater. Consequently, fracture networks, which are known to dominate englacial water drainage, are highly dynamic and change their volumes by 90-180 % over subdaily time scales.