Mapping Glacier Ablation With a UAV in the North Cascades: A Structure-from-Motion Approach

The glaciers of the North Cascades have experienced mass loss and terminus retreat due to climate change. The meltwater from these glaciers provides a flux of cold glacier meltwater into the river systems, which supports salmon spawning during the late summer dry season. The Nooksack Indian Tribe monitors the outlet flow of the Sholes Glacier within the North Cascades range with the goal of understanding the health of the glacier and the ability of the Tribe to continue to harvest sustainable populations of salmon. This study compares the UAV derived glacier ablation with the discharge data collected by the Tribe. We surveyed the Sholes Glacier twice throughout the 2020 melt season and, using Structure-from-Motion technology, generated high resolution multispectral orthomosaics and Digital Elevation Models (DEMs) of the glacier on each of the survey dates. The DEMs were differenced to reveal the surface height change of the glacier. The spectral data of the orthomosaics were used to conduct IsoData unsupervised classification. This process divided the survey area into Snow, Ice, and Rock classes that were then used to attribute the surface height changes of the DEMs to either snow or ice melt. The analysis revealed the glacier lost an average thickness of −0.132 m per day (m d−1) with snow and ice losing thickness at similar rates, −0.130 m d−1 and −0.132 m d−1 respectively. DEM differencing reveals that a total of −550,161 ± 45,206 m3 water equivalent (w.e.) was discharged into Wells Creek between the survey dates whereas the stream gauge station measured a total discharge of 350,023 m3. This study demonstrates the ability to spectrally classify the UAV data and derive discharge measurements while evaluating the small-scale spatial variability of glacier melt. Assessing ablation in small alpine glaciers is of great importance to downstream communities, like the Nooksack Indian Tribe who seek to understand the magnitude and timing of glacier melt in order to better protect their salmon populations. With this paper, we provide a baseline for future glacier monitoring and the potential to connect the snow surface properties with the rate of snow melt into a warming future.

Surface energy balance of the Sygyktinsky Glacier, south Eastern Siberia, during the ablation period and its sensitivity to meteorological fluctuations

The physically based melt of the low elevation Eastern Siberian glaciers is poorly understood due to the lack of direct micrometeorological studies. We used an automatic meteorological station to record the meteorological and energy characteristics of the Sygyktinsky Glacier, south Eastern Siberia (56.8° N, 117.4° E, 2,560 m a.s.l.), during two ablation seasons and computed the surface energy balance (SEB) for 30-min intervals. The glacier ablation was both modeled and measured by stakes and a thermistor cable. The net radiation (Rnet) was the main contributor (71–75 W m−2, 89–95%) to the SEB (79 W m−2, 100%), followed by sensible (2–4 W m−2, 3–5%) and latent (2–3 W m−2, 2–4%) heat fluxes. The net shortwave radiation was the main positive component of Rnet, while the net longwave radiation was weak and either negative (− 15 W m−2 in 2019) or positive (4 W m−2 in 2020). The small proportion of turbulent fluxes in the SEB is explained by the low wind speed (1.2 m s−1). The glacier ablation was found to be more sensitive to changes in shortwave radiation and wind speed, suggesting the need to consider the atmospheric conditions of the ablation period (summer snowfalls, cloudiness, wind speed) when analyzing long-term trends in glacial changes.

Susceptibility Analysis of Glacier Debris Flow by Investigating the Changes in Glaciers Based on Remote Sensing: A Case Study

Glacier debris flow is one of the most critical categories of geological hazards in high-mountain regions. To reduce its potential negative effects, it needs to investigate the susceptibility of glacier debris flow. However, when evaluating the susceptibility of glacier debris flow, most research work considered the impact of existing glacier area, while ignoring the impact of changes in glacier ablation volume. In this paper, we considered the impact of the changes in the glacier ablation volume to investigate the susceptibility of glacier debris flow. We proposed to evaluate the susceptibility analysis in G217 gullies with frequent glacial debris flow on the Duku highway, Xinjiang Province. Specifically, by using the simple band ratio method with the manual correction to identify glacier outlines, we identified the ablation zone by comparing the glacier boundary in 2000 with that in 2015. We then calculated ablation volume by changes in glacier elevation and ablation area from 2000 to 2015. Finally, we used the volume of glacier melting in different watersheds as the main factor to evaluate the susceptibility based on the improved geomorphic information entropy (GIE) method. We found that, overall, the improved GIE method with a correction coefficient based on the glacier ablation volume is better than the previous method. Deglaciation can be adapted to analyze glacier debris flow susceptibility based on glaciology and geomorphology. Our presented work can be applied to other similar glacial debris flow events in high-mountain regions.

Health and sustainability of glaciers in High Mountain Asia

Glaciers in High Mountain Asia generate meltwater that supports the water needs of 250 million people, but current knowledge of annual accumulation and ablation is limited to sparse field measurements biased in location and glacier size. Here, we present altitudinally-resolved specific mass balances (surface, internal, and basal combined) for 5527 glaciers in High Mountain Asia for 2000–2016, derived by correcting observed glacier thinning patterns for mass redistribution due to ice flow. We find that 41% of glaciers accumulated mass over less than 20% of their area, and only 60% ± 10% of regional annual ablation was compensated by accumulation. Even without 21st century warming, 21% ± 1% of ice volume will be lost by 2100 due to current climatic-geometric imbalance, representing a reduction in glacier ablation into rivers of 28% ± 1%. The ablation of glaciers in the Himalayas and Tien Shan was mostly unsustainable and ice volume in these regions will reduce by at least 30% by 2100. The most important and vulnerable glacier-fed river basins (Amu Darya, Indus, Syr Darya, Tarim Interior) were supplied with >50% sustainable glacier ablation but will see long-term reductions in ice mass and glacier meltwater supply regardless of the Karakoram Anomaly.

Intensified paraglacial slope failures due to accelerating downwasting of a temperate glacier in Mt. Gongga, Southeastern Tibet Plateau

Topographic development via paraglacial slope failure (PSF) represents a complex interplay between geological structure, climate, and glacial denudation. Where debris generated by PSFs is deposited on the surface of a glacier, this debris can increase the extent or thickness of a supraglacial debris-cover, in turn modifying glacier ablation and affecting meltwater generation. To date, little attention has been paid to intensity and frequency of PSFs in glacierised, monsoon temperate regions of Southeast Tibet. We mapped PSFs along the 5 km-long, west-east trending ice tongue of Hailuogou Glacier (HLG), Mt. Gongga, using repeat satellite- and UAV-derived imagery between 1990 and 2020. Three types of PSF were identified: (A) rock fall, (B) sediment-mantled slopes slide and collapse, and (C) gully headwards erosion. We analyzed the formation, evolution and current state of these PSFs and discuss these aspects with relation to glacier dynamics and paraglacial geomorphological history. South-facing slopes (true left of HLG) showed more destabilization and higher PSF activity than north-facing slopes. We observed annual average rates of downslope sliding for type B PSFs of 1.6–2.6 ± 0.04 cm d−1, whereas the average upward denudation rate for type C PSFs was 0.7–3.39 cm d−1. We show that type A PSFs are non-ice-contact rock collapses that occur as a long-term paraglacial response following glacier downwasting and the exposure of steep rocky cliffs and which could also be influenced by precipitation, freeze-thaw cycling, earthquakes or other factors. In contrast, type B and C PSFs are a more immediate response to recent glacier downwasting. We further argue that the accelerating downwasting of glacier are used as a preparatory or triggering factor, which could directly or indirectly cause the PSFs.

Intensified paraglacial slope failures due to accelerating downwasting of a temperate glacier in Mt. Gongga, Southeastern Tibet Plateau

<p>Topographic development via paraglacial slope failure (PSF) represents a complex interplay between geological structure, climate, and glacial denudation. Where debris generated by PSFs is deposited on the surface of a glacier, this debris can increase the extent or thickness of a supraglacial debris-cover, in turn modifying glacier ablation and affecting meltwater generation. To date, little attention has been paid to intensity and frequency of PSFs and their significance as a geomorphic agent and hazard in glacierised, monsoon temperate regions of Southeast Tibet. We mapped PSFs along the 5 km-long, west-east trending ice tongue of Hailuogou Glacier (HLG), Mt. Gongga, using repeat satellite- and UAV-derived imagery between 1990 and 2020. Three types of PSF were identified: (A) rock fall, (B) slide and collapse of sediment-mantled slopes, and (C) gulley headwards erosion. We analyzed the formation, evolution and current state of these PSFs and discuss these aspects with relation to glacier dynamics and paraglacial geomorphological history. South-facing slopes (true left of HLG) showed more destabilization and higher PSF activity than north-facing slopes. We observed annual average rates of downslope sliding for type B PSFs of 1.6-2.6 cm d<sup>-1</sup>, whereas the average upward denudation rate for type C PSFs was 0.7-3.39 cm d<sup>-1</sup>. We show that type A PSFs are non-ice-contact rock collapses that occur as a long-term paraglacial response following glacier downwasting and the exposure of steep rocky cliffs and which could also be influenced by precipitation, freeze-thaw cycling, earthquakes or other factors. In contrast, type B and C PSFs are a more immediate response to recent glacier downwasting. We further argue that the accelerating downwasting of glacier are used as a preparatory or triggering factor, which could directly or indirectly cause the PSFs.</p>

Seasonally stable temperature gradients through supraglacial debris in the Everest region of Nepal, Central Himalaya

Rock debris covers ~30% of glacier ablation areas in the Central Himalaya and modifies the impact of atmospheric conditions on mass balance. The thermal properties of supraglacial debris are diurnally variable but remain poorly constrained for monsoon-influenced glaciers over the timescale of the ablation season. We measured vertical debris profile temperatures at 12 sites on four glaciers in the Everest region with debris thickness ranging from 0.08 to 2.8 m. Typically, the length of the ice ablation season beneath supraglacial debris was 160 days (15 May to 22 October)—a month longer than the monsoon season. Debris temperature gradients were approximately linear (r2 > 0.83), measured as −40°C m–1 where debris was up to 0.1 m thick, −20°C m–1 for debris 0.1–0.5 m thick, and −4°C m–1 for debris greater than 0.5 m thick. Our results demonstrate that the influence of supraglacial debris on the temperature of the underlying ice surface, and therefore melt, is stable at a seasonal timescale and can be estimated from near-surface temperature. These results have the potential to greatly improve the representation of ablation in calculations of debris-covered glacier mass balance and projections of their response to climate change.

Distributed summer air temperatures across mountain glaciers: climatic sensitivity and glacier size

Near-surface air temperature (Ta) is highly important for modelling glacier ablation, though its spatio-temporal variability over melting glaciers still remains largely unknown. We present a new dataset of distributed Ta for three glaciers of different size in the south-east Tibetan Plateau during two monsoon-dominated summer seasons. We compare on-glacier Ta to ambient Ta extrapolated from several, local off-glacier stations. We parameterise the along-flowline climatic sensitivity of Ta on these glaciers to changes in off-glacier temperatures and present the results in the context of several available distributed on-glacier datasets around the world. Climatic sensitivity decreases rapidly up to 2000–3000 m along the down-glacier flowline distance. Beyond this distance, both the Ta of the Tibetan glaciers and global glacier datasets show a slower decrease of climatic sensitivity. In general, observations on small glaciers (with

The challenge of non-stationary feedbacks within the response of debris-covered glaciers to climate forcing

<p><strong>The challenge of non-stationary feedbacks within the response of debris-covered glaciers to climate forcing</strong></p><p>Debris-covered glaciers are a feature of many mountain ranges around the world and their proportion is expected to increase under continued climate warming.</p><p>The impact of debris cover on glacier behavior, via its profound modification of the glacier ablation regime, causes debris-covered glaciers to respond to the same climate forcing in a markedly different way to clean ice glaciers. In order to better understand how debris cover impacts the glacier’s response to climate forcing, we revisit the concept of steady state and examine it for a debris-covered glacier system. We present simple modeling results to explore how the development and evolution of debris cover affects the potential for steady-state and how feedbacks instigated by supraglacial debris cover complicate the glacier’s response to a prescribed steady climate. These investigations highlight the non-stationarity induced by the presence of debris and as a result, that debris cannot be considered as a static component, as it is a highly dynamic component which affects the glacier system in different ways.</p><p><br><br></p>