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

Topographic development via paraglacial slope failure (PSF) represents a complex interplay between geological structure, climate, and glacial denudation. Southeastern Tibet has experienced amongst the highest rates of ice mass loss in High Mountain Asia in recent decades, but few studies have focused on the implications of this mass loss on the stability of paraglacial slopes. We used repeat satellite- and unpiloted aerial vehicle (UAV)-derived imagery between 1990 and 2020 as the basis for mapping PSFs from slopes adjacent to Hailuogou Glacier (HLG), a 5 km long monsoon temperate valley glacier in the Mt. Gongga region. We observed recent lowering of the glacier tongue surface at rates of up to 0.88 m a−1 in the period 2000 to 2016, whilst overall paraglacial bare ground area (PBGA) on glacier-adjacent slopes increased from 0.31 ± 0.27 km2 in 1990 to 1.38 ± 0.06 km2 in 2020. Decadal PBGA expansion rates were ∼ 0.01 km2 a−1, 0.02 km2 a−1, and 0.08 km2 in the periods 1990–2000, 2000–2011, and 2011–2020 respectively, indicating an increasing rate of expansion of PBGA. Three types of PSFs, including rockfalls, sediment-mantled slope slides, and headward gully erosion, were mapped, with a total area of 0.75 ± 0.03 km2 in 2020. South-facing valley slopes (true left of the glacier) exhibited more destabilization (56 % of the total PSF area) than north-facing (true right) valley slopes (44 % of the total PSF area). Deformation of sediment-mantled moraine slopes (mean 1.65–2.63 ± 0.04 cm d−1) and an increase in erosion activity in ice-marginal tributary valleys caused by a drop in local base level (gully headward erosion rates are 0.76–3.39 cm d−1) have occurred in tandem with recent glacier downwasting. We also observe deformation of glacier ice, possibly driven by destabilization of lateral moraine, as has been reported in other deglaciating mountain glacier catchments. The formation, evolution, and future trajectory of PSFs at HLG (as well as other monsoon-dominated deglaciating mountain areas) are related to glacial history, including recent rapid downwasting leading to the exposure of steep, unstable bedrock and moraine slopes, and climatic conditions that promote slope instability, such as very high seasonal precipitation and seasonal temperature fluctuations that are conducive to freeze–thaw and ice segregation processes.

The glacial history of Tongariro and Ruapehu volcanoes, New Zealand

<p>Understanding the drivers and mechanisms of past, natural changes in Earth’s climate is a fundamental goal of palaeoclimate science. Recent advances in cosmogenic surface exposure dating and numerical glacier modelling have greatly improved the utility of geological glacial records for palaeoclimatic reconstruction. Here, I apply these techniques to investigate the timing and magnitude of late Quaternary mountain glacier fluctuations on Tongariro massif and Mt. Ruapehu volcanoes in central North Island, New Zealand (39°S). First, I constrain the local cosmogenic ³He production rate, in order to compare my subsequent ³He moraine chronologies with other well-dated palaeoclimate records. I present a new radiocarbon age for a large debris avalanche event on the northwest slopes of Mt. Ruapehu that occurred at 10.4-10.6 cal. ka BP. Cosmogenic ³He concentrations in surficial boulders deposited during this event are consistent with that predicted by a global compilation of similar production rate calibrations. Thus, I conclude that this globally compiled production rate is suitable for cosmogenic ³He exposure age calculations in New Zealand. Exposure ages from moraine boulders on both volcanoes constrain the timing of two periods of glaciation during the last glacial cycle, when the termini of valley glaciers reached c. 1200 m asl. The most recent of these events occurred between c. 31-17 ka, which corresponds with the global Last Glacial Maximum. During this period, the local equilibrium line altitude was depressed by c. 800-1100 m. Numerical model simulations of the glaciers, using a coupled energy balance/ice flow model, suggest that local atmospheric temperature was 4-7 °C colder than present. This palaeotemperature estimate is not greatly impacted by post-glacial topographic change on these active volcanoes. Surface exposure ages from a degraded lateral moraine on Tongariro massif indicate that an earlier period of glaciation, of similar extent to that at the LGM, culminated during Marine Isotope Stage 4. During the last glacial-interglacial transition (c. 18-11 ka), glacial retreat on Mt. Ruapehu was interrupted by a re-advance during the late-glacial (c. 15-11 ka). Exposure ages for this event exhibit some scatter, likely due to surface processes. Accounting for these processes with a topographic diffusion model yields a best-estimate age of 14-13 ka, corresponding to the Lateglacial reversal in New Zealand. Glacier model experiments indicate this re-advance resulted from a temperature lowering of 2.5-3.4 °C relative to present. Comparison with other proxy records suggests that this cooling was most pronounced during summer. Due to its lower elevation, it is unlikely that glaciers were present on Tongariro massif at this time. The results of this research provide the first direct age constraint and quantitative palaeoclimate reconstructions for late Quaternary glacier fluctuations in central North Island, New Zealand. The timing and magnitude of these changes are in good agreement with glacial records from the Southern Alps and South America. This suggests that glaciers in the southern mid-latitudes were responding to common climatic forcings at orbital- and millennial-timescales, during the last glacial cycle.</p>

The glacial history of Tongariro and Ruapehu volcanoes, New Zealand

<p>Understanding the drivers and mechanisms of past, natural changes in Earth’s climate is a fundamental goal of palaeoclimate science. Recent advances in cosmogenic surface exposure dating and numerical glacier modelling have greatly improved the utility of geological glacial records for palaeoclimatic reconstruction. Here, I apply these techniques to investigate the timing and magnitude of late Quaternary mountain glacier fluctuations on Tongariro massif and Mt. Ruapehu volcanoes in central North Island, New Zealand (39°S). First, I constrain the local cosmogenic ³He production rate, in order to compare my subsequent ³He moraine chronologies with other well-dated palaeoclimate records. I present a new radiocarbon age for a large debris avalanche event on the northwest slopes of Mt. Ruapehu that occurred at 10.4-10.6 cal. ka BP. Cosmogenic ³He concentrations in surficial boulders deposited during this event are consistent with that predicted by a global compilation of similar production rate calibrations. Thus, I conclude that this globally compiled production rate is suitable for cosmogenic ³He exposure age calculations in New Zealand. Exposure ages from moraine boulders on both volcanoes constrain the timing of two periods of glaciation during the last glacial cycle, when the termini of valley glaciers reached c. 1200 m asl. The most recent of these events occurred between c. 31-17 ka, which corresponds with the global Last Glacial Maximum. During this period, the local equilibrium line altitude was depressed by c. 800-1100 m. Numerical model simulations of the glaciers, using a coupled energy balance/ice flow model, suggest that local atmospheric temperature was 4-7 °C colder than present. This palaeotemperature estimate is not greatly impacted by post-glacial topographic change on these active volcanoes. Surface exposure ages from a degraded lateral moraine on Tongariro massif indicate that an earlier period of glaciation, of similar extent to that at the LGM, culminated during Marine Isotope Stage 4. During the last glacial-interglacial transition (c. 18-11 ka), glacial retreat on Mt. Ruapehu was interrupted by a re-advance during the late-glacial (c. 15-11 ka). Exposure ages for this event exhibit some scatter, likely due to surface processes. Accounting for these processes with a topographic diffusion model yields a best-estimate age of 14-13 ka, corresponding to the Lateglacial reversal in New Zealand. Glacier model experiments indicate this re-advance resulted from a temperature lowering of 2.5-3.4 °C relative to present. Comparison with other proxy records suggests that this cooling was most pronounced during summer. Due to its lower elevation, it is unlikely that glaciers were present on Tongariro massif at this time. The results of this research provide the first direct age constraint and quantitative palaeoclimate reconstructions for late Quaternary glacier fluctuations in central North Island, New Zealand. The timing and magnitude of these changes are in good agreement with glacial records from the Southern Alps and South America. This suggests that glaciers in the southern mid-latitudes were responding to common climatic forcings at orbital- and millennial-timescales, during the last glacial cycle.</p>

The 2020 glacial lake outburst flood at Jinwuco, Tibet: causes, impacts, and implications for hazard and risk assessment

We analyze and reconstruct a recent glacial lake outburst flood (GLOF) process chain on 26 June 2020, involving the moraine-dammed proglacial lake – Jinwuco (30.356∘ N, 93.631∘ E) in eastern Nyainqentanglha, Tibet, China. Satellite images reveal that from 1965 to 2020, the surface area of Jinwuco has expanded by 0.2 km2 (+56 %) to 0.56 km2 and subsequently decreased to 0.26 km2 (−54 %) after the GLOF. Estimates based on topographic reconstruction and sets of published empirical relationships indicate that the GLOF had a volume of 10 million cubic meters, an average breach time of 0.62 h, and an average peak discharge of 5602 m3/s at the dam. Based on pre- and post-event high-resolution satellite scenes, we identified a large debris landslide originating from western lateral moraine that was most likely triggered by extremely heavy, south-Asian-monsoon-associated rainfall in June 2020. We back-calculate part of the GLOF process chain, using the GIS-based open-source numerical simulation tool r.avaflow. Two scenarios are considered, assuming a debris-landslide-induced impact wave with overtopping and resulting retrogressive erosion of the moraine dam (Scenario A), as well as retrogressive erosion without a major impact wave (Scenario B). Both scenarios are in line with empirically derived ranges of peak discharge and breach time. The breaching process is characterized by a slower onset and a resulting delay in Scenario B compared to Scenario A. Comparison of the simulation results with field evidence points towards Scenario B, with a peak discharge of 4600 m3/s. There were no casualties from this GLOF, but it caused severe destruction of infrastructure (e.g., roads and bridges) and property losses in downstream areas. Given the clear role of continued glacial retreat in destabilizing the adjacent lateral moraine slopes and directly enabling the landslide to deposit into the expanding lake body, the GLOF process chain can be plausibly linked to anthropogenic climate change, while downstream consequences have been enhanced by the development of infrastructure on exposed flood plains. Such process chains could become more frequent under a warmer and wetter future climate, calling for comprehensive and forward-looking risk reduction planning.

Influence of prokaryotic microorganisms on initial soil formation along a glacier forefield on King George Island, maritime Antarctica

Compared to the 1970s, the edge of the Ecology Glacier on King George Island, maritime Antarctica, is positioned more than 500 m inwards, exposing a large area of new terrain to soil-forming processes and periglacial climate for more than 40 years. To gain information on the state of soil formation and its interplay with microbial activity, three hyperskeletic Cryosols (vegetation cover of 0–80%) deglaciated after 1979 in the foreland of the Ecology Glacier and a Cambic Cryosol (vegetation cover of 100%) distal to the lateral moraine deglaciated before 1956 were investigated by combining soil chemical and microbiological methods. In the upper part of all soils, a decrease in soil pH was observed, but only the Cambic Cryosol showed a clear direction of pedogenic and weathering processes, such as initial silicate weathering indicated by a decreasing Chemical Index of Alteration with depth. Differences in the development of these initial soils could be related to different microbial community compositions and vegetation coverage, despite the short distance among them. We observed—decreasing with depth—the highest bacterial abundances and microbial diversity at vegetated sites. Multiple clusters of abundant amplicon sequence variants were found depending on the site-specific characteristics as well as a distinct shift in the microbial community structure towards more similar communities at soil depths > 10 cm. In the foreland of the Ecology Glacier, the main soil-forming processes on a decadal timescale are acidification and accumulation of soil organic carbon and nitrogen, accompanied by changes in microbial abundances, microbial community compositions, and plant coverage, whereas quantifiable silicate weathering and the formation of pedogenic oxides occur on a centennial to a millennial timescale after deglaciation.

Debris-induced stagnation and ensuing morphological evolution of a central Himalayan glacier

&lt;p&gt;This study presents field evidences (October 2018) and remote sensing measurements (2000-2020) to show stagnant conditions of lower ablation zone (LAZ) of the &amp;#8216;companion glacier&amp;#8217;, central Himalaya, India and its implication on the morphological evolution. The Companion glacier is named so as it accompanied the Chorabari glacier (widely studied benchmark glacier in the central Himalaya) in the distant past. Supraglacial debris thickness, supraglacial ponds anf other morphological features (e.g. lateral moraine height, supraglacial mounds) were measured/observed in the field. Glacier area, length, debris extent, surface elevation change and surface ice velocity were estimated using satellite remote sensing data from Landsat-TM/ETM+/OLI, Sentinel-MSI, Terra-ASTER and SRTM, Cartosat-1 and Google Earth images. Results show that the glacier has very small accumulation area and it is mainly fed by avalanches. The headwall of glacier is very steep which causes frequent avalanches leading to voluminous debris addition to the glacier system. Consequently, about 80% area of the glacier is debris-covered. The debris is very thick in the LAZ exceeding several meters in the LAZ and comprised of big boulders making debris thickness measurements practically impossible particularly in the snout region. However, debris thickness decreases with increasing distance from the snout and is in the order of 20-40 cm at about 2.5 km upglacier. The huge debris cover has protected the glacier ice from rapid melting. That&amp;#8217;s why surface lowering of the glacier is less as compared to nearby Chorabari glacier. Moreover, due to (a) less mass supply from upper reaches and (b) huge debris cover, the glacier movement is very slow. The movement is too low that is allowed vegetation (some big grasses with wooded stems) to grow and survive on the glacier surface. The slow moving LAZ also causing bulging on the upper ablation zone (UAZ). Consequently, several mounds have developed on the UAZ. Thin debris slides down from mounds exposing the ice underneath for melting. Owing to these processes, spot melting is now a dominant mechanism of glacier wastage in the companion glacier. Thus, it can be summarized that careful field observations along with remote sensing estimates can be very important for understanding the glacier evolution.&lt;/p&gt;

Moraine destabilization leading to the 2013 landslide onto Svínafellsjökull glacier, SE Iceland

&lt;p&gt;On February 27&lt;sup&gt;th&lt;/sup&gt; 2013 a large landslide fell onto Sv&amp;#237;nafellsj&amp;#246;kull glacier, on the western slope of &amp;#214;r&amp;#230;faj&amp;#246;kull volcano, SE Iceland. The slide occurred during an intensive rainstorm event between February 24&lt;sup&gt;th&lt;/sup&gt; and 27&lt;sup&gt;th&lt;/sup&gt;. The slide was detected at 20:30 o&amp;#8217;clock at a seismic station located several kilometres away. It originated from lateral moraine and talus material below the steep north-eastern slope of Mt. Skar&amp;#240;atindur above a small contributory glacier. The debris flowed down-glacier towards the west with an approximate runout distance of 3000 m and a width of 500-600 m, covering about 1,4 km&lt;sup&gt;2&lt;/sup&gt; or about 17% of the glaciers&amp;#8217; surface. The extent of the debris deposit suggests a highly water saturated debris flow. Based on Digital Elevation Models (DEMs) from 2011 and 2013 the estimated volume of the slide was 5,4&amp;#177;0,1 million m&lt;sup&gt;3&lt;/sup&gt; which makes it one of the largest debris slides in Iceland over the last decades. &lt;br&gt;Long term destabilization by glacier unloading was investigated by comparing DEMs from 1994 to 2011. Meteorological data suggests that record breaking amounts of precipitation in combination with snowmelt due to relatively warm temperatures in late February caused a significant water inflow into the system which is likely to have caused the failure. &lt;br&gt;Analysis of aerial imagery and DEMs after the failure suggest a complex slide. The debris cover on the glacier reduced the surface ablation which resulted in an up to 30 m height difference between the debris free glacier surface and the debris covered part in 2020.&lt;/p&gt;

Tree-ring and 14C dates of moraines of the Greater Azau Glacier (Baksan valley, Northern Caucasus)

&lt;p&gt;The age of moraines of the Greater Azau Glacier was identified by tree-ring analysis of more than 150 Scots pines, by historical and cartographic data, remote sensing, lichenometric and radiocarbon dating. We determined the limits of the area covered by the glacier tongue at the end of the 19th century. We also discuss the controversial issue of the position of the moraine of 1849 CE, which was described by H. Abich [1]. The highest and most clearly shaped lateral moraine, conventionally called the &quot;17th century moraine&quot;, was formed earlier than the end of the 16th century (tree-ring minimum age). The oldest tree in the valley (1598 CE) was found at the &quot;forested island&quot; end moraine (2294 m asl). Judging by the size of the lichens &lt;em&gt;Rhizocarpon geographicum &lt;/em&gt;(120-130 mm) on this surface the moraine may be several centuries older. We re-examined the trunk of a pine which was discovered in the 1960s buried in the fluvio-glacial sediments presumably formed in 1880s (historical descriptions). It was dated earlier by radiocarbon (140 +/- 75 BP [2] (calibrated date - 1650-1960 CE). According to the ring width cross-dating, the most probable dates of the buried tree are 1759-1883 CE, however, the second likely dates are 1826-1950 CE. Suppressions of pine growth at the forefields of the Greater Azau in the 1640s, 1710s, 1800s, 1840s-1860s CE are synchronous with the advances of the Bosson, Mer de Glace and Grindelwald glaciers in the Alps [2]. Three soil horizons buried in the moraine of the Greater Azau glacier were identified in the artificial outcrop on the left side of the valley (N43.26583, E42.4767, 2370 m asl). The uppermost horizon located 0.6 m below the surface of the moraine is a thin layer of loam developed in a short time interval (130&amp;#177;20 BP (IGAN ams - 6826) 1680-1939cal BP (charcoal). Two lower thicker horizons (buried 13 and 15 m below the surface) indicate longer periods of continuous soil formation lasting for about 720 years (between 774-89 CE and 1496-1641 CE) and for 1750 years (between ca 3 ka BP and 7-8 centuries CE), respectively. They both are well developed soils formed within the loam layers without detrital material, containing a thick dark humus horizon with a high content of soil organic matter, as well as fragments of charcoal and tree bark. During these three periods, the glacier was relatively small.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;References&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;1. Abich H., Geologische Beobachtungen auf Reisen im Kaukasus um Jahre 1873. Moskau, 1875. 138 p.&lt;/p&gt;&lt;p&gt;2. Nussbaumer S., Zumb&amp;#252;hl H. The Little Ice Age history of the Glacier des Bossons (Mont Blanc massif, France): A new high-resolution glacier length curve based on historical documents. Climatic Change, 111, 2012. 301-334 pp.&lt;/p&gt;

Assessing the performance of geophysical survey techniques for characterising the subsurface around glacier margins

&lt;p&gt;Glacier forelands contain valuable information on past glacier dynamics and associated climatic conditions, particularly at small mountain glaciers where responses to climate change are rapid. To maximize the potential of glacial landforms as palaeoclimate indicators, a thorough understanding of the controls on landform genesis and subsequent evolution is required. Traditionally, such landforms have been studied using glacial geological techniques such as sedimentary logging. While these provide valuable in situ information they have numerous limitations, namely poor availability and spatial extent of exposures. Near-surface geophysics provides an efficient and non-invasive means of studying subsurface conditions in numerous sedimentary settings, offering spatially extensive information on substrate material properties and architecture. However, the logistically challenging terrain, remote location and complex structure of proglacial environments has limited the development of geophysical techniques for studying the internal architecture of glacial landforms.&lt;/p&gt;&lt;p&gt;Here, we explore the application of three geophysical methods to investigate proglacial substrates: ground penetrating radar (GPR), seismic refraction and multi-channel analysis of surface waves (MASW). Three sites with contrasting sediment properties were surveyed at the foreland of Midtdalsbreen glacier in southern Norway; (a) a 100 m&lt;sup&gt;2&lt;/sup&gt; area of glaciotectonised sandy sediments, (b) a ~2 m high lateral moraine ridge containing stratified silts, sands, and gravel and (c) a terminal moraine ridge with a peak crest height of ~5 m and an open blockwork of cobbles and boulders at its surface. At all sites, we deployed 25 MHz and 100 MHz GPR antennas and undertook seismic surveys with 50&amp;#8722;75 m long geophone spreads and a sledge-hammer source to sample to target depths of around 10&amp;#8722;15 m. Through comparing the results from sites (a) to (c), we assess the capabilities and limitations of each of the aforementioned techniques for proglacial substrate imaging and characterisation, we analyse how their performances vary across these settings and outline factors that contribute to a successful geophysical investigation.&amp;#160;&lt;/p&gt;&lt;p&gt;The ease of analysis and achievable investigation depths of the geophysical data and the applicability of seismic interpretation methods varied considerably depending on the surface terrain and structural complexity of the site. Our results show how the combination of GPR and seismic data can assist with the internal characterisation of glacial moraines when a relatively simple subsurface structure is present. However, basic seismic inversions likely lack the sophistication to resolve seismic structure in all but the simplest of layered models. We offer suggestions on how to optimise field time in more complex settings, where more sophisticated seismic inversion algorithms (e.g. tomography) or 3-D GPR surveys could be better-suited.&lt;/p&gt;&lt;p&gt;Our experience should help advance the use of geophysics in proglacial studies. It should serve as a guide for future survey planning, and help avoid typical pitfalls such that field time can be optimised. &amp;#160;It is hoped that geophysical survey methods will play an increasing role in the understanding of proglacial sedimentary landforms and their associated palaeoenvironments.&lt;/p&gt;

Landslide-GLOF cascade at the expanding Jinwuco in Tibet, 2020: a clear consequence of anthropogenic climate change

&lt;p&gt;Glacial Lake Outburst Floods (GLOFs) are amongst the most common and high-magnitude natural hydrological disasters in high-mountain regions that have resulted in severe casualties and socioeconomic losses over the last century. Here, we integrate various data and methods to analyse and reconstruct the GLOF process chain involving the moraine-dammed proglacial lake &amp;#8210; Jinwuco (30.356&amp;#176;N, 93.631&amp;#176;E) in eastern Nyainqentanglha, Tibet, China, which occurred on 26&lt;sup&gt;th&lt;/sup&gt; June 2020. This lake underwent rapid expansion in area from 0.2 km&lt;sup&gt;2&lt;/sup&gt; to 0.56 km&lt;sup&gt;2&lt;/sup&gt; (1965-2020), and subsequently shrank to 0.26 km&lt;sup&gt;2&lt;/sup&gt; after the GLOF. Topographic reconstruction and empirical relationships indicate that the GLOF had a volume of 10 million m&lt;sup&gt;3&lt;/sup&gt;, an average breach time of 0.62 hours, and an average peak discharge of 5,390 m&lt;sup&gt;3&lt;/sup&gt;/s at the dam. Pre- and post-event high-resolution satellite scenes reveal a large progressive debris landslide originating from western lateral moraine. This landslide which occurred 5-17 days before the GLOF was most likely triggered by extremely heavy, south Asian monsoon-associated rainfall in June. The time lag between the landslide and the GLOF suggests that pre-weakening of the dam due to landslide-induced outflow pushed the system towards a tipping point, that was finally exceeded following subsequent rainfall, snowmelt, a secondary landslide, or calving of ice into the lake. We back-calculate a part of the GLOF process chain, using the GIS-based open source numerical simulation tool r.avaflow, considering two scenarios: Scenario A - a debris landslide-induced impact wave with overtopping and resulting retrogressive erosion of the moraine dam; and Scenario B - retrogressive erosion due to pre-weakening of the dam without a major impact wave. Both back-calculated scenarios yield plausible results which are in line with empirically derived ranges of peak discharge and breach time. The breaching process is characterized by a slower onset and a resulting delay in Scenario B, compared to Scenario A. Our evidence, however, points towards Scenario B. The 2020 Jinwuco GLOF caused severe destruction of infrastructure (e.g. roads and bridges) and property losses in downstream areas (no fatalities were reported).&lt;/p&gt;&lt;p&gt;This study corroborates the clear role of continued glacial retreat in destabilizing the adjacent lateral moraine slopes, and directly enabling the landslide to deposit into the expanding lake body. As such, the GLOF process chain can be robustly attributable to anthropogenic climate change, while downstream consequences have been driven by recent development of infrastructure on exposed flood plains. Such glacial lake related process chains could become more frequent under a warmer and wetter future climate, calling for comprehensive and forward-looking risk reduction planning. We anticipate our findings will provide critical new process understanding on GLOF triggering mechanisms and these new insights will improve GLOF hazard and risk assessment frameworks, highlighting the need to consider both complex instantaneous and gradual process chains.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;