ID21: Glacier and permafrost risks in a changing climate

Abstract ID 190 | Date: 2022-09-12 13:40 – 13:50 | Type: Oral Presentation | Place: SOWI – Seminar room U3 |

Weber, Samuel (1,2,3); Beutel, Jan (4); Häusler, Mauro (5); Geimer, Paul R. (6); Fäh, Donat (5); Moore, Jeffrey R. (6)

Amplification of seismic energy in steep topography is widespread and plays an important role affecting the locations of earthquake-induced damage and the distribution of earthquake-triggered landslides. Mountains, and especially the large freestanding massifs of the European Alps, represent extreme topography and may thus exhibit larger topographic amplification than features with less relief. However, suitable broadband seismic data from these locations are rare, in part due to difficult and often dangerous site access. Here we present ambient seismic data collected on two mountains in the Swiss Alps (the Matterhorn and Grosser Mythen), similar in shape but different in scale. At the Matterhorn, comparing data from seismic stations on the summit and ridge to a nearby local reference showed elevated spectral power on the mountain between 0.4 and 1 Hz, and directional site-to-reference spectral amplitude ratios up to 14, which we attribute in part to topographic resonance. We used ambient vibration modal analysis and numerical eigenfrequency modeling to identify the fundamental mode of the Matterhorn at 0.42 Hz, as well as evidence for a second, mutually-perpendicular mode at a similar frequency. Our data further show high modal damping ratios of ∼20% for these modes, which we ascribe to radiative energy loss. A short campaign measurement at Grosser Mythen, showed similar modal properties with a higher fundamental frequency of 1.8 Hz and peak spectral ratios of 6. At the Matterhorn, we analyzed 13 months of continuous data, showing that spectral peaks are stable over time and that the fundamental frequency of the mountain does not measurably vary. Our results aid estimation of topographic amplification for other mountain features.

Abstract ID 256 | Date: 2022-09-12 14:00 – 14:10 | Type: Oral Presentation | Place: SOWI – Seminar room U3 |

Baral, Prashant (1); Steiner, Jakob Friedrich (1); Fiddes, Joel (2); Allen, Simon (3); Gurung, Tika Ram (1)

Thawing mountain permafrost is expected to introduce changes in land surface cover, flow regimes, and ecosystem structure in high mountain regions. Existing infrastructure and communities near steep mountain slopes are living under the direct threat of slope failures. Permafrost degradation increases sediment loading, therefore, it is also anticipated to contribute to the frequency and distribution of compound and cascading hazards, which can cause devastation far downstream. To understand the implications of thawing permafrost under a warming climate in the Himalaya, more comprehensive knowledge of permafrost distribution and dynamics in the region is necessary.

Existing information about permafrost occurrence and distribution in the Himalaya is essentially limited to permafrost zonation index maps and global estimates of permafrost area. A few field-based studies have focused on the estimation of the lower limit of mountain permafrost using geophysical techniques. Some remote sensing based studies have combined meteorological records, global climate projections and computational modeling to understand the spatial extent and distribution of permafrost for specific areas. Permafrost monitoring using long term ground temperature measurements in this region is almost non-existent. While satellite temperature products, such as Moderate Resolution Imaging Spectroradiometer (MODIS) land surface temperature (LST) data, have been applied to investigate permafrost distribution in some parts of the Himalaya, these products are not validated against ground temperature measurements.

We develop permafrost probability distribution maps for the Langtang Valley, in the Central Himalaya using downscaled reanalysis based climate data, global climate projections, MODIS LST products and neural networks. Climate data from different sources are downscaled to 30 m grid size to produce probability distribution maps with same spatial resolution. These maps are compared to define the past and present extent of permafrost and understand the changes in permafrost distribution in recent decades. Additionally, these maps are cross-validated using recent ground-based temperature data, available between 2014 and 2021 from an elevation range of 4520 to 5542 m a.s.l. MODIS LST products are compared with ground temperature measurements to evaluate the use of satellite temperature records in future monitoring of permafrost in the region. Changes in permafrost extent are correlated with the spatial distribution of slope-failures, debris flows and other documented hazards in the valley to understand the potential influence of permafrost change on the occurrence of these hazards.

Abstract ID 260 | Date: 2022-09-12 14:10 – 14:20 | Type: Oral Presentation | Place: SOWI – Seminar room U3 |

Saha, Aniruddha (1); Jain, Manoj Kumar (1); Schwanhart, Wolfgang (2)

The glaciers in the Himalayas are rapidly retreating. With the increasing loss of glacial mass, there is an increase in the number of glacial lakes and thereby, the potential threat of GLOF (Glacial Lake Outburst Flood) events. We aim to forecast the evolution and growth of proglacial lakes over Gangotri Glacier (Uttarakhand, India). Proglacial lakes are formed by damming action of a moraine, resulting due to retreat of melting glaciers. As the glacier melts and loses its mass, the glacier bed gets exposed, and any possible over-deepening, if available in “thereby exposed bed-topography”, shall act as a bedrock dam, to hold the meltwater, forming a moraine-dammed lake. As the glacier melts, more and more of such bedrock dams shall get exposed. The lakes shall not evolve to the full of its size at once, but slowly and gradually, as it loses the glacier mass above it. The present research aims to identify the potential sites for such glacial lake formation and forecast the growth of each of these lakes over time. This is done in two-fold steps. Firstly, identifying the potential sites of formation of glacial lakes, by preparing the glacier bed topography using the GlabTop2_IITB model. This model has a self-calibration feature, that could calibrate even in the absence of field measurements. Secondly, a glacier evolution model is operated using a simple parameterisation approach, i.e., an empirical glacier specific function is used for updating the glacier surface using the climate model datasets. The updated glacier surface data helps us forecast the evolution and growth of glacial lakes. The spatial distribution of ice thickness for Gangotri was found to be within a range of 19m to 343m for the year 2014, having a glacier volume of 13.49 km3. Fifty potential sites for glacial lake formation were identified using the bedrock topography modelling, having a total storage capacity of 37.04m3. Our results shall help determine the possibility of further expansion of the glacial lakes present and their maximum storage capacities. Having an idea of the formation and growth of lakes in future can help us forecast the: hazard potential of a lake, its flood peak, and the downstream effect of its dam break events as it evolves over time.

Abstract ID 498 | Date: 2022-09-12 14:20 – 14:30 | Type: Oral Presentation | Place: SOWI – Seminar room U3 |

Shrestha, Finu (1); Steiner, Jakob (1); Shrestha, Reeju (2); Dhungel, Yathartha (3); Joshi, Sharad Prasad (1); Inglis, Sam (4)

Glacial lake outburst floods (GLOFs) occur in various parts of the Hindu Kush Himalaya (HKH). However, a comprehensive record comprising precise location, frequency, triggering cause and scale of their effects does not exist to date. In this study, we present an open access and version controlled database of historical GLOFs from 1840s to 2021 from scientific literature, reports, news articles, social media, satellite imagery and local testimony. Information associated to triggering factors, floodpeak discharge, transboundary nature of an event, furthest documented reach of the GLOF and socioeconomic impacts are recorded. We identified 360 events in the HKH, covering 124events from the Eastern Himalaya, 18 each from the Central and Western Himalaya, 180 from the Karakoram and 20 from the HinduKush. Most GLOFs occurred from moraine dammed lakes in the Eastern(85%), Central(85%) and Western(57%) Himalaya, and in HinduKush(50%). In the Karakoram, GLOFs occurred mostly from ice dammed lakes (79%). Repeating GLOFs from the same lake happen more often in the Karakoram. GLOFs from Khurdopin and Kyagar glacial lakes drained 30 and 28 times between 1882 and 2021 due to an increase in meltwater inflow after glacier surges blocked a valley. Most of the GLOFs in the Eastern Himalaya triggered from mass movements (ice avalanche and rockfall) and after glacier surges in the Karakoram. Intense rainfall and high melt events caused GLOFs in the remaining other regions.

As the database is paired with a detailed lake inventory as well as the Randolph Glacier Inventory, rapid queries to understand regional drivers and impacts are possible. For example, the mean area of lakes that produced GLOFs was considerably larger (0.2km²) than those that never breached (0.06km²). The database also reveals that GLOFs on average reached 49 km (0.28 − 293) downstream and covered 1030m (19 – 4300) in elevation. The mean slope of GLOF paths was ~8 ° (0.8 − 21), with big variations between regions. Such values provide the possibility to constrain future modelling efforts of GLOF runout paths.

A total of 798 fatalities were recorded in the HKH. These fatalities happened from just 15 of the recorded events, all of which occurred in the Eastern Himalaya (7 events, 759 fatalities), Karakoram (4, 19) and the HinduKush (4, 20). Direct financial damages were only recorded at 8 events, where they amounted to 5.2 billion USD, indicating that few destructive events can result in large damages, but records on downstream impacts so far remain patchy.

Abstract ID 160 | Date: 2022-09-12 14:30 – 14:40 | Type: Oral Presentation | Place: SOWI – Seminar room U3 |

Guerini, Michele (1); Giardino, Marco (1); Paranunzio, Roberta (3); Nigrelli, Guido (2); Turconi, Laura (2); Luino, Fabio (2); Chiarle, Marta (2)

This work is focused on the impact of climate change on slope stability by analysing a dataset of 392 slope instability events documented from 2000 to 2020 at high elevation (above 1500 m asl) in the Italian Alps (doi.org/10.1594/PANGAEA.931824). At present, this is the most comprehensive dataset of slope failures occurred at high elevation in the Italian Alps in the last two decades. For this work, we analysed the dataset with the aim of 1) recognizing trends of slope failure occurrence; 2) highlighting the different susceptibility to instability of slopes with specific geomorphological characteristics and 3) investigating how climate change may have affected the occurrence of slope instability at high altitude. To address these questions, spatial and temporal analyses were performed using GIS and statistical software. We applied inferential statistic tests such as Man-Kendall test and Pettit test (in comparison with other non-parametric tests).

Interestingly, spatial and temporal analyses highlighted a positive linear trend both in the annual frequency of slope instability events throughout the Italian Alps for the considered period, with a break point in the series in 2011, and in the annual temperature series, especially minimum temperatures. North-facing slopes over 2000 m asl resulted to be more susceptible to instability. In addition, the seasonality of slope failure occurrence depends on the altitude. Between 1500 and 2000 m asl, two maxima were detected respectively in May and October, while at higher altitudes a single maximum was observed in August. Finally, there was a clear trend towards an increase in instability events on slopes in permafrost conditions, compared to a substantial stationarity in the number of events for slopes without permafrost: in particular, the increase is more rapid in the period 2011-2020 compared to the period 2000-2010, with a break point in the series in 2012.

The outcomes of the present work provided further evidence that climate change is causing an increase in the frequency of instability events on high-altitude slopes. Further studies, including the implementation of the dataset of events and the test of new data analysis methods, are needed to deepen the knowledge on the processes that cause the instability of high altitude slopes and on the role of predisposing and triggering factors, and in particular of climate change, allowing to define hazard scenarios.

Abstract ID 882 | Date: 2022-09-12 15:19 – 15:29 | Type: Oral Presentation | Place: SOWI – Garden |

Bock, Josué; Magnin, Florence; Josnin, Jean-Yves; Ben-Asher, Matan

Water infiltration and circulation in frozen bedrock fractures may enhance heat transport from the surface to the permafrost body and play a role in rock slope failure. However, such processes occurring in steep rock slope permafrost are difficult to investigate because of their non-linearity and anisotropy.

In this communication, we will present recent developments conducted in the frame of the WISPER project (“Water and Ice related thermo-mechanical processes in the fractures of Steep alpine bedrock Permafrost”, funded by the French National Agency for Research).

The FeFlow® (DHI-WASY) software is used to model and study the coupled heat and mass transfer in a simple alpine geometry that typically represents steep rock slope affected by permafrost and seasonal freeze and thaw cycles at c.a.3500 m a.s.l. Using a synthetic annual forcing for rock surface temperature, several case studies are implemented to investigate the sensitivity of permafrost degradation to various fracture networks features: aperture and density, orientation, dip, shape, amount and seasonality of the input water flux. The thermal and hydrogeological variables (notably temperature fields, and hydrostatic pressure field, are compared to a base case without any fracture, in order to assess their sensitivity to the studied parameters.

A direct comparison between these simulations and field measurements is foreseen, to bring further constrain on the model settings, and ultimately to validate its outcome. These results will allow to better understand non-linear response of permafrost to climate signals and will bring new insights to understand steep rock slope destabilisation.

permafrost ; steep rock slope ; numerical modelling : hydrological processes ; sensitivity study

Abstract ID 235 | Date: 2022-09-12 16:00 – 16:10 | Type: Oral Presentation | Place: SOWI – Seminar room U3 |

Ravanel, Ludovic (1,2); Kaushik, Suvrat (1,3); Guillet, Grégoire (1,4); Preunkert, Susanne (5); Trouve, Emmanuel (3); Montagnat, Maurine (5); Magnin, Florence (1); Yan, Yajing (3); Deline, Philip (1)

Ice aprons (IAs) are very poorly studied components of the Alpine cryosphere. They are thin ice bodies adhering to high altitude steep rock faces above the equilibrium line altitude. In the Mont-Blanc massif (MBM), we mapped 423 IAs (from 0.001 to 0.04 km²) using very high-resolution optical satellite images from 2019.

To understand their evolution, we used three methods in the MBM:

– between c. 1850 and 2018, we quantified their surface area variations from terrestrial and aerial oblique photographs via photogrammetry; the studied IAs on four different faces shrank from 1854 to the 1950s, before expanding until the end of the 1990s, while the beginning of the 21^st century shows a strong decrease in surface area;

– to precise the first results, we precisely mapped the surface area of the IAs using high-resolution aerial and satellite photographs from 1952, 2001, 2012 and 2019; the total area, from 7.93 km² in 1952, was reduced to 5.91 km² in 2001 (-25.5 %) before collapsing to 4.21 km² in 2019 (-47 % since 1952);

– over the 5 last years, we monitored an IA on the Triangle du Tacul (TDT) using ablation stakes; it loses a thickness of several tens of cm each year.

We found a very robust correlation for temperature proxies with the relative area loss of IAs, indicating the strong influence of the changing climate on the evolution of IAs. This retreat is generally accompanied by a sharp increase in the frequency of rockfalls from recently deglaciated areas.

We also studied the dynamics and age of few IAs using ice cores from the MBM. Texture (microstructure and lattice-preferred orientation, LPO) analyses showed that IAs deforms under a low strain-rate simple shear regime. Micro-radiocarbon dating indicates that the TDT ice can be older than 6000 years BP at the rock-ice interface, making IAs probably interesting environmental archives.

Abstract ID 602 | Date: 2022-09-12 16:10 – 16:20 | Type: Oral Presentation | Place: SOWI – Seminar room U3 |

Cathala, Maëva (1,2); Magnin, Florence (1); Ravanel, Ludovic (1); Dorren, Luuk (3); Berger, Frédéric (4); Bourrier, Franck (4); Zuanon, Nicolas (5); Deline, Philip (1)

High mountains environments are highly affected by the effects of climate change. The main impacts of rising air temperature on the Alpine cryosphere are glacier retreat and permafrost degradation, which lead to rock slopes instabilities. Investigations in the Europeans Alps have shown an increase of rock slope failures, especially during summer heatwaves. These events can provoke cascading hazards like debris flows threatening human lives and infrastructure, which underlines the need of knowledge about their triggering mechanism and propagation. Conform the GAPHAZ guidelines for hazard assessment (GAPHAZ, 2017), the aims of this study are (i) to propose a mapping approach of susceptible release areas of rock slope failures and resulting runout distances at a regional scale (10⁵ km2) and (ii) to identify hotspots for hazard assessment.

To do so, we used an inventory containing 1172 rock slope failures events with volumes larger than 10² m³ recorded in the Mont Blanc massif between 2007 and 2019. A statistical analysis of this database revealed the distribution of the rock slope failures according to the topographical conditions (slope) and the permafrost conditions (Mean Annual Rock Surface Temperatures) that are most favourable to their triggering. These conditions are used in a multi-criteria GIS approach to identify the potential unstable slopes at a regional scale.

Then, the potential release area maps are used as input to map the propagation of potential events, using a model based on a normalised area dependant energy line principle (NELA). The calibration of the NELA model was done with 3630 alpine wide rockfall events covering all possible volumes. The validation of the modelled propagation was based on 70 events from the Mont Blanc database.

In a next step, the resulting maps of release and propagation areas will be intersected with human assets (mountaineering routes, high mountain infrastructure, tourism areas) and lakes (that can provoke cascading hazards) in order to identify areas which could be impacted by rock slope failure related hazards at a regional scale.

This work is a first step to point out hot spots where more detailed analyses will be required to evaluate the possible risks.

References:

GAPHAZ 2017: Assessment of Glacier and Permafrost Hazards in Mountain Regions. Prepared by Allen, S., Frey, H., Huggel, C. et al. Standing Group on Glacier and Permafrost Hazards in Mountains (GAPHAZ) of the International Association of Cryospheric Sciences (IACS) and the International Permafrost Association (IPA). Zurich, Switzerland / Lima, Peru, 72 pp.

Abstract ID 608 | Date: 2022-09-12 16:20 – 16:30 | Type: Oral Presentation | Place: SOWI – Seminar room U3 |

Jóhannesson, Tómas (1); Råback, Peter (2); Zwinger, Thomas (2)

Glacier outburst floods or jökulhlaups from subglacial geothermal areas, marginal lakes and subglacial volcanic eruptions are common in Iceland and they pose a substantial hazard to settled areas as well as to roads, communication lines and other infrastructure near glaciers. They can be categorized into two groups, slowly and rapidly rising, with marked differences in the flood hydrographs. Slowly-rising jökulhlaups are traditionally explained by the theory of Nye (1976) through a conduit-melt–discharge feedback mechanism. The initial subglacial propagation and the development of the flood hydrograph of rapidly-rising jökulhlaups is, on the other hand, not quantitatively understood. We present a glacier outburst flood model for rapidly-rising jökulhlaups implemented with the Elmer/Ice Open-Source Finite-Element Software. The model describes the subglacial propagation of the jökulhlaup front using a visco-elastic model for the overlying glacier ice combined with a turbulent sheet model for the subglacial water flood. The evolution of the subglacial flooded area is simulated numerically through the solution of a contact problem that represents the lifting of the ice from the underlying glacier bed where the subglacial water pressure exceeds the normal stress in the ice at the sole of the glacier. The aim of the model is to explain the speed of propagation of the subglacial flood front at the beginning of the flood as well as the time-dependent flood hydrograph after the flood bursts out from under the glacier at the ice margin.

Abstract ID 150 | Date: 2022-09-12 16:30 – 16:40 | Type: Oral Presentation | Place: SOWI – Seminar room U3 |

Emmer, Adam

Glacial lake outburst floods (GLOFs) – sudden releases of water from glacial lakes – are often characterized by substantial geomorphological imprints, some of which are process-specific. Analysis of these – so called “GLOF diagnostic features” – can be exploited for the reconstructions of GLOF occurrence in space and time, and so enhance our understanding to GLOF frequencies under changing conditions on longer timescales. However, similar to other landforms in dynamic high mountain environments, also GLOF diagnostic features are a subject to degradational processes and further geomorphic / biogeomorphic reworking, possibly blurring their recognizability and attributability to GLOFs. In this contribution, the longevity of different types of GLOF diagnostic features ranging from breached moraine dams, preserved evidence of pre-GLOF lake water levels, various erosional features and landforms, outwash fans and depositions of large boulders is explored. Using examples of dated GLOFs from different parts of the world (Andes, Alps, High Asia), the ability to identify GLOF diagnostic features of certain age is linked to a GLOF magnitude as well as other characteristics such as lake dam type and GLOF mechanism. It is shown that the longevity of the GLOF diagnostic features is in decades (low magnitude events) to centuries (high magnitude events), suggesting good applicability and reliability for building and enhancing GLOF inventories.

Abstract ID 251 | Date: 2022-09-12 16:40 – 16:50 | Type: Oral Presentation | Place: SOWI – Seminar room U3 |

Tamburini, Andrea (1,3); Mortara, Gianni (2,3)

In early summer 2002, the Belvedere glacier experienced a surge-type evolution, which resulted in a rapid increase of ice thickness along the 4 km long glacial tongue and the formation of a huge supraglacial lake known as “Effimero Lake” which drained in summer 2003. The effects of surge were evident in the lowermost part of the tongue until 2005, and then a dramatic shrinking of the glacial tongue followed. A cumulative mass balance of -50 to -70 meters of ice was recorded until now, resulting in a generalized destabilization of LIA moraines, which are now collapsing towards the glacier with metric to decametric lowering of the moraine crest. Moreover, frequent ice and rockfalls have been recorded as a response to rapid deglaciation of the slopes surrounding the Belvedere Glacier basin. In the last couple of years, an unexpected increase of ice thickness is occurring in the uppermost part of the glacial tongue, followed by an increase of surface displacement velocity: is a new surge starting?

The glacier regime is continuously monitored by means of a network of ablation stakes that provide regular ablation and surface displacement measurements. Moreover, repeated topographic surveys with GNSS, UAV and terrestrial laser scanner are supporting a quantitative analysis of the morphological modifications occurred in periglacial areas around the Belvedere Glacier valley tongue.

By integrating the results of all measurements carried out during the last 20 years it is now possible to outline the evolution of the glacier and surrounding areas in such a unique environment, which can be undoubtedly considered a unique open-air laboratory in the Alps.

Abstract ID 495 | Date: 2022-09-12 16:50 – 17:00 | Type: Oral Presentation | Place: SOWI – Seminar room U3 |

Cicoira, Alessandro (1); Marcer, Marco (2,3,4); Cusicanqui, Diego (2,5); Bodin, Xavier (2); Echelard, Thomas (4); Obregon, Renée (4); Schoeneich, Philippe (4)

In the past decades, the research community on alpine periglacial landforms reported several cases of increasing rock glacier displacement rates up to abnormally high values. This process is often bond with the development of surface features typical of landslide processes, such as crevasses and cracks. Existing studies of this phenomenon, commonly referred as “rock glacier destabilization”, have been limited to a small number of landforms and short time spans. This study aims to contribute to our understanding of rock glacier destabilization using a regional scale approach over a multi-decadal period. Our methodological pillar is the assessment of displacement rates on the basis of orthophoto comparison. First, we identified destabilizing landforms by coarsely evaluating displacement rates on all rock glacier in the French Alps since the 50s using readily available orthoimages provided by the national geographical institute. Then, we computed a database of orthoimages at high temporal resolution (5-10 years interval) for all destabilized rockglaciers in the region for the past seven decades, allowing the evaluation of the evolution of their displacement rates in greater detail. Our analysis shows that rock glacier velocities have significantly increased since the 1990s, concurrent with the development of destabilization in 18 landforms that represent 5% of the 337 active rock glaciers. This pattern of activity correlates with rising air temperatures in the region, which suggests that a warming climate plays a triggering role in this process. Surface crevassing shortly preludes the acceleration phase in most of the cases, although some landforms display crevasses in a quiescent phase for decades before destabilization onsets. Destabilized landforms can reach displacement rates up to 25 m/y, although most values range around 3-5 m/y. Destabilizing landforms show sliding dynamics, and this process lasts until a tipping point is reached and the destabilized mass is depleted or reaches flatter terrain.

Abstract ID 485 | Date: 2022-09-12 13:50 – 14:00 | Type: Poster Presentation | Place: SOWI – Seminar room U3 |

Ben-Asher, Matan (1); Magnin, Florence (1); Josnin, Jean-Yves (1); Bock, Josué (1); Westermann, Sebastian (2); Ravanel, Ludovic (1); Malet, Emmanuel (1); Deline, Philip (1)

The increased rockfall activity in high Alpine ranges observed during the last two decades is commonly attributed to permafrost degradation associated with atmospheric warming. Although the connection between mountain permafrost thawing and rockfall initiation is intuitive and supported by field and lab observations, the physical processes behind it are still poorly understood. In this study, we focus on the role of hydrologic and thermal processes acting in fractures of steep Alpine permafrost-affected bedrock.

We use a unique set of decadal field measurements which include subsurface and borehole temperatures and snow depth time series, from a high elevation Alpine site in the Mont Blanc massif (Aiguille du Midi, 3842 m a.s.l) to calibrate a permafrost surface energy balance model that is coupled with snow pack simulations (CryoGrid), and apply it to the complex topographic settings on a steep rock slope. The model provides first-order quantification of the potential water equivalent snow melt that is available for infiltration in rock fractures.

Preliminary results from a south facing slope show 3 orders of magnitude of variability in annual excess water amounts, with maximum amounts approaching 100 mm/yr. In addition, snow melt volume is predominantly produced between April to June (>95%).

The new snow melt data, together with available meteorological data will be used in a coupled thermal and hydrologic model (FEFLOW) to simulate groundwater flow and heat transport in fractured rock. We expect that our findings will give better understanding of how hydrological processes affect subsurface temperature patterns, which are commonly simulated using simple thermal conduction processes and ignore water flow, as well as its influence on the local stress field and slope stability.

The results of this study will help us decipher the governing processes in the degradation of high mountain permafrost and its link with rockfall occurrence.

Abstract ID 390 | Date: 2022-09-12 15:15 – 15:17 | Type: Poster Presentation | Place: SOWI – Garden |

Bazilova, Varvara O.; De Haas, Tjalling; Immerzeel, Walter

Glacier and snow-melt in High Mountain Asia (HMA) play an important role in the water supply for the densely populated regions in the surrounding area. Despite the climatic heterogeneity of the region, ice mass loss has been observed over the entire area including the retreat of glaciers and the thawing of permafrost. This leads to the exposure of unconsolidated moraine debris and sediment deposits, the development of new glacial lakes, and the expansion of existing lakes. These changes in the state of the high mountain cryosphere increase landslide, debris flow, and flood hazards. In this study, we aim to detect and explain spatial differences within HMA in the past occurrence of these hazards. We select different regions with distinct climatic and geomorphological conditions. We disaggregate each region in small drainage basins and for each basin, we derive a number of hazard predictors. These data include static morphometric parameters of the catchments derived from elevation models, and dynamic climatic features, such as precipitation indicators, freeze-thaw cycles, and glacier changes. Using a machine learning approach, these data are used to identify explanatory mechanisms and responsible triggers. The algorithm is trained by using satellite observed sediment deposits and alluvial fan properties. Preliminary results show large differences between different regions in the occurrence and drivers of debris flows and floods.

Abstract ID 123 | Date: 2022-09-12 15:17 – 15:19 | Type: Poster Presentation | Place: SOWI – Garden |

Frolov, Denis (1); Gagarin, Vladimir (1); Koshurnikov, Andrey (1); Nabiev, Islom (2); Dodoboev, Ehson (2)

One of the factors of soil stability on slopes during the construction of avalanche-protecting geotechnical constructures in mountainous areas is the freezing of the underlying soil, since in mountainous areas the soil can be in a frozen state for eight or more months. However, the recent changes in air temperature and precipitation (primarily in the form of snow) lead to a change in the depth and duration of freezing of the soil and, as a consequence, a decrease in its stability. In this work, based on the developed calculation scheme, the depth of soil freezing is estimated for the last few winter seasons based on data on the thickness of the snow cover and air temperature for the Anzob pass (Tajikistan). Aznob Pass (Tajikistan) is located at latitude 39.07 and longitude 68.88 with an altitude of 3373 m above sea level. The average annual temperature there is -2.7 °C, but due to heavy snow accumulation, there is no long-term freezing and only seasonal is observed. Computational modeling showed the presence of seasonal frozen rocks on the slope of the northern exposure at a depth of up to 1.5 m. Thus, in the winter of 2018, the depth of seasonal soil freezing on the slopes of the northern exposure was 1.5 meters. In the winter of 2020, on the slopes of the northern exposure, the depth of seasonal soil freezing was 1.2 meters at an average annual soil temperature of 2.42 °C. Calculations of changes in the depth of soil freezing were carried out according to the proposed calculation scheme based on data on the thickness of snow cover and air temperature based on a three-layer model of the medium (thawed soil, frozen soil, snow) and assuming a linear change in temperature in the media and heat flow according to Fourier’s law. Calculations of the effect of the thickness of the snow cover and air temperature on the depth of freezing of the soil were carried out according to the proposed calculation scheme. The work was performed in the frame of state topic “Danger and risk of natural processes and phenomena” (121051300175-4) and “Evolution of the cryosphere under climate change and anthropogenic impact” (121051100164-0).