Conference Agenda

Here we combine the latest complementary expert knowledge to decipher the 1 Mio. m³ Fluchthorn rock slope failure that detached on June 12, 2023, from the before 3399 m high summit causing a rock avalanche that additionally eroded ca. 120.000 m³ of ice. InSAR data shows deformation rates from April 2021 to March 2023, linked to a westward deformation of the entire Silvretta nappe oversteepening the Fluchthorn. Mountain guides observed singular failures before the event. IR drone flights immediately after the event indicate rock temperatures at the failure planes in the range of 0°C - -2°C and ice-filled fractures. Solid, scarcely fractured pseudotachilitic sequences in the summit regions may have contributed to the massive oversteepening of the Fluchthorn Westface without significant pre-failures. The grain size compositions shows massive material take up of fine-grained material and fragmentation.

In a seismic analysis we can for the first time exactly reconstruct the temporal and spatial trajectory of a rock-ice avalanche, velocities and energy release during the 120-second rock-ice-avalanche propagation consistent with fragmentation and deposits. High-resolution photogrammetry highlights massive ice erosion and accumulation patterns during the rock avalanche propagation. In addition, we analyse all precursors in the last two years before the failure in detail. These include small prefailure volumes, seismic precursors, kinematic precursors and kinematic precursors detected in UltraCam & LiDAR surveys.

In an IRAZU model, capable of nucleation and growth of fractures based on nonlinear fracture mechanics applied stresses act to produce a progressive fracturing path that closely resembles the real failure and we can show the impact of the solid pseudotachilitic roof on the oversteepening. In a discontinuum model (UDEC), we can show the stabilizing effect of permafrost on developing fracturing patterns in a combined rock-ice mechanical approach including temperature-dependent rock mechanical and destabilization processes in ice-filled fractures and along rock-ice interfaces

In high mountains environments, permafrost degradation causes rockwall instabilities, sometimes leading to rock slope failures threatening human lives and activities. It is therefore essential to improve our knowledge about their triggering and propagation mechanisms.

This study focuses on two rock slope failures which occurred in the Vallon d'Étache (Maurienne Valley, France) and the Crête des Grangettes (Écrins massif, France) in 2020. These events have respectively volumes around 225 000 m3 and 35 800 m3. In both cases, ice in the scars suggests the presence of permafrost, but its local distribution and its role in the triggering of the events remain to be confirmed. The aims of this study are (i) to assess thermal conditions in which both events were triggered and (ii) understand the propagation mechanisms in the Vallon d’Étache. To do so, we combine rockwalls temperature monitoring, permafrost statistical modelling, geophysical surveys (Electrical Resistivity Tomography) and laboratory measurements (petrophysical model) to explain the thermal conditions predisposing and triggering the events. Depth-averaged flow simulations are used to model the runout characteristics of the Vallon d’Étache rock avalanche.

This multi-method approach shows that both of the events occurred in a bedrock with permafrost subject to intense warming since 1990’s with a sharp acceleration in the ground temperature rise since 2015. In the Vallon d’Étache, thermal analysis suggests that the rock avalanche may have been triggered by permafrost warming (from cold to warm permafrost) combined with heavy rainfall and water infiltration. This likely interacted with ice within rock fractures, increasing hydrostatic pressure and/or accelerating ice degradation within the fractures. At the Crête des Grangettes, the warming of temperate permafrost, nearing its melting point, likely reduced the strength of the ice within the fractures, triggering the rockfalls.

The unprecedented occurrence of cryogenic, secondary lahars in the last decade posed a major threat at glacierised volcanoes in Ecuador. The lahars originate close to the glacier margins of rapidly retreating tropical glaciers with unknown trigger mechanism. Ecuadorian glaciers have experienced a rapid decline of up to 50% of surface area within the last 40 years, and future rise of the ELA with up to 200 m within the next 50 years.

In this study, we develop a conceptual model and employ meteorological, geophysical and geomorphological reconnaissance and IR UAV-surveys at Chimborazo (EC, 4700-4900 m asl) to decipher starting conditions of secondary cryogenic lahars, a scientifically nearly undescribed phenomenon. Along the covered ice body extending below Glacier Nicolas Martínez, we investigate known starting zone of at least 5 secondary cryogenic lahars with 2 ERT cross-sections (approx. 200 & 300 m long) to decipher ice contents, 6 temperature loggers along transects and at known debris-covered ice sites to calibrate IR surveys flown with a Mavic 2 EA drone. Optical data and geomorphological field reconnaissance found exposed ice in former debris-covered glaciers but also in former side moraines which are now ice-cored, underlining the transition into a permafrost-dominated setting. By a systematical comparison with our conceptual model we can show that only few genetic types comprise a majority of relevant starting conditions for cryogenic secondary lahars. Here we show, how cryogenic secondary lahars evolve in degrading debris-covered glaciers subsequent to rapid glacier retreat along tropical volcanoes, a problem whose importance is rapidly growing in the foreseeable future.    

Retrogressive Thaw Slumps (RTSs) are slope failures triggered by abrupt permafrost thaw, occurring in the Arctic and on the Qinghai-Tibet Plateau in regions with high ground ice content. RTSs tend to grow rapidly, posing risks to local infrastructure and releasing formerly frozen soil organic carbon (SOC). The increasing availability of optical RTS inventories and geophysical permafrost datasets, facilitated by advanced machine learning techniques, enables enhanced analysis. By integrating optical and Synthetic Aperture Radar (SAR)-based remote sensing data, we developed a novel method to quantify RTS mass wasting through estimations of material and ground ice loss, as well as associated SOC mobilisation.

We utilised single-pass Interferometric SAR (InSAR) from the TanDEM-X mission to generate Digital Elevation Models (DEMs) with a 10 m spatial resolution and approximately 2 m height accuracy for the years 2010 and 2018. RTS annotations derived from high-resolution optical imagery and deep learning defined the affected thaw area, enabling material loss calculations based on difference DEMs (dDEMs). By incorporating datasets on ground ice content, active layer thickness, and SOC content, we estimated the ground ice lost and SOC mobilised due to RTS activity on the Qinghai-Tibet Plateau during the study period.

Typically, RTS annotations based on optical imagery depict the entire geomorphological landform showing vegetation disturbance, while dDEM-based annotations highlight only the actively eroding parts of RTSs. Comparing RTS mass wasting characteristics estimated from manually annotated DEM-based RTS labels with optical annotations revealed high agreement, with deviations of only 5% for volume loss, 12% for ground ice loss, and 13% for SOC mobilisation at a test site on the Qinghai-Tibet Plateau.

This new method potentially allows for the upscaling of RTS mass wasting quantification and associated ground ice loss and SOC mobilisation to Arctic permafrost regions by combining optical RTS inventories and InSAR-based DEMs.

Presenting our findings on scientific level via publications and presentations is an integral part of our scientific work. While teaching in universities and training the next generation of early career researchers seems a natural responsibility in our careers too, sharing our findings and experience with a wider audience is often neglected. However, isn’t the society at large where we want to place our discoveries and make humanity transition into a climate friendly future?

This presentation shows examples of effective science communication within the realm of Arctic permafrost research. Why is permafrost an important element of the cryosphere? What do Arctic permafrost landscapes look like and how are they changing? How to visualize carbon pools? Based on numerous activities with school classes, youth and other audiences, learnings and best-practice cases are discussed – including a live test of outreach materials developed in the dedicated outreach project “Permafrost im Wandel”, funded by the BMBF. The presentation will conclude with another step forward in the concept of knowledge transfer: Including citizens into participatory research and why this is a win-win for science and society.