Andreas Grøvan Aspaas

• Aspaas, Andreas Grøvan; Bievre, Grégory; Lacroix, Pascal; Langet, Nadege; Aga, Juditha & Skrede, Ingrid [Vis alle 9 forfattere av denne artikkelen] (2026). Seasonal and inter-annual evolution of the deformation of two Arctic landslides. Earth Surface Dynamics. ISSN 2196-6311. 14(5), s. 729–761. doi: 10.5194/esurf-14-729-2026. Fulltekst i vitenarkiv Vis sammendrag

  Landslides in glacial and periglacial environments are increasingly affected by climate change, with sudden failures reported in high mountain regions and the Arctic. The complex mechanisms behind these events are often poorly understood due to a lack of dense in situ data. We investigate two slow-moving landslides in Arctic Norway (70° N), the Jettan and Gámanjunni landslides, located approximately 10 km apart: Jettan, a complex slide in micaschist and calcite marble situated below the permafrost boundary, and Gámanjunni, a rotational slide in micaschist situated above the permafrost boundary. Using over a decade of multi-physics observations, including geodetic, borehole, seismic, and hydrological data, we examine surface and subsurface deformation. Both landslides display similar seasonal surface velocity patterns, with peaks in spring and autumn, likely influenced by pore-water infiltration. At Jettan, twelve years of inclinometer data in boreholes reveal a transition from steady state to seasonal deformation in two shear zones. Since 2020, spring accelerations have intensified in years coinciding with deeper snowpacks and associated melt. These observations, together with statistical modeling, suggest that the shear-zones are becoming increasingly localized and sensitive to pore-water pressure. Conversely, autumn acceleration is not seen in localized shear zones but manifests as distributed volumetric deformation. Seismic velocity variations within the landslide body also exhibit seasonal patterns that correspond with geodetic velocity, interpreted as changes in landslide rigidity due to water infiltration. This integrated analysis of surface and subsurface data offers new insights into the evolving deformation of Arctic landslides, emphasizing the influence of hydrological forcings on both seasonal and long-term deformation processes.

• Aspaas, Andreas Grøvan; Lacroix, Pascal; Sena, Clara; Kristensen, Lene; Langet, Nadege & Renard, Francois (2024). Creep Bursts on the Åknes Landslide, Norway: Detection, Characterization and Possible Mechanisms. Journal of Geophysical Research (JGR): Earth Surface. ISSN 2169-9003. 129(12). doi: 10.1029/2024JF007733. Fulltekst i vitenarkiv Vis sammendrag

  Creeping landslides may fail catastrophically, posing significant threats to infrastructure and lives. Landslides weaken over time through rock mass damage processes that may occur by steady-state creep or transient accelerations of slip, called creep bursts. Creep bursts may control landslide stability by inducing short-term damage and strain localization. This study focuses on the Åknes landslide in Norway, which moves up to 6 cm per year and could potentially trigger a large tsunami in the fjord below. An 11-year data set is compiled and analyzed, including kinematic, seismic, and hydrogeological data acquired at the landslide surface and in a series of boreholes. An annual average of two creep bursts with millimeter amplitude has been recorded within the shear zone in each borehole, accounting for approximately 11% of the total displacement. Creep bursts detected simultaneously in multiple boreholes are preceded by increased seismic activity and rising water pressure. However, most creep bursts are observed in only one or a few boreholes. These bursts often happen during seasonal high and low groundwater levels in autumn and spring, respectively, correlating with local peaks in water pressure. No such correlation is observed during summer. We propose that creep bursts can have different causes and hypothesize that rock degradation leads to some creep bursts independent of water pressure variations. In contrast, the largest creep bursts are correlated with variations in absolute water pressure or gradients of water pressure within the shear zone. Our findings emphasize the complexity of a dense data set requiring multiple mechanisms to explain creep burst dynamics.

• Etzelmüller, Bernd; Czekirda, Justyna; Magnin, Florence; Duvillard, Pierre-Allain; Ravanel, Ludovic & Malet, Emanuelle [Vis alle 20 forfattere av denne artikkelen] (2022). Permafrost in monitored unstable rock slopes in Norway – new insights from temperature and surface velocity measurements, geophysical surveying, and ground temperature modelling. Earth Surface Dynamics. ISSN 2196-6311. 10(1), s. 97–129. doi: 10.5194/esurf-10-97-2022. Fulltekst i vitenarkiv Vis sammendrag

  Abstract. The warming and subsequent degradation of mountain permafrost within alpine areas represent an important process influencing the stability of steep slopes and rock faces. The unstable and monitored slopes of Mannen (Møre and Romsdal county, southern Norway) and Gámanjunni-3 (Troms and Finnmark county, northern Norway) were classified as high-risk sites by the Norwegian Geological Survey (NGU). Failure initiation has been suggested to be linked to permafrost degradation, but the detailed permafrost distribution at the sites is unknown. Rock wall (RW) temperature loggers at both sites have measured the thermal regime since 2015, showing mean rock surface temperatures between 2.5 and −1.6 ∘C depending on site and topographic aspect. Between 2016 and 2019 we conducted 2D and 3D electrical resistivity tomography (ERT) surveys on the plateau and directly within the rock wall back scarp of the unstable slopes at both sites. In combination with geophysical laboratory analysis of rock wall samples from both sites, the ERT soundings indicate widespread permafrost areas, especially at Gámanjunni-3. Finally, we conducted 2D thermal modelling to evaluate the potential thermal regime, along with an analysis of available displacement rate measurements based on Global Navigation Satellite System (GNSS) and ground- and satellite-based interferometric synthetic aperture radar (InSAR) methods. Surface air and ground temperatures have increased significantly since ca. 1900 by 1 and 1.5 ∘C, and the highest temperatures have been measured and modelled since 2000 at both study sites. We observed a seasonality of displacement, with increasing velocities during late winter and early spring and the highest velocities in June, probably related to water pressure variations during snowmelt. The displacement rates of Gámanjunni-3 rockslide co-vary with subsurface resistivity and modelled ground temperature. Increased displacement rates seem to be associated with sub-zero ground temperatures and higher ground resistivity. This might be related to the presence of ground ice in fractures and pores close to the melting point, facilitating increased deformation. The study demonstrates and discusses the possible influence of permafrost, at least locally, on the dynamics of large rock slope instabilities.

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• Barras, Fabian; Aspaas, Andreas Grøvan; Aharonov, Einat & Renard, Francois (2026). Unveiling the role of seepage forces in the acceleration of frictional creep in fluid-saturated shear zone. doi: 10.5194/egusphere-egu26-17167. Fulltekst i vitenarkiv Vis sammendrag

  How fluid impact frictional slip is a central question in various geological settings, from tectonic faults to friction at the base of glaciers. In this work, we study the impact of fluid infiltration on the creep dynamics of the shear zone located at the base of a densely monitored landslide in Western Norway. In Åknes, approximately 50 million cubic meter of rock mass continuously creeps over a shear zone made of rock fragments, with seasonal accelerations that strongly correlate with rainfall. In this natural laboratory for fluid-induced frictional creep, unprecedented monitoring equipment reveals low fluid pressure across the shear zone, thereby challenging the conventional theory of fluid-driven instability in landslides. Here, we show that a generic micromechanical model can disentangle the effects of fluid flow from those of fluid pressure, and demonstrate that seepage forces applied by channelized flow along the shear zone are the main driver of creep accelerations. We conclude by discussing the significance of seepage forces, the implications for hazard mitigation and the broader applicability of our model to various geological contexts governed by friction across saturated shear zones.

• Oye, Volker; Langet, Nadege; Bogner, Laura; Bruland, Charlotte; Aspaas, Andreas Grøvan & Hadziioannou, Celine (2025). Decoding Instability: Linking Microseismicity Patterns, Deformation Monitoring and Ambient Seismic Noise at the Åknes Rock Slope”. Fulltekst i vitenarkiv
• Langet, Nadege; Bogner, Laura; Oye, Volker; Bruland, Charlotte; Hadziioannou, Céline & Aspaas, Andreas Grøvan (2025). Passive Seismic Monitoring of the Åknes Unstable Rockslope: Unveiling the Potential of Borehole Sensors. Fulltekst i vitenarkiv
• Langet, Nadege; Oye, Volker; Aspaas, Andreas Grøvan; Lacroix, Pascal & Renard, François (2024). New insights on the Åknes rockslide (Norway) using borehole microseismic data. Fulltekst i vitenarkiv
• Aspaas, Andreas Grøvan; Lacroix, Pascal; Langet, Nadege; Sena, Clara; Kristensen, Lene & Etzelmüller, Bernd [Vis alle 7 forfattere av denne artikkelen] (2023). What causes creep bursts in the Åknes landslide, Norway. Fulltekst i vitenarkiv
• Aspaas, Andreas Grøvan; Renard, Francois; Lacroix, Pascal; Kristensen, Lene & Etzelmüller, Bernd (2022). What causes transient deformations in the Åknes landslide, Norway? Fulltekst i vitenarkiv
• Oye, Volker; Langet, Nadege & Aspaas, Andreas Grøvan (2022). Geohazards, Norway, Åknes, rockslide, seismic monitoring. Fulltekst i vitenarkiv
• Aspaas, Andreas Grøvan; Anda, Einar; Kristensen, Lene; Blikra, Lars Harald; Majala, Gudrun & Pless, Gustav [Vis alle 7 forfattere av denne artikkelen] (2020). Managing an increasing number of medium risk unstable rock slopes. Fulltekst i vitenarkiv
• Aspaas, Andreas Grøvan; Krautblatter, Michael; Renard, Francois & Etzelmüller, Bernd (2019). Effects of glimmer rich rocks on the failure criterion of ice-filled permafrost rock joints. Fulltekst i vitenarkiv
• Aspaas, Andreas Grøvan (2026). Creep bursts in landslides - Characterization and modeling of transient deformations. Universitetet i Oslo. Fulltekst i vitenarkiv Vis sammendrag

  Landslides pose severe hazards worldwide, and in Norway they are one of the most deadly natural hazards with three catastrophic events per century in average. Predicting the timing of failure requires a clearer understanding of the processes that govern the transition from steady creep to accelerated motion and failure. This thesis investigates these mechanisms through detailed studies of the Åknes landslide in southwestern Norway and two Arctic landslides, Jettan and Gámanjunni, in northern Norway. We first examined the Åknes landslide, which creeps up to six centimeters per year and poses a tsunami hazard to the adjacent fjord. Eleven years of kinematic, seismic, and hydrological data from surface instruments and boreholes were analyzed to characterize deformation patterns. Transient accelerations, termed creep bursts, were identified within the shear zone. These events occurred on average twice annually in each borehole, exhibited millimeter-scale amplitudes, and accounted for approximately eleven percent of total displacement. Increased seismic activity preceded some bursts that occurred across multiple boreholes, although most events were isolated or involved only a few boreholes. Creep bursts frequently coincided with seasonal groundwater highs and lows in autumn and spring and correlated with local peaks in borehole water pressure, while none were recorded during summer. These patterns suggest multiple contributing mechanisms. We hypothesize that rock degradation may drive some bursts independently of water pressure, whereas the largest bursts, which correlate with water-pressure variations, may be triggered by absolute pressure or pressure gradients within the shear zone. To evaluate these hypotheses, we developed a micromechanical model that accounts both for effective stress reduction due to pressurization and flow-induced seepage forces, enabling us to test their respective impacts on landslide creep rates and to demonstrate that seepage forces generated by channelized flow along the shear zone as a plausible driver of the largest creep bursts. The second part of this study focused on the Jettan and Gámanjunni landslides to assess how Arctic climate and permafrost influence landslide kinematics. These sites are located approximately ten kilometers apart, with Jettan situated below the permafrost boundary and Gámanjunni slightly above it. Jettan exhibits a displacement rate of up to five centimeters per year and poses a tsunami hazard to the adjacent fjord, whereas Gámanjunni exhibits rates of up to six centimeters per year and threatens infrastructure through direct impact from the rock mass and river damming. We analyzed twelve years of kinematic, seismic, and hydrological data from surface and subsurface instruments at Jettan and four years of surface kinematic data at Gámanjunni. A comparison of average surface velocities shows that both landslides exhibit similar seasonal acceleration in spring and autumn, consistent with periods of snowmelt and increased precipitation. Gámanjunni shows approximately three times the annual velocity of Jettan, suggesting that permafrost may influence long-term creep rates. At Jettan, long time series monitoring data in boreholes reveal a transition from steady-state displacement to seasonal deformation within two shear zones. Spring accelerations intensify during years with deeper snowpack and associated melt. Statistical modeling suggests that the shear zone interface is becoming increasingly localized and sensitive to pore water pressure. In contrast, autumn acceleration is primarily detected from GNSS measurements and coincides with seasonal reductions in seismic velocity, indicating distributed volumetric deformation associated with a transition from a rigid to a more compliant rock mass. The results of this thesis highlight the complexity of landslide dynamics revealed by long-term observations and illustrate the need for expanded and higher-resolution monitoring to constrain the controlling processes. By integrating statistical analyses with a micromechanical model, we identify seepage forces as a key driver of creep bursts at Åknes, challenging the prevailing assumption that water pressurization alone governs acceleration. This finding has important implications for hazard mitigation. Future numerical models and stability assessments should incorporate both water pressurization and seepage forces, and drainage solutions should account for pressure gradients and water table height. For Arctic landslides, water infiltration is the dominant control on seasonal accelerations, while permafrost appears to modulate long-term creep rates. Understanding landslide kinematics is inherently complex. This thesis demonstrates that integrating statistical analysis of multiparameter datasets with theoretical modeling can significantly improve understanding of the processes that govern landslide motion.

• Aspaas, Andreas Grøvan (2019). Characterization and simulation of permafrost rock slope failures in mica-rich rocks - An integrated laboratory study of temperature-resistivity measurements and direct shear tests. Universitetet i Oslo. Fulltekst i vitenarkiv Vis sammendrag

  Degrading permafrost is an increasingly important problem in high altitude alpine mountains and Arctic regions around the world because it exerts a primary control on rock falls and landslides in these areas. The present study focuses on the effect of ice in permafrost conditions on i) the electrical resistivity of rocks; and ii) the shear strength of ice-filled joints. Freezing gradients in metamorphic rocks have previously been described by linear temperature-resistivity (T-p) paths. Electric resistivity measurements of low porosity mica-rich rocks from the Mannen active landslide and the Ramnanosi active landslide in southwestern Norway have been used to verify the linear relationship. The two samples were drilled and fitted with electrodes in linear Wenner arrays. The experiment were conducted with a resistivity meter automatically measuring every 15 minutes. The samples were cooled at temperature steps of 2 °C, -2 °C, -8 °C, and subsequently thawed by turning the cooling machine off. The measured T-p paths can be described by a bilinear relationship separated at 0 °C. The results showed one order of magnitude higher frozen gradients compared to unfrozen gradients, and one order of magnitude difference in resistivity values of the two samples. The results emphasize the importance of calibrated T-p measurements when characterizing permafrost as frozen conditions resistivity values in one sample represents unfrozen conditions in the other. Rock type dependence on the failure criterion of permafrost rock joints has not yet been studied. The present study focuses on mica-rich rocks with well developed foliation sampled from the Ramnanosi active landslide in southwestern Norway, the Nordnesfjellet active landslide in northern Norway and the Matterhorn mountain rock falls in the Swiss Alps. In these three areas, the cohesion of the rock volume is partly controlled by the presence of ice in mica-rich rock joints. The samples have been sheared to test the potential rock type dependent shear strength. The samples sliding surface were ground to ensure reproducibility of the initial roughness. A direct shear machine, developed at the Technical University of Munich, was used to conduct 36 tests on mica-rich rock-ice-mica-rich rock sandwich samples. A constant mean strain rate of 9.16 ± 5.9 × 10^-4 s^-1 was applied, provoking fracturing while a constant normal stress equivalent to 4 or 15 meters overburden was maintained. The temperature was constant and controlled at -10 °C, -6 °C and -2 °C. Results showed a 45\% and 39\% reduction in the shear strength for a temperature rise from -10 °C to -2 °C for 100 and 400 kPa normal stress, respectively. During the same temperature range, cohesion degrades by 47\%. The static friction coefficient were found independent of temperature. The results were compared to Wetterstein limestones, and a possible porosity dependent static friction is proposed. The mechanism is explained by an increase in rock-ice contact surface with increased porosity. A reduced dynamic friction coefficient with increased normal load were also found. The dynamic friction is suggested to decrease with increasing normal load because of frictional heating. The integration of rocks electric properties and shear properties may improve estimations of rock slope failures in the degrading permafrost rock slopes in Arctic and alpine mountain areas, where the effects of global warming are known to be large.

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