| 22 Jan 2026
Seasonal and Inter-Annual Evolution of the Deformation of Two Arctic Landslides
Abstract. Landslides in glacial and periglacial environments are increasingly affected by climate change, with rapid 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 about 10 km apart, with Jettan below and Gámanjunni 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-band interface is 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 GNSS 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.
The submitted manuscript investigates processes driving arctic/permafrost-affected rock slope failures. By analyzing monitoring data (6 to 12 years collection periods) of two well-researched landslides in Norway, the authors discuss the role of climatic influences (rain, snow, permafrost degradation) on failure kinematics, and provide insights into seasonal controls and deformation behaviour of rock slope beyond millions of cubic meters. The strength of the manuscript lies in the fusion of datasets (meteorological, seismic, surface and subsurface displacement & velocities, hydrogeological data) and their combined interpretation, and the data itself (scarcity of in-situ data). Moreover, the authors demonstrate the use of an Auto Regressive Distributed Lags model in predicting sliding velocity on the basis of past sliding velocity and exogenous parameters (precipitation, temperature, relative seismic velocity change). The model was used to backcalculate the individual share of the parameters in contributing to overall deformation. With a detailed analysis of in-situ records, this manuscript substantially contributes to deciphering the complex driving mechanism of arctic rock slope deformations.
The data, data processing, and methodology are precisely described and sound. Overall manuscript quality is good. I have minor remarks on the figures and the discussion section. Literature is adequate.
I suggest publication after minor revisions:
Discussion: A “synthesis” section or “synoptic discussion” would strengthen understanding of the interwoven process. An illustrated conceptual model (i.e., a figure showing two cross-sections) of both landslides could be really nice to highlight the differences and similarities. I.e., permafrost distribution, geological structures, shear planes/zones, and location/degree of fractured rock mass, water availability/height of pressure head, differential kinematics, and reaction time lag. You demonstrated multiple relationships effectively, but a clear synthesis of the core insights would strengthen the overall message. The writing can be somewhat technical at times (many numbers), making some aspects difficult to read, though it is generally acceptable given the type of analysis presented.
Strong discussion in general. Focus is yet specific on the studied sites. A designated section on transferability, intercomparability to other arctic/permafrost rock slope studies would be appreciated. Were the same seasonal shifts in hydrogeology or in slope velocities and their magnitudes reported elsewhere in comparable settings?
Maybe compare your results to Scondroglio et al. (2025) – long-term joint seepage record in sporadic permafrost terrain; Offer et al. also (2025) show seasonal permeability changes through ERT, and piezometric records in mountain permafrost.
Scandroglio, R., Weber, S., Rehm, T., and Krautblatter, M.: Decadal in Situ Hydrological Observations and Empirical Modeling of Pressure Head in a High-Alpine, Fractured Calcareous Rock Slope, Earth Surface Dynamics, 13, 295–314, https://doi.org/10.5194/esurf-13-2952025, 2025.
Offer, M., Weber, S., Krautblatter, M., Hartmeyer, I., and Keuschnig, M.: Pressurised water flow in fractured permafrost rocks revealed by borehole temperature, electrical resistivity tomography, and piezometric pressure, The Cryosphere, 19, 485–506, https://doi.org/10.5194/tc-19-485-2025, 2025.
Concerning hydrogeological flow paths: It would be interesting to show how piezometric measurements in boreholes correlate with snowmelt and rainfall. Maybe add a paragraph or figure on the connection between surface water availability and subsurface water or infiltration times. As I understood, slope kinematics are mainly explained by surface water (rain/snow) rather than recorded borehole hydraulic heads (except BH-2 upper; Figure A2). Typically, transient hydrostatic pressure buildup in the rock mass may explain kinematics. I am aware you noted “…because open boreholes can misrepresent subsurface water flow (Aspaas et al., 2024),..“ in line 460. Still, it might be interesting to see!
% Minor Remarks
“Catastrophic landslide” is used throughout the text. Please clarify what you mean. You study slow-moving gravitational rock slope deformations. I guess you mean rapid rock detachment evolving into highly mobile mass movements? Catastrophic is related to damage to humans/infrastructure and not to the process itself.
Ln21: How are they highlighted? More specifically.
Ln27: Not only permafrost thaw, but also warming permafrost temperatures may be relevant in the final detachment phase (Mamot et al. 2018).
Mamot, P., Weber, S., Schröder, T., and Krautblatter, M.: A Temperature- and Stress-Controlled Failure Criterion for Ice-Filled Permafrost Rock Joints, The Cryosphere, 12, 3333–3353, https://doi.org/10.5194/tc-12-3333-2018, 2018.
Ln27ff: Rather than singular individual drivers, the coupling of processes typically leads to enhanced progressive failure (Grämiger et al., 2020) or may peak in final detachment (Pfluger et al., 2025): Polythermal shifts in glacier or rock slope regimes impact hydrogeology – previous impermeable areas are fed with infiltraing meltwater. Hydrogeology impacts deformation and thermal conditions in turn (hydro-thermo-mechanical feedbacks). Often impossible to decipher individual factors for destabilization.
Grämiger, L. M., Moore, J. R., Gischig, V. S., Loew, S., Funk, M., and Limpach, P.: Hydromechanical Rock Slope Damage During Late Pleistocene and Holocene Glacial Cycles in an Alpine Valley, Journal of Geophysical Research: Earth Surface, 125, https://doi.org/10.1029/2019JF005494, 2020.
Pfluger, F., Weber, S., Steinhauser, J., Zangerl, C., Fey, C., Fürst, J., and Krautblatter, M.: Massive Permafrost Rock Slide under a Warming Polythermal Glacier Deciphered through Mechanical Modeling (Bliggspitze, Austria), Earth Surface Dynamics, 13, 41–70, https://doi.org/10.5194/esurf-13-41-2025, 2025.
Table 1: *Sloping Local Base Level (SLBL) -> Reference to calculation, publication, or the model is missing.
Figure 2: Figures and subfigures should be labeled uniformly throughout the manuscript (a),(b),…
I would recommend each subfigure with its own legend for clarity.
Highlight location for displayed monitoring records (b), (c) in the map (a).
Figure 2. Caption. Borehole displacement given for what depth/location? Specify. Please give a reference altitude for the temperature. Was the temperature/precipitation measured at the local site or from seNorge? (same for Figure 3).
Figure 4. The figure appears before the notion in the text. For what period is the displacement shown, add in the figure or caption.
Figure 5. Both temperatures look almost the same; It would be good to have a reference altitude for the temperature. i.e., use the location of the head scarp, as the two landslides vary distinctly in elevation range.
Ln310: If a central driver is water pressure, show the plot also in the main manuscript rather than the appendix. Best add it into one and the same with snow/rainfall data to show if there is a link in the records.
Section 3.4.2: Correlations: Please use a table to show the correlations of tested pairs. Visually, it is easier to compare in a table than written in text form.
Ln366: This first paragraph is a bit generic. Rather than using it as an introduction (as it was anyway in section 1), I would skip it here, and emphasize your own subsections on comparability and transferability of your results.
Ln498: Please refer to the Figures accordingly.
ff. For me, it is unclear what dv/v decrease is associated with shear plane wetting and what is associated with localized/volumetric deformation. The impact of deformation is likely higher, but both processes affect the measured data at the same time. Can you estimate orders of magnitude for the dv/v reduction impact of deformation and of water availability?
Ln519: Conclusion: First paragraph is repetitive; I would not cite literature in the conclusion; it is about your work. For my taste this paragraph can be skipped. I.e. merge the last sentence with the first of line 525.
Ln537: Be specific. How does it improve hazard assessment and monitoring strategies? It is easy to say through more data (i.e., surface and subsurface observations), but how many boreholes do we have at such locations? I would put the emphasis more on the processes.
I was happy reviewing the manuscript. Detailed insights into spatio-temporal deformation processes of permafrost/arctic rock slopes. Great contribution!