| 17 Nov 2025
Glacial decline next to stable permafrost in the Dry Andes? Vertical glacier surface changes and rock glacier kinematics based on Pléiades imagery (Rodeo basin, 2019–2025)
Abstract. The presence and volume of high-mountain cryospheric features are drastically affected by rising air temperatures – on global scale. In the Dry Andes, precipitation is extremely scarce, shifting the hydrological significance towards the solid water storages, glaciers and ground ice. While glaciers decrease in surface area and volume, periglacially stored waters, e.g., in rock glaciers, react more retarded to atmospheric forcing, potentially buffering future water availability. Despite rising air temperatures, recent studies suggest stable permafrost conditions in the Dry Andes based on borehole investigation and rock glacier kinematics for the last decade.
We investigate vertical surface changes of 19 glaciers, three debris-covered glaciers and 59 rock glaciers in the Rodeo basin (Dry Andes, Argentina) for the time period 2019–2025. Further, we calculate rock glacier velocities for 47 of the 59 rock glaciers for which we have data for all time periods. We follow photogrammetric principles using (tri)stereo, panchromatic Pléiades imagery to generate projected optical imagery and DEMs in Ames Stereo Pipeline that we co-register prior to DEM differencing for vertical surface change calculation. We conduct feature tracking on the panchromatic Pléiades imagery for the calculation of rock glacier velocities.
We detect glacier surface lowering of up to −8.99 m (cumulative, 2019–2025) and dominantly negative annual surface lowering for all glaciers investigated. We find vertical surface lowering on debris-covered glaciers to be well below the magnitude of glaciers but higher than for rock glaciers – the latter not exceeding a decimetre. We quantify rock glacier velocities of in average 0.28 to 0.82 m/yr (LoDs: ± 0.16, ± 0.61) and can categorize three rock glacier groups – large and fast, small and fast and small and slow. Across the 47 rock glaciers investigated, we do not find a regional trend of increasing velocities.
In conclusion, we observe a declining glacial domain to contrast with rock glacier velocities which elucidate stable permafrost conditions. We infer a delayed reaction of the periglacial domain to the rising temperatures that lead to the surface lowering of glaciers and highlight the need for ongoing, long(er)-time surface change monitoring in this crucial, dynamic point in time.
General comment
The paper presents a detailed investigation of glacial and, in particular, periglacial landforms in the Rodeo Basin of the Dry Andes. Using Pléiades stereo and tri-stereo imagery, the authors derive both vertical and horizontal surface displacements through DEM generation, DEM differencing, and feature-tracking techniques. They also provide an in-depth assessment of their methodology, including a rigorous quantification of landform velocities and the associated Levels of Detection (LoD).
The results indicate that the monitored rock glaciers show no consistent trend toward acceleration or deceleration. This suggests that permafrost-related landforms in the region currently exhibit a relatively stable deformation regime, highlighting their greater resilience to climate warming when compared with the faster melt rates observed for glaciers and debris-covered glaciers.
The paper is well structured, but some improvements and minor reorganizations could help make the text more fluent and clearer. Additionally, a broader discussion addressing some of the open issues (outlined in the following section) would strengthen the manuscript and contribute to a more comprehensive and robust overall presentation.
I suggest refining the writing in sections 4.5 and 5.3 to enhance fluency. Section 4.5 is presented largely as a sequence of results, and section 5.3 combines multiple themes, which affects the coherence of the argument.
Detailed comment
Abstract
The abstract is clear and presents the analyses conducted with a good level of detail. However, reading it, it sounds like a list of activities done, with maybe too many “we” in a row. E.g. “We investigate”, “we calculate”, “we follow”, “we conduct”, “we detect”, “we find” in only few lines. I would suggest revising it making the text more homogeneous and fluent.
Line 28: please insert the extended name of LoD acronym.
Line 130: Do the mapped rock glaciers already have an activity attribute (active/ inactive)? How is this attributed to them?
Line 170 and caption of Tab. 2: Stammler et a., YEAR (?)
Lines 177-178: It is not clear how the bounding box are created. First a buffer of 500m is extracted around glacier and rock glaciers polygons and then a bounding box is created around the so extracted features, right? Please try to clarify this better.
Lines 186-189: I find it quite difficult to understand the meaning of the cumulative median and how it is computed. Also, I don’t get if the vertical change is computed only as cumulative median over time or as vertical surface change normalized to full years. Could you please better formulate this sentence?
Lines 192-195: I suggest moving the section explaining how the LoD is derived right after the description of the image coregistration process (around line 186). This will make it immediately clear how the LoD is determined before you introduce the vertical surface-change quantification.
Lines 212: In the LoD estimation, the terrain outside the landform polygons is assumed stable (line 194). Yet, the text notes that the LoD for horizontal displacements accounts for potential true surface change (e.g., fluvial processes) occurring outside these polygons. Could you clarify this apparent inconsistency? If fluvial dynamics may be active, how is the ‘stable terrain’ assumption justified for LoD estimation?
Line 271: “an LoD”
Line 322- 327: The manuscript states that large and fast rock glaciers occur at higher elevations, on gentler slopes, and exhibit lower median vertical surface change. Could you elaborate on the physical mechanisms that might explain this pattern? If vertical deformation is limited, motion must be predominantly horizontal. What factors, beyond surface slope, could control this horizontal displacement? In addition, the relationships between elevation, slope, and the different rock-glacier classes are not immediately clear from the current figure. I suggest expanding this section and perhaps exploring a combined plot of elevation versus slope, with median velocity represented through a color gradient. Such a visualization could help clarify the spatial distribution and dynamics of the landforms.
Line 340: are these vertical or surface velocities? I would suggest always clarifying this in the text.
Lines 358-360: the sentence seems to miss a part, and it is not totally clear.
Lines 394-400: In these sentences, the differences between the DGNSS and Pléiades-based velocities are sometimes reported in meters (m), although velocities are expressed in m/yr. It is therefore unclear whether these values refer to differences in annualized velocities or to absolute positional offsets. Please clarify what these numbers represent and adjust the units or wording accordingly to avoid confusion.
Section 4.5: The section presents many numerical values (errors, medians, LoDs, differences, per year changes) for three sites and two time periods but rarely summarizes what these numbers mean.
Line 445: remove rock glaciers at the end of the sentence.
Line 494: by is repeated 2 times
Line 517: How were the UAV-derived surface changes obtained? From differences between point clouds or offset tracking on images?
Section 5.3: Overall, the section contains valuable comparisons and a solid contextualization of your vertical surface change results with previous studies. However, the text would benefit from clarification and improved structure to enhance readability. Several paragraphs are dense, and the narrative flow is sometimes difficult to follow. For example a reorganization of the text into smaller thematic paragraphs on snow cover impact, comparison with published mass balances and debris-coverd glaciers could make the text easier to read.
Figures:
Fig.2: What are the triangles, square and circles? It is not clear in the caption.
Fig. 3: Is the reported vertical surface change derived directly from the DoD between the 2019 and 2025 DEMs, or is it calculated as the cumulative sum of DoDs from consecutive DEMs?
Fig.5: As for Fig.2 it is not clear what squares, triangles and circles refer to. As also stated in the detailed comment (Line 322-327) I would suggest trying to plot elevation and slope in the same graph to see if the different types of rock glaciers cluster in specific areas.
Fig.7: In the vertical axis I would explicitly state “median horizontal velocity”
Fig.8: I suggest putting a title to this graph with also the position of the point considered.
Thanks