Geomorphological assessment of glacial landforms in the Patagonian mountain valleys

Patagonia's glacial landforms are written in a language of moraines, cirques, and U-shaped valleys that, once decoded, tells the story of how South American ice sheets advanced and retreated over the past two million years. This research presents a geomorphological assessment of glacial landforms across four adjacent valleys in the northern Patagonian Andes of Argentina (41°S-42°S), based on field mapping, morphometric analysis, and remote sensing interpretation. The valleys — Manso, Foyel, Villegas, and Steffen — were mapped at 1:25,000 scale using a combination of high-resolution satellite imagery (Pleiades, 0.5 m), a 12.5 m resolution ALOS PALSAR digital elevation model, and three field campaigns totalling 68 days between November 2021 and March 2023. A total of 184 glacial landforms were identified and classified: 42 morainic ridges (18 lateral, 14 terminal, 10 recessional), 28 cirques, 16 roches moutonnées, 22 glacial striations/grooves, 34 erratic boulders, 18 outwash terraces, and 24 other features including kame terraces and glacial lake shorelines. Moraine positions defined three major glacial advances: a Last Glacial Maximum (LGM) extent reaching 16.4 km from modern headwalls, a Late Glacial readvance at 8.2-10.6 km, and a Neoglacial position at 2.4-4.8 km. Cirque morphometry revealed a strong north-south asymmetry: 71% of well-developed cirques faced south to southeast, with mean floor elevations 180 m lower on south-facing slopes than equivalent north-facing positions. The equilibrium line altitude during the LGM was estimated at 1,420±60 m, approximately 780 m below the present snowline, implying a mean annual temperature depression of 4.8-5.6°C relative to present. These data contribute to the regional glacial chronology of northern Patagonia and support the development of palaeoclimate reconstructions for the Southern Hemisphere mid-latitudes.

Illustrations explain the paper; charts are replotted from the paper's own table values.

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Glacial Advance SequenceClose ×

AI-generated conceptual illustration (Patagonian mountain valley with glacial moraines). It explains the idea and does not show study data.

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Cirque Aspect AsymmetryClose ×

AI-generated conceptual illustration (Patagonian mountain peak with glacial cirques). It explains the idea and does not show study data.

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Steffen: Morainic Ridges vs Cirques vs Roches Moutonnées vs Striations/Grooves vs Erratic BouldersClose ×

Replotted from Table 1 (page 2) of the original paper. Every bar is the paper's own table value.

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Introduction

One can learn to read a glaciated landscape the way a detective reads a crime scenethe evidence is all there if you know what to look for. A lateral moraine running along a valley wall marks the edge of where ice once stood. A polished roche moutonnée records the direction the glacier flowed. A cirque headwall tells you where snow accumulated and compacted into ice. And the distance between the cirque and the terminal moraine tells you how far that ice managed to travel before climate caught up with it and melted it back [1] . The Patagonian Andes between 40°S and 43°S represent one of the best-preserved glacial landscapes in the Southern Hemisphere. During the Last Glacial Maximum (roughly 26,000-18,000 years ago), piedmont glaciers up to 20 km long descended from the Andean cordillera into the steppe lowlands east of the range, building massive moraine complexes that remain largely intact because the dry climate east of the Andes has minimised post-glacial erosion [2] . The moraines of the Argentine Lake District have been mapped and dated extensively using cosmogenic nuclide exposure dating, but coverage remains unevensome valleys have detailed chronologies while others lack even basic geomorphological maps [3] . The four valleys examined in this research -Manso, Foyel, Villegas, and Steffendrain the eastern flank of the Patagonian Andes between Bariloche and El Bolsón. Despite their proximity to the well-studied Nahuel Huapi Lake basin, these valleys have received less geomorphological attention, partly because their road access is limited and their upper reaches require multi-day field traverses [4] . This research produced the first comprehensive glacial landform inventory for these four valleys, using a combination of remote sensing and detailed field mapping to characterise landform types, positions, and morphometry [5] .

Extraction Protocol

Glacial landform identification followed a two-stage workflow. In the first stage, potential landforms were mapped remotely using stereo interpretation of Pleiades satellite imagery (0.5 m panchromatic, acquired February 2022) draped over the 12.5 m ALOS PALSAR DEM in ArcGIS Pro 3.0. Moraines were identified by their characteristic ridge morphology and asymmetric crossprofiles; cirques by their amphitheatre-shaped headwalls and flat floors; roches moutonnées by their asymmetric profiles with smooth stoss and rough lee sides; and outwash terraces by their flat treads and gravel surface texture [6] . In the second stage, all remotely identified features were visited in the field and verified, measured, and classified. Features that couldn't be confirmed in the field were removed from the inventory. Additional features identified during field traverses but missed in remote sensingprimarily smaller erosional forms like striations and grooves were added.

Instrumentation

Field measurements employed standard geomorphological survey equipment. Moraine ridge heights and cross-profiles were measured using a laser rangefinder (TruPulse 360, ±0.3 m accuracy) and clinometer at 5 m intervals along transects perpendicular to the ridge crest. Cirque dimensions (length, width, headwall height, floor elevation) were determined from a combination of DEM extraction and field verification with handheld GPS (Garmin GPSMAP 66sr, ±2 m horizontal accuracy) [7] . Glacial striations were recorded using a Brunton compass for orientation and a ruler for groove dimensions. Erratic boulder positions were logged by GPS, with lithological identification in the field and size measurements (three orthogonal axes). All field data were entered into a GIS database using QGIS 3.28 field mapping tools on a tablet computer.

Material and Methods

Material and Methods

Material

This research was coordinated from the Varanasi College of Earth and Mineral Sciences, Uttar Pradesh, India, with three field campaigns in the northern Patagonian Andes of Río Negro Province, Argentina: November-December 2021 (22 days), February-March 2022 (24 days), and January-February 2023 (22 days). The mapped area covers approximately 840 km² across four valleys between 41°08'S and 42°04'S, 71°10'W and 71°45'W, spanning elevations from 780 m at the valley mouths to 2,380 m at the cirque headwalls. The Pleiades satellite imagery was acquired in tri-stereo mode (three overlapping acquisitions) to enable stereo viewing and DEM generation. ALOS PALSAR DEM data (12.5 m resolution) were obtained from the Alaska Satellite Facility for topographic analysis beyond the satellite imagery footprint [8] .

Methods

Morphometric parameters for moraines included ridge height, crest width, proximal and distal slope angles, and distance from the headwall cirque. Cirque morphometry followed the parameters defined by Evans and Cox: length, width, amplitude (headwall height), floor altitude, aspect, and the circularity index (width/length ratio) [9] . The equilibrium line altitude (ELA) for each glacial advance was estimated using the toe-to-headwall altitude ratio (THAR) method with a ratio of 0.4, following the regional calibration of Meierding [10] . Modern snowline elevation was determined from the average lowest persistent snow patches visible in late-summer satellite imagery (March 2022). Aspect analysis of cirque orientations used circular statistics (mean vector direction, Rayleigh test for non-uniformity) in R 4.2. The relationship between cirque floor altitude and aspect was tested using ANOVA. All geomorphological mapping used ArcGIS Pro 3.0 with projected coordinate system POSGAR 2007 Zone 2 [11] . A total of 184 glacial landforms were mapped across the four valleys (Table 1). The Manso Valley contained the highest density of features (63), reflecting its larger catchment area and longer glacial history. Morainic ridges were the most abundant landform category (22.8%), followed by erratic boulders (18.5%) and cirques (15.2%). The Villegas Valley had the fewest features (34), consistent with its shorter length and smaller source area. Cirque morphometry showed consistent patterns across the four valleys (Table 2). Mean cirque length was 1.08 km, width 0.81 km, and headwall amplitude 190 m, giving a circularity index (W/L) of 0.75within the range typical of well-developed cirques in other glaciated mountain ranges. South and southeast-facing cirques accounted for 71% of the total, significantly non-random by the Rayleigh test (p< 0.001), and their floor elevations averaged 180 m lower than north-facing equivalents at comparable positions along the range.

Parameter	Manso	Foyel	Villegas	Steffen	All
Mean Length (km)	1.24	1.08	0.82	1.14	1.08
Mean Width (km)	0.92	0.78	0.64	0.84	0.81
Mean Amplitude (m)	218	186	148	194	190
Mean Floor Elev. (m)	1,680	1,720	1,760	1,640	1,700
S-SE Facing (%)	74	68	72	71	71

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Table 2Close ×

Cirque morphometry and aspect distribution across the

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Landform	Manso	Foyel	Villegas	Steffen	Total	% of Total
Morainic Ridges	14	10	8	10	42	22.8
Cirques	9	7	5	7	28	15.2
Roches Moutonnées	6	4	3	3	16	8.7
Striations/Grooves	8	6	4	4	22	12.0
Erratic Boulders	12	8	6	8	34	18.5
Outwash Terraces	6	4	4	4	18	9.8
Other Features	8	6	4	6	24	13.0
Total	63	45	34	42	184	100

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Table 1Close ×

Glacial landform inventory across four Patagonian

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Results

Results

Comprehensive Interpretation

The moraine profiles (Figure 1) show the clear separation between the three glacial advances, with the LGM moraines extending roughly twice as far down-valley as the Late Glacial limits. The bubble plot (Figure 2) confirms the aspect control on cirque development: south-facing cirques (which receive less direct solar radiation in the Southern Hemisphere) are generally larger, deeper, and lower in elevationconditions that favour longer snow retention and more effective glacial erosion.

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Figure 2Close ×

Cirque dimensions (length vs width) with bubble size proportional to headwall amplitude and colour indicating aspect. North-facing

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Figure 1Close ×

Elevation profiles of the three main moraine systems across the Manso Valley, corresponding to the Last Glacial Maximum (M1),

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Original paper figureSource PDF · page 3 ↗

Discussion

The LGM glacier length of 16.4 km in the Manso Valley is consistent with reconstructed glacier lengths from adjacent valleys in the Nahuel Huapi region, where cosmogenic ¹⁰Be dates place the maximum extent at roughly 26,000-22,000 years ago [12] . The implied ELA depression of 780 m, translating to a temperature reduction of 4.8-5.6°C using a standard environmental lapse rate of 6.2-7.2°C/km, falls within the 4-6°C range estimated from other Southern Hemisphere mid-latitude glacial records [13] .

The strong south-southeast orientation of cirques (71%) reflects the fundamental asymmetry of solar radiation receipt in the Southern Hemisphere. South-facing slopes receive less insolation, accumulate more snow, and lose it more slowly through the melt season, favouring cirque excavation on those aspects. This pattern has been documented across the Patagonian Andes by multiple authors, though the 180 m altitude difference between north and south-facing cirque floors reported here is at the high end of published values, possibly reflecting the strong precipitation gradient across the study area that enhances the aspect effect [14] .

The three-stage glacial advance model (LGM, Late Glacial, Neoglacial) is now well established across northern Patagonia, but the spacing between moraine sets varies considerably between valleys. In the Manso Valley, the Late Glacial moraines sit at 8.2-10.6 km from the headwall -roughly 50-65% of the LGM extentwhile in the shorter Villegas Valley they're at 70-75% of the LGM distance. This difference may reflect valley geometry: wider, lowergradient valleys allow glaciers to retreat farther before reaching a stable position, while narrow, steep valleys constrain retreat distances [15,16,17] . One limitation of this research is the absence of absolute age dating for the moraine systems. The landform positions and relative chronology are well constrained by morphostratigraphy, but without cosmogenic nuclide or radiocarbon dates, the assignment of moraines to specific glacial events relies on morphological correlation with dated moraines in adjacent valleysa method that works well for the LGM but becomes less reliable for younger advances [18, 19] .

Conclusion

This geomorphological assessment identified and mapped 184 glacial landforms across four valleys in the northern Patagonian Andes, including 42 morainic ridges, 28 cirques, and 16 roches moutonnées. Three major glacial advances were defined by moraine positions: an LGM advance extending 16.4 km from modern headwalls, a Late Glacial readvance at 8.2-10.6 km, and a Neoglacial position at 2.4-4.8 km. Cirque morphometry confirmed a strong aspect control, with 71% of well-developed cirques facing south to southeast and their floor elevations averaging 180 m lower than north-facing equivalents. The implied LGM temperature depression of 4.8-5.6°C is consistent with regional paleoclimate estimates and provides an additional data point for calibrating Southern Hemisphere climate models. Future work should pursue cosmogenic exposure dating of moraine boulders to establish absolute ages for the three advance phases and extend the geomorphological mapping to the less-studied western (Chilean) side of the same drainage divide, where higher precipitation may have produced different glacial geometries.

Acknowledgement

Acknowledgements Funding SourcesThis research was supported by departmental funds at Varanasi College of Earth and Mineral Sciences. Institutional SupportThe authors thank the Department of Geology, Varanasi College of Earth and Mineral Sciences, Uttar Pradesh, India, for GIS facilities and field equipment.

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