Edinburgh Research Explorer The glacial geomorphology of the Río Corcovado, Río Huemul and Lago Palena/Lago General Vintter valleys, northeastern Patagonia (43°S, 71°W)

This study presents the ﬁ rst detailed glacial geomorphological map of the sediment-landform assemblages formed by three eastern outlet glaciers of the former Patagonian Ice Sheet. These glaciers occupied the Río Corcovado, Río Huemul and Lago Palena/General Vintter valleys, Chubut province, Argentina (43°S, 71°W). By combining remote sensing and ﬁ eld-mapping, we build on previous ice-sheet scale mapping and geological surveys to provide high-resolution spatial information on local ice-contact glaciogenic, glacio ﬂ uvial, glaciolacustrine, and subglacial landforms. Twenty- ﬁ ve landform types, many of which are newly mapped in the region, were digitized as georeferenced shape ﬁ les over a 5300 km 2 area. This map enables the identi ﬁ cation of former ice- ﬂ ow directions, relative ice-margin positions and glacio ﬂ uvial drainage pathways for each preserved Quaternary glaciation. It also elucidates the former areal extent, geolocation and spillways of glaciolacustrine bodies formed during the last deglaciation. The map delivers an essential framework on which to build robust glacier-scale geomorphological and geochronological reconstructions.


Introduction
The Patagonian region of southern South America was host to the most extensive Quaternary ice sheet of the southern hemisphere outside of Antarctica, the Patagonian Ice Sheet (PIS). The PIS covered a latitudinal extent of ∼2000 km (38°S-56°S; Figure 1) along the spine of the Patagonian and Fuegian Andes (Caldenius, 1932;Davies et al., 2018Davies et al., , 2020Martínez et al., 2011). Patagonia is part of the only continental landmass that fully intersects the precipitationbearing southern westerly winds (Garreaud et al., 2013) and is one of few regions in the southern mid-latitudes containing a well-developed Quaternary glacial geomorphological record (Clapperton, 1993;. Patagonia therefore offers a unique opportunity to study Quaternary climatic and environmental change in the southern mid-latitudes. Robust palaeoglaciological reconstructions of PIS outlet glaciers can help us to investigate the landscape evolution and climate-forcing mechanisms responsible for Quaternary ice-sheet fluctuations (e.g. Hein et al., 2010;Rabassa et al., 2000). They can provide insights into the timing and causes of Quaternary glacial cycles in the southern mid-latitudes, and enable determination of the regional drivers of glaciation as well as inter-hemispheric glacial (a)synchronicity (Bentley et al., 2005;Denton et al., 1999;. For these reasons, the PIS has been subject to an increasing number of glacial geochronological reconstructions. However, with a few exceptions (e.g. García et al., 2019;Iglesias et al., 2016;Van Daele et al., 2016) there remains a general lack of published detailed mapping and geochronological data across the northeastern sector of the former ice sheet, between ∼39°S and ∼46.5°S (Darvill et al., 2015;Davies et al., 2020;Mendelová et al., 2017). Robust reconstructions from this region are needed to understand fully the PIS response to the Last Glacial Maximum (LGM) at these latitudes, and to investigate latitudinal dependencies on the timing of the local LGM throughout Patagonia (Darvill et al., 2015;Davies et al., 2020;García et al., 2018;Sagredo et al., 2011). A vital component of such reconstructions is detailed, glacier-scale geomorphological mapping (Chandler et al., 2018;Clark et al., 2018;Evans & Orton, 2015). This provides spatial information that facilitates interpretations of palaeoglaciological behaviour and equips glacial geologists with an essential framework upon which to build robust chronologies (Chandler et al., 2018;Bendle et al., 2017a;Darvill et al., 2016). We thus present in this paper the first detailed glacial geomorphological map of three valleys in northeastern Patagonia (43.5°S), the Río Corcovado, Río Huemul and Lago Palena/General Vintter valleys (Figure 1b). Our aim is to provide benchmark geomorphological data for future geochronological interpretations of their glacial history.

Study location and previous work
The geomorphological map is centred on a region located east of the Patagonian Andes, between 43.3°S and 44.0°S, and covers an area of ∼5300 km 2 ( Figure  1b). At these latitudes, a major westward-dipping over-deepened valley, the Río Palena trough, cuts through the Andes to drain the contemporary Río Corcovado, Río Huemul and Lago Palena/General Vintter catchments westward to the Pacific Ocean. At this location, the PIS was characterised by ice flowing towards the east-northeast from the centre of the former ice sheet, located near Macizo Nevado. Glacier ice thus flowed along the Río Palena trough to the mountain front, where it diverged into two glaciers occupying the Río Huemul valley to the east, and the Río Corcovado valley to the south (Figure 1b). The two outlet glaciers extended up to 60 km to the east and southeast of the Argentinian town of Corcovado   and . Overlain in white are the contemporary North Patagonian (NPI), South Patagonian (SPI), and Cordillera Darwin (CDI) Icefields. Major eastern PIS glaciers are designated; BI: Bahía Inútil, EM: Estrecho de Magallanes, SS: Seno Skyring, BV: Bella Vista, LA: Lago Argentino, LV: Lago Viedma, LC/P: Lago Cochrane/Pueyrredón, LBA: Lago Buenos Aires. Bathymetric data of ocean basins were obtained from the General Bathymetric Chart of the Oceans (GEBCO) and are displayed in greyscale. A −125 m contour line is applied to simulate the approximate former position of coastlines at the LGM (Lambeck et al., 2014). The Chile/Argentina border is highlighted in red. (B) Digital elevation model (DEM) of northern Patagonian region from the ALOS WORLD 3D missions (version 2.2; JAXA; https://www.Eorc.jaxa.jp/ALOS/en/ aw3d30/) with a shaded relief background and a black sea level contour line highlighting modern coastlines . White arrows indicate former ice-flow of major northeastern PIS outlets, including the Río Corcovado, Río Huemul and Lago Palena/General Vintter glaciers. The yellow line designates the contemporary Atlantic/Pacific drainage divide. Lake bodies and key river channels are drawn in blue. The black dotted box delineates the extent of the geomorphological map presented with this paper.
(43°54 ′ S; 71°46 ′ W) (Caldenius, 1932;Haller et al., 2003;Martínez et al., 2011). Here, we refer to these as the Río Huemul glacier and the Río Corcovado glacier; the latter to distinguish it from the Golfo Corcovado outlet glacier that drained the western side of the PIS (Denton et al., 1999). The Lago Palena/General Vintter outlet glacier drained a separate, smaller catchment located ∼30 km southeast of the Río Palena trough. This glacier flowed eastward, at times extending to converge with the Río Corcovado glacier coming from the north (Figure 2). Subsequent retreat into an over-deepened basin led to the formation of the moraine-dammed Lago Palena/General Vintter lake, still present to this day (43°55 ′ S; 71°31 ′ W) ( Figure 2). Our mapping focuses on the former terminal environment of these three outlet glaciers. Subglacial erosion and over-deepening of the Río Palena trough is greater towards the centre of the former PIS where ice thickness and duration of ice cover were largest (Clapperton, 1993;Hubbard et al., 2005;Kaplan et al., 2009). Thus, at our study site, asymmetrical subglacial erosion generated a progressive eastward migration of the Atlantic-Pacific drainage divide following each Quaternary glaciation, causing the contemporary drainage divide to be located ∼70-80 km east of the central spine of the Andes (Davies et al., 2020;Kaplan et al., 2009) (Figure 2). The semi-arid eastern sectors of the Río Corcovado, Río Huemul and Lago Palena/General Vintter valleys, which belong to the Patagonian steppe climate zone, are characterised by extensive, well-preserved and easily discernible moraine complexes, along with their associated glaciofluvial and glaciolacustrine sediment-landform assemblages (Haller et al., 2003;Martínez et al., 2011).
Geomorphological mapping of major moraine limits in the Río Corcovado, Río Huemul and Lago Palena/General Vintter valleys was conducted by Caldenius (1932), , and Davies et al. (2020), in their respective efforts to record the glacial geomorphology of the entire PIS (Table 1). Haller et al. (2003), meanwhile, produced a regionally-focused geological map of the three valleys including main glaciogenic deposits (area located between 43-44°S and 72-70.3°W). These deposits were also mentioned in studies by Lapido (1990) and Martínez (2002;Martínez et al., 2011). However, all previous mapping was part of ice-sheet-wide geomorphological investigations or geological surveys and was focused primarily on identifying the most prominent moraines and glaciofluvial deposits for each glaciated valley. All previous studies interpreted the landforms as Pleistocene glaciogenic deposits associated with three distinct glaciation  Easily identified on DEM hillshade if prominent enough as light-shadowing highlights positive relief with arcuate, narrow shape. Dark grey in colour on DG imagery. Different in texture to surrounding terrain ( Figure 5d).
May be difficult to identify heavily subdued ridges from imagery for oldest ice marginal deposits. Lower relief moraine ridges can in some cases be confused with palaeo- shorelines.
Indicate former ice-front position. Prominence, crest undulation, continuity and slope gradients combined can be indicators of erosion and relative age of moraine deposit / glacial advance. ; Davies et al. (2020) (main features only)

Hummocks
Rounded to sub-rounded mounds of glaciogenic sediments arranged chaotically.
Best identified on high-resolution imagery although sometimes possible from DEM. Dark grey or brown in colour on Digital Globe (DG) imagery, although lighter than meltwater channels. Sub-rounded light shadowing demonstrates positive relief ( Figure 4a).
May be challenging to identify limits of feature from remote sensing for relatively old, subdued deposits, or in vegetated areas.
Indicate marginal ice contact. Unmapped Hummocky ridges Mounds of glaciogenic sediments arranged in a linear fashion and generating a distinct ridge crest of limited length (<300 m).
Best identified on high-resolution imagery although sometimes possible from DEM. Dark grey or brown in colour on DG imagery, although lighter than meltwater channels. Narrow, linear light shadowing demonstrates positive relief and ridge structure ( Figure 3a) May be challenging to map accurately for older deposits due to erosion and lack of prominence, thus creating potential for under-discovery. In such cases, differentiation between moraine and hummocky ridges can be less conspicuous.
Although no eskers were explicitely identified in the area, some may have been mis-interpreted as hummocky ridges.
Indicate marginal ice contact. Abundant, prominent, and parallel ridges are likely to suggest substantial till deposition and thus a relatively stable, long-lasting glacier margin.

Moraine complexes
Relatively confined, narrow (<3 km) and easily discernible drift belts of arcuate shape comprising prominent and continuous moraines ridges as well as concentrated, parallel hummocky ridges.
Best identified on high-resolution imagery. Dark grey or brown in colour deposit belts composed of hummocks, hummocky and moraine ridges, and different in colour to surrounding terrain e.g. proglacial outwash plains ( Figure 3a).
May be challenging to identify limits of feature for relatively old deposits, or vegetated areas.
Indicate former glacier front positions following glacial advance or still-stand. Kettle holes Circular to semi-circular / elongate hollows and pits of shallow depth (<20 m).
Best identified from high-resolution imagery. Light grey/white circular to elongate pockmarks, may be water-filled. No percievable light-shadowing as no positive relief ( Figure 4a).
Potential for under-discovery in areas exploited by subsequent and/or modern drainage. Depressions can also be exploited by modern lacustrine bodies and thus be confused with features characteristic of modern hydrology.
Indicates former presence of ice front. High feature concentration can mark presence of progressively thinning and stagnant ice.

Unmapped
Kettle-kame topography Extensive (>3 km in width) drift deposits composed of chaotic and disorganised hummocks (or kames) irregularly interspersed with hollows and kettle holes.
Best identified from high-resolution imagery. Areas comprising high concentration of chaotically arranged kettle holes, small lakes, hummocks and hummocky ridges. Such glaciogenic deposits gives the ensemble a dark grey or brown colour on DG imagery ( Figure 4a).
May in some cases be difficult to identify the boundary with moraine complexes as difference between an organised, arcuate group of glaciogenic sediment and a more scattered form of hummocky terrain can be open to doubt.
Indicates former ice-marginal zone, possibly under a stagnant, dead-ice front scenario.

Proglacial outwash plains
Broad, low-gradient surfaces composed of fluvially-rounded sand-and gravel-sized sediment, in some cases prograding from former ice-margins. Can demonstrate former braided meltwater channel networks on their surfaces.
Feature limits identified from imagery, although broad terrace characteristics make it distinguishable from DEM. Little to no positive relief, light brown to orange in colour, and imagery can reveal surface channels. Feature limits often associated with fluvial incision scarps (Figure 6a,f).
Surface grading can be difficult to distinguish from remote sensing (DEM only) and it can be challenging to identify the limits of outwash features from imagery.
Indicates former pathways of meltwater during glacier advance or still-stand.  (>30 m) isolated channels can display lightshadowing due to negative relief (e.g. Figure 6a,f).
be challenging to distinguish from imagery on older outwash plain deposits.
abundance and ease of discovery can be a good proxy for age of glaciofluvial deposit.
Discernible from DEM in cases of significant incision (>20 m) due to break in slope, but also from imagery in vegetation-free areas, due to sudden colour and/or texture change between features and light shadowing due to steep incision slope (e.g. Figure 5e,d) Can be mis-interpreted and/or difficult to identify from remote sensing when fluvial incision is not sufficient to appear on DEM (<20-30 m). Possible confusion (although unlikely) with landslide/rockslide or tectonic scarps.
Marks location and patterns of fluvial incision into deposits. If located across outwash plains, they mark different regimes of meltwater flux and sediment loading, which can sometimes serve as a proxy for glacial advances / stillstands.

Possible GLOF deposits
Fan-shaped, sub-aerial deposit prograding from the mouth of a tributary valley and demonstrating fluvial sorting, but displaying large (b axis >1 m) imbricated boulders and braided surface channels wider than modern runnoff allows. Such features can also be associated with large breaches in terminal moraines damming nested lakes.
Characteristics and sedimentology of unique feature identified as such were discussed on the field. (see paragraph 4.3.4.). Smooth terrace characteristics and post-deposition incision of feature are discernible from DEM. Fan shape and wide surface channels can be distinguished from imagery.
Although mapped seperately, the one deposit mapped as such requires a more specific and detailed geomorphological and sedimentological investigation to produce a more confident interpretation. There is potential for mis-interpretation here.
Indicate former high-magnitude, sudden flood event mobilising substantial quantities of till material.

Unmapped
Palaeo-shorelines Very linear, continuous, undulating and smooth outline of sediment, characterised by a mono elevation-interaction with topography. Sometimes easy to discern from imagery when numerous, parallel ridges can be observed following contour lines over tens of kilometres.
Only visible from high-resolution imagery due to lack of positive relief. Appear as gently curving lines spread across slopes at single elevations and alternating in colour between light and dark brown (in vegetation-free areas), particularly discernible when numerous shorelines run parallell to each other ( Figure 7a).
If one isolated, discontinuous feature is identified, there is potential for confusion with a low-relief moraine ridge or other linear features such as an esker (although not so likely).
Mark former lake surface level. In the case of an ice-dammed lacustrine system, it can also indicate the lowest elevation of a usable drainage spillway.

Unmapped
Raised deltas Fan-shaped feature of fluvially deposited sands and gravel, deposited near tributary valley mouths, with similar properties to alluvial fans. However a raised delta is nested on modern valley slopes and unused by modern hydrology (often incised post-depositionally). It's prograding slope does not reach the valley floor: but instead an elevation matching observed palaeoshorelines, in some cases.
Can be identified from DEM due to homogeneous and smooth surface prograding towards valley floors and further incised by modern river channel. Fanshaped and often lighter and different in texture than surrounding terrain. For vegetation-free cases, braided surface palaeochannels typical of alluvial fans can be distinguished.
Although features mapped as such were checked to match elevation of mapped and field-verified palaeo-shorelines, there is possibility of confusion (although unlikely) with ice-dammed proglacial outwash deposits from tributary glacier meltwater. If sedimentology wasn't verified on the field: such alluvial deposits could also be related to former GLOF deposits occuring during proglacial lake residence.
Can further designate former lake level. Unmapped

Glaciolacustrine deposits
Deposit accumulations are characterised by distinctive white and light grey colouration on imagery. Easily eroded due to unconsolidated fine nature of sediments leading to distinct incision patterns and sharp crests.
Best visible in flat basins from imagery due to lack of positive relief. However DEM can reveal deeply incised exposures forming steep gorges through dark/light shadowing. Light grey to white in colour on DG imagery, their texture is distinct from surrounding terrain. (Figure 7g).
True extent of the sediment accumculations is easily underestimated from imagery. Field investigation is required to reduce such uncertainty.
Demonstrates existence and extent of former proglacial lake system.

Unmapped
Glacial lineations Highly linear, parallel and relatively narrow landforms with length-to-width ratios of approximately 10:1 and aligned to former interpreted ice flow.  (Figure 8a,b).
instead related to tectonics, geological structural properties, slope failures or other geomorphic processes.
flutes for instance) or erosional (in the case of streamlined bedrock).
Drumlinoid forms Depositional linear hills characterised by oval to ellipsoidal shapes, significant positive relief (>10 m), and which are aligned to former interpreted ice flow.
Visible either on DEM (if prominent enough) or imagery. Features appear dark grey to brown in colour and display dark/light shadowing due to significant positive relief. They are non-undulating (linear) and oval/ ellipsoidal in shape ( Figure 4).
May be challenging to identify limits of feature for relatively old deposits (pre-LGM) and can be confused with sediment flutes (lineations). Identification bias due to former ice-flow knowledge is possible.
Marks former areas of relatively thick, fast flowing ice on low-gradient glaciogenic sediment surfaces.

Unmapped
Ice-moulded bedrock Prominent bedrock outcrops ranging from 20 m to 1 km in width, displaying significant positief relief (>30 m) and located in areas of warm-based ice-flow (with high concentrations of lineations).
Large outcrops visible from DEM due to significant positive relief. Steep side-walls generate light shadowing on imagery. The light-to-dark grey and sometimes brown colour of exposed surfaces is often different than adjacent terrain, especially in more vegetated areas. Exposed surfaces display an irregular, rough texture ( Figure 8d).
Possible confusion of small features with human infrastructure, although very unlikely given remoteness of field site. Computed using DEM (AW3D30). Geolocation uncertainties associated with DEM accuracy. Tarolli and Mudd (2019) report 90% linear errors to vary between 5 and 10 metres with a positive correlation to slope gradients for this dataset.
Current position of drainage divide indicates the effect and magnitude of subglacial erosion and valley over-deepening during cycles of Quaternary glaciations. It can also inform on the potential location of Atlanticward spillways of former ice-dammed lake systems following ice retreat into overdeepened basins.

Unmapped
Boglands Accumulation of surface water and thus vegetation in areas of low surface gradients.
Appear as light to dark green areas composed of numerous small creeks / channels and/or small lakes, they are characterised by little to no positive relief (e.g. Figure 3).
When relying on imagery, natural bogland formation can be sometimes confused with anthropogenic irrigation of fields and agricultural practice.
Extensive bogland surfaces in arid steppe landscape can sometimes indicate former lacustrine and/or fluvial sediment deposition: as vegetation favours fine sediments. Can also indicate patterns of former meltwater pathways exploited by modern hydrology.

Rotational slump and landslides
Bowl-shaped area of a slope demonstrating a depression with steep upper break in slope (crown scarp), highlighting the exposed part of the steeper failure surface, and numerous parallel (transverse) scarps or fissures accumulated below.
Large features can be distinguished from DEM due to steep upper break in slope displaying dark/light shadowing. Transverse failure fissures and ridges located below the crown scarp are best identified on high-resolution imagery.
Possible confusion with large rock-slope failures in heavily vegetated zones. Transverse ridges or fissures enabling identification of slump can be confused with moraine or hummocky ridges, thus requiring field verification.
Demonstrates slope instability and large-scale mass wasting event; common in former paraglacial environments due to combination of glacial debuttressing and atmospheric exposure of unconsolidated, unsorted and non-vegetated sediments. events, with the innermost preserved moraines suggested to relate to the local LGM. However, the ages of Río Corcovado, Río Huemul and Lago Palena/General Vintter deposits were inferred solely from morpho-stratigraphic observations and comparisons with other dated Patagonian records (e.g. the Lago Buenos Aires record, 46.5°S), with numerical dating yet to be applied. Here, we thus undertake the first detailed mapping of the complex glacial sediment-landform assemblages preserved in the three valleys. This work will serve as a geomorphological framework for new geochronological reconstructions in progress.

Remote sensing
Initial identification of major landforms and topographic features was conducted using the ALOS WORLD 3D -30 m resolution (AW3D30) Digital Elevation Model (DEM) (version 2.2; https://www. Eorc.jaxa.jp/ALOS/en/aw3d30/) ( Figure 2). Hillshade backgrounds of different azimuths were produced using ArcGIS (v10.5), along with topographic contour lines. When displaying significant positive relief (>15 m), cross-section elevation profile graphs were generated to further distinguish major landforms according to their morphometry. All mapped landforms were digitised manually in the WGS84 geographic reference coordinate system using the ESRI TM World Imagery layer, characterised by 1.0 m resolution images from DigitalGlobe (GeoEye, IKO-NOS, 2000 at the study site. To increase landform identification potential, three-dimensional views of this imagery layer were produced in the 'Windows Maps' application (Microsoft Corporation). In areas with high vegetation cover, different colour-rendering comparisons were made using 10 m resolution Sentinel 2A true colour (TCI) and false colour (

Field mapping
Field mapping was conducted over the austral summers of 2018 (Lago Palena/General Vintter only), 2019 and 2020 (all three valleys). Fieldwork focussed primarily on ground-truthing and/or corrections of preliminary landform interpretations, with additional geomorphological mapping undertaken in key accessible locations (Chandler et al., 2018). To aid understanding of landform genesis, landform sedimentology was also analysed where possible.

Glacial geomorphology
The glacial geomorphology in the study area records the terminus positions of the Río Corcovado, Río Huemul and Lago Palena/General Vintter outlet glaciers over multiple glacial cycles. Glacial depositional and erosional features thus heavily dominate the three valleys' geomorphological records. Our mapping reveals twenty-five landform types, classified and manually digitised as polyline and polygon shapefiles (Table 1). These comprise seventeen glacial geomorphological landform types, including a variety of ice-contact glaciogenic landforms (e.g. moraines, hummocks), glaciofluvial (e.g. outwash plains, meltwater channels), glaciolacustrine landforms (e.g. palaeo-shorelines, raised deltas) and subglacial landforms (e.g. ice-moulded bedrock, lineations). Identification criteria for these seventeen landforms are described below, and uncertainty assessments related to landform identification are summarised in Table 1. The map also features six geomorphological features providing wider geographical context, including empty cirques, alluvial fans, rotational slumps or landslides, and modern hydrological features (e.g. rivers, lakes etc.). Furthermore, a polyline delineates the contemporary Atlantic-Pacific drainage divide, extrapolated from the DEM (Figure 2).

Moraine complexes and kettle-kame topography
We differentiate here between two types of ice-contact glaciogenic sediment composites. Relatively confined, narrow (<3 km wide) and easily discernible sediment complexes of arcuate shape comprising prominent and continuous moraine ridges (Section 4.2.2), as well as concentrated, hummocky ridges in parallel to each other (Section 4.2.3), are here termed moraine complexes ( Figure 3). In contrast, large (>3 km) deposits composed of chaotic hummocks (or kames) irregularly interspersed with hollows and kettle holes, presenting few moraine ridges and low concentrations of hummocky ridges, are here defined as kettle-kame topography (Darvill et al., 2014; Figure 4). Although both composites essentially highlight former glacier margins, we feel that it is important to distinguish between their dissimilar morphologies to highlight possible variability in former ice-marginal environments (e.g. Benn & Clapperton, 2000;Darvill et al., 2014;Raedeke, 1978). In contrast to well-defined moraine complexes diagnostic of the less extensive, younger deposits (Figure 3), the most distal deposits discernible from imagery and in the field in the Río Huemul valley consist of a large belt of kettle-kame topography, previously termed the 'Tecka drift' (Haller et al., 2003;Lapido, 1990; Martínez et al., 2011) ( Figure 4). Consequently, differentiating between distinct glaciogenic sediment compounds morphologies in our mapping can prove useful when producing subsequent geomorphological interpretations of local palaeoglaciological behaviour (Darvill et al., 2014).

Moraine ridges
The eastern sector of the mapped area exhibits numerous well-preserved landforms identified as linear-to arcuate-shaped, steep-sided (20°-40°) ridges displaying positive relief (5-45 m), a clear break-of-slope, and sharp undulating crests. Such features were interpreted as moraine ridges (Benn & Evans, 2014) delineating former lateral and terminal ice-front margins; the moraine crests were mapped as polylines. Moraine ridges in the field can occur as well-preserved, cross-valley continuous ridges outlining former latero-terminal ice margins over several kilometres ( Figure 5). However, they can also occur as fragmented, discontinuous and shorter ridges (a few hundred metres in length), clustered alongside multiple, smaller hummocky features. Well-preserved, prominent and continuous moraine ridges can be discerned from the DEM due to their significant positive relief and arcuate shape ( Figure 2). Such moraine ridges are characteristic of the innermost moraine sequences of the Río Corcovado, Río Huemul and Lago Palena/General Vintter valleys, which are likely associated with the local LGM (Lapido, 1990;Martínez et al., 2011;Figure 5a,c). The older, more distal moraine complexes are morphologically distinct and characterised by wider, more subdued and broad-crested ridges. They also display lower slope gradients, making them more challenging to distinguish and map from imagery. In such older environments, identifying ice limits can be problematic, and often requires the adjacent detection of other proglacial deposits such as kettle holes, meltwater channels and proglacial outwash plains, which on the Argentine forelands tend to remain better preserved than moraine ridges due to lower erosion and mass-wasting potential (Dunai, 2010;Hein et al., 2009Hein et al., , 2011. Thus, fewer prominent, continuous moraine ridges could be mapped for the older, most extensive moraine complexes of the study site.

Hummocks and hummocky ridges
Throughout the three valleys mapped in this study, we find an abundance of rounded to sub-rounded mounds of glaciogenic sediments, often termed hummocks in glacial geomorphology (Benn & Evans, 2014). When hummocks are arranged in short (<300 m wide) ridges of limited relief (<30 m), they are often described as hummocky ridges/moraines (Darvill et al., 2014;Eyles et al., 1999). Hummocky ridges were mapped as polylines along identified crestlines while distinct hummocks were mapped as polygons. These features are widespread throughout our study site and occur as; (1) isolated features in kettle-kame topography, where their linearity often originates from supraglacial or ice-contact glaciofluvial deposition (Darvill et al., 2014), or (2) ridges observed in latero-terminal moraine complexes, clustered in parallel successions orientated perpendicular to ice flow, sometimes alongside prominent moraine ridges (Figure 5e). In this latter case, hummocky ridges are likely to represent discontinuous recessional moraines, eroded and diminished by meltwater runoff  (Clapperton et al., 1995;Eyles et al., 1999). On the other hand; abundant, highly concentrated, parallel-and perpendicular-to-ice-flow hummocky ridges can indicate a relatively stable ice margin, such as observed within the well-defined younger terminal moraine complexes located in the Río Corcovado valley, to the southeast of the Arroyo El Fango headwaters (Figure 3a,b).

Kettle holes
In both moraine complexes and kettle-kame topography of the Río Corcovado, Río Huemul and Lago Palena/ General Vintter valleys, numerous examples of circular to semi-circular hollows and dry pits of shallow depth (<20 m) can be observed chaotically dispersed within hummocky terrain. We interpreted these features as kettle holes, which are landforms commonly associated with slowly retreating or stagnant glacier fronts (Evans & Orton, 2015;Price, 1969;Russell et al., 2006). Kettle holes are typically formed through burial of ice blocks by till and glaciofluvial sediments, leading to the formation of enclosed rounded depressions near the icemargin as the ice block subsequently melts (Benn et al., 2007;Knight, 2011). Figure 4 depicts a complex of kettle holes distributed across kettle-kame topography within the southeastern latero-terminal margin of the former Río Huemul glacier (43°40 ′ S; 70°55 ′ W).

Proglacial outwash plains
Glaciofluvial outwash plains are characterised by broad, low-gradient surfaces composed of fluviallyrounded sands and gravels (Alloway et al., 2018;Darvill et al., 2015;Denton et al., 1999;Evans & Orton, 2015;Hein et al., 2009). They often occur adjacent and downvalley to latero-frontal moraine systems and are sometimes associated with the presence of palaeo-meltwater channels (Coronato et al., 2013;Darvill et al., 2014). In the Río Corcovado, Río Huemul and Lago Palena/General Vintter valleys, numerous well-preserved outwash plains prograde on the ice-distal sides of moraine complexes and kettle-kame belts, with average slopes of ∼0.5°-1°( Figure 6). The younger outwash plains are often characterised by well-preserved former meltwater channels with clear braiding patterns (Figure 6c,g), while these features are less common for older deposits. At the older margins, the flat nature of outwash plains combined with the arid, windy conditions of the Argentine foreland often enables better preservation levels than their associated moraines (Bentley et al., 2005;Darvill et al., 2015;Hein et al., 2009Hein et al., , 2011Hein et al., , 2017Smedley et al., 2016). Such long-term preservation properties make identifying outwash surfaces a vital component of mapping older ice-marginal environments.

Meltwater channels
Abandoned sinuous channels associated with former ice margins, and formed by larger discharge regimes than contemporary runoff would enable, are common across the glaciofluvial and glaciogenic depositional environments of the Río Corcovado, Río Huemul and Lago Palena/General Vintter valleys (Figure 6a,c,f,g). They were interpreted as former glacial meltwater channels, and commonly occur as concentrated multi-channel systems, braided and etched into the  Haller et al., 2003;Lapido, 1990; located to the east of the Río Huemul valley. This deposit is characterised, unlike moraine complexes, by a chaotic and extensive array of ice-contact glaciogenic mounds such as hummocks and hummocky ridges with low parallelism, interspersed with numerous kettle-holes and large (>30 m wide) former meltwater channels. Such a low-gradient deposit is diagnostic of a stagnant, progressively thinning ice front (dead-ice scenario), and was here mapped as kettle-kame topography. See Figure 2 for location.
surface of glaciofluvial outwash plains, with up to 5-10 m relief. Individual traceable channels vary in length between 100 m and 5 km and between 5 and 250 m in width. In low-gradient, lateral ice-marginal environments, wider palaeo channels (>30 m) can be found isolated within moraine complexes and oriented parallel to lateral moraine ridges and former ice flow. Such channels are abundant within the Río Huemul glacier's latero-terminal kettle-kame topography (Haller et al., 2003;Lapido, 1990; Martínez et al., 2011) ( Figure 5).
In many instances across the field site, such large meltwater channels now act as natural pathways for contemporary, lower discharge drainage systems.

Fluvial incision scarps
Incision scarps are characterised by relatively steep surface gradients (20°-40°), curving basal concavities and sharp convex crests and are locally formed by former or active river incision into till or glaciofluvial terrace deposits. These landforms were mapped as polylines highlighting their upper breaks in slope. The location, concentration and preservation of incision scarps can prove useful when assessing changes in glacial and postglacial fluvial discharge and sediment-load regimes. Identifying such features and their distribution can help to understand the incision and erosion patterns of former glaciogenic deposits and thus help to elucidate the lack of preserved glacial sediment-landform assemblages at a given location . Mapping such features can also facilitate the interpretation of former shifts in proglacial meltwater drainage pathways associated with different glacier front positions (Bentley et al., 2005). Furthermore, mapped scarps constitute useful data for fluvial geomorphologists wishing to investigate former terrace aggradations as indicators of former runoff regimes, sediment loads and local postglacial isostatic response (Moreiras et al., 2017;Olszak, 2011).

Glacial lake outburst flood deposits
At 43°33 ′ S; 71°29 ′ W, 2 km to the southwest of Corcovado, a unique deposit covering an area of ∼2 km 2 was investigated. The landform is a fan-shaped, subaerial deposit prograding from the mouth of a tributary valley to the valley floor of the Río Corcovado valley. Its valley-floor elevation suggests it was deposited after the drainage of the proglacial lake occupying the valley. It is associated with a 500 m-wide breach through lineated subglacial deposits of the Río Corcovado glacier and has been incised into by the narrow (<10 m width) modern tributary river. A road-cut section of the 5 m thick deposit exhibits some evidence of fluvial sediment sorting. However, the deposit comprises a high concentration of large (b axis >1 m) rounded to sub-rounded imbricated boulders of varied lithologies, and exhibits wide (up to 25 m) braided surface channels discernible from imagery. Such characteristics are diagnostic of a sudden, high-magnitude mass-wasting event causing mobilisation of substantial till volumes (Blair, 2002;Russell et al., 2006). The landform was thus interpreted and mapped as a potential glacial lake outburst flood deposit. One possible source of floodwaters could have been waters dammed by ice or glacial deposits at the tributary head, now an empty cirque occupied by a 1200 m 2 lake (43°36 ′ 2 ′′ S; 71°33 ′ 2 ′′ W). Although this deposit requires further geomorphological and sedimentological investigation to produce a confident interpretation, we believe it is pertinent here to distinguish it from other alluvial deposits.

Glaciolacustrine deposits
Numerous examples of extensive laminated glaciolacustrine sediment outcrops were found in the Río Corcovado and Río Huemul valleys along road and river cuttings, particularly in areas located on the ice-proximal side of the innermost moraine complexes, at elevations below 790 m (Figure 7). The glaciolacustrine sediments are characterised by fine, occasionally laminated deposits of clay and silts (cf. Evans, 2014;Henríquez et al., 2017;Rabassa et al., 2000;Thorndycraft et al., 2019) (Figure 7e). On imagery, large sediment accumulations can appear as white and grey-coloured assemblages of heavily incised, fragmentary landforms ( Figure 7g). Indeed, soft and unconsolidated glaciolacustrine deposits are more susceptible to post-depositional erosion than coarser till deposits and other proglacial sediment assemblages (e.g. glaciofluvial sands and gravels), especially in the semi-arid Argentine foreland (Bendle et al., 2017b;Thorndycraft et al., 2019). Such deposits indicate the former presence of substantial proglacial lake bodies following glacier recession. To decrease the potential for misinterpretation, we exclusively mapped glaciolacustrine deposits within flat basins enclosed by conspicuous palaeoshorelines (Figure 7c,h).

Palaeo-shorelines
Platforms demonstrating a gently curving and convex frontal break of slope nested at single elevations and stretching over extensive distances (sometimes tens of kilometres) were interpreted as former notched proglacial lake shorelines Hein et al., 2010;Sissons, 1978) (Figure 7d,f). Such erosional features can be discriminated from continuous moraine ridges through a lack of positive relief, a lower degree of sinuosity, and their occurrence at continuous elevations over great distances. Moreover, lake level fluctuations often lead to several palaeo-shorelines running parallel to each other and to topographic contour lines, which were used additionally to aid feature identification (Figure 7a

Raised deltas
The mapped region features several fan-shaped, smooth terrace surfaces gently sloping towards valley floors, yet nested distinctively above the valley floors. These deposits are composed of well-sorted, rounded sands and gravels indicating fluvial deposition near the mouths of tributary valleys. After matching the elevations of such features with abandoned palaeoshorelines, we interpreted these terraces as raised lacustrine deltas formed by tributary rivers flowing into former proglacial lake systems (Bendle et al., 2017a(Bendle et al., , 2017bGlasser et al., 2016). Raised deltas can serve as additional geomorphological evidence of former glaciolacustrine systems and help to identify their former surface elevations. For instance, a well-preserved raised delta can be discerned on the western flank of the Río Corcovado trough, perched on the southern edge of the Río Poncho Moro valley mouth (43°40 ′ 5 ′′ S; 71°2 5 ′ 4 ′′ W). This landform sits at a similar elevation than the prominent 680 m palaeo-shoreline discerned within the valley. Large raised deltas like this specific example can be strong indicators of relatively stable proglacial lake systems (Bendle et al., 2017a;Hein et al., 2010;Turner et al., 2005).

Subglacial landforms
4.5.1. Glacial lineations, flutings, drumlinoid forms and ice-moulded bedrock We identified linear, parallel and relatively narrow landforms displaying positive relief with length-towidth ratios of ∼10:1 (Figure 8). Such features are  common in areas of assumed greater former ice-thicknesses, where warm-based, fast-flowing ice could generate either substantial subglacial bedrock erosion, or deposition and/or re-arrangement of glaciogenic sediment along flow lines (Bingham et al., 2017;Clark et al., 2018;Darvill et al., 2014Darvill et al., , 2017Smith et al., 2008). The latter case can lead to the formation of sediment flutes (<10 m in height, Figure 8a-c). Depositional lineations characterised by oval to ellipsoidal shapes and significant positive relief (>10 m) were interpreted and mapped as drumlinoid forms (Knight, 1997;Spagnolo et al., 2012). In the mapped regions, prominent bedrock outcrops ranging from 20 m to 1 km in width often demonstrate large-scale streamlining (Davies et al., 2020; Figure 8d,e). Individual outcrops displaying such properties were interpreted and mapped as ice-moulded bedrock. The regional distribution and orientation of subglacial lineations including sediment flutes, drumlinoid features and ice-moulded bedrock outcrops are useful indicators of former ice-flow direction (Bentley et al., 2005;Boulton & Clark, 1990). For instance, at our field site, they enable asserting the former convergence of the Río Corcovado and Río Huemul outlets (Figure 8a-c).

Summary and conclusions
Our map illustrates the sediment-landform assemblages formed by the Quaternary fluctuations of three outlet glaciers in the northeastern sector of the former Patagonian Ice Sheet, the Río Corcovado, Río Huemul and Lago Palena/General Vintter outlet glaciers. This map builds on previous local geological (Haller et al., 2003) and broad-scale glacial geomorphological mapping (Caldenius, 1932;Davies et al., 2020; to deliver the first detailed glacial geomorphological map of these valley systems. The mapped landforms incorporate wellestablished glacial geomorphological features of four major depositional and erosional domains: (1) icecontact glaciogenic landforms (moraine ridges, hummocks, hummocky ridges, kettle holes, moraine complexes and kettle-kame topography) highlighting the former expansion of outlet glaciers into the Argentine foreland; (2) glaciofluvial landforms (proglacial outwash plains, meltwater channels, fluvial incision scarps, potential glacial lake outburst flood deposits) providing detailed geolocation of former meltwater drainage pathways; (3) glaciolacustrine landforms (palaeo-shorelines, raised deltas and glaciolacustrine deposits) indicating the past formation of icedammed proglacial lakes following glacier retreat; and (4) subglacial landforms (ice moulded bedrock, glacial lineations and drumlinoid forms) diagnostic of ice-flow direction and glacier basal conditions. This map will underpin geomorphological and geochronological investigations aimed at reconstructing the former behaviour of the Río Corcovado, Río Huemul and Lago Palena/General Vintter outlet glaciers during Quaternary glacial cycles. It will also represent an essential geographical dataset for investigations aiming to reconstruct former glaciolacustrine systems as well as major shifts in fluvial drainage pathways during and following local glaciations. Finally, this map provides local empirical boundaries that could be used for high-resolution glacial or ice sheet-scale numerical modelling investigations.

Software
Geomorphological mapping through polyline and polygon shapefile digitisation was conducted using ArcGIS 10.6 software. Final map and figure editing was produced using Adobe Illustrator CC 2020 and Inkscape 0.92.4.

Geolocation information
The study area presented within this map is located between these coordinates:

Open Scholarship
This article has earned the Center for Open Science badges for Open Data and Open Materials through Open Practices Disclosure. The data and materials are openly accessible at 10.17632/c2hy8rkbyd.1 and 10.17632/c2hy8rkbyd.1.

Disclosure statement
No potential conflict of interest was reported by the authors.

Map Shapefiles
The data produced for this map are freely available online, as long as original publication is cited when used and/or referred to. This includes twenty-six shapefiles (.shp) necessary for visualising and analysing the data on a geographical information system such as ArcGIS software. The data are deposited in a Mendeley Data online repository, accessible using this DOI:https:// data.mendeley.com/datasets/c2hy8rkbyd/1.