Glacier dynamics during a phase of Late Quaternary warming in Patagonia reconstructed from sediment-landform associations

Article history: Received 28 November 2018 Received in revised form 4 March 2019 Accepted 4 March 2019 Available online 01 April 2019 The geomorphological record in glaciated landscapes can provide important information for the study of the response of glaciers to rapid climate change. This study presents a new reconstruction of the glacial history of the northern Monte San Lorenzo ice cap, southern South America, during a period of accelerated warming and deglaciation following the Antarctic Cold Reversal (14.5–12.8 ka). We present a detailed geomorphological map of the valleys to the north of Monte San Lorenzo. Sediment-landform assemblages identified include lateral and terminalmoraine ridges, flutes, deltas, ice-contact fans, palaeoshorelines, kame terraces and outwash plains. Wemap 14primary ice-limits, 7 ofwhich are newly identified, and 7 ofwhich are fromprevious studies,mapped here in greater detail. We devise landsystem models to formalise and document spatial and temporal changes in glacial processes and environments. Our new geomorphological mapping and landsystem reconstructions provide an important insight into the response of temperate Patagonian glaciers to rapidly-warming climate. © 2019 Published by Elsevier B.V.


Introduction
Atmospheric cooling during the Antarctic Cold Reversal (ACR, 14.5-12.8 ka) resulted in glacier readvance in the Southern Hemisphere midlatitudes as shown by cosmogenic nuclide dating from moraine systems in Patagonia (García et al., 2012;Nimick et al., 2016;Darvill et al., 2017;Davies et al., 2018;Sagredo et al., 2018) and New Zealand (Putnam et al., 2010). In central Patagonia, the outlet glaciers of the Northern Patagonia Icefield had receded back to the valleys of the Andean Cordillera by the time of the ACR readvance and many were terminating in large proglacial lakes (Davies et al., 2018;Thorndycraft et al., 2019). Antarctic ice core records, such as the WAIS Divide, show that the ACR in the Southern Hemisphere high latitudes was followed by ca. 4000 years of warming from ca. 13.0-9.0 ka, with rapid warming of 2°C between ca. 13.0 and 12.0 ka (Buizert et al., 2015). The geomorphic setting and evolution of Patagonian valley glaciers during post-ACR warming make them an interesting analogue for understanding present-day glacial dynamics in rapidly-warming, temperate climatic settings. During this period and the subsequent Holocene, glacier recession and punctuated readvances left behind discrete geomorphological features, revealing past glaciolacustrine, fjord-terminating and land-terminating glacier landsystems (Glasser et al., 2009;Davies et al., 2018). Little work has been done to investigate the evolution and interaction of these landsystems, in particular those associated with the smaller ice caps located in the Cordillera east of the Patagonian icefields (72-73°W). These localities provide opportunities for elucidating the roles of climatic, topographic and glaciolacustrine controls on the evolution of late Quaternary glaciated valleys found in Patagonia (Glasser et al., 2009). Morphological and sedimentological data from low-altitude, shallowly-sloping, steep-sided interlinked valleys, are currently limited and furthermore subsequent paraglacial modification has also received little attention in Patagonia.
Herein we establish sediment-landform assemblages and use a landsystems framework to examine the sedimentology and geomorphology of landforms in valleys to the north of the Monte San Lorenzo ice cap in Chile, formed during a period of overall atmospheric warming. These valleys represent contrasting styles of landsystems, including glaciolacustrine, land-terminating and glaciofluvial, but with significant paraglacial modification, and juxtaposed with small-scale mountain glaciers. Comparing these different landsystems will provide a template for understanding the roles different processes play in landscape evolution and modification in Patagonia. We aim to elucidate the nature and relative timing of changes in glacial environments, dynamics and processes since the ACR in order to assess the role of topography and ice-dammed lakes on palaeoglacier dynamics. Our objectives are: 1) to determine sediment-landform assemblages across a spectrum of palaeoglacial and glacial environments; 2) generate landsystems' models explaining the processes of sediment-landform generation in central Patagonia; and 3) elucidate the influence of ice-dammed lakes and other controls on palaeoglacier dynamics.

Study area
Monte San Lorenzo (47°35′S, 72°18′W) is an isolated granodioritic to granitic massif (Ramos et al., 1982) on the eastern flank of the Andean range, located ca. 70 km east of the southern point of the Northern Patagonian Icefield (NPI) (Fig. 1). It experiences a temperate climate with mean annual air temperature of 8.4°C and average annual precipitation of 750 mm w.e. (Direccion Meteologica de Chile, 2001) recorded at the nearest meteorological station in the town of Cochrane 40 km to the north (47°14′S, 72°33′W; 182 m asl).
At the LGM, ice from glaciers on the western and northern flanks of Monte San Lorenzo discharged into the Salto and Tranquilo valleys, coalescing with the Cochrane/Pueyrredón (CP) outlet lobe from the NPI (Wenzens, 2002). The CP and General Carrera/Buenos Aires (GCBA) outlet lobes reached the Argentinian lowlands (Fig. 1B) forming large moraine sequences (Caldenius, 1932;Mercer, 1976;Douglass et al., 2006;Hein et al., 2010;Bendle et al., 2017a;Mendelova et al., 2017). Upon ice recession, large ice-dammed lakes formed in the Lago GCBA and Lago CP valleys, draining to the Atlantic (Turner et al., 2005;Bell, 2008;García et al., 2014). Subsequent punctuated drops in lake level occurred as lower elevation drainage pathways opened and drainage switched to the Pacific (Turner et al., 2005;Bell, 2008Bell, , 2009Hein et al., 2010;Bourgois et al., 2016;Glasser et al., 2016;Davies et al., 2018;Thorndycraft et al., 2019). During this period, the large unified palaeolake "Lago Chelenko" occupied the Cochrane and Lago GCBA valleys at 340-350 m asl, dammed by Pared Norte Glacier to the east (Davies et al., 2018;Thorndycraft et al., 2019). Ice discharging from Monte San Lorenzo and the eastern Barrancos Mountains contributed to large glaciers in the Salto and Tranquilo valleys (Davies et al., 2018). Ice in the Salto valley coalesced to terminate in Lago Chelenko, forming the ACR Esmeralda moraines at 13.2 ± 0.2 ka (Davies et al., 2018;Thorndycraft et al., 2019) (this and dates that follow are recalculated as per protocols in Section 3). Recession of ice formed a series of inset moraines, including the "Moraine Mounds" (Fig. 1) dated to ca. 12.3 ± 0.4 ka (Glasser et al., 2012). A radiocarbon date below the H1 tephra layer at the Tranquilo-Salto confluence (Gardeweg and Sellés, 2013) is recalculated to 10.5 ± 0.1 cal ka BP providing a minimum age for ice-free conditions at the Tranquilo-Salto confluence. The H1 tephra has been found in bog cores in the Tranquilo and upper Tranquilo valleys with an average age across localities of 7.9 cal ka BP (Stern et al., 2016) (Fig. 1).
In the upper Tranquilo valley, Tranquilo Glacier formed moraines prior to the ACR with a maximum age limit of 19.1 ± 0.8 ka. A cluster of moraines in the upper Tranquilo valley also date to the ACR at 13.8 ± 0.1 ka (Sagredo et al., 2018). Subsequent moraine sets in the upper Tranquilo valley have been dated to between 13.5 and 13.2 ka, and 12.0 ± 0.3 ka (Sagredo et al., 2018). Finally, a mid-Holocene moraine in the upper Tranquilo valley is dated to 5.6 ± 0.1 ka (Sagredo et al., 2018).
Today, small-scale glaciers occupy high ground on Cordon Esmeralda (Fig. 1). Monte San Lorenzo supports a small ice cap with an area of ca. 139 km 2 , with the largest outlet glacier, Calluqueo Glacier, descending down to 520 m asl (Falaschi et al., 2013). There is asymmetry in the snowline attributed to regional precipitation gradients: 1700-1750 m asl in the wetter western sectors and 1800 m asl in the drier eastern sectors (Falaschi et al., 2013). The glacial, glaciolacustrine, glaciofluvial and paraglacial landforms and deposits in the Salto, Tranquilo and Pedregoso valleys formed through the late Pleistocene and Holocene make up the basis for our sediment-landform study.

Methods
The Salto, Tranquilo and Pedregoso valleys were mapped and digitised in ArcMap 10.3 at 1:5000 scale using 1 m resolution DigitalGlobe imagery, part of the Esri™ World Imagery. Google Earth Pro (DigitalGlobe imagery) was used in conjunction to this, alongside Google Earth's digital elevation model to view landforms from an oblique perspective, aiding identification. Additional elevation data were taken from an ASTER G-DEM (20 m vertical and 30 m horizontal resolution, 95% confidence; cf. ASTER GDEM Validation Team, 2011). Field mapping (Nov-Dec 2016 and Dec 2017) was used to ground-truth remotely sensed mapping and improve landform identification and mapping detail. Roadside cuttings along the Salto and Tranquilo valleys provided sediment exposures for landforms. Landforms in the field were mapped using handheld GPS with a documented accuracy of ±10 m.
Well established criteria for landform identification, both by remote sensing and in the field, were used Bendle et al., 2017b;Darvill et al., 2017;Chandler et al., 2018) and adapted to account for the specific characteristics of landforms found in the study area (Table 1). Moraine ridges were grouped into 'sets' based upon their relative position within a valley to delineate a period of ice-marginal stability. Frontal and lateral moraines which could be traced to one another, or lateral moraines at the same altitude on opposite valley sides, were grouped into the same set. We group landforms into 5 sediment-landform associations that we outline in Sections 4.2 to 4.6: ice-marginal, subglacial, glaciolacustrine, glaciofluvial and paraglacial.
Sedimentological and stratigraphical studies were undertaken at exposures through landforms (road cuttings and quarry sites) along the Salto and Tranquilo valleys using standard procedures (Evans and Benn, 2004). Clast morphology data (shape and roundness) were collected from representative facies, following Benn (2004), to investigate transportation and erosion histories. Shape data were plotted on a general shape ternary diagram (Sneed and Folk, 1958;Benn and Ballantyne, 1993) and from this C 40 indices (Benn and Ballantyne, 1993) were calculated. Roundness data were plotted as histograms and analysed statistically using RA and RWR indices (Evans and Benn, 2004). We use RWR indices alongside RA to mitigate for the influence of glaciofluvial reworking on the effectiveness of the RA index to distinguish transport pathways Lukas et al., 2013). Cosmogenic nuclide surface exposure ages were recalculated ( Fig. 1) using version 3 of the online exposure age calculator formerly known as the CRONUS-Earth online exposure age calculator (Balco et al., 2008) with a regional Patagonian production rate calculated from the Kaplan et al. (2011) calibration data set. Ages presented assume a 0 mm/kyr erosion rate, use the time dependent Lm scaling method (Lal, 1991;Stone, 2000) and are calculated as uncertainty weighted means (UWM) of multiple samples taken over single moraine ridges/contemporaneous sets, rounded to the nearest 0.1 ka.

Landform inventory of the northern Monte San Lorenzo sector
Combining remote sensing and field mapping, including within forested areas, has allowed us to map in greater detail the landforms of the study area. Subsequently we have identified previously unmapped landforms and increased the extent and detail of those mapped in previous studies in this region that have relied on satellite imagery Jansson, 2005, 2008;Turner et al., 2005;Glasser et al., 2009Glasser et al., , 2012Bendle et al., 2017b;Davies et al., 2018). The landform inventory for the northern Monte San Lorenzo sector contains 19 primary landform types (Fig. 2) which includes 1083 individual moraine ridges mapped alongside rivers, lakes, outcropping bedrock and bedrock  Table 1 Landform identification criteria used in this study, after , Bendle et al. (2017b), Darvill et al. (2017), andChandler et al. (2018).

Landform
Morphology ID criteria from imagery ID criteria in field Uncertainties Significance Visible as extensive area of sloping, uniform terrain.
May be difficult to identify on a low-resolution DEM if change in elevation across slope is small.
Marks terminal position of ice margin.
Morainal bank Wedge shaped positive topography over a km scale with one very gently-sloping ice-proximal side and one more steeply-sloping ice-distal side, separated by a crest marked by horse-shoe shaped crescentic scars.
Extensive area of well-vegetated, uniform texture. May show sinuous, linked palaeochannels.
Visible as extensive area of very gently-sloping, uniform vegetated terrain.
May not be obvious in field if well-vegetated and due to the very gently-sloping surface.
Marks terminal position of ice margin. May indicate subaqueous deposition and lacustrine glacier termination.
Kettle hole Rounded depression within area of morainic or glaciofluvial material (e.g. kame terrace).
Often filled with water but can also be dried. May be vegetated. Contrast in colour from surrounding terrain. Rounded form, associated with morainic complexes or glaciofluvial deposits.
Rounded depression visible from a position of higher topography. May be able to walk into depression if not filled with water.
More obvious from satellite imagery. Can be confused with small lakes formed in bedrock or non-ice related depressions.
Indicates previously-glaciated area and area of deposition of morainic or glaciofluvial material.

Subglacial
Ice-scoured bedrock Areas of bare or sparsely-vegetated bedrock with visible inherent structures.
Dark brown to grey to pink. Rough and irregular surface texture with visible joints, faults and fractures, distinctive from neighbouring sediment cover.
Rough texture and inherent structures evident. Distinctive in colour. Spatially extensive. Not practical to map in detail in the field.
May be difficult to distinguish from areas of thin/sparse sediment cover over bedrock, where boundary is gradational.
Shows areas of extensive ice at its pressure melting point.

Glacial diamicton
Gently-mounded material deposited on bedrock, ranging in extent, often on valley sides.
Yellow/pale brown in colour, with smooth texture in contrast to often neighbouring rough bedrock. Can be found in association with small channel gorges with clear breaks in slope. Often vegetated.
Where accessible and exposed (e.g. road cuttings) material can be identified as diamicton. Often difficult to identify due to inaccessibility and/or vegetation cover.
May be difficult to distinguish where cover is thin and boundary with bedrock is unclear Indicates area of glacier deposition.

Flutes
Linear, elongated, parallel features formed in sediment Occur in groups, often aligned differently to any inherent bedrock structure. May appear dark and light on opposite sides indicating positive relief. Commonly found in high-mountain areas in this study region, close to glacier cirques, and recently exposed (inside Little Ice Age moraines).
May be visible from distance although best identified from satellite imagery as spatially-extensive and can be partly obscured locally by vegetation or hidden in high-mountain areas.
Potential confusion with bedrock structures or medial moraines. Difficult to identify if short in length.
Indicative of former flow direction of warm-based ice and fast ice flow when laterally-extensive and highly-attenuated.

Glaciolacustrine
Raised deltas Flat-topped, steep-sided surface extending along and out from valley side, above valley floor, at the opening of a ravine. Often found in stepped sequence, incised by a palaeo or active river channel.
Uniform smooth-textured surface, in contrast to often adjoining rough bedrock. Light/dark contrast indicates breaks of slope at former delta front and incised channel.
Levels above the valley floor, in stepped sequence with an incised channel is often clearly visible from distance/opposite side of valley.
May be misidentified as a shoreline or kame terrace due to its planar nature at the valley side.
Height at the delta front at break of slope indicates former lake level.
Ice contact fan Surfaces sloping to the valley floor from a flat/more gently-sloping top surface, the two separated by a slight break in slope.
Uniform smooth-texture surface may be vegetated. Contains sinuous lines of light/dark contrast indicating palaeochannels, which may also be wider and densely-vegetated with light/dark breaks in slope at their edge.
Prominent feature of positive, sloping relief above the valley floor.
Large channels cut into the feature may be visible in the field.
May be misidentified as a raised delta due to its similar sloping morphology, although distinctively lacks a clear valley sediment source (ravine).
Indicates the frontal ice position of a marine or lacustrine-terminating glacier.

Palaeoshorelines
Narrow terrace surface on valley side with break in slope away from the valley side.
Approximate constant-elevation surface locally along valley. Light/dark contrast either side of break in slope. May be contrast in vegetation cover. Distinctive from exposed bedrock.
Often visible in the field as a distinctive flat surface on the valley side elevated above the valley floor.
Especially identifiable when laterally-extensive.
May be misidentified as a kame terrace, although such a feature would be expected to gently slope down valley. Difficult to identify if discontinuous and/or well-vegetated Indicates the former lake level.

Glaciofluvial
Outwash plain Large, gently-sloping flat plain cut by palaeochannels. Grades from former ice limit (e.g. a moraine ridge).
Large, smooth surface, uniform in texture and colour, and in contrast to surrounding topography. Palaeochannels on surface identifiable by light/dark colour change indicating negative relief. Also highlighted by vegetation change.
Extensive, flat, gently-sloping plains are visible in the field. Palaeochannel depressions can also be visible when looking across the plain's surface.
Exact limits of outwash plain may be difficult to distinguish.
Indicates major meltwater outflow pathways.
Fluvial terraces Terraces running extensively along the valley side, extending out into the valley, sloping gently down valley and often stepped, separated by breaks in slope.
Uniformly-textured, vegetated surface. Break in slope is often unvegetated and lighter in colour.
Often occur next to an active river system.
Visible in the field as terraces running extensively along the valley side above the valley floor, with steep scarp slopes visible along their edge.
May be mistaken for kame terraces or shorelines, although are distinctively stepped and may be more laterally extensive away from the valley side.
Indicate the former floodplain of a river and subsequent down cutting. May be indicative of a drop in base level and/or decrease in sediment supply. Palaeochannels Linear channels forming shallow depressions or deeper incisions. May have gently or steeply-sloping slides with scarps. Incised into fluvial, glaciofluvial, or glacial deposits.
Often appear darker than surrounding sediment and preferentially vegetated. May be sinuous, braided and extensive over valley-fill flood and outwash plains.
Visible in field as deep gorges or shallow laterally-extensive channels.
May be mistaken for breaks of slope at edge of outwash plain. Shallow palaeochannels often not visible in satellite imagery and certainly not on widely-available low-resolution DEMs.
Indicative of former path of river/stream flow. Marks position of former lateral or frontal ice-margin and indicates ice thickness. Suggestive of high meltwater discharge and sediment transport.
Boulder bar Elongated, positive relief, valley-floor feature with tapered ends. 100 s m in length.
Uniformly-textured, apparently-flat surface appears speckled with vegetation.
Visible in the field as an isolated, large feature in the valley floor. Boulders present on the surface.
Possible confusion with a point bar.
Often indicative of a large-hydrological-erosion and sediment-transport event, such as a flood. May form as a result of a glacier lake outburst flood in a glaciated region.

Paraglacial
Alluvial fans Sloping fans from valley sides fed by a small river or stream.
Smooth surface, splaying out in fan shape from valley side on to valley floor. Sharp boundary with surrounding topography through change in vegetation cover.
Distinct morphology identifiable from enough distance to provide context within valley. Cobble/gravel texture may be identifiable from distance.
Possible to misidentify as palaeo-delta or ice-contact deposit although unlikely.
Reworking of unconsolidated material by meltwater channels and streams.
Debris slopes Steeply-sloping surface of sediment at the valley side, accumulating and sloping gently at valley floor. Can be laterally-extensive or more locally-confined.
Grey/pale brown in colour depending on composition. Smooth texture, may contain series of cone forms. Largely unvegetated. Common in high-mountain settings above upper vegetation line but also found as shattered bedrock and remobilised moraines in low valleys.
May be visible from valley floor. Texture, colour, morphology and composition clear when visible and/or accessible. Likely to be inaccessible and not visible in high-mountain settings.
Limits of extent in high-mountain areas above upper vegetation line may be difficult to identify.
Floodplain Sediment accumulated in valley floor often cut by a braided river system and found in association with channel bars.
Flat surface in valley floor cut by river system. Densely vegetated in places, often between braided active or palaeochannels.
Visible from valley side and on surface if accessible.
Possible confusion with outwash plain although more densely-vegetated and clearly associated with an established fluvial system.
When abandoned, may indicate area of past paraglacial activity. May contain active glaciofluvial system.

gorges. Mapping of sections of the Upper Tranquilo valley and eastern
Tranquilo valley is in part after Araya et al. (2014). Mapping in the north of the Salto valley is after Davies et al. (2018). Critically, using field mapping to assist mapping from satellite imagery, we have identified 14 primary moraine sets (labelled M1a, M1b and M2 to M13) including 7 newly identified ice margin positions (M5 to 8 and M10 to 12) (Fig. 3). Previously identified sets have been ground-truthed and extended in their mapped extent. The Esmeralda and Brown moraines are labelled M1a and M1b respectively, as the furthest advanced moraine sets in their respective Salto and Tranquilo valleys. Moraines of the same colour are interpreted as forming coevally as part of the same moraine system. The Esmeralda (M1a, cf. Davies et al., 2018) and Brown (M1b) moraines situated at the northern and eastern ends of the Salto and Río Tranquilo valleys respectively are the most substantial frontal moraines. The M1a frontal moraine has been dated to the ACR and formed coevally with the 7.5 km long, valley-parallel lateral moraine component (Davies et al., 2018) (Fig. 3). We speculate that the M1b moraine also formed at this time, due to their similar relative size and position in the Tranquilo valley (Fig. 3). Inset of M1a in the Salto valley are a series of cross-valley, sharp-crested, both arcuate and more straight frontal moraines (M4 to M9) formed sequentially after the ACR, positioned periodically along the eastern valley side stretching south until show RA-C 40 % and RWR-C 40 % plots respectively. Moraine sets, delta, lake sediment and diamicton section sites are labelled M1 to M13, D1 to D4, L1 to L3 and S1 to S2 respectively. the confluence with the Río Tranquilo valley. They are up to 40 m in height above the valley floor and up to 300 m long (Fig. 3). M4 (also known as the "Moraine Mounds", ca. 12.3 ± 0.4 ka cf. Glasser et al., 2012;Davies et al., 2018) and M6 are associated with semi-isolated masses of moraine producing an uneven surface of material on the ridges' ice-proximal side (Figs. 2 and 3). M6, 7, 8, and 9 notably extend perpendicular from terraces on the eastern valley side, only part way across the valley floor, east of the Río Salto (Figs. 2 and 3). The moraine ridges are composed of stratified massive and laminated sands, coarse sub-rounded to sub-angular gravels, and diamictons (e.g., M5: Figs. 3E and 5, M8: Figs. 3I and 6). Multiple sub-rounded to sub-angular, faceted granitic to dioritic boulders, up to 1 m in size, can be found along the ridge crests, strewn over larger areas of associated morainic material and within exposed sections.
Across the study area, clast-shape data taken from moraine sites shows predominantly blocky clasts, with C 40 percentages below 50% (Fig. 3). The moraines in the Salto valley are dominated by subangular to sub-rounded clasts, whilst those in the Tranquilo valley have a largely sub-angular to very-angular form. The M1b moraines consist of a series of discontinuous, sinuous ridges between 60 and 700 m long, arranged in an arcuate form, spanning 2 km across the valley. They occur on a topographic high, ca. 120 m about the valley floor to the east, with a steep ice-contact slope on the western, ice-proximal side, and a more gently-sloping outwash plain on the eastern, ice-distal side.

Lateral moraines
Valley-parallel, lateral moraine ridges in the study region have three primary morphologies. The first are large, laterally-extensive ridges with narrow crests and broadly symmetrical sides ( Fig. 3M1 to M3, Fig. 7A, C to F). The second group consists of smaller, closely-spaced pairs or groups of laterally-discontinuous ridges with broadly equally-dipping sides, dissected by meltwater channels. They are found on topographically-flat bedrock plateaus on the northern flank of Cordon Esmeralda below M1 and at the southern end of the Salto valley (M11 and M12) (Fig. 3). The third are small, discontinuous, ridges up to a meter high and 100 m long, found on the sloping valley side southeast of Lago Esmeralda, between M1 and M4, forming the lateral component of M3 (Fig. 3).
The ACR M1a (Davies et al., 2018), M1b and post ACR M2 ridges are characterised by massive, silty and sandy diamictons and gravels, with numerous faceted granitic and dioritic cobbles and boulders up to 2 m along the a-axis (Figs. 7A, 8). M2 is overtopped by poorly defined units of clast-supported, sandy coarse gravel, and clast-supported silty fine gravel, edge rounded and faceted pebbles. Stones are primarily sub-angular to sub-rounded, blocky and elongated (Fig. 3D).

High-altitude valley moraines
Alongside the moraines in the lower valleys, well-preserved late Holocene lateral and frontal moraines are found close to the present-day Calluqueo glacier margin (Fig. 2), in part damming Calluqueo proglacial lake, and in high altitude cirques in the upper Tranquilo valley and on Cordon Esmeralda. The largest Calluqueo moraine (M13) manifests as a sharp-crested, steep-sided arcuate frontal terminal moraine ridge, ca. 100 m above the valley floor and a broader-crested lateral moraine on the southern side of Lago Calluqueo. Numerous smaller, closely-spaced sinuous elongated parallel ridges are found along the broad lateral moraine ridge at the southwestern end of the lake. They are up to 3 m high with surfaces scattered with numerous lose, angular to subangular granodiorite cobbles and boulders. The small valleys on Cordon Esmeralda also contain numerous well-preserved, densely-spaced terminal ridges close to cirques, between 5 and 20 m apart superimposed over valley-parallel flutings (Fig. 10). In front of these are larger moraine ridges with a classic saw-tooth morphology (cf. Evans et al., 2017).

Meltwater channels
Meltwater channels are found in association with the groups of laterally-discontinuous ridges on the bedrock plateaus on the northern flank of Cordon Esmeralda below M1. The largest is a gently-sloping, approximately-straight channel running the 200 m along the length of the complex, parallel to contemporary contours and the axis of moraine ridges. We interpret this channel as ice-marginal (Greenwood, 2007). There is a notable lack of meltwater channels observed elsewhere.

Ice-scoured bedrock
Isolated areas of ice-scoured bedrock occur along the lower sides of the Esmeralda, Salto and Río Tranquilo valleys, obscured in places by vegetation cover and separated by areas of diamicton plastered on to the valley sides and floor (Fig. 2). It is not found at higher elevations or topographic crests between valleys, where instead bedrock crops out as blocky or sharp-sided exposures. Ice-scoured bedrock is also reported in neighbouring valleys east of the NPI (Glasser et al., 2009;Bendle et al., 2017b;Davies et al., 2018). Bedrock lineations can be identified orientated broadly NE-SW at the confluence of the Salto and Río Tranquilo valleys on a bedrock high set away from the valley side (Fig. 11).

Glacial diamicton
Areas of diamicton can be found plastered along the valley sides and at elevations both above and below ice-scoured bedrock. A flat-topped surface of diamicton is found on the eastern side of the Esmeralda valley on the western flank of Cordon Esmeralda (Figs. 3S1, 9) showing a stonerich, silty diamicton, stratified into a clast-supported layer below a matrix supported layer. Both layers contain boulders up to 30 cm in size. A small section of laminated sands is found at the base of the lower unit. Near the confluence of the Esmeralda and Río Tranquilo valleys (Fig. 3S2), a road cutting reveals a section of sediment plastered onto the side of bedrock. This comprises a silty diamicton, stratified in places, containing faceted boulders and rich in striated, faceted stones and interbedded with a layer of stratified, planer-bedded gravels. These are disrupted by inverted triangular structures of massive gravels. The lower diamicton is dissected by a sub-vertical unit of matrix-supported massive gravel and contains a discontinuous unit of partly-laminated medium sand at its base.

Flutes
In the high-altitude cirque on Cordon Esmeralda elongated parallel flutings 3 m to 7 m wide run along the valley length, found in association with closely-spaced moraine ridges, inset of large saw-tooth moraines (Fig. 10). They are predominantly straight but curve with the profile of the valley. They are not found in the less recently deglaciated lowland Salto, Pedregoso and Tranquilo valleys.

Raised deltas
Large flat-topped, steep-fronted bodies of sediment are found along the length of the Río Tranquilo valley at three main sites: the western end (D1), centre (D2 and D3) and eastern end (D4) of the valley (Figs. 2 and 3). They are found in stepped sequence, incised by active and abandoned river channels at the opening of a ravine. Three primary terrace levels are defined: 600 m asl (at D1), 520 m asl (at D3 and D4) and 425 m asl (at D1, D2 and D3). D1 (Fig. 12) reveals alternating well-defined beds of clast and coarse sand matrix-supported gravels, coarse gravely sands and hyper-concentrated clast-supported cobble beds up to 50 cm in thickness. Clasts are sub-rounded to rounded. These beds dip at 25°west-northwest towards the valley floor and are overtopped and truncated by a coarse, clast-supported, cobble-rich gravel bed. At the northern end of the section, the dipping beds give way to a clast-supported unit of cobbles up to 30 cm in size (Fig. 12B). A section in the D4 delta (Fig. 4) reveals a structure of dipping foresets.

Morainal banks
Next to the steep-sided Esmeralda moraines (M1b) is a distinctlydifferent moraine landform interpreted as a subaqueous morainal bank formed at the ACR (Davies et al., 2018). It is wedge-shaped and dips gently west towards Lago Esmeralda while the eastern flank is much steeper. Exposures show a silty, stone-rich diamictic composition interbedded with sands and gravels (Davies et al., 2018).

Glaciolacustrine sediment
Roadside exposures north of Lago Esmeralda show diamicton overtopped by 2 mm thick silt and clay rhythmites with isolated stones (Figs. 3L1, 13A). Similar facies are found on the eastern side of the Salto valley within the broader M7 moraine complex (Figs. 3L2, 13B). A 3 m high section through the top of a small ridge reveals upward-fining sands overtopped with rhythmites, interbedded with sands at their top, and a stone-rich silty diamicton. The rhythmites contain numerous dropstones with associated deformed and draped laminations. Up a small tributary valley from D2, between two bedrock highs are large roadside exposures of bedded sands and gravels (Fig. 3L3). On the western side is 4 m of well-sorted, bedded, fine sand with occasional gravel dropstones and ripple-cross laminations in places (Fig. 13C). This is  separated by a sharp erosional contact from overlying trough crossbedded, and then massive gravelly sands. These contain inclusions of planar laminated fine sands. On the eastern side of the tributary valley, and ca. 70 m below the western site, is a 6 m high exposure of well sorted sands with draped ripple cross-laminations and massive sand beds (Fig. 13D).

Palaeoshorelines
Inside the Esmeralda moraines, palaeoshorelines are carved into valley-side diamicton in the northern Salto valley on the eastern side of the Juncal Massif, on the southern side of Cerro Ataud and southeast of Lago Esmeralda (Davies et al., 2018). The palaeoshorelines form of gently-dipping platforms with scarp slopes on the valley floor side, running flat or shallowly-dipping in long profile.

Outwash plains
A palaeo-outwash plain of glaciofluvial sands and gravels is located east of the M1b moraines sloping gently down towards and terminating at Lago Brown (Fig. 2). The surface is covered by cross-cutting sinuous palaeochannels. Narrow valley constrained outwash, or 'valley trains', cover the entire floor of the southern section of the Pedregoso valley and contain active braided river channels.

Fluvial terraces
Stepped, fluvial terraces are found at the eastern end of the Tranquilo valley, either side of Rio Tranquilo (Fig. 2). The western terraces run for 1.6 km along the valley side on two levels, separated by a small scarp slope. The upper terrace slopes from 470 m to 415 m asl and the lower terraces slope from 450 m to 405 m asl, grading down to the valley floor level at their northern-most point. The two eastern terraces are adjacent to the ice-contact slope and grade south to the valley floor, with large scarp slopes on the northern sides.

Kame terraces
Along the eastern side of the Salto valley, masses of sediment with flat tops at ca. 370 m asl run discontinuously south to the confluence with the Río Tranquilo valley (Fig. 2). The top surface slopes gently away from the valley side before a steep break in slope forms a scarp down to the valley floor. The terrace surfaces are ca. 40 m above the valley floor, gently undulating and dissected by channels from the valley side. They contain hollows in places, some manifesting as lakes, producing kame and kettle topography (Livingstone et al., 2010). The largest terrace is 3.9 km long and up to 550 m wide, located just north of the confluence with the Tranquilo valley, and found in association with moraine ridge M9 (Fig. 4E). At the opening on the Salto valley, an exposure at the terrace base shows cross-bedded alternating coarse sands and gravels, dipping 20°southwest towards the valley floor, fining upwards in places (Fig. 14). Pebbles are faceted and edge-rounded and can be found in lags at the base of beds. These alternating sand and gravel beds are topped by gravel lenses and broad, shallow scours of trough crossbedded gravels and sands.

Boulder bar
Inset of the terminal Salto moraine complex is an elongated, 360 m long by 160 m wide bar of morainic material (Figs. 2, 15C), topped by sporadic boulders on its surface. Its elongated, tapered form is analogous to boulder bars observed in valleys to the north, formed by large outburst floods of Lago General Carrera/Buenos Aires likely reworking valley floor morainic material (Thorndycraft et al., 2019).

Fluvial bars and palaeochannels
Both mid-channel, bank-attached and point bars are found as part of the active Rio Tranquilo, Pedregoso and Salto glaciofluvial systems (cf. Collinson, 1996). Palaeobars are found on the floodplain bordering these rivers and in conjunction with glaciofluvial palaeochannels (Fig. 15).

Floodplain
The floors of the Salto and Tranquilo valleys are covered by floodplain associated with sand and gravel bar deposits. This differs from the morphology of the outwash plain east of the M1b Brown moraines, which is built up above the level of the valley floor. Numerous abandoned river-channels are found across the valley floor throughout the Salto and Tranquilo valleys and within the floodplain are a number of small lakes infilling pits (Fig. 15) (cf. Benn and Evans, 2010;Brynjólfsson, 2015;Giles et al., 2017).

Slope deposits
Unvegetated, modified drift-mantled slopes are found at the sides of the most recently deglaciated (post-LIA) valleys. They comprise upper sections of gullies cut into glaciogenic deposits (including lateralmoraine ridges), above coalescing debris cones and fans of reworked sediment (cf. Curry, 1999;Ballantyne, 2002;Curry et al., 2006). The clearest example is on the northern and southern valley sides above Lago Calluqueo. We also find examples of paraglacial rock-slope failure. Fig. 9. Section through diamicton at site S1 to the southeast of Lago Esmeralda, with lateral moraine ridges in Fig. 7B visible on the side of the slope.

Alluvial fans
Alluvial fans are found at the opening of gullies at the sides of the Pedregoso and Tranquilo valleys, where the valley side meets the valley floor floodplain. They slope gently between 2°and 10°, are well vegetated, and often associated with active river systems and fluvial downcutting.

Discussion
The observed geomorphology and sedimentology of the Salto, Pedregoso, Tranquilo and surrounding high-altitude valleys allows us to produce landsystem models which operated during and following a period of late Quaternary warming. The region can be divided into distinctive areas whose core sediment-landforms associations are characterised by either glaciolacustrine, landterminating glacial or mountain-valley landsystems. These are then overprinted by both glaciofluvial and paraglacial landsystems,  with varying degrees of modification of the glaciated landscape. These palimpsest environments can be thought of as existing within an overarching glaciated valley landsystem acting as a 'family of landsystems', documenting significant variability (Benn et al., 2003).
The D1 delta terrace (Figs. 3, 12A) at 600 m asl likely reflects a higher elevation ice-marginal lake formed when ice occupied the Tranquilo valley, damming valley side tributaries. Further, such higher elevation terrace surfaces are found in neighbouring small tributary valleys. Deltas at D3 and D4 and bedded sands south of D2 indicate that when the lake level was at 520 m asl the frontal ice-margin sat between D2 and D3 and the confluence with the Salto valley for a period of relative stability or slow recession to allow for such masses of sediment to accumulate (Fig. 16C). The bedded sands at L3 likely formed through relatively lowenergy deposition of well-sorted sediment into the lake. The draped ripple-cross laminations indicates a high rate of sediment aggradation relative to horizontal transport and flow (Evans and Benn, 2004). The formation of these deltas is reliant on both the presence of the large water body and local topography channelling rivers and fluvially-transported sediment from the mountain valley catchments through tributary valleys and gullies into the main valley. A topographic control is also evident through the absence of deltas in the northern Salto valley glaciolacustrine landsystem which lacks sediment input from tributary valleys.
The Brown moraines in the east sit on a topographic high with ridges up to ca. 535 m asl and a glacial outflow channel at ca. 520 m asl dissecting these ridges. An outwash plain east of the Brown moraines is incised by the large primary glacial outflow channel and multiple glaciofluvial braided palaeochannels. This provides evidence for a 520 m asl col. at the Brown moraines for the upper, 520 m asl palaeolake Tranquilo lake level and drainage to the east into Lago Brown and on into Lago Cochrane/Pueyrredón (Fig. 16B). With the Tranquilo valley floor dropping in elevation to the west, the lake was dammed by ice flowing north from the Pedregoso valley into the Tranquilo valley, having receded from its frontal position at the Brown moraines ( Fig. 16B and C). Both topography and the location of the ice mass therefore control the extent and depth of the lake.
There is a notable absence of cross-valley ridges in the Tranquilo valley which could be due to a number of factors. Benn (1989) elucidates a requirement of grounding line stability for the formation of ridges at Achnasheen in Scotland. Subaerial cross-valley ridges formed in the neighbouring Salto valley during this same period suggest that periodic local ice stability did occur. Therefore the calving of ice into palaeolake Tranquilo may have caused the instability of the ice front and its steady continuous retreat (cf. Carrivick and Tweed, 2013).
Following ice recession a lower elevation drainage pathway, and potentially subglacial drainage indicated by a bedrock incised channel, opened into the Salto valley at the Tranquilo-Salto confluence and the lake stabilised at 425 m asl (Fig. 16D). This punctuated drainage and later final drainage of palaeolake Tranquilo may have resulted in outburst floods down the Salto valley. Evidence for large flood events may be provided by the aforementioned inset boulder bar of the Salto moraine complex, and bedrock incision in the lowermost reach of the Rio Tranquilo and in the middle of the Salto moraines, downstream of the Lago Esmeralda reach (Fig. 15C). The boulder bar and bedrock incision are consistent with flood evidence in the Baker valley (Thorndycraft et al., 2019). Davies et al. (2018) present a glaciolacustrine landsystem model for the northern Salto valley to document the formation of the asymmetric Esmeralda moraine ridge and bank, and Juncal fan as part of a landform assemblage formed as ice terminated into Lago Chelenko palaeolake and subsequently receded to the more steeply topographically constrained section of the Salto valley south of the present-day Lago Esmeralda.  Subaerial and subaqueous moraines, subaqueous fans and constantaltitude palaeoshorelines are all found in conjunction.
Silt and clay rhythmites north of Lago Esmeralda (Figs. 3L1, 13A) are typical of ice-distal glaciolacustrine sediments deposited in proglacial lakes, sourced from underflows from the ice front, accompanied by the periodic deposition of ice rafted debris (Church and Gilbert, 1975;Smith and Ashley, 1985;Palmer et al., 2008;Sugiyama et al., 2016). We interpret those exposed at L1 to have formed in this way, in palaeolake Chelenko following ice recession. Those at L2 likely formed in a short-lived ice-contact proglacial lake following ice recession up the Salto valley, dammed by the large M7 moraine ridge. Coarsening to the top of the section into interbedded sands and a diamicton cap is suggestive of a minor readvance, however could also be the product of increased meltwater input and sediment capacity during the onset of further ice recession.

Land-terminating glacial landsystem
The main landform components of the Salto valley are the crossvalley terminal moraine ridges (M6-M9). (Fig. 4C-E). Due to their substantial size, sharp-crested form and absence of internal deformation structures, we interpret these as dump moraines, formed at the glacier's terminus by the remobilisation of supraglacial debris by roll, fall or glaciofluvial transport during periods of glacier stillstand (Boulton and Eyles, 1979;Benn and Owen, 2002;Benn and Evans, 2010) as ice receded up the Salto valley. Their association with kame terraces and stratified gravel and sand and diamictic composition (e.g., M8, Fig. 6) indicate significant sediment transport and deposition by meltwater at the glacier margins. RA-C 40 and RWR-C 40 covariance clast data at moraine sites throughout the Salto valley (Fig. 3) suggest glaciofluvial input and reworking within the subglacial transport system (Lukas et al., 2013). The shallow bed gradient of the Salto valley provides a setting in which an extensive, gently-sloping glacier would be sensitive to small changes in climate and ELA, leading to the formation of multiple cross valley moraine ridges due to numerous small ice margin fluctuations during overall recession. The lack of cross valley moraines in the Pedregoso valley could be the product of an ice mass less responsive to minor climate fluctuations having now receded into a more steeply-sloping valley (Barr and Lovell, 2014). We interpret M11 and M12 as having formed at minor glacier stillstands during glacier recession. Their location, confined to bedrock plateaus on the valley side, suggest that their formation had an element of topographic control.
Significant meltwater input from the glacier terminus proximal to the moraine ridges and from the surrounding catchment, likely contributed to the partial erosion of the M6-M9 moraine ridges. Increased river flow and migration during ice recession up valley would have been significant and, alongside any glacier lake outburst floods, exploited and widened any opening between the ridge and western valley-side. The valley floor is covered by a floodplain, containing a series of kettle-hole lakes, indicating breakoff of ice from the glacier tongue and subsequent burial by glacial outwash.
The exposure of diamicton at S2 is interpreted as subglacial till (Benn and Evans, 2010) with a combination of homogenised material and stratified sediments deposited by water. The presence of water deposited sands and gravels and lack of widespread deformation suggests water flow at the ice-bed interface and ice-bed decoupling (Eyles et al., 1983;Piotrowski and Tulaczyk, 1999;Phillips et al., 2013Phillips et al., , 2018. We interpret the two massive gravel features as burst out and simple clastic dyke fluid escape structures, indicating high levels of subglacial water pressure.

Mountain-valley landsystem
The upland valley landsystem in the study area is characterised by a landform assemblage of cirques, saw-tooth moraines, closely-spaced cross-valley moraines, flutes on the valley floor and talus slopes on the surrounding steep valley-sides; the product of recent deglaciation. The closely-spaced moraine ridges are interpreted as push moraines formed during frequent minor readvances or stillstands (cf. Evans et al., 1999Evans et al., , 2018. The larger saw-tooth terminal moraines formed as a result of a more sustained readvance. As ice opens into a less well constrained valley section, radial crevasses form in the glacier tongue resulting in a saw-toothed shaped ice front and moraine ridges with distinctive tooth and notch pairings upon the push up of glacially-reworked material (Matthews et al., 1979;Burki et al., 2009).
Cirques and headwalls with over-deepenings formed by erosion at the base of the glacier through freeze-thaw weathering and plucking (Hooke, 1991) indicating warm-based ice as well as abundant meltwater (Glasser and Bennett, 2004). Flutes are a product of subglacial sediment deformation, forming ridges running parallel to the direction of ice flow under temperate conditions (Boulton, 1976;Gordon et al., 1992;Benn and Evans, 2010). It is to be expected that flutes and small valley-bottom recessional moraine ridges are most commonly found in areas proximal to present-day ice fronts (Benn, 1995;Evans and Twigg, 2002) due to their poor preservation potential (Benn and Evans, 2010). Closely-spaced moraines superimposed on these subglacial bedforms indicate both numerous oscillations of the frontal ice margin and an exposed valley bed not subsequently covered by debris, both indicative of a 'clean' valley glacier (Eyles, 1979;Benn and Evans, 2010).
Unlike in the lower valleys, the glaciofluvial component to the landsystem has a minor impact, manifesting as only narrow single channels, dissecting the cross-valley and saw-tooth moraines in places. The sediment transport pathway is short, with subglacial material sourced from the headwall and cirque bed, and paraglacial processes creating talus slopes bringing material into the valley bottom from the valley sides. Similar cirque architectures are seen on the Isle of Skye at the Coire Lagan formed during the Younger Dryas (Benn and Evans, 2010), as well as in front of present-day, actively-receding glaciers such as at Maradalsbreen, Norway (Benn et al., 2003) and Charquini Sur, Bolivia (Malecki et al., 2018).

Paraglacial landsystem
The paraglacial landsystem is the product of fluvial, flood and slope based processes reshaping the glaciated landscape and can be broken down into a combination of sediment sources, stores, sinks and transport pathways (Ballantyne, 2002). Recently deglaciated and exposed bedrock and drift-mantled slopes in high-altitude valleys and on the slopes above the present-day Calluqueo glacier terminus provide the sediment source for talus slopes and debris cones on the valley sides following rockfall and slope failure. The former are a product of initially large, and later smaller scale rockfalls as part of progressive bedrock adjustment following deglaciation and debutressing (Wyrwoll, 1977;Ballantyne, 2002). Material is glaciofluvially transported and reworked down into the lowland valleys either directly through the main Pedregoso, Salto and Tranquilo river systems or via valley side gullies. At such gullies material manifests as alluvial fans (Figs. 2, 15) forming a secondary sediment store. Material within the primary river systems, and that subsequently reworked from alluvial fans, is redistributed as floodplain valley-fill deposits. The product of this is a floodplain with a braided river system and associated point bar deposits. Meltwater fed rivers with variable annual and seasonal discharge lead to a dynamic migratory river system, producing braiding and abandoned palaeochannels. A lack of subsequently formed river terraces along the Salto valley suggest a maintained sediment supply and balance between sediment input, transport through and redistribution across the valley. There may be slight positive balance in favour of sediment input to counter incision expected as a product of isostatic uplift.

Glaciofluvial landsystem
Glaciofluvial process operate at the lateral and frontal ice-margins forming kame terraces and outwash plains in the Salto and Tranquilo valleys respectively in conjunction with the land-terminating glacial landsystem, and as part of the paraglacial landsystem following deglaciation as in Section 5.1.4. Glaciofluvial processes dominate the proglacial environment forming braided valley trains in sparsely vegetated, non-cohesive material; a product of high bedloads and fluctuations in glacially fed discharge (Miall, 1992;Marren, 2005). Such a feature is found in the southern reach of the Pedregoso valley at the outflow of Lago Calluqueo a steep gradient of 6 to 7 m km −1 , typical of braided systems (Benn and Evans, 2010). In the more gently sloping Salto and Tranquilo valleys (1.5 to 2 m km −1 ), through to the northern reach of the Salto valley adjacent to Lago Esmeralda, the river transitions from a braided system to an increasingly sinuous main river channel with channel bars, islands and occasional subsidiary channels. Finally the Rio Salto establishes a meandering fluvial landsystem with point bars, palaeochannels and palaeobars in a wider floodplain (Fig. 15C) (Miall, 1985). Davies et al. (2018) found that during an ACR readvance, ice sourced from Monte San Lorenzo occupying the northern Salto valley discharged into the ca. 350 m asl Lago Chelenko, and formed the Esmeralda moraines (M1a) at 13.2 ± 0.6 ka (Fig. 16A). The glacier terminus remained in a glaciolacustrine environment likely during the first ca. 1000 years of subsequent recession until drainage of Lago Chelenko at ca. 12.4-11.8 ka (Thorndycraft et al., 2019) (Fig. 16B). At this time the glacier terminus was approximately at the margin of M5. Following lake drainage, the glacier became land-terminating and receded up the Salto valley with periodic stillstands or minor readvances (Fig. 16C). A land-terminating glacial landsystem operated during the Holocene in the Salto valley and then continuing in the Pedregoso valley as ice receded further (Fig. 16C to F). Following the Little Ice Age and the formation of M13 the presentday Calluqueo glacier terminated into Lago Calluqueo in a glaciolacustrine setting, before receding to its present-day, land-terminating position.

Spatial and temporal evolution of landsystems
Ice occupying the Tranquilo valley, after initially existing in a landterminating setting and forming the Brown moraines (Fig. 16A), receded west into the newly formed 520 m asl ice-dammed palaeolake Tranquilo, in turn transitioning into a glaciolacustrine landsystem ( Fig. 16B and C). Further recession and the resulting opening of the 425 m spillway at the Tranquilo-Salto confluence produced a drainage reversal of palaeolake Tranquilo ( Fig. 16C and D) with the Brown moraines outflow pathway abandoned at 520 m asl when lake level fell to 425 m asl. This drainage reversal would therefore have contributed increased meltwater flux as well as likely GLOF drainage events, a hypothesis supported by the Salto moraine boulder bar and incised bedrock reaches (Fig. 15C).
Following final drainage of palaeolake Tranquilo as ice receded out of the Tranquilo valley, ice receded up the Pedregoso valley ( Fig. 16D and E). Radiocarbon dated organics at a road cutting at the confluence of the Tranquilo and Pedregoso valleys (Fig. 1) suggests that ice must have receded out of the Tranquilo valley by at least 10.5 ka, a minimum distance of ca. 23 km from the Esmeralda moraines (M1a) in 2700 years, and a minimum recession rate of 8.5 m/yr.
Once ice had receded up the Pedregoso valleys a paraglacial landsystem operated with rock-slope failure forming talus slopes and cones, and the glaciofluvial remobilisation of glaciogenic sediment deposited as alluvial fans and valley floor floodplain (Fig. 16E). It is evident that the well-vegetated and fluvially-entrenched alluvial fans are no longer depositionally active, but formed during the Holocene following ice recession, and as such resemble Holocene fans found elsewhere (Ryder, 1971;Ballantyne, 1991;Beaudoin and King, 1994). Alongside this, there is little evidence for significant active large scale rock-slope failure, with only isolated minor rock falls on the high valley sides. An evident reduction in glacially conditioned sediment release through either exhaustion of sediment or sediment stability being attained, suggests that the paraglacial period in the Salto, Tranquilo and Pedregoso valleys has ended and moved towards a 'non-glacial' state (Ballantyne, 2003). Clearly active remobilisation of drift-mantled slopes in the most recently deglaciated sections of high-altitude mountain valleys and near present-day ice margins, particularly at Calluqueo, suggest that paraglacial processes currently operate in these areas. The highsinuosity meanders of the lower Salto valley suggest a transitioning to a fluvial landsystem (Fig. 16F).

Temperate Patagonian glacier systems during Late Quaternary deglaciation
Most landsystem studies of contemporary glaciers come from terrestrial-terminating, and topographically-unconstrained, piedmont glacier and ice-lobe settings (Bentley, 1996;Andersen et al., 1999;Schlüchter et al., 1999;Glasser et al., 2009) so are not appropriate analogues for the type of mountain icefield landsystems encountered in Patagonia. Furthermore, many formerly glaciated valleys in Patagonia are forested and inaccessible. Therefore, the detailed Late Quaternary landsystem of Monte San Lorenzo, afforded by good availability of sections, provides an important new geomorphological dataset to help understand the dynamics of temperate Patagonian glacier response to warming climate. In particular our geomorphological and sedimentological data will be relevant for understanding the smaller ice caps located in the cordillera (72-73°W) to the east of the Patagonian Icefields (e.g., Araos et al., 2018;Sagredo et al., 2018). These smaller ice-caps have important implications for understanding palaeoclimate (Sagredo et al., 2018) given their position in the Andean rain-shadow. Furthermore, they potentially play a role in controlling regional drainage as demonstrated in the Baker valley through the separation of Monte San Lorenzo and NPI ice (Thorndycraft et al., 2019).
Our sediment-landform data from Monte San Lorenzo demonstrate that the regional glacial geomorphology conforms to the concept of a mountain icefield landsystem (Benn and Evans, 2010). The diverse topography and climatic settings of Monte San Lorenzo result in a broad landsystem encompassing elements of multiple smaller-scale landsystems. Benn et al. (2003) discuss the spatial and temporal changes in glacial landsystems at the Ben Ohau Range in New Zealand, citing long term climate change as the key driver of spatial and temporal landsystem evolution. Similarly, in central Patagonia, atmospheric warming at the end of the ACR caused regional ice recession, and the subsequent drainage of Lago Chelenko to the Pacific (Thorndycraft et al., 2019) and Lago Tranquilo into the Salto valley, changing the terminal ice environment from lacustrine to terrestrial. The glaciolacustrine dynamics of Lago Tranquilo, and in particular the drainage reversal, highlight the important role of topography in local to regional scale landscape change. Across Patagonia, Thorndycraft et al. (2019) hypothesise that although the broad pattern of ice recession may be similar, driven by Southern Hemisphere palaeoclimate, the timing of palaeolake drainage events is diachronous due to regional topographic settings.
Understanding the spatial and temporal glaciolacustrine dynamics of Patagonian glaciers provides insights for the interpretation of the Late Quaternary landform record. As an illustrative example from this study, the only fluvial terraces in the study area are at the upstream end of the former 425 m asl Lago Tranquilo lake level. Repeat satellitederived valley floor DEMs from the Cachet II ice-dammed lake (Colonia valley, NPI) provide a modern analogue that demonstrates valley floor incision and upstream enlargement of the lake during successive lake drainage-refill events (Jacquet et al., 2017). Using this analogue for palaeolake Tranquilo, we interpret that the formation of the Tranquilo terraces were caused by base-level fall from palaeolake drainage rather than regional tectonic (Guillaume et al., 2013) or isostatic uplift (Thorndycraft et al., 2019). Our study therefore demonstrates the need for a detailed, holistic approach to the elucidation of glacier, lakes and topographic interactions.

Summary and conclusions
We have used detailed geomorphological mapping and sedimentology to describe the landforms and sediments found in valleys directly north of Monte San Lorenzo in Chilean Patagonia.
• The primary landforms identified in the study area are lateral and terminal moraine ridges, ice-scoured bedrock, cirques and headwalls, flutes, deltas, ice-contact fans, glaciolacustrine deposits, palaeoshorelines, kame terraces and outwash and floodplains. These form ice-marginal, subglacial, glaciolacustrine, glaciofluvial and paraglacial sediment-landform associations, from which we infer a range of glacial and paraglacial processes which led to their formation through the Late Pleistocene and Holocene.
• We have identified 7 new moraine sets and ground-truthed and extended the spatial extent of a further 7 through extensive field mapping. This highlights the limitations of identifying and mapping ice margins from satellite imagery alone and in the absence of highresolution LiDAR DEMs. It is clear that when possible geomorphological field mapping is required to comprehensively identify icemarginal glacial landforms. • Our study reveals glaciolacustrine, land-terminating glacial, mountain valley and paraglacial landsystems within the same valley systems, evolving and transitioning during deglaciation. We identify and constrain for the first time an ice-dammed palaeolake Tranquilo which occupied the Tranquilo valley following recession of ice from the Brown moraines. • For the period of warming after the ACR we have identified three key controls on sediment-landform associations and landsystem development. Firstly this study region illustrates how climate provides a broad-scale control by both dictating the temperate thermal regime of the glacier and the subglacial bedforms created and by causing overall ice recession. As ice recedes, ice-dammed lake drainage pathways open and frontal margins move to higher elevations, transitioning through landsystems as they do so. Secondly, icedammed lakes provide a control on glacier frontal stability and in turn ice-marginal landform formation. Finally, topography operates as a control on both a local scale determining the location of sediment supply, and regionally in combination with ice masses to control the extent and level of ice dammed lakes.