Proglacial Lake Research Articles

Holocene Environmental Dynamics of the Lago Cochrane/Pueyrredón Valley, Central West Patagonia (47°S)

Deglaciation modeling of the Patagonian Ice Field since the Last Glacial Maximum has been a topic of intensive research in Central West Patagonia (44°–49°S). However, the chronology of deglaciation onset, acceleration, and the subsequent thinning and recession of the different ice lobes as well as the timing and extension of large proglacial systems are still a matter of discussion. The maximum eastward extension the Lago Cochrane/Pueyrredón ice lobe was around ∼20,000–27,000 cal yrs BP; its associated proglacial lake drained toward the Pacific between 12,600 and 8,000 cal yrs BP. This study presents the first two pollen and charcoal records from the Lago Cochrane/Pueyrredón valley, spanning the last 11,650 cal yrs BP. The Laguna Maldonado record spans between 11,650 and 8,500 cal yrs BP, while the Laguna Anónima record the last 8,500 cal yrs BP, thereby overlapping chronologically. The lithological record of Laguna Maldonado shows that organic sedimentation began at the onset of the Holocene (11,650 cal yrs BP), once the site was free of glacio-lacustrine influence. Between 11,650 and 10,500 cal yrs BP, an open Nothofagus forest developed associated with high fire occurrence/frequency, followed by a transitional phase to a closer forest associated with a shift from low to high fire activity up to 9,400 cal yrs BP. Between 9,400 and 8,500 cal yrs BP, the Laguna Maldonado record suggests the development of an open forest or probably scattered patches of forest of variable size in a steppe matrix, probably related to geomorphological and paraglacial dynamics as well as climatic forcings, while the Laguna Anónima record indicates the development of a closed Nothofagus forest and high to low fire occurrence/frequency from 8,200 to 3,800 cal yrs BP. Since 3,800 cal yrs BP, a highly dynamic open forest or forest patches scattered in a grass/shrub–grass steppe matrix occurred around Laguna Anónima associated with high fire occurrence/frequency synchronous with an important increase in the presence of hunter-gatherers during the last 3,000 years. The results from the Lago Cochrane/Pueyrredón valley are integrated and discussed at the regional scale alongside other records from Central West Patagonia.

Unravelling a 2300 year long sedimentary record of megathrust and intraslab earthquakes in proglacial Skilak Lake, south‐central Alaska

AbstractSeismic hazards in subduction settings typically arise from megathrust, intraslab and crustal earthquake sources. Despite the frequent occurrence of intraslab earthquakes in subduction zones and their potential threat to communities, their long‐term recurrence behaviour is barely studied. Sedimentary sequences in lakes may register ground shaking from different seismic sources. This study investigates two long sediment cores (13 m and 16 m) from Skilak Lake, a proglacial lake in south‐central Alaska, to evaluate whether different seismic sources leave a distinct imprint. The sedimentary record shows a continuously varved sediment sequence, occasionally interrupted by turbidites, slump deposits and tephra beds. Turbidites and slump deposits were objectively identified using a statistical outlier analysis on varve thickness. The earthquake origin of these deposits was ascertained by resemblance with deposits induced by instrumentally recorded earthquakes (for example, 1964 ce Mw 9.2 megathrust and 1954 ce Mw 6.4 intraslab earthquakes) and correlation with multiple coeval landslide deposits on sub‐bottom profiles. The Skilak Lake record chronicles 19 earthquakes with moderate to very high confidence level in the past 1350 years. The sedimentary evidence of instrumentally‐recorded intraslab and megathrust earthquakes within the past 70 years demonstrates that not only megathrust earthquakes, but also past intraslab events are recorded. Although reported seismic intensities at Skilak Lake are comparable for the 1964 ce megathrust and the 1954 ce intraslab earthquakes, the long duration and low frequency content of seismic ground motion during megathrust earthquakes facilitate the triggering of multiple, voluminous landslides and the generation of megaturbidites. In contrast, the shorter duration and higher frequency source spectrum of intraslab earthquakes may only induce surficial slope remobilization and the generation of thinner turbidites. This study demonstrates that the sedimentary record of Skilak Lake has the potential to decipher multiple seismic sources, which opens possibilities for a comprehensive seismic hazard analysis for south‐central Alaska.

Hydrology and thermal regime of an ice‐contact proglacial lake: Implications for stream temperature and lake evaporation

AbstractThe formation of lakes as glaciers retreat can potentially influence stream temperature and enhance catchment water losses via evaporation. This study quantified the summer water and energy budgets and thermal regime of an ice‐contact proglacial lake below Bridge Glacier, British Columbia, to link ongoing glacier retreat with downstream effects. The ice‐proximal and distal portions of the lake behave differently due to a mid‐lake recessional moraine, against which icebergs are pinned by the dominant katabatic wind. Iceberg cover of the ice‐proximal basin ranged from 16% to 75%. Temperature profiles in the ice‐proximal basin were dominantly near‐isothermal at 1 to 1.4°C, with the exception of diurnal warming of the top 1 m of water and the presence of a colder layer near the lake bed at some sites, presumably caused by subglacial discharge of turbid water. Subaqueous iceberg melt limited warming by consuming heat from the water column. The distal basin exhibited varying degrees of thermal stratification, with turbidity inferred to have a greater influence on water density than temperature. Most of the warming between lake inflow and outflow occurred in the distal basin, where net radiation was the dominant surface energy input and net lateral advection the dominant energy sink. As a result of the suppressed water temperature, humidity gradients over the lake favoured condensation, not evaporation. Estimates of iceberg melt volume for 2013 exceeded glacier discharge into the lake. Therefore, when the glacier eventually becomes land‐terminating, icebergs are expected to disappear within a year, resulting in higher water temperatures both in the lake and downstream. Higher lake temperatures could also cause an eventual shift from condensation to evaporation, which would tend to reduce catchment water yield over and above reductions associated with loss of glacier area.

Coincident evolution of glaciers and ice-marginal proglacial lakes across the Southern Alps, New Zealand: Past, present and future

Global glacier mass loss is causing expansion of proglacial landscapes and producing meltwater that can become impounded as lakes within natural topographic depressions or ‘overdeepenings’. It is important to understand the evolution of these proglacial landscapes for water resources, natural hazards and ecosystem services. In this study we (i) overview contemporary loss of glacier ice across the Southern Alps of New Zealand, (ii) analyse ice-marginal lake development since the 1980s, (iii) utilise modelled glacier ice thickness to suggest the position and size of future lakes, and (iv) employ a large-scale glacier evolution model to suggest the timing of future lake formation and future lake expansion rate. In recent decades, hundreds of Southern Alps glaciers have been lost and those remaining have fragmented both by separation of tributaries and by detachment of ablation zones. Glaciers with ice-contact margins in proglacial lakes (n > 0.1 km2 = 20 in 2020) have experienced the greatest terminus retreat and typically twice as negative mass balance compared to similar-sized land-terminating glaciers. Our analysis indicates a positive relationship between mean glacier mass balance and rate of lake growth (R2 = 0.34) and also with length of an ice-contact lake boundary (R2 = 0.44). We project sustained and relatively homogenous glacier volume loss for east-draining basins but in contrast a heterogeneous pattern of volume loss for west-draining basins. Our model results show that ice-marginal lakes will increase in combined size by ~150% towards 2050 and then decrease to 2100 as glaciers disconnect from them. Overall, our findings should inform (i) glacier evolution models into which ice-marginal lake effects need incorporating, (ii) studies of rapid landscape evolution and especially of meltwater and sediment delivery, and (iii) considerations of future meltwater supply and water quality.

PISM-LakeCC: Implementing an adaptive proglacial lake boundary in an ice sheet model

Abstract. During the Late Pleistocene and Holocene retreat of paleo-ice sheets in North America and Europe, vast proglacial lakes existed along the land terminating margins. These proglacial lakes impacted ice sheet dynamics by imposing boundary conditions analogous to a marine terminating margin. Such lacustrine boundary conditions cause changes in the ice sheet geometry, stress balance and frontal ablation and therefore affect the mass balance of the entire ice sheet. Despite this, dynamically evolving proglacial lakes have rarely been considered in detail in ice sheet modeling endeavors. In this study, we describe the implementation of an adaptive lake boundary in the Parallel Ice Sheet Model (PISM), which we call PISM-LakeCC. We test our model with a simplified glacial retreat setup of the Laurentide Ice Sheet (LIS). By comparing the experiments with lakes to control runs with no lakes, we show that the presence of proglacial lakes locally enhances the ice flow, which leads to a lowering of the ice sheet surface. In some cases, this also results in an advance of the ice margin and the emergence of ice lobes. In the warming climate, increased melting on the lowered ice surface drives the glacial retreat. For the LIS, the presence of lakes triggers a process similar to marine ice sheet instability, which caused the collapse of the ice saddle over Hudson Bay. In the control experiments without lakes, Hudson Bay is still glaciated when the climate reaches present-day (PD) conditions. The results of our study demonstrate that glacio-lacustrine interactions play a significant role in the retreat of land terminating ice sheet margins.

Ice-Dynamics and Morphological Changes during Proglacial Lake Development at Exploradores Glacier, Patagonia.

Ice-Dynamics and Morphological Changes during Proglacial Lake Development at Exploradores Glacier, Patagonia.

New geomorphic evidence for a multi‐stage proglacial lake associated with the former British–Irish Ice Sheet in the Vale of Pickering, Yorkshire, UK

ABSTRACTFormer proglacial lakes provide insight into the temporal and spatial evolution of past ice sheet dynamics and the glaciohydrological systems associated with them. Glacial Lake Pickering was a proglacial lake in North Yorkshire impounded by the British–Irish Ice Sheet. However, geomorphic evidence for its existence and extent is weak and contested. This paper presents, for the first time, systematic mapping of geomorphic features from high‐resolution (50 cm to 5 m) digital terrain model data and undertakes palaeogeographical reconstructions to establish Palaeolake Pickering's extent and levels. Results show only weak evidence for a 70‐m lake. This and the fact that the present landscape configuration is unable to impound such a large lake suggests that it either did not exist or is much older and that considerable landscape erosion has since taken place. There is good geomorphological evidence to support lake levels between 45 and 20 m. The new palaeogeographical reconstructions show these lake levels were initially controlled by the balance between the North Sea and the Vale of York Lobes of the British–Irish Ice Sheet with lower and later levels impounded by the Filey moraine. A multi‐stage Palaeolake Pickering with various extents and levels possibly spanning more than one glacial period has implications for other British–Irish Ice Sheet palaeolake extents reconstructed only from undifferentiated lacustrine sediments and their maximal elevation. The existence of an extensive multi‐phase proglacial Palaeolake Pickering along with other similar ones in Eastern England would have impacted mass loss and frontal dynamics via subaqueous melting and iceberg calving, potentially playing a role in controlling the dynamic behaviour of the North Sea Lobe.

The development and impact of an ice‐contact proglacial lake during the Last Glacial Termination, Palaeolake Riada, central Ireland

ABSTRACTThe retreat of the last Irish Ice Sheet across the Irish midlands resulted in the formation of an ice‐contact lake, Palaeolake Riada, along its eastern margin during recession. However, the full extent and characteristics of the lake and its impact on ice dynamics are unknown, as glacigenic landforms and deposits relating to the lake have not been mapped in sufficient detail to allow reconstruction of ice‐marginal behaviour. This paper presents new mapping of subglacial, ice‐marginal and glaciolacustrine landforms and deposits in the Irish midlands. Glacial landforms and landform associations across this wide area have been identified using aerial photographs and high‐resolution digital elevation models derived from LiDAR and radar data. Reconstructions of successive ice‐margin retreat positions are combined with glacio‐isostatically adjusted digital elevation models to identify the probable position of lake outflows and reconstruct the development of the proglacial Palaeolake Riada through time. These reconstructions indicate that at its largest, Palaeolake Riada had an ice‐contact margin of 113 km, and covered an area of over 2300 km2. Initially, ice recession was concentrated around meltwater discharge outlets, but these became less important as the lake expanded and thermo‐mechanical erosion occurred along the entire subaqueous margin.

Psychosocial response to a no-build zone: Managing landslide risk in Iceland

Land use planning has been promoted as a key measure to decrease the risk of natural disasters including landslides, however, there is a dearth of research on how the impact it has on the psychosocial wellbeing of affected people. This ethnographic study examines the risk management of the Svínafellsheiði mountain in south-east Iceland. Scientific monitoring suggests that an estimated 60–100 million cubic metres of bedrock could fall onto the glacier below, and cause flooding or a tsunami in the proglacial lake. A no-build zone was in place between 2018 and 2020 to prevent a further increase in the number of people exposed to the hazard. Our results indicate that the no-build zone had adverse effects on the psychosocial wellbeing of those affected including frustration about a perceived inability to make changes to their home and business operations, leaving them feeling that their future was uncertain or on hold. These frustrations also acted as a persistent reminder of the risk posed by the unstable slope, reinforcing anxiety and undermining people’s ability to gain respite through day-to-day routine. Based on the findings, we recommend that land use planners take the psychosocial wellbeing of affected communities into account when contemplating no-build zones, and that psychosocial support be offered especially when a small group of people face an existential threat for an extended period.

Geomorphology of a recently deglaciated high mountain area in Eastern Anatolia (Turkey)

ABSTRACT We present a geomorphological map of the Cilo Mountain range located in southeast Turkey that illustrates the recent evolution of the second-most glacierized area of Turkey. The map was produced by the manual delineating of landforms from highresolution satellite imagery (Pleiades and Google EarthTM images). Cilo Mountain glaciation played a crucial role in the evolution of the local physical landscape and even today glaciers are significant features. After the termination of Little Ice Age, deglaciation promoted the onset of multiple and intense surface processes; widespread slope instabilities, due to permafrost melting and frost weathering processes, are still the most active processes. Such processes are further promoted by the scarcity of vegetation. The occurrence of several proglacial lakes significantly contributes to the reduction of sediment output from glaciated watersheds, influencing the evolution of proglacial plains and resulting in a variety of landforms that we identified and described in this work.

Glacier Surface Speed Variations on the Kenai Peninsula, Alaska, 2014–2019

AbstractTo characterize the spatiotemporal variations of glacier surface speed on the Kenai Peninsula, Alaska (∼3,900 km2), we derived 92 surface speed fields between October 2014 and December 2019 using intensity offset tracking on Sentinel‐1 data. On average, speeds are 50% greater in spring (March‐May) than the annual mean (69 m a−1) while winter speeds are close to the annual mean. While marine‐terminating glaciers have their maximum speed near the terminus, both land‐ and lake‐terminating glaciers flow fastest around the median glacier elevation. On average, the lake‐terminating and tidewater glaciers flow 1.7 and 2.3 times faster than the land‐terminating glaciers, respectively. Monthly variations over the 5‐year period are strikingly synchronous regardless of terminus type suggesting that regional‐scale meteorological drivers govern the temporal variability. Mean annual speeds fluctuate roughly ±10% of the period mean without an apparent trend. At lake‐terminating Bear Glacier, a short‐term tripling in ice speed in fall 2019 over the area below an ice‐dammed lake coincides with an observed glacier lake outburst flood (GLOF). An earlier GLOF caused a persistent breach of the beach barrier between the proglacial lake and ocean which likely led to overall speed‐up of the lower glacier part throughout 2019. A significant speedup was also observed at the lower part of the lake‐terminating Ellsworth Glacier and attributed to rapid glacier retreat and lake expansion, probably further amplified by the terminus area becoming buoyant and a large tabular iceberg breaking off. Our results highlight the impact of GLOFs and proglacial characteristics in spatial and temporal glacier speed variations.

Physical Limnology and Sediment Dynamics of Lago Argentino, the World's Largest Ice‐Contact Lake

AbstractProglacial lakes, whose numbers have been growing around the world, may drive accelerated glacier retreat and provide valuable records of past glacier and climatic changes. Despite their importance, few studies have investigated the sedimentary properties and processes acting within large proglacial lakes. Lago Argentino (LArg) is a 1,500 km2 ice‐contact lake on the eastern flank of the Southern Patagonian Icefield. Here, we describe the results from a detailed analysis of 47 sediment cores obtained throughout this lake basin, supplemented with remotely sensed data. We show that: (a) LArg exhibits a seasonal variation in sediment properties (varves); (b) varve formation results from three distinct processes, driven by seasonal changes in glacial sediment input, seasonal changes in fluvial sediment input, and seasonal variations in lake mixing; and (c) distance from glacier calving fronts provides the first‐order control on sediment grain size and accumulation rate. Our findings highlight the exceptional preservation of annual laminations within proglacial lakes, their potential for reconstructing past glacier changes, and their relevance for forecasting future glacier–lake interactions.

Assessment of Proglacial Lakes in Sikkim Himalaya, India for Glacial Lake Outburst Flood (GLOF) Risk Analysis using HEC-RAS and Geospatial Techniques

Assessment of Proglacial Lakes in Sikkim Himalaya, India for Glacial Lake Outburst Flood (GLOF) Risk Analysis using HEC-RAS and Geospatial Techniques

From glacial erosion to basin overfill: a 240 m-thick overdeepening–fill sequence in Bern, Switzerland

Abstract. We drilled a 210 m-thick succession of Quaternary sediments and extended it 30 m upsection with information that we collected from an adjacent outcrop. In the 240 m-thick succession we identified 12 different lithofacies, grouped them into five facies assemblages, and distinguished two major sedimentary sequences. A sharp contact at 103 m depth cuts off cross-beds in sequence A and separates them from the overlying horizontal beds in sequence B. Although the lowermost facies assemblage of each sequence includes a till deposited during a period of ice cover, the two tills differ from each other. In particular, the till at the base of sequence A is dominated by large clasts derived from the underlying Molasse bedrock, whereas the till at the base of sequence B has no such Molasse components. Furthermore, the till in sequence A bears evidence of glaciotectonic deformation. Both tills are overlain by thick assemblages of subaqueous, most likely glaciolacustrine and lacustrine facies elements. The cross-bedded and steeply inclined sand, gravel, and diamictic beds of sequence A are interpreted as deposits of density currents in a subaqueous ice-contact fan system within a proglacial lake. In contrast, the lacustrine sediments in sequence B are considered to record a less energetic environment where the material was most likely deposited in a prodelta setting that gradually developed into a delta plain. Towards the top, sequence B evolves into a fluvial system recorded in sequence C, when large sediment fluxes of a possibly advancing glacier resulted in a widespread cover of the region by a thick gravel unit. Feldspar luminescence dating on two samples from a sand layer at the top of sequence B provided uncorrected ages of 250.3 ± 80.2 and 251.3 ± 59.8 ka. The combination of these ages with lithostratigraphic correlations of sedimentary sequences encountered in neighboring scientific drillings suggests that sequence B was deposited between Marine Isotope Stage 8 (MIS 8; 300–243 ka) and MIS 7 (243–191 ka). This depositional age marks the end of one stage of overdeepening–fill in the perialpine Aare Valley near Bern.

Dulung Proglacial Lake, Suru Sub-Basin, Western Himalaya: Evolution, Controls and Impacts on Glacier Stability

Proglacial lakes are continually developing and expanding across the Himalayan glaciered terrain in response to climate change. These lakes are known to destabilize the glaciers by enhancing their frontal ablation, causing higher than average glacier area and mass losses. Thus, to comprehend the dynamics of proglacial lakes and their influence on the overall glacier health, we study the lake-terminating Dulung Glacier located in the Suru sub-basin, Ladakh, western Himalaya and compare it with the adjacent land-terminating Chilung Glacier. The pronounced melting of the Dulung Glacier, supported by glacier topography (surface gradient between accumulation and ablation zone) and valley morphology (wider near the snout and narrower downwards), seems to be the prime reason for the formation, accommodation and sustenance of the proglacial lake. The expansion in proglacial lake (.008 km2a−1) during 1977–2018 is accompanied by an enhanced degeneration of the Dulung Glacier (mass balance: −.47 ± .06 m w.e.a−1, shrinkage rate: .3 ± .001% a−1; retreat rate: 32 ± .7 ma−1, surface ice velocity reduction: 16%), which has accelerated post-1993. In comparison, land-terminating Chilung Glacier shows lower degeneration rates (mass balance: −.28 ± .02 m w.e.a−1; shrinkage rate: .2 ± .001% a−1; retreat rate: 17 ± 0.7 ma−1, surface ice velocity reduction: 8%) during 1971–2018. This suggests a substantial impact of the proglacial lake in enhancing the Dulung Glacier’s sensitivity towards climate change compared to the Chilung Glacier. If the current rate of lake expansion continues, it would further enhance the Dulung Glaciers’ degeneration rates, thus impacting its stability.

High resolution inventory and hazard assessment of potentially dangerous glacial lakes in upper Jhelum basin, Kashmir Himalaya, India

In the Himalayan Mountain region, a large number of glacial lakes have developed in the recent past due to glacier recession under the influence of climate change. In this study, we used high resolution satellite data such as Indian Remote Sensing (IRS) LISS-IV (5.8 m) and Google earth images supplemented with field survey to generate an updated glacial lake inventory of Upper Jhelum Basin (UJB) of Kashmir Himalaya. The Sentinel-2A (10 m), Landsat-OLI (30 m) and MSS (60 m), and Cartosat-DEM (30 m) were additional data sources used for glacial lake mapping and change detection analysis. A total of 393 glacial lakes covering an area of 21.55 ± 3.8 km2 were identified, mapped and inventoried. The lake inventory includes 102 proglacial lakes, 13 supraglacial lakes and 278 unconnected glacial lakes. Using the weighted index-based method, 21 glacial lakes were found as Potentially Dangerous Glacial Lakes (PDGLs). Out of these, 7 lakes were classified as High, 9 as Medium and 5 as Low hazard glacial lakes as per the hazard assessment. Change detection analysis of PDGLs from 1980 to 2020 revealed an increase in area from 5.92 km2 to 8.46 km2 thereby, indicating a growth of 2.51 ±0.9 km2(30%) at a rate of 0.063 km2/year. The formation and growth of glacial lakes in this area is attributed to continuous glacier recession under the warming trend of temperature and declining nature of precipitation. In this study, the findings showed that Tavg and Tmin are rising significantly at a rate of 0.004ºC/year and 0.013ºC/year respectively. This study provides an important database for future GLOF studies in the region.

Isotopic signature of a glacial influenced hydrological system in northern Patagonia, Argentina

AbstractHigh glacial mountain environments around the world are important water reservoirs and are extremely sensitive to the effects of climate change. Considering that climate change affects snow accumulation and glacial melting, it is essential to understand the runoff generation and hydrological dynamics in these type of systems. Andean glaciers have shown a retreating and thinning pattern since the start of the 21st century. Regarding this, the stable isotopic composition of waters is useful to assess the contributions from different sources (i.e., glaciers, precipitation, and tributaries' inputs) to rivers. Several Patagonian mountain rivers have Andean glaciers in their headwaters, one of which is the Manso River. In this basin, over the last 30 years, the Ventisquero Negro Glacier (Manso Glacier's regenerated tongue) experienced a rapid thinning and recession that generated a proglacial lake, called Manso proglacial Lake. In this study, topographic effects upon the stable isotopic composition of river waters (δ2H and δ18O) are recognized, particularly, the altitude effect. The stable isotope composition of the Manso River varies downstream, evolving to a composition more enriched in heavy isotopes in the lower basin, likely due to altitude effects and the progressive evaporation that mainly occurs in the lakes' surfaces that the river crosses. Results show that glacial meltwater is the major water contributor in the upper basin during early fall. In the rest of the basin the stable isotopic composition of the Manso River is mainly controlled by the lakes' isotopic signatures and is highly influenced by two tributary rivers. The concordance between isotopic models and hydrological data demonstrates that stable isotopes constitute a valuable tool to quantify the contribution of different water sources. This has the potential to be particularly useful in areas where discharge data is unavailable.

10Be chronology of deglaciation and ice-dammed lake regression in the vicinity of the Mylodon Cave (Cerro Benítez, Patagonia, Chile)

Located 51.5°S in the vicinity of the Southern Patagonian Ice Field, Cerro Benítez and the glacial valley of Lago Sofía host several caves and rock shelters that were occupied by megafauna and humans during the Late Pleistocene, including the Mylodon Cave and two of the oldest archaeological sites in Patagonia. During the last glaciation, Cerro Benítez was alternately covered by the Patagonian Ice Sheet and surrounded by an ice-dammed lake which restricted the access to the caves and rock shelters located under its uppermost level, 155 m a.s.l. This study aims to provide a detailed chronology of the deglaciation and lake regression in Cerro Benítez. The glacial fluctuations and the variations of lake level were reconstructed from multi-scale, remote-sensing data and field geomorphological mapping. In addition, we calculated the surface exposure age of 11 erratic blocks located above and on the lacustrine erosional platform using terrestrial cosmogenic 10Be in order to date ice downwasting and lake regression, respectively. Dates of ice downwasting and lake regression events were modelled from prior surface exposure ages using Bayesian statistics. The results suggest that the Patagonian Ice Sheet locally thinned by at least 300 m during MIS 3 in the aftermath of a major glacial advance. Following deglaciation, the ice-dammed lake experienced a slow local regression (ca. 2.5 mm. a−1) until 16.9 ka B2k, interpreted as the result of lake basin tilting due to differential post-glacial isostatic rebound. This initial phase of lake regression was followed by a faster regression caused by the reversal of the lake drainage between 16.9 and 15.4 ka B2k. We assess the chronological model by comparison with uplift and lakeshore erosion rates from the literature and eventually discuss the implications for megafaunal colonisation of the area.

Dam type and lake location characterize ice-marginal lake area change in Alaska and NW Canada between 1984 and 2019

Abstract. Ice-marginal lakes impact glacier mass balance, water resources, and ecosystem dynamics and can produce catastrophic glacial lake outburst floods (GLOFs) via sudden drainage. Multitemporal inventories of ice-marginal lakes are a critical first step in understanding the drivers of historic change, predicting future lake evolution, and assessing GLOF hazards. Here, we use Landsat-era satellite imagery and supervised classification to semi-automatically delineate lake outlines for four ∼5-year time periods between 1984 and 2019 in Alaska and northwest Canada. Overall, ice-marginal lakes in the region have grown in total number (+183 lakes, 38 % increase) and area (+483 km2, 59 % increase) between the time periods of 1984–1988 and 2016–2019. However, changes in lake numbers and area were notably unsteady and nonuniform. We demonstrate that lake area changes are connected to dam type (moraine, bedrock, ice, or supraglacial) and topological position (proglacial, detached, unconnected, ice, or supraglacial), with important differences in lake behavior between the sub-groups. In strong contrast to all other dam types, ice-dammed lakes decreased in number (six fewer, 9 % decrease) and area (−51 km2, 40 % decrease), while moraine-dammed lakes increased (56 more, 26 % and +479 km2, 87 % increase for number and area, respectively) at a faster rate than the average when considering all dam types together. Proglacial lakes experienced the largest area changes and rate of change out of any lake position throughout the period of study and moraine-dammed lakes which experienced the largest increases are associated with clean-ice glaciers (<19 % debris cover). By tracking individual lakes through time and categorizing lakes by dam type, subregion, and topological position, we are able to parse trends that would otherwise be aliased if these characteristics were not considered. This work highlights the importance of such lake characterization when performing ice-marginal lake inventories and provides insight into the physical processes driving recent ice-marginal lake evolution.

Evolution of Glacial Lake Cochrane During the Last Glacial Termination, Central Chilean Patagonia (∼47°S)

Large ice-dammed lakes developed along the eastern margin of the Patagonian Ice Sheet (PIS) during the Last Glacial Termination (T1). Their spatial/temporal evolution, however, remains poorly constrained despite their importance for deciphering fluctuations of the shrinking PIS, isostatic adjustments, and climate forcing. Here we examine the distribution and age of shoreline features deposited or sculpted by Glacial Lake Cochrane (GLC) in the Lago Cochrane/Pueyrredón (LCP) basin, Central Patagonia, following recession of the LCP glacier lobe from its final Last Glacial Maximum (LGM) moraines. GLC drained initially toward the Atlantic Ocean and continuing ice shrinking opened new drainage routes allowing the discharge toward the Pacific Ocean. We identify five clusters of lake terraces, shorelines, and deltas between elevations ∼600–500 (N5), ∼470–400 (N4), ∼360–300 (N3), ∼230–220 (N2), and ∼180–170 masl (N1) throughout the LCP basin. The distribution of these clusters and associated glaciolacustrine deposits provide constraints for the evolving position of the damming glacier bodies. Elevation gradients within the landform clusters reveal glacio-isostatic adjustments that enable us to quantify the magnitude of deglacial rebound and construct isostatically corrected surfaces for the different phases in the evolution of GLC. Our chronology, based principally on radiocarbon dates from lake sediment cores and new OSL dating, suggests that these phases developed between ∼20.7–19.3 ka (N5), ∼19.3–14.8 ka (N4), ∼14.8–11.3 ka (N3), and shortly thereafter (N2 and N1). The N3 landforms are the most ubiquitous, well-preserved, and voluminous, attributes that resulted from a ∼3,500-year long period of glacial stability, enhanced sediment supply by peak precipitation regime, and profuse snow and ice melting during the most recent half of T1. This scenario differs from the cold and dry conditions that prevailed during the brief N5 phase and the moderate amount of precipitation during the N4 phase. We interpret the limited development of the N2 and N1 landforms as ephemeral stabilization events following the final and irreversible disappearance of GLC after N3. This event commenced shortly after the onset of an early Holocene westerly minimum at pan-Patagonian scale at ∼11.7 ka, contemporaneous with peak atmospheric and oceanic temperatures in the middle and high latitudes of the Southern Hemisphere.