Lateral Moraines Research Articles

Very large convergent multi-fluted glacigenic deposits in the NW Highlands, Scotland

We describe two large convergent multi-fluted glacigenic deposits in the NW Highlands, Scotland, and point out their resemblance to a number of landforms emerging from presently deglaciating areas of Greenland and Antarctica. We suggest that they all result from locally sourced sediment being deposited by local ice-flow, which was laterally confined by the margins of much larger adjacent glaciers or ice-streams. The NW Highlands features thus seem likely to be the result of processes active during the latter part of the Devensian Glaciation. One of these deposits, on the peninsula between Loch Broom and Little Loch Broom, is evidently sourced from the west-facing Coire Dearg of Beinn Ghobhlach, but was emplaced in a WNW direction rather than along the WSW fall-line. This suggests that the ice that emplaced it was confined by the margins of large glaciers then occupying the adjacent valleys of Loch Broom and Little Loch Broom. The second much larger and more prominent deposit, in Applecross, is composed of bouldery Torridonian sandstone till emplaced on to glacially scoured bedrock; the only feasible source location for this material is about 12 km distant, which requires that the deposit was carried by ice across the trough of Strath Maol Chalum and emplaced while active ice-streams confined it laterally to its present-day location. This, in turn, requires that ice lay in the Inner Sound between Applecross and Skye to an elevation 400–500 m above present-day sea-level. The Wester Ross Re-advance of 15–14 ka left a fragment of lateral moraine against the most easterly flute and buried the distal end of the flutes with hummocky moraine. We hypothesize that the fluted deposits reflect the locations of the ice-stream margins that constrained deposition of locally derived ice-transported sediment, rather than the flow-lines of the ice-stream itself.

Last Glacial Maximum and Younger Dryas piedmont glaciations in Blidinje, the Dinaric Mountains (Bosnia and Herzegovina): insights from 36Cl cosmogenic dating

The highest parts of the Dinaric Mountains along the eastern Adriatic coast of the southern Europe, known for their typical Mediterranean karst-dominated landscape and very humid climate, were glaciated during the Late Pleistocene. Palaeo-piedmont type glaciers that originated from Cvrsnica Mountain (2226 m a.s.l.; above sea level) in Bosnia and Herzegovina deposited hummocky, lateral and terminal moraines into the Blidinje Polje. We constrained the timing of the largest recognized glacier extent on Svinjaca and Glavice piedmont glaciers by applying the cosmogenic 36Cl surface exposure dating method on twelve boulder samples collected from lateral, terminal and hummocky moraines. Using 40 mm ka–1 bedrock erosion rate due to high precipitation rates, we obtained 36Cl ages of Last Glacial Maximum (LGM; 22.7 ± 3.8 ka) from the hummocky moraines, and Younger Dryas (13.2 ± 1.8 ka) from the lateral moraine in Svinjaca area. The amphitheater shaped terminal moraine in Glavice area also yielded a Younger Dryas (13.5 ± 1.8 ka) age within the error margins. Our results provide a new dataset, and present a relevant contribution towards a better understanding of the glacial chronologies of the Dinaric Mountains. Because our boulder ages reflect complex exhumation and denudation histories, future work is needed to better understand these processes and their influence on the cosmogenic exposure dating approach in a karstic landscape.

Geomorphologic and Glacial Evolution of the Cachapoal and southern Maipo catchments in the Andean Principal Cordillera, Central Chile (34°-35º S)

We present here a reconstruction of the post late Miocene landscape evolution of the western slope of the Andean Cordillera Principal near 34°20’ S. We base our analysis on the available geological information, a morphological characterization of the landform assemblages in the Cachapoal and southern Maipo catchments, and the first 10Be exposure ages for moraines in this area. The Cachapoal drainage basin is characterized by a variety of morphological features, like an elevated low-relief surface, volcanoes and lava flows on valley slopes, U-shaped valley sections, roches moutonnées, and large glaciated areas. Different kinds of deposits have been included in the study, such as moraines, lacustrine and landslide deposits, and a well-developed system of fluvial terraces in the more distal part of the Cachapoal catchment. Landslides are mostly developed on rocks of the late Eocene-early Miocene Abanico Formation. and are less frequent in outcrops of the overlying, early to middle Miocene Farellones Formation. We estimate that the lowest end moraine in the Cachapoal catchment is located next to the locality Bocatoma Chacayes (~950 m altitude), though covered by a major landslide. No evidence exist for glacial deposits further down stream in this region. Lateral moraine ridges of the Cachapoal Glacier at Los Cerrillos yielded 10Be exposure ages of 20.3±2.9 and 21.9±5.3 ka that indicate they are associated with the Last Glacial Maximum (LGM). Holocene moraines exist next to all glacier tongues. Of particular interest in this region is the 12 km-long debris-covered Cachapoal Glacier, the longest valley glacier in the central Chilean Andes, and its distal and proximal moraine deposits. Two lateral moraines adjacent to the present-day Cachapoal Glacier yielded exposure average ages of 13.5±2.4 ka for the external ridge, indicating the Younger Dryas, and 3.8±0.8 ka for the internal ridge, an age that coincides with the 4.2 ka global climatic event that marks the beginning of the Meghalayan Age, at the end of the Holocene. The large size of this moraine on both sides of the ice tongue indicates the great development of the glacier at that time. Some of these ages coincide with ages obtained further north in the Maipo drainage basin, at the latitude of Santiago, and in the eastern flank of the cordillera, however, no pre-LGM deposits were found here, unlike the other mentioned regions. This difference together with the much lower altitude of the LGM moraine deposits in the study region suggests that the Cachapoal catchment is a transition zone to a more humid region further south, and indicates the great need for further reconnaissance and dating of glacial deposits in this Andean region. Our analysis of the geomorphological evolution is consistent with incision start for the Cachapoal Valley in latest Miocene. In this process, glacier incision was apparently not much effective until mid-Pleistocene time, when volcanism was active in the higher regions of the mountain range covering areas not yet incised, whereas in the western Principal Cordillera lavas flowed in deeply incised valleys. Pleistocene glaciers deepened and shaped the already incised valleys, which are presently mostly occupied by rivers.

Sediment supply from lateral moraines to a debris-covered glacier in the Himalaya

Abstract. Debris-covered glaciers in the Himalaya play an important role in the high-altitude water cycle. The thickness of the debris layer is a key control of the melt rate of those glaciers, yet little is known about the relative importance of the three potential sources of debris supply: the rockwalls, the glacier bed and the lateral moraines. In this study, we hypothesize that mass movement from the lateral moraines is a significant debris supply to debris-covered glaciers, in particular when the glacier is disconnected from the rockwall due to downwasting. To test this hypothesis, eight high-resolution and accurate digital elevation models from the lateral moraines of the debris-covered Lirung Glacier in Nepal are used. These are created using structure from motion (SfM), based on images captured using an unmanned aerial vehicle between May 2013 and April 2018. The analysis shows that mass transport results in an elevation change on the lateral moraines with an average rate of -0.31±0.26 m year−1 during this period, partly related to sub-moraine ice melt. There is a higher elevation change rate observed in the monsoon (-0.39±0.74 m year−1) than in the dry season (-0.23±0.68 m year−1). The lower debris aprons of the lateral moraines decrease in elevation at a faster rate during both seasons, probably due to the melt of ice below. The surface lowering rates of the upper gullied moraine, with no ice core below, translate into an annual increase in debris thickness of 0.08 m year−1 along a narrow margin of the glacier surface, with an observed absolute thickness of approximately 1 m, reducing melt rates of underlying glacier ice. Further research should focus on how large this negative feedback is in controlling melt and how debris is redistributed on the glacier surface.

Drivers of peatland water table dynamics in the central Andes, Bolivia and Peru

AbstractCushion plant dominated peatlands are key ecosystems in tropical alpine regions of the Andes in South America. The cushion plants have formed peat bodies over thousands of years that fill many valley bottoms, and the forage produced by the plants is critical for native and nonnative domesticated mammals. The sources and flow paths of water supporting these peatlands remain largely unknown. Some studies have suggested that glacier meltwater streams support some peatlands, and that the ongoing loss of glaciers and their meltwaters could lead to the loss or diminishment of peatlands. We analysed the hydrologic regime of 10 peatlands in four mountain regions of Bolivia and Peru using groundwater monitoring. Groundwater levels in peatlands were relatively stable and within 20 cm of the ground surface during the rainy season, and many sites had water tables 40–90 cm below the ground surface in the dry season. Topographic and groundwater elevations in the peatlands demonstrated that the water source of all 10 peatlands was hillslope groundwater flowing from lateral moraines, talus, colluvium, or bedrock aquifers into the peatlands. There was little to no input from streams, whether derived from glacier melt or other sources, and glacier melt could not have recharged the hillslope aquifers supporting peatlands. We measured the stable water isotopes in water samples taken during different seasons, distributed throughout the catchments, and the values are consistent with this interpretation. Our findings indicate that peatlands in the study region are recharged by hillslope groundwater discharge rather than stream water and may not be as vulnerable to glacial decline as other studies have indicated. However, both glaciers and peatlands are susceptible to changing thermal and precipitation regimes that could affect the persistence of peatlands.

Evolution of debris flow and moraine failure in the Gangotri Glacier region, Garhwal Himalaya: Hydro-geomorphological aspects

A debris flow occurred in the foreland of Gangotri Glacier by its former tributary, Meru (Bamak) Glacier between 16 and 19 July 2017. We investigated the debris flow using pre- and post-event field observations; hydro-meteorological data along with remote sensing assessments to understand the mechanism and evolution of the debris flow. A large volume of sediments (−7.9 × 106 m3 ± 0.1 × 106 m3) moved from the Meru Bamak and adjoining Neela Taal (4380 m a.s.l) during the debris flow, depositing 6.5 × 106 m3 ± 0.1 × 106 m3 of sediments in the frontal region (4050 m a.s.l) of the Gangotri Glacier. This event transported sediments up to 1.5 km downstream, as a debris flow fan-type feature. During the event, ~18% of the sediments were transferred by the meltwater stream. The stream of the Meru Bamak completely dissected and exposed the ice-cored left lateral moraine of the Gangotri Glacier. This event comprehensively reworked the morainic material and entirely changed the morphology of the pro-glacial area. A small pro-glacial lake (area: 5075 m2) is also observed at the snout of Gangotri Glacier because of the blockage by morainic material and sediments. A sharp increase in the concentration of suspended sediments (SSC), reaching 11,370 and 10,605 mg/l on July 18 and 19, respectively was recorded at Bhojwasa (~3 km downstream). Multiple factors such as recession of Gangotri Glacier, degraded ice-cored moraine, loose sediments at the front of the Meru Bamak, and continuous rainfall created favourable conditions for the debris flow. Therefore, geomorphic hazards associated with glacial retreat need to be investigated intensively in the Himalaya especially, in areas where significant glacial retreat is observed, lateral moraines are exposed, and the unstable slopes are occupied by the tributary glaciers.

First 36Cl cosmogenic moraine geochronology of the Dinaric mountain karst: Velež and Crvanj Mountains of Bosnia and Herzegovina

This article presents the first attempt to date moraines in the Dinaric mountain karst using cosmogenic 36Cl surface exposure dating technique. Twenty samples were collected from moraine boulders from two sets of the lowest and largest lateral moraines on the Velež (1965 m asl) and Crvanj mountains (1920 m asl) in Bosnia and Herzegovina. The dated lateral-terminal moraine complexes, spanning elevations from ∼980 to 1350 m asl, are up to 2.7 km long and rise more than 100 m above the valley floor. The moraine boulders yielded 36Cl ages spanning from Oldest Dryas for Velež (14.9 ± 1.1 ka) to Younger Dryas for Crvanj (11.9 ± 0.9 ka), considering the average age of the two oldest samples from each lateral moraine as the most representative time of moraine emplacement. The dated moraines mark the largest extent of glaciers in both study areas, which have been reconstructed to ∼28 km2 for Velež and ∼24 km2 for Crvanj, having a mean equilibrium line altitude at 1388 m and 1541 m, respectively. Under modern precipitation values, which account for ∼2000 mm, the temperature depression between 8 and 10 °C is required to sustain the palaeoglaciers with reconstructed equilibrium line altitudes. Glaciers of similar size with such low equilibrium line altitudes during the Lateglacial have not been reported until now for the Balkan Peninsula. It is very likely that the boulder ages reflect complex exhumation and denudation histories, which at this point do not allow obtaining more precise moraine chronologies for the study areas. Nevertheless, this article delivers new data on the extent and timing of Quaternary glaciations in the Mediterranean mountains, where records of glacier fluctuations seem to be asynchronous amongst different areas. It is clear that dating moraines with cosmogenic 36Cl surface exposure dating in carbonate lithologies in areas of high precipitation like the Dinaric karst, remains challenging.

Pre-Late Wisconsin Valley-Glacier Erratics between Leavenworth and Peshastin, Wenatchee Valley, Washington

The late Wisconsin Icicle Creek alpine glacier transported tonalite boulders from the Mount Stuart batholith to arcuate end moraines in Icicle valley and Wenatchee valley near Leavenworth. Some previous workers considered sparsely weathered Mount Stuart boulders lying outside these moraines and draped by silt as having been ice rafted in a late Wisconsin lake. But the boulders are more likely within drift or end moraines of pre-late Wisconsin glaciations correlative to lateral moraines on Boundary Butte. The silt—a younger deposit that covers the boulders—derives not from a physically ponded lake but apparently from brief Missoula flood(s) backflooding up the valley.

Late Quaternary glaciations and cosmogenic 36Cl geochronology of Mount Dedegöl, south‐west Turkey

ABSTRACTWe present details on the timing of glaciations during the late Quaternary in the western Taurus Mountain Range of Turkey. Twenty‐five boulders from prominent moraines in three northern glacial valleys of Mount Dedegöl (37.40°N, 31.17°E, 2992 m above sea level, ∼15 km west of Lake Beyşehir) were dated based on cosmogenic 36Cl surface exposure. The geomorphological mapping of the N‐NE‐trending Sayacak, Kisbe and Karagöl valleys and their in situ produced 36Cl glacial chronology revealed several glacial episodes during the late Quaternary from (pre‐Last Glacial Maximum (pre‐LGM) to early Holocene. Pre‐LGM glaciations are represented by a push‐hummocky moraine complex in the northern Sayacak Valley and dated to 29.7 ± 2.9 ka. The ages obtained from these hummocky moraines give substantial evidence regarding ice accumulation before the global LGM. In the same valley, glaciers reached their maximum positions at the LGM and deposited lateral moraines at 19.7 ± 1.6 ka. Lateglacial moraines were dated to between 16.4 ± 0.7 and 12.0 ± 1.0 ka in the nearby east‐facing Karagöl valley. The youngest glacial stages occurred during the Younger Dryas stadial (11.5 ± 0.8 ka) and early Holocene (9.8 ± 1.4 ka) in Mount Dedegöl.

Slope instability analysis in South Patagonia applying multivariate and bivariate techniques on Landsat images during 2001–2015 period

We present results of the estimation of surface changes associated with slope instability processes on the Upsala Channel by remote sensing and statistic techniques. Hillslopes, involving lateral moraines, of Upsala Channel at the Argentino Lake have become potentially unstable due to the retreat of Upsala Glacier during the last century. The glaciation and deglaciation processes modify the tensions on the slope stability and may generate landslide processes. A landslide movement destroyed the western edge of the Upsala Channel in February 2013. In addition, the region represents a great tourist attraction usually ships navigate through the Upsala Channel seeing impressive landscapes, especially the Upsala Glacier, stand out. Due to this risky situation the necessity of increasing the knowledge in the area has arisen but has not been addressed yet. Therefore, the main goal of the present study is to investigate the multivariate statistical techniques by the principal component analysis (PCA) and discriminative analysis (DA) in four testing areas (TASn). Besides, we include Pearson's correlation coefficient (PCC) and normal distribution (ND) to determine whether the testing areas suffered slope movements or were temporally stable. The study is based on Landsat optical satellite images, acquired during the period from October 2001 to April 2015. The results show that TAS1,2,4 are less stable, whereas TAS5 is a more stable area as compared to another TAS. The PC1 and PC2 principal components explained the total variability of the 76% data. The total apparent error of DA reached 2.2% points. The PCC achieved a positive trend during the years when movement on the slope surface was not observed; while during the periods when slope instability was observed, the correlation showed a negative trend. The TASn that had shown a different behavior presented contrasted Gaussian bells; they are more flattened in those years with instability events.

Asynchronous glacier dynamics during the Antarctic Cold Reversal in central Patagonia

We present 14 new 10Be cosmogenic nuclide exposure ages quantifying asynchronous readvances during the Antarctic Cold Reversal from glaciers in the Baker Valley region of central Patagonia. We constrain glacier and ice-dammed palaeolake dynamics using a landsystems approach, concentrating on outlet glaciers from the eastern Northern Patagonian Icefield (NPI) and Monte San Lorenzo (MSL). Soler Glacier (NPI) produced lateral moraines above Lago Bertrand from 15.1 ± 0.7 to 14.0 ± 0.6 ka, when it dammed the drainage of Lago General Carrera/Buenos Aires through Río Baker at a bedrock pinning point. At this time, Soler Glacier terminated into the 400 m “Deseado” level of the ice-dammed palaeolake. Later, Calluqueo Glacier (MSL) deposited subaerial and subaqueous moraines in the Salto Valley near Cochrane at 13.0 ± 0.6 ka. These moraines were deposited in an ice-dammed palaeolake unified through the Baker Valley (Lago Chalenko; 350 m asl). The Salto Valley glaciolacustrine landsystem includes subaqueous morainal banks, ice-scoured bedrock, glacial diamicton plastered onto valley sides, perched delta terraces, kame terraces, ice-contact fans, palaeoshorelines and subaerial push and lateral moraines. Boulders from the subaqueous Salto Moraine became exposed at 12.1 ± 0.6 years, indicating palaeolake drainage. These data show an asynchronous advance of outlet glaciers from the Northern Patagonian Icefield and Monte San Lorenzo during the Antarctic Cold Reversal. These advances occurred during a period of regional climatic cooling, but differential moraine extent and timing of advance was controlled by topography and calving processes.

From active to stable: Paraglacial transition of Alpine lateral moraine slopes

AbstractMany retreating Alpine valley glaciers leave large lateral moraines behind. Reworking of these landforms by geomorphic processes is one of the most important paraglacial processes in many Alpine environments. Although several studies investigated moraine reworking by gullying processes, it is not well known what happens when gullying ceases and why and when lateral moraine slopes become stable. This study improves the understanding of the paraglacial transition from active to stable Alpine lateral moraine slopes by assessing potential influencing factors, indicators for completed paraglacial adjustment, and its spatiotemporal patterns using a combination of geomorphic and ecologic data. A geomorphic and ecologic permanent plot survey and geomorphic mapping were carried out on three lateral moraine complexes in the Turtmann glacier foreland (Switzerland). Subsequently, permanent plot data were analysed using multivariate statistics. Our study suggests that ecosystem engineering by colonizing plant species, slope geomorphometry, and material properties are important factors influencing the paraglacial transition from active to stable slopes. Geomorphic processes are often absent once vertical vegetation layers and soil horizons develop, showing that mature vegetation and advanced soil development are valuable indicators for slope stability and completed paraglacial adjustment. In a conceptual model, we describe the paraglacial transition of Alpine lateral moraine slopes as a temporal sequence in which gullying (Stage I), solifluction (Stage II), and finally stabilization (Stage III) follow one after another. In space, paraglacial adjustment is heterogeneous, and resulting patterns can be explained by the identified influencing factors.

Piecing together the Lateglacial advance phases of the Reussgletscher (central Swiss Alps)

Abstract. Exposure dating has substantially improved our knowledge about glacier advances during the Younger Dryas (YD) and the early Holocene. The glacier development after the Last Glacial Maximum (LGM) and the timing of morphologically evidenced, earlier Lateglacial re-advances is, however, still widely unknown. In this study we used 10Be surface exposure and radiocarbon dating to address these phases and corresponding landforms in the catchment of the former Reussgletscher (central Swiss Alps). We obtained clear indication for moraine deposition prior to the YD. The oldest samples predate the Bølling–Allerød interstadial (>14.6 ka). Morphostratigraphically even older lateral moraines, probably corresponding to terminal positions in the Lake Lucerne, could not be dated conclusively. Due to the geomorphological constraints of the sampling environment, the establishment of a local pre-YD chronology remains a challenge: moraines with adequate numbers of datable boulders were rarely preserved, and age attributions based on few samples are complicated by outliers.

Structural glaciology of Isunguata Sermia, West Greenland

ABSTRACTWe present a 1:42,000 scale map of Isunguata Sermia, a land-terminating outlet glacier draining the western-sector of the Greenland Ice Sheet. Structure-from-Motion software applied to ∼3,600 aerial images collected by a fixed-wing unmanned aerial vehicle in July 2015 allowed us to produce a high resolution (0.3 m ground sampling distance (GSD)) orthomosaic and digital elevation model (DEM; 1.5 m GSD).These products were used to map and describe the structural, geomorphological and hydrological features of the lower 16 km terminus of Isunguata Sermia and include many thousands of crevasses, crevasse traces and supraglacial channels. Additionally, several geomorphological features and pro-glacial hydrological features were identified, including debris-covered ice, lateral moraines and ice-marginal lakes. The map has potential for informing and reconstructing the long-term dynamic history of the glacier, including its response to variable environmental forcing.

Bird population changes reconstructed from isotopic signals of peat developed in a nutrient enriched tundra

Five peat sequences were studied to identify the time the little auk Alle alle colonies originated in the Hornsund area (Spitsbergen). Elemental and stable isotope analysis of nitrogen and carbon was applied as markers for bird activity. The peat sequences were dated with 210Pb and radiocarbon methods. The results showed that peat development related to seabird activity is significantly older (at least 300 years old) in localities closer to the fjord's mouth (west) than those located deeper in the fjord (east), which are ~100 years old. Isotopic signals indicated that bird activity in the western localities decreased simultaneously with the growth of the eastern colonies. Colonization by birds of new localities correlated with the termination of the Little Ice Age and the meaningful decrease in the glacier area of the region. Hence, we suggest that the availability of new localities for nesting in talus cones, nival moraines and lateral moraines on gentle mountain slopes with south-eastern exposition attracted the little auk due to better thermal conditions, isolation from strong westerly winds and better protection from predation by gull Larus hyperboreus. The expansion of little auks to the new localities was fast (20–30 yrs), and there are no records of changes in bird impacts on the tundra environment after 1920.

Technical note: A low-cost albedometer for snow and ice measurements – theoretical results and application on a tropical mountain in Bolivia

Abstract. This study presents a new instrument called a low-cost albedometer (LCA) composed of two illuminance sensors that are used to measure in situ incident and reflected illuminance values on a daily timescale. The ratio between reflected vs. incident illuminances is called the albedo index and can be compared with actual albedo values. Due to the shape of the sensor, the direct radiation for zenith angles ranging from 55 to 90∘ is not measured. The spectral response of the LCA varies with the solar irradiance wavelengths within the range 0.26 to 1.195 µm, and the LCA detects 85 % of the total spectral solar irradiance for clear sky conditions. We first consider the theoretical results obtained for 10 different ice and snow surfaces with clear sky and cloudy sky incident solar irradiance that show that the LCA spectral response may be responsible for an overestimation of the theoretical albedo values by roughly 9 % at most. Then, the LCA values are compared with two “traditional” albedometers, which are CM3 pyranometers (Kipp & Zonen), in the shortwave domain from 0.305 to 2.800 µm over a 1-year measurement period (2013) for two sites in a tropical mountainous catchment in Bolivia. One site is located on the Zongo Glacier (i.e., snow and ice surfaces) and the second one is found on the crest of the lateral moraine (bare soil and snow surfaces), which present a horizontal surface and a sky view factor of 0.98. The results, at daily time steps (256 days), given by the LCA are in good agreement with the classic albedo measurements taken with pyranometers with R2=0.83 (RMSD = 0.10) and R2=0.92 (RMSD = 0.08) for the Zongo Glacier and the right-hand side lateral moraine, respectively. This demonstrates that our system performs well and thus provides relevant opportunities to document spatiotemporal changes in the surface albedo from direct observations at the scale of an entire catchment at a low cost. Finally, during the period from September 2015 to June 2016, direct observations were collected with 15 LCAs on the Zongo Glacier and successfully compared with LANDSAT images showing the surface conditions of the glacier (i.e., snow or ice). This comparison illustrates the efficiency of this system to monitor the daily time step changes in the snow and ice coverage distributed on the glacier. Despite the limits imposed by the angle view restrictions, the LCA can be used between 45∘ N and 45∘ S during the ablation season (spring and summer) when the melt rate related to the albedo is the most important.

The glacial landsystem of a tropical glacier: Charquini Sur, Bolivian Andes

AbstractThe geomorphological signature of tropical glaciers has the potential to provide important information on the response of ice masses in high‐mountain environments to climate warming. This study investigates the glacial geomorphology of Charquini Sur, Bolivia. Detailed geomorphological mapping was conducted both in the field and from satellite imagery in order to produce a 1:4000 scale geomorphological map of the glacier foreland. Sedimentological analyses (description of physical characteristics, clast shape and roundness, particle‐size distribution) provided additional insight into the landform–sediment assemblage. Glacial landforms are well preserved and include up to 11 moraine ridge suites, seven of which are cross‐valley frontal moraine arcs. These can be linked to an existing lichenometric chronology from previous work and record glacier recession since the local Little Ice Age (LIA) maximum in the late‐1600s. Lateral moraine ridges also record continuous thinning of the glacier over this time period. Smaller groups of parallel ridges are interpreted as annual moraines formed during recession. Intermorainic areas consist of flutings and a typically thin sediment cover of subglacial, supraglacial and glaciofluvial origin, with prominent ice‐moulded bedrock protuberances in places. Analysis of the landform–sediment assemblage provides an insight into the main controls on landform genesis in the basin and implies there have been temporal changes in ice‐marginal dynamics since the LIA. We present the first landsystem model for a tropical cirque glacier, documenting its behaviour since the LIA and providing an indication of glacier response in rapidly‐warming high‐mountain environments. Copyright © 2018 John Wiley & Sons, Ltd.

Divergence, convergence, and path dependency of paraglacial adjustment of alpine lateral moraine slopes

AbstractLateral moraines represent important sediment storages and are one of the most dynamic areas within glacier forelands. Following glacier retreat, lateral moraine slopes adjust as their material is reworked by paraglacial processes. Previous research focused primarily on the role of gullying, however, path‐dependent slope adjustment and divergent adjustment of lateral moraine slopes are poorly understood. We report data from geomorphic and vegetation mapping, electrical resistivity tomography, soil moisture measurements, and soil texture analysis acquired in the Turtmann glacier foreland in the Swiss Alps where periglacial processes are abundant. We demonstrate that paraglacial slope adjustment shows divergent, convergent, and path‐dependent behaviour. Steep proximal moraine slopes are first eroded by gullying processes. When moraine slopes reach a threshold angle of 30°, the importance of solifluction increases, and solifluction processes subsequently rework debris flow deposits. In contrast, more gently inclined distal slopes are below the threshold angle immediately following glacier retreat and biogeomorphic feedbacks result in an earlier onset of solifluction processes. We identified two different types of turf‐banked solifluction lobes based on their temporal development and genesis. Lobe Type 1 develops on distal moraine slopes and reworks glacial till, whereas Lobe Type 2 evolves from debris flow deposits at the footslopes of the lateral moraines. Both lobe types can only be differentiated using actual shape. Overprinting by subsequent geomorphic processes can result in equifinal and convergent forms such as solifluction sheets from the Last Glaciation. Our study provides an actualistic example of how paraglacial solifluction in 90 to 150 years rapidly reworks glacial sediments.

Luminescence chronology and climatic implication of the late quaternary glaciation in the Nubra valley, Karakoram Himalaya, India

The present study investigates moraines, outwash gravel terraces, relict lake deposits and alluvial fans to reconstruct the pattern of glacier advances and associated climate variability in the Nubra Valley, Karakoram Himalaya, India. Optical chronologies obtained on stratigraphically constrained lateral moraines indicate that the oldest preserved record of glacier advance (Tirith-II) is dated to 60.4 ± 5.2 ka and corresponds to Marine Isotopic Stage-4 (MIS-4). During MIS-4, the Nubra valley was occupied by ~700 m thick ice cover that extended beyond the Nubra-Shyok confluence. It was followed by pulsating decrease in the ice-volume (vertical shrinking) with an insignificant lateral recession that continued until around 42.0 ± 3.0 ka (mid- MIS-3). The second major glacial advance (Tirith-I) is dated to 30 ± 2.5 ka (beginning of MIS-2) when the Siachen glacier reached up to the Nubra-Shyok confluence albeit, with lesser ice thickness (~300 m). The Tirith-I glacier advance continued to occupy the entire Nubra valley until around 18.2 ± 1.8 ka (Last Glacial Maximum). A deglaciation followed after 15.8 ± 1.6 ka and continued until the early Holocene (10.3 ± 1.3 ka). The third minor glacial advance-Siachen Glacial Advance (SGA) is dated to the mid-Holocene (6.8 ± 1.0/7.2 ± 1.4 ka) when the glacier extended below the Siachen glacier snout, whereas the youngest glacial expansion reached a few hundred meters below the present day snout and is dated between 1.0 ± 0.4 ka and 0.5 ± 0.2 ka.The study suggests that glacier advances were driven by a decrease in temperature with corresponding increase in the moisture contribution due to the enhanced mid-latitude westerlies during MIS-4, MIS-2, and the mid-Holocene. Within the age uncertainty, it can be suggested that the snout-proximal recessional moraines indicate marginal glacier expansion during the Little Ice Age (LIA). Following this, the glacier receded to its present position and seems to have stabilized since then. Unlike other Himalayan glaciers, the Siachen glacier does not show any alarming retreat after the LIA and is in conformity with recent observations suggesting that the glaciers in Karakoram region are either marginally advancing or stand still.

Valley glaciers persisted in the Lake District, north‐west England, until ∼16–15 ka as revealed by terrestrial cosmogenic nuclide (10Be) dating: a response to Heinrich event 1?

ABSTRACTThe Lake District of north‐west England acted as an independent centre of ice dispersal within the more extensive British–Irish Ice Sheet (BIIS) during the Last Glacial Maximum, but relatively little is known about the pattern and timing of glacier retreat. Four new terrestrial cosmogenic nuclide (10Be) surface exposure ages from boulders from a lateral moraine in the Duddon valley, south‐west Lake District, have yielded internally consistent ages with uncertainty‐weighted means of 16.51 ± 0.78 ka (using the Loch Lomond production rate with Lm scaling and 1 mm ka−1 erosion rate) and 16.15 ± 1.30 ka (using CRONUScalc with SA scaling and 1 mm ka−1 erosion rate). It is inferred that glacier retreat from the moraine occurred in the interval ∼16.5–16.1 ka but that a valley glacier continued to exist, probably until ∼15 ka. The Duddon valley ages agree with other surface exposure ages from Wasdale, Watendlath and the Shap fells, together demonstrating that glacier ice was still widespread in the Lake District at ∼17–15 ka. There is also consistency with ages from other sectors of the BIIS that are considered to have responded to North Atlantic Heinrich event 1.