GM7.3

GM7 EDI
Mountain glaciations: Developments in geomorphology, geochronology, glaciology and climate change 

Mountain glaciations have a long research heritage since they provide an invaluable record for past and present climate change. However, complex glaciological conditions, geomorphological processes and topography can make regional and intra-hemispheric correlations challenging. This problem is further enhanced by ongoing specialisation within the scientific community, whereby working groups often focus on individual aspects or selected mountain regions, thus frequently remain disconnected.

The main incentive for this session is to evaluate the potential of mountain glaciation records and stimulate further discussion to work towards bridging between specialised research communities. Contributions on all relevant aspects are welcomed, including (but not limited to): (a) glacial landforms and glacier reconstructions, (b) dating techniques and glacier chronologies, (c) glaciology and palaeoclimatic interpretations, (d) impacts on ecosystems and human society.

A special regional focus within the session will be dedicated to the Andean Cordillera and topics such as glaciers and palaeoclimatic records from the Andean Cordillera or model-data comparisons that aim to improve projections of future climate and ice-mass behaviour in the Andes and beyond.

Submissions involving interdisciplinary studies, complex interactions or highlighting the specific conditions of mountain glaciations, from continental to maritime regions at any latitude, are encouraged. The potential of related studies should be highlighted alongside strategies to tackle existing challenges as this will enable the session to fully address the diversity of the topic.

In past years, precursors of this session have steadily become a popular platform for everyone interested in the emerging collaborative research network, “The Legacy of Mountain Glaciations”. This network continues to grow, and we hope the 2022 session will provide an opportunity to meet and exchange new ideas and expertise.

Co-organized by CL4/CR5
Convener: Stefan Winkler | Co-conveners: Bethan Davies, Danni Pearce, Jacob BendleECSECS, Emma Cooper, Neil Glasser, Giovanni Monegato, Rachel OienECSECS, Jürgen Reitner
Presentations
| Mon, 23 May, 15:10–18:30 (CEST)
 
Room G2

Session assets

Session materials

Presentations: Mon, 23 May | Room G2

Chairpersons: Stefan Winkler, Giovanni Monegato
15:10–15:12
15:12–15:18
|
EGU22-250
|
ECS
|
On-site presentation
Onur Altinay, Mehmet Akif Sarıkaya, Attila Çiner, Cengiz Yıldırım, Manja Žebre, and Uroš Stepišnik

The Taurus Mountain Range extends parallel to the Mediterranean coast of Turkey. It hosts lofty mountains (>3000 m above sea level, a.s.l.) carved by glaciers in the Late Pleistocene. Despite the recent studies in Anatolia, Mt. Davraz (2635 m a.s.l.) has not been studied in detail and its glacial chronology was lacking. This study presents our first findings of the glacial history, origin and geochronology of Mt. Davraz, which is located SW of Eğirdir Lake (915 m a.s.l.), 100 km north of Antalya city. Tectonics, karstification, glaciation, and periglaciation have led a distinctive geomorphology of the area. The main landscape of the area is predominantly shaped by paleoglaciers. Cirques are the dominant glacial erosional landforms, and most of them were developed on the northern slopes of Mt. Davraz. Based on the topographical limitations, cirque paleoglaciers could not to transformed into valley glaciers. Although it is one of the lowest mountains in the Taurus Mountain Range, it has a large hummocky field with an area of about 3 km2 on the northern slope. It was developed by a paleo-ice cap. There is also a smaller hummocky field deformed by a rock glacier advancements on the E-NE slopes of the mountain. In order to understand the timing of paleoglaciations, we obtained 6 cosmogenic 36Cl surface exposure ages from the moraine boulders on hummocky field. Based on the preliminary results, Mt. Davraz hummocky field yielded sequential retreat history; the eastern hummocky field deposited their moraines at 21.7 ± 1.5 ka ago, while the western hummocky field at 17.7 ± 1.2 ka ago. Our results show that the glaciers started to retreat by the Last Glacial Maximum (LGM) and continued to the earlier stages of Late-glacial.

This work was supported by TÜBİTAK 118Y052 and 118C329 projects.

 

How to cite: Altinay, O., Sarıkaya, M. A., Çiner, A., Yıldırım, C., Žebre, M., and Stepišnik, U.: Timing of Glacier Retreat on Mt. Davraz by Cosmogenic Chlorine-36 in the Western Turkey, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-250, https://doi.org/10.5194/egusphere-egu22-250, 2022.

15:18–15:24
|
EGU22-7360
|
Virtual presentation
Zsófia Ruszkiczay-Rüdiger, Zoltán Kern, Marjan Temovski, Balázs Madarász, Ivica Milevski, Johannes Lachner, and Peter Steier

In the Jakupica Mt. (North Macedonia, Central Balkan Peninsula; ~41.7° N, ~21.4 E; maximum elevation: 2540 m asl) a large plateau glacier was reconstructed. The lowest mapped moraines in the northeastern valleys are at elevations of 1490-1720 m asl and suggest the former existence of glacier tongues of ~3 km length. The maximum ice extent and five deglaciation phases were reconstructed. The equilibrium line altitude (ELA) of the most extended glacial phase is 2073+37/-25 m asl. The 10Be Cosmic Ray Exposure (CRE) age (n=8) of this phase was estimated at 19.3+1.7/-1.3 ka, conformable with the LGM similarly to the nearby Jablanica Mt [1]. CRE ages from the next moraine generation placed the first phase of deglaciation to 18.2+1.0/-3.0 ka (n=8). The samples from the moraine of the penultimate deglaciation phase (n=5) provided CRE ages with large scatter and biased towards old ages, which is probably the result of inherited cosmogenic nuclide concentrations within the rock [2, 3], as it was suggested in the cirques of the Retezat Mt. [4].

Glacio-climatological modelling was performed under constrains of geomorphological evidence in order to make paleoclimatological inferences. The degree-day model was used to calculate the amount of accumulation required to sustain the glaciological equilibrium assuming a certain temperature drop at the ELA for the most extended stage.

If the LGM mean annual temperature and the increased annual temperature range suggested by pollen-based paleoclimate reconstructions [5] are placed into the glaciological model the estimated annual total melt at the LGM ELA implies much wetter conditions compared to the current climate. This is in contrast with the regional LGM annual precipitation reconstructions of the same dataset, which suggests ~25% decrease in the Jakupica Mt. Alternatively, the model can be constrained with the current annual temperature range and the regional estimates of LGM temperature drop at 6-7 °C. This suggests 1.3 to 1.8 times more simulated precipitation than today.

These results support paleoclimate models, which predict increased precipitation in this region and suggest that in the Central Balkan region either the precipitation or the annual temperature amplitude (or both) are inaccurate in the pollen-based paleoclimate reconstruction database.

 

Funding: NKFIH FK124807; GINOP-2.3.2-15-2016-00009; RADIATE 19001688-ST.

 

 

[1] Ruszkiczay-Rüdiger et al. 2020. Geomorphology 351: 106985

[2] Ruszkiczay-Rüdiger et al. 2021. GRA, EGU21-4573

[3] Ruszkiczay-Rüdiger et al. 2021. vDEUQUA2021, Book of Abstracts, DOI: 10.5281/zenodo.5526214

[4] Ruszkiczay-Rüdiger et al. 2021. Geomorphology, 107719.

[5] Bartlein, et al. 2011. Clim. Dyn. 37, 775–802.

How to cite: Ruszkiczay-Rüdiger, Z., Kern, Z., Temovski, M., Madarász, B., Milevski, I., Lachner, J., and Steier, P.: Late Pleistocene glacial advances, equilibrium-line altitude changes and paleoclimate in the Jakupica Mt. (North Macedonia), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7360, https://doi.org/10.5194/egusphere-egu22-7360, 2022.

15:24–15:30
|
EGU22-2910
|
ECS
|
On-site presentation
Cristina-Ioana Balaban, David H. Roberts, David J.A. Evans, and Stewart S.R. Jamieson

Reconstructing the extent, style, timing and drivers of past mountain glaciation is crucial in both understanding past atmospheric circulation and predicting future climate change. Unlike in high-elevation mountains situated in maritime and continental climates, less is known of past glaciation in mid-altitude mountains, located in transitional climates, such as the Southern Carpathians of Romania. Despite these mountains harbouring a rich glacial geomorphology, this has never been systematically mapped according to well-established morphological criteria, nor confidently related to former styles of glaciation. Therefore, filling this gap is important for not only accurately identifying glacial extents, but also for establishing past glaciation styles and relating them to past ice dynamics and climate. We aim to understand the extent and timing of past glaciation in the Godeanu Mountains, Southern Carpathians. We present a new geomorphological map of the area, highlighting landforms associated with glaciation of the Scărișoara plateau and surrounding valleys. Using both remote (orthophotographs and Google Earth) and field mapping techniques, we describe and interpret the origins of glacial erosional landforms (ice-moulded bedrock, ice-marginal meltwater channels), and of depositional discrete debris assemblages of likely glacial (moraines), periglacial (pronival ramparts, protalus lobes, rock glaciers) and paraglacial (rock slope failure) origins. We also hypothesize the relationship of these landforms with former styles of glaciation. The field study results aid the interpretation of the geomorphology in the wider mountain range. Once absolute chronological results have been produced, the mapping will be used as a spatial constraint for numerical ice-flow modelling in the Parallel Ice Sheet Model (PISM).

How to cite: Balaban, C.-I., Roberts, D. H., Evans, D. J. A., and Jamieson, S. S. R.: The glacial geomorphology of the Scărișoara Plateau, Godeanu Mountains, Southern Carpathians, Romania, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2910, https://doi.org/10.5194/egusphere-egu22-2910, 2022.

15:30–15:36
|
EGU22-1698
|
ECS
|
On-site presentation
Marcelo Fernandes, Marc Oliva, Gonçalo Vieira, David Palacios, José Maria Fernández-Fernández, Magali Delmas, Julia García-Oteyza, Irene Schimmelpfennig, Josep Ventura, and Aster Team

The Upper Garonne Basin constituted the longest glacier of the Pyrenean ice field during the Late Pleistocene. From the peaks of the axial Pyrenees that exceed 2,800-3,000 m, the Garonne palaeoglacier flowed along ~80 km northwards during the major glacial advances reaching only 420-440 m. This palaeoglacier reached the Pyrenean foreland, at the Loures-Barouse-Barbazan basin (LBBB) where it formed a terminal moraine complex that is examined in this work. We have constrained the timing of the maximum glacial extent as well as the onset of the deglaciation from the end of the Last Glacial Cycle (LGC) based on the geomorphological observations and a 12-sample dataset of 10Be Cosmic-Ray Exposure (CRE) ages. There are two moraine systems at the LBBB, where the first is composed of weathered ridges at the outermost part of the basin and the second encompasses well-preserved ridges stretching across the innermost part of the basin. Chronological data shows that the external moraines were abandoned by the ice at the end of the Penultimate Glacial Cycle (PGC) and the onset of the Eemian Interglacial, at ~129 ka. The few existing reliable boulders to date in the internal moraine showed inconsistent ages as they were probably affected by post-glacial processes and therefore, this work adds no evidence of subsequent glacial advances or standstills during the LGC in the LBBB. However, the terminal basin was already deglaciated during the global Last Glacial Maximum (GLGM) at 24-21 ka, as revealed by exposure ages from polished surfaces at the confluence of the Garonne-la Pique valleys, 13 km south of the entrance of the LBBB. This study introduces the first solid CRE database in the Pyrenees for the glacial advance that occurred during the PGC and provides also new evidence from the GLGM when the Garonne palaeoglacier had already significantly shrunk.

How to cite: Fernandes, M., Oliva, M., Vieira, G., Palacios, D., Fernández-Fernández, J. M., Delmas, M., García-Oteyza, J., Schimmelpfennig, I., Ventura, J., and Team, A.: Maximum glacier extent of the Penultimate Glacial Cycle in the Upper Garonne Basin (Pyrenees): new chronological evidence, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1698, https://doi.org/10.5194/egusphere-egu22-1698, 2022.

15:36–15:42
|
EGU22-12198
|
ECS
|
Virtual presentation
Margaret Jackson, Gordon Bromley, and Brenda Hall

Mapping and dating former glacial margins is a key tool for assessing the sensitivity of glaciers to changing climate conditions, both past and future. However in many regions, such as along the northeastern margins of the North Atlantic, direct chronologic control on past glacier extent can be sparse. In particular, the former extent and elevation of the Irish Ice Sheet (IIS) during the Last Glacial Maximum (LGM; 26-19 ka) and subsequent termination remain a topic of debate - due in part to the coarse resolution of existing (direct) age control on glacial margins. This includes the margins of former valley and cirque glaciers that nucleated in the Irish highlands after local retreat of the IIS. In eastern Ireland, the Wicklow Mountains host numerous valley and cirque moraines that are largely undated, evidence of past glacial fluctuations following the LGM. Here we report new geomorphic mapping and cosmogenic beryllium-10 surface-exposure ages of moraines in the Glen of Imaal in the southwestern Wicklow Mountains. Our preliminary beryllium-10 ages provide new chronologic constraint on the extent of glaciers in the Glen of Imaal following the LGM. We also compare our preliminary glacial chronology with records of wider North Atlantic climate to investigate the response of ice in the Glen of Imaal to changing climate conditions. These data provide new insight on Ireland’s glacial past, and yield vital information on climate and glaciation in the wider North Atlantic region. 

How to cite: Jackson, M., Bromley, G., and Hall, B.: Glacial fluctuations in the southwestern Wicklow Mountains, Ireland., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12198, https://doi.org/10.5194/egusphere-egu22-12198, 2022.

15:42–15:48
|
EGU22-7499
|
ECS
|
On-site presentation
Lukas Rettig, Irka Hajdas, Giovanni Monegato, Paolo Mozzi, and Matteo Spagnolo

Recent studies have shown that during the last glacial cycle the extent, timing and style of glaciation was not uniform across the European Alps but influenced by local topographic or climatic factors. In the south-eastern part of the mountain range, for example, glaciers not only developed in the inner-Alpine sectors but also along the pre-Alpine chains, probably fuelled by high orographic precipitation in these regions. Despite their high climatic sensitivity, the evolution of these glaciers throughout the last glacial cycle is still not fully understood and more field data are needed to enable comparisons among different sites. To address this issue, we present new results from the Monte Cavallo Group (Venetian Prealps, NE-Italy), based on detailed geomorphological mapping, glacier reconstructions and Equilibrium Line Altitude (ELA) modelling; then we compare our findings to other paleoglaciers that existed along the fringe of the southern Alps.

The oldest sediments in the Monte Cavallo Group are deposits of a small lake basin, rich in organic macrofossils such as branches and bark remains. These sediments likely date back to at least the earliest part of MIS 3, or potentially even previous interglacial periods. As climate deteriorated towards the Last Glacial Maximum (LGM), glacier tongues advanced from the peak regions into the main valleys. While towards the west, some small tributaries merged with the large Piave glacier, most of the glacial system of the Monte Cavallo remained independent. Its maximum extent is marked by prominent lateral and frontal moraine ridges that allowed reconstructing the geometry and ELA of the glaciers during the LGM. Besides the valley glaciers, also mid-altitude plateaus were at least temporarily covered by ice, however these plateau glaciers probably quickly vanished after the LGM acme, due to their restricted elevation range. Glacial retreat in the valleys, on the other hand, was intermitted by phases of stagnancy or readvance, as indicated by smaller moraine ridges up-valley. Comparing these Late Glacial moraines with other regional records may reveal important patterns regarding the early stages of post-LGM deglaciation in the south-eastern Alps.

How to cite: Rettig, L., Hajdas, I., Monegato, G., Mozzi, P., and Spagnolo, M.: New insights into the last glacial cycle in the south-eastern European Alps from the glacial geomorphological record of the Monte Cavallo (NE Italy), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7499, https://doi.org/10.5194/egusphere-egu22-7499, 2022.

15:48–15:54
|
EGU22-7124
|
ECS
|
On-site presentation
Gerit E.U. Griesmeier, Jürgen M. Reitner, and Daniel P. Le Heron

The Gröbminger Mitterberg, an isolated flat hill located within the Enns Valley, consists of fluvial, deltaic and lake bottom sediments on top of bedrock, which are covered by subglacial till. In comparison, the sedimentary succession in the Sölk Valleys, which drain into the Enns Valley, is more divers. The highest peaks reaching 2680 m a.s.l. and cirques are dominated by talus, relict rock glaciers and two groups of moraine ridges. Latero-frontal moraine ridges located higher than 1900 m a.s.l. are remarkable. Frequently, two or three ridges are located close to each other and have a morphologically fresh shape. Further downvalley, single laterao-frontal moraine ridges occur, which are often flattened and less prominent. They appear in different altitudes according to their catchment area. However, they do not reach the main valley floor. The slopes of the main valleys and secondary valleys are often covered by subglacial till and reworked slope deposit,s which are dominated by a silty-sandy matrix and angular to subrounded clasts. Additionally, many slopes have been affected by mass movements. At the valley mouth of secondary valleys, ice marginal sediments occur consisting of very rounded pebbles in a sandy matrix and in some areas, cross bedding can be observed. Slightly above the valley floor of the main valleys, gently sloping terrace bodies interfingering with truncated alluvial fans and slope sediments described above occur. These deposits are diamicts, which consist of sandy or silty matrix with rounded and angular clasts.

An interpretation of these findings suggests the following landscape evolution:

The sedimentological record of Gröbminger Mitterberg suggests aggradation of the Enns Valley floor to at least 850 m a.s.l. (200 m higher than today) prior to the Last Glacial Maximum (LGM). During the LGM, the area was covered by the Enns Glacier with tributary glaciers from the Sölk Valleys. The ice surface reached 1800 m a.s.l. in the northernmost part (in the Enns Valley), roughly 2100 m a.s.l. in the southernmost part at a transfluence pass (Sölkpass) and even higher altitudes in cirques. During that time, large areas were covered by basal till. With the breakdown of the ice mass and ice surface lowering at the onset of the phase of ice-decay, trunk glaciers and cirque glaciers got separated resulting in the formation of ice-marginal lakes. On the already ice-free slopes, reworking of the previously deposited sediment and mixing with talus started. Further, climate warming proceeded and ice retreat resulted in mass movements and rock falls. As soon as the valley floor was ice-free, aggradation started by large river systems accumulating sediment in the valley floor. This was followed by two separate cold stages, the Gschnitz Stadial (Heinrich Event 1, ~16-17 ka) and the Egesen Stadial (Younger Dryas, ~12-13 ka), where cirque glaciers developed in equilibrium with climate oscillations (up to three stabilisation phases recognised during Egesen Stadial). In the Holocene, climate warming led to river incision in the main valleys and resulted in today´s landscape.

How to cite: Griesmeier, G. E. U., Reitner, J. M., and Le Heron, D. P.: Landscape evolution of the Sölk Valleys and adjacent regions from the last Interglacial to today (Niedere Tauern range, Austria), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7124, https://doi.org/10.5194/egusphere-egu22-7124, 2022.

15:54–16:00
|
EGU22-9602
|
ECS
|
On-site presentation
Sandra M. Braumann, Joerg M. Schaefer, Stephanie Neuhuber, and Markus Fiebig

Glaciers provide an excellent natural laboratory for reconstructing the climate of the past as they respond sensitively to climate oscillations with advance or retreat. Therefore, we study glacier systems and their behavior during the transition from colder to warmer climate episodes in glaciated valleys of the Silvretta Massif in the Austrian Alps.  

Using a combination of geomorphological mapping and beryllium-10 surface exposure dating, we reconstruct ice extents of the past and find that glaciers stabilized during the Pre-Bølling to Bølling transition (14.4 ± 1.0 ka, n=3), during the Younger Dryas (ca. 12.9-11.7 ka; n=7), and during the earliest Holocene (ca. 12-10 ka; n=2). The first, (pre)-Bølling age group indicates a stable ice margin that postdates the Gschnitz stadial (ca. 17-16 ka) and predates the Younger Dryas. It shows that local inner-alpine glaciers prevailed until the onset of the Bølling warm phase (ca. 14.6 ka) or possibly even into the Bølling. The second Younger Dryas age group captures the spatial and temporal fine structure of glacier retreat during the Egesen stadial prior to Holocene warming. It evidences ice surface lowering of several tens of meters throughout the Younger Dryas, which is indicative of milder climate conditions at the end of the stadial compared to its beginning. The third age group falls into a period of substantial warming, the Younger Dryas-Holocene transition. The deposition of moraines during a period of abrupt warming implies centennial-scale cold snaps that were probably caused by feedback in the climate system. An explanation proposed in the Younger Dryas-Holocene context is the deglaciation of ice sheets in the Northern hemisphere and resulting freshwater input into the Atlantic ocean, which in turn slowed down ocean circulations and thus reduced heat transport toward (Northern) Europe.

The new geochronologies synthesized with pre-existing moraine records from the Silvretta Massif show that the transition from glacial to interglacial climate conditions occurred within a few centuries and illustrate the sensitive response of Silvretta glaciers to abrupt warming events in the past. Our ice-margin reconstructions provide an example of the response of glaciers and the climate system in a warming world.

How to cite: Braumann, S. M., Schaefer, J. M., Neuhuber, S., and Fiebig, M.: Climate transitions during the Late Glacial and the Early Holocene reconstructed from moraine records in the Austrian Alps, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9602, https://doi.org/10.5194/egusphere-egu22-9602, 2022.

16:00–16:06
|
EGU22-4623
|
ECS
|
Virtual presentation
Laura Simoncelli, Alberto Bosino, Vít Vilímek, Jan Kropáček, and Michael Maerker

The origin of the Southern sub-Alpine lakes was intensively discussed in the past century. Morphological observations, combined with seismic reflection acquisitions provided the fluvio-glacial origin of them. However, the formation and the post-Messinian evolution of the smaller lakes between the two branches of the Como Lake, Southern Alps, Italy, was only marginally investigated so far. This area is regionally named Triangolo Lariano, and several authors hypothesised the post-Messinian evolution of Segrino Lake area connecting its formation with the initial Messinian incision followed by the morainic block during the Last Glacial Maximum (LGM). The proposed study re-evaluates the origin of Segrino Lake as well as the lower Triangolo Lariano area, using morphological observation, orthophoto interpretation, detailed Terrain analysis on high-resolution DEM and finally, the interpretation and correlation of borehole stratigraphy. The results highlight a complex morphological evolution of the area up to the pre-Messinian times. In fact, considering the morphology and the geological characteristics of the bedrock as well as the morphometry of the area, fluvial and glacial phases were observed. Deep incised valleys linked with the Messinian Sea level change, and a complex drainage system are clearly detectable on the field and from detailed Terrain analysis. Finally, to reconstruct the paleogeography and order the chronology of the geological events that have occurred in the area, a set of borehole data were interpreted. These analyses allowed to observe an alternation of strata characterized by heterogeneous and interstratified deposits, that reflected a sequence of lacustrine, fluvial, glacial, lacustrine, and fluvial deposits. In fact, the careful evaluation of the stratigraphy highlights the presence of a pre-Messinian lacustrine phase in the area North of Segrino Lake. In addition, fluvial deposits, suspended valleys and paleo-meanders suggest a strong erosive phase dating back to the Messinian age. During this period, the Lambro River deeply incised into the bedrock forming the actual Segrino Valley. Subsequently, the glaciation phase remodelled the area, depositing erratic boulders and morainic material that caused changes in the drainage settings. In particular, the morainic barrier South of Segrino Lake is responsible for the formation of a new lake in the Segrino-Canzo area as well as in the lower part of the study area were the Pusiano and Alserio Lakes are located nowadays. In the following period the deglaciation and the new hydrological asset of the area led to a shrinking of Segrino-Canzo Lake, and finally a drainage inversion of Segrino Lake, with the outflow directed towards North, and the formation of an alluvial fan which isolated the actual Segrino Lake. Finally, the hypothesis already formulated in the past by some other authors, regarding the presence of a lake that he would fill the study area after the LGM, is therefore supported. New evidence due to the available borehole stratigraphy allowed us to recognize a new and more complex and highly heterogeneous evolution of the study area from Messinian time onwards.

How to cite: Simoncelli, L., Bosino, A., Vilímek, V., Kropáček, J., and Maerker, M.: Paleogeographic reconstruction of Segrino Lake area: Southern Alps, Northern Italy, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4623, https://doi.org/10.5194/egusphere-egu22-4623, 2022.

16:06–16:12
|
EGU22-8595
|
ECS
|
On-site presentation
Ferdinando Musso Piantelli, Sandro Truttmann, and Marco Herwegh

The susceptibility of catchment rocks to glacial erosion may control the evolution of valley morphology in high-relief mountain ranges such as the Alps. Non-uniform proneness to bedrock erosion may indeed localize knickpoints and overdeepenings characteristic of glacial valleys. Yet, little is known about the explicit influence of bedrock properties (i.e. lithology, hardness, and geological structures) on glacial erosion processes. In this study, we select the Great Aletsch Glacier (Swiss Alps) as a natural laboratory to document and investigate the relationship between bedrock properties and subglacial erosion mechanisms. The Great Aletsch Glacier with a length of more than 20km and an ice thickness of up to 800m is the largest glacier in Central Europe. The underlying bedrock consists of the crystalline basement units of the Aar massif (gneiss, granite, and granodiorite) and is dissected by a large number of steep faults and former ductile shear zones. Geological and remote sensing lineament mapping combined with 3D geological modelling allowed us to make a large-scale characterization of the lithologies and structures’ spatial frequency over the entire length of the glacier. Additionally, we performed field-based rock hardness analyses (Schmidt hammer) along the glacier’s bedrocks (intact rock and faulted/sheared domains) to testify for structure-controlled erosion behaviour. Obtained results demonstrate that: (i) the typology and distribution of faults and shear zones are not uniform over the entire length of the glacier; (ii) high-frequency structure domains correlate with overdeepenings and/or abrupt glacier flow deflection in the direction of the strike of the structures; (iii) low-frequency structure domains correlate to the absence of overdeepenings and a straight glacier trajectory. In terms of erosive resistance domains of intact rock masses show high hardness values for each of the investigated lithologies without substantial variability between the different basement rocks (rebound values ranging from 45 to 60 N/mm2). On the contrary, faulted or sheared domains show a significant drop in hardness value (rebound values ranging from 10 to 40 N/mm2). Based on these results we propose that, for the case of the Great Aletsch Glacier, differences in crystalline basement lithologies do not exert an important role in glacial erosion. We postulate instead that the non-uniform spatial distribution of geological structures imposes a major control on the development of the glacial valley. The substantially reduced bulk hardness within high-frequency structure domains renders indeed the bedrock to be more prone to efficient glacial erosion process at these sites (i.e. glacial quarrying) and therefore to the development of large-scale overdeepenings, local scouring, or changes in the glacier flow direction. By contrast, the more massive undeformed and therefore less erosive low-frequency structures domains coincide with sections with no knickpoints or overdeepenings. In times of global warming and glacial retreat, such structure-controlled bedrock incisions are prone for further enhanced surface weathering and gravitation-controlled erosion processes, such as rockfalls and landslides, providing sites of enhances natural hazard potential.

How to cite: Musso Piantelli, F., Truttmann, S., and Herwegh, M.: Structural-controlled valley morphology of the largest Central Alpine Glacier, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8595, https://doi.org/10.5194/egusphere-egu22-8595, 2022.

16:12–16:18
|
EGU22-10709
|
On-site presentation
Glenn Thackray and Braedon Warner

The Big Lost River Floods impacted the Basin and Range landscape of east-central Idaho during Late Pleistocene time, exerting geomorphic and sedimentologic effects preserved primarily in the flood source and sink areas.  The floods resulted from ice dam rupture in the Pioneer Mountains, traversed the wide tectonic basin of the Big Lost River valley, and terminated in a closed lacustrine basin on the Eastern Snake River Plain. We elucidate the history of multiple floods, their magnitudes, and their timing through surficial geologic mapping, cosmogenic radionuclide dating, and hydraulic modeling. 

The East Fork Big Lost River was dammed by the Wildhorse Canyon glacier at its maximum extent, forming Glacial Lake East Fork (GLEF). Flood-transported boulders extend ca. 20 km downvalley from the dam.  Distinct boulder bars and meso-scale cataracts cover several hundred hectares of basalt plains landscape in the Arco Scablands, 100 km downstream from the source, with isolated boulders from the source area.  Very little flood evidence has been identified in the intervening segment of the floodway. 

In the source area, ice damming occurred only during near-maximum ice extent, with GLEF volume and outburst flood discharge assumed to be correlative with dam thickness. Ages from new 10Be CRN and OSL dating reveal that GLEF was most recently dammed ca. 20.6 ka.  This age is similar to a published 3He chronology from Arco Scabland flood boulders. However, we have conducted additional dating in the Arco Scablands, and a second age mode of 35 ka is clear from the combined 3He datasets, suggesting extensive glaciation of the flood source area at that time. A closed-basin lake in the river-terminating basin further downstream has also yielded unpublished results from other workers, demonstrating correlative MIS 3 and 2 lake highstands.

HEC-RAS 2-D hydraulic modeling constrains likely flood discharges in the Arco Scablands. The results suggest MIS 3 flood discharge of ca. 30,000 m3/s and MIS 2 flood discharge of ca. 10,000 m3/s.

The concentration of apparent flood evidence likely reflects the variability of stream power along the floodway.  In the upstream reach, floodwaters were confined within a 1 km-wide valley, concentrating stream power. Erratic boulders mantle outwash terraces throughout this reach.  Downstream, the valley widens to 3-10 km; the wide valley would have dramatically reduced stream power and, thus, limited the capacity for geomorphic work.  Flood deposits in that reach were presumably either eroded or buried. In this context, it is surprising that flood evidence is dramatic in the Arco Scablands, which occupy low-relief, basalt-mantled Eastern Snake River Plain landscape.  Despite the overall low relief, two factors appear to have focused floodwaters into the Scablands.  First, simple topographic variability amongst individual basalt flows and monogenetic shield volcano slopes appear to have been sufficient to limit the floodway width and concentrate stream power, despite the general low relief.  Second, a ca. 1 km wide structural graben at the mouth of the Big Lost River valley appears to have focused the floodwaters into that low-relief floodway.

How to cite: Thackray, G. and Warner, B.: Geomorphic and sedimentologic impacts of the Big Lost River Floods, east-central Idaho, USA, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10709, https://doi.org/10.5194/egusphere-egu22-10709, 2022.

16:18–16:24
|
EGU22-2466
|
ECS
|
Virtual presentation
Avinesh Kumar, Daniel Gavin, and Nicolas Waldmann

Lakes acts as the ubiquitous substitutes of oceans by effectively imprinting the signatures of varying environments in their sediments. A multiproxy sedimentary record from Bells Lake (N Idaho, USA) has been investigated to ascribe the postglacial paleoenvironment of NW USA. It is a 5 m deep, 6.3 ha lateral lake situated on the floodplain of the St. Joe River. It receives its sedimentary input from the central part of the Rocky Mountains. Therefore, perfectly situated for archiving environmental variability related to alpine glacial variability and precipitation fluctuations in relation with millennial-scale latitudinal migrations of the Northern Hemisphere Westerlies (NHW) since the Last Glacial Maximum (LGM). We recovered a continuous 15 m core using a Livingstone corer at the centre of the lake for this study. The core stratigraphy consists of five major units ranging from black organic-rich clay towards the top and clayey sand-silt in the bottom units. The bottom of the core consists of stiff clayey sediments that prevented further penetration and were dated by radiocarbon to 15.2 ka. Therefore, it appears to represent sediments that shortly post-date the last Missoula Flood event. The whole record was framed by seven radiocarbon dates and three tephra isochrons. The record shows that during the early Holocene, an increase in detrital geochemical proxies (Al, K, Fe, and Ti) and a high sedimentation rate (3.72 mm/yr) point towards high terrestrial input in a warm and humid environment, probably inducing high productivity in the lake. These changes likely resulted from intensified weathering conditions and high surface runoff with the latitudinal migration of the NHW, which induced diminishing conditions of the continental alpine glaciers in the Rockies. The Younger Dryas (12.9-11.7 ka) is clearly recorded by several parameters, including paleo-redox proxies (e.g., Mn/Fe), weathering indices (Chemical Index of Alteration), Fe-S plot, a decrease in TOC, and an increase in clay content. This suggests oxic hypolimnion (due to lower lake levels or increased wind strength) and increased fine detrital input (possibly from glacial expansion). Occasional flooding might have been responsible for the deposition of fine sand layers at 11.6-11.2 ka. Following this episode, the 8.2 ka & 4.2 ka events of aridity were also well identified by the sudden drops in the detrital proxies and magnetic susceptibility values, probably pointing to reduced weathering conditions during a short return to a cold and arid phase; later was possibly due to the dramatic warming of North Pacific Ocean might be caused by increased solar irradiance or volcanism disrupting the SST gradient between tropical eastern and the western Pacific Ocean. A thick Mt. Mazama tephra (7.6 ka), a confounding event, is also capsuled in the record likely contributing to the rapid formation of long gun barrel levees that extended into Lake Coeur d'Alene (CDA). A major change in the limnological conditions appear to occur at 6.1 ka and is interpreted as the isolation of Bells Lake basin from the larger Lake CDA, currently occupying the lowlands in the west within the modern mean state Mediterranean type of climate system. 

How to cite: Kumar, A., Gavin, D., and Waldmann, N.: Postglacial environment reconstruction of the northwestern USA from the lacustrine record: Bells Lake, northern Idaho, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2466, https://doi.org/10.5194/egusphere-egu22-2466, 2022.

16:24–16:30
|
EGU22-10767
|
ECS
|
Virtual presentation
Manasi Debnath, Milap Chand Sharma, Hiambok Jones Syiemlieh, and Arindam Chowdhury

The glaciated Changme Khangpu basin (CKB) covering an area of 767.8 km2, constitutes an important region in the Eastern Himalayas for palaeoclimate research to assess variability over recent geological times. Climatically, this part of the Himalayas is mainly controlled by the Indian Summer Monsoon (ISM). We provide a combination of multiproxy data, i.e., geomorphological, sedimentological, geochemical, Accelerator Mass Spectrometry 14C dating and Schmidt Hammer rebound value dating methods in reconstructing glacier and climatic changes related to the post global Last Glacial Maximum (gLGM) in the Changme Khangpu basin of the Sikkim Himalaya. The four set of well-preserved moraines depicted four advances of this glacier and palaeoclimate has been reconstructed after the Phase-II glacier advances i.e. post gLGM period. The post gLGM glacier recession in the Changme Khangpu (CK) valley witnessed a prolonged humid climate phase from <14.29 ± 0.22 ka to 7.08 ± 0.08 ka cal BP that inferred from the sedimentary log in this valley and incidentally correlate with the monsoonal reactivation (15 ka to 12 ka BP) in Southern Asia. This humid period was succeeded by dry climatic phases from 7.08 ka to 5.4 ka cal BP and from 5.18 to 4.65 ka cal BP, which well correlates with the dry phases in the Chopta valley, west of this area in Sikkim Himalaya. The glacier had receded from its Phase-III advance in between <4 and >1.3 ka BP. This period was followed by the active paraglacial fan formation and witnessed historical outburst events in this valley.

 

Keywords: Changme Khangpu glacier (Sikkim); Eastern Himalayas; Last Glacial Maximum; Palaeoclimate; Glacier geomorphology; 14C AMS dating; Chemical index of alteration.

How to cite: Debnath, M., Sharma, M. C., Syiemlieh, H. J., and Chowdhury, A.: Reconstructed post gLGM glacier recession and climatic variability of the Changme Khangpu valley, Eastern Himalayas, INDIA, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10767, https://doi.org/10.5194/egusphere-egu22-10767, 2022.

16:30–16:40
Coffee break
Chairpersons: Bethan Davies, Emma Cooper, Neil Glasser
17:00–17:02
17:02–17:08
|
EGU22-1502
|
On-site presentation
Stefan Winkler

The investigation of Holocene glacier chronologies has been recognised as a key element of research on mountain glaciations in the light of current global change. They can be utilised as high-resolution palaeoclimatic archives for the immediate and more distant geological past. During the past few decades considerable progress has been achieved, in particular due to substantial improvements of the ability to accurately date glacial landforms such as terminal moraines essential for reconstructing past glacier margins and subsequent analysis of glacier advance/retreat periods. The Southern Alps of New Zealand are among the few suitable regions for the investigation of Holocene glacier chronologies in the mid-latitudinal Southern Hemisphere.

Since early studies of Holocene glacier chronologies in the mid-20th century, mapping of the investigated glacier forelands has been an integrated part of almost all scientific approaches regardless of the individual dating methods applied. These mapping attempts serve the identification and positioning of certain glacial or glaciofluvial landforms and allow the reconstruction of former glacier margins. They frequently also provide information on the location of sample sites selected for subsequent dating. If detailed geomorphological mapping schemes are in use, such maps additionally support the interpretation of any chronological data by identifying the genetic origin of any landform investigated. This enables the latter to be causally related to different dynamic stages of the glacier. Additionally, such maps may highlight potential uncertainties such as postdepositional disturbance or unclear morphodynamic connections between landforms and the glacier.

Reviewing recent publications it seems, however, that some appraisal of such detailed geomorphological mapping is often traded-off against the impressive progress with up-to-date dating techniques and high-resolution digital elevation models or satellite/aerial imagery. Unfortunately, the latter do neither qualify as geomorphological maps per se nor fully serve the abovementioned purpose. The widespread applied common GIS software has, furthermore, limitations with respect to its graphic capabilities and unintentionally entails negligence of established and well-suited signatures or geomorphological mapping schemes.

A detailed geomorphological map of the glacier foreland of Mueller Glacier, Southern Alps/New Zealand will be presented. It follows an established geomorphological mapping scheme ("GMK 25") that has been adequately modified to fit both purpose and selected scale. Despite several glacier chronological studies have been conducted on this glacier foreland and the site is considered a regional 'key site', this map constitutes the first of its kind. The detailed geomorphological map is utilised to assess discrepancies among existing chronologies by reviewing the morphometric properties and genetic origin of those landforms that have been dated. It reveals that potential postdepositional modification of some landforms investigated had not been appropriately considered with certain previous studies. As a result, the evidence for some glacier advances needs to be classified as 'weak'.  

Summarising, detailed geomorphological mapping is still essential for the study of Holocene glacier chronologies and should not lose its prominent position - or even disappear.

How to cite: Winkler, S.: Potential of detailed geomorphological mapping for the study of Holocene glacier chronologies: Mueller Glacier, Southern Alps/New Zealand, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1502, https://doi.org/10.5194/egusphere-egu22-1502, 2022.

17:08–17:14
|
EGU22-3235
|
ECS
|
Virtual presentation
Levan Tielidze, Shaun Eaves, Kevin Norton, Andrew Mackintosh, and Alan Hidy

Geochronological dating of glacial landforms, such as terminal and lateral moraines, are useful for determining the extent and timing of past glaciation and for reconstructing the magnitude and rate of past climate changes. Here we report the first dataset of Late Quaternary glacial maximum extent and its deglaciation from the Ahuriri River valley, Southern Alps, New Zealand (44°23'54''S, 169°39'48''E) based on 66 beryllium-10 (10Be) surface-exposure ages from terminal-lateral moraine systems and glaciated bedrock surfaces situated at different sites of the valley. Our results show that the former Ahuriri Glacier reached its maximum extent 19.8±0.3 ka, which coincides with the global Last Glacial Maximum. By 16.7±0.3 ka, the glacier had retreat ~18 km up-valley and this deglaciation was accompanied by the formation of a shallow proglacial lake. Our surface-exposure chronology from the moraines situated upper right tributary of the Ahuriri River valley also indicates that other subsequent advance of the palaeo glacier culminated at 14.5±0.3 ka ago, while the next re-advance or still stand phases occurred at 13.6±0.3 ka. About 1000 yr later (12.6±0.2 ka), the former glacier built another prominent terminal-lateral moraine ridge in the lower section of the upper right tributary valley. In overall, our result supports the hypothesis that climate was ~5°C colder (ELA depression ~880 m) than present at 19.8±0.3 ka, while it was ~4.4°C colder (ELA depression ~770 m) at 16.7±0.3 ka. Furthermore, local air temperature was lower by 3.6°C (ELA depression ~630 m) during the 14.5-13.6 ka and by 2.0°C (ELA depression ~360 m) at 12.6 ka respectively relative to present. Our results clearly demonstrate the structure of last glacial termination in New Zealand such as strong glacier recession during this time-period in accordance of at least five glacier re advances or still stand phases. This new 10Be surface exposure dataset will help us in better understanding of past glacier-climate interactions in the Southern Alps and in the Southern Hemisphere in general.

How to cite: Tielidze, L., Eaves, S., Norton, K., Mackintosh, A., and Hidy, A.: Late Quaternary glacier-based climate reconstruction from the Southern Alps, New Zealand, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3235, https://doi.org/10.5194/egusphere-egu22-3235, 2022.

17:14–17:20
|
EGU22-5052
|
ECS
|
On-site presentation
Jenna Sutherland, Jonathan Carrivick, Matthias Huss, Heather Purdie, Christopher Stringer, Michael Grimes, William James, and James Shulmesiter

Mountain glaciers are rapidly diminishing and causing widespread environmental and socio-economic concern. The stability of mountain glaciers is influenced by the expansion of proglacial landscapes and meltwater impounded as lakes within natural topographic depressions or ‘overdeepenings’. In particular, the relative sensitivity of mid-latitude glaciers to modern climate change makes them especially important to consider. One of the most striking features of South Island, New Zealand, is the sequence of glacial lakes that occupy mountain valleys along the Southern Alps. Our previous work has highlighted that the presence of these lakes is likely to have had an impact on ice-marginal dynamics of their adjacent glaciers, thereby influencing the rate of deglaciation on sub-millennial timescales. This emphasizes the need to incorporate proglacial lakes into palaeoglacier reconstructions and into analyses of future glacier evolution. In this new study we (i) document contemporary loss of glacier ice across the Southern Alps, (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, Southern Alps glaciers have fragmented both by separation of tributaries and by detachment of ablation zones. Glacier margins in contact with a proglacial lake have experienced the greatest terminus retreat. Our analysis indicates a positive relationship between mean glacier mass balance and rate of lake growth and with length of an ice-contact lake boundary. We project sustained and relatively homogenous glacier volume loss for east-draining basins but in contrast a heterogenous pattern of volume loss for west-draining basins. Our model results show that ice-marginal lakes will increase in number and combined size 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.

How to cite: Sutherland, J., Carrivick, J., Huss, M., Purdie, H., Stringer, C., Grimes, M., James, W., and Shulmesiter, J.: Coincident glacier and lake evolution across New Zealand: Past, present, and future, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5052, https://doi.org/10.5194/egusphere-egu22-5052, 2022.

17:20–17:22
17:22–17:28
|
EGU22-9576
|
ECS
|
Highlight
|
On-site presentation
Emily Potter, Catriona Fyffe, Andrew Orr, Duncan Quincey, Andrew N Ross, Sally Rangecroft, Katy Medina, Helen Burns, Alan Llacza, Gerardo Jacome, Robert Hellström, Joshua Castro, J Scott Hosking, Alejo Cochachin, Cornelia Klein, Edwin Loarte, and Francesca Pellicciotti

Precipitation, snow and ice melt from Andean river basins provide a crucial water source to mountain and downstream communities equally. Precipitation and temperature changes due to global climate change are likely to affect agriculture, hydropower generation and hazard risks, but are poorly constrained, especially in future projections.

Here we focus on two heavily glacierised regions of the Peruvian Andes, the Cordillera Blanca, and the Cordillera Vilcanota-Urubamba, to assess projected changes in extreme meteorological events and droughts. Previous work suggests increasing temperatures in both regions in the 21st century, with contrasting projections of precipitation trends. There has been little focus, however, on how extremes in precipitation and temperature might vary in the future. Having created a bias-corrected regional climate model from 1980-2018, we use empirical quantile mapping to statistically downscale 30 CMIP5 models. This ensemble is analysed to determine future changes in climate extremes.  

Both minimum and maximum daily temperatures are projected to increase in the from 2018 to 2100. This leads to a large reduction in the number of frost days in both regions, and suggests that under a high-emissions scenario, almost every day in the late 21st century will be in the 90th percentile of temperatures experienced during 1980-2018. The number of wet and dry days is not projected to change, but precipitation falling on very wet days (in the 95th percentile of the 1980-2018 period) is projected to increase significantly.

Lastly, we consider changes in future meteorological droughts using the standardised precipitation evapotranspiration index (SPEI) which considers potential evapotranspiration, as well as precipitation. We estimate potential evapotranspiration from temperature projections, using the Hargreaves method. Despite projected precipitation increases, temperature increases leading to an increase in evaporation may be large enough to increase meteorological droughts in the future, with the total number of drought months projected to almost double under high emission scenarios by the end of the 21st century. In a region that already experiences water stress and hazards, these changes to both extreme rainfall and drought could have a significant impact for communities in the Peruvian Andes, and for the downstream urban areas and industry that rely on mountain river flow.

 

How to cite: Potter, E., Fyffe, C., Orr, A., Quincey, D., Ross, A. N., Rangecroft, S., Medina, K., Burns, H., Llacza, A., Jacome, G., Hellström, R., Castro, J., Hosking, J. S., Cochachin, A., Klein, C., Loarte, E., and Pellicciotti, F.: Projected increases in climate extremes and temperature-induced drought over the Peruvian Andes, 1980-2100, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9576, https://doi.org/10.5194/egusphere-egu22-9576, 2022.

17:28–17:34
|
EGU22-4999
|
ECS
|
On-site presentation
Tancrède Leger, Andrew Hein, Daniel Goldberg, and Derek Fabel

Cordillera Blanca glaciers represent the greatest glacial freshwater reserve in tropical South America and have been shrinking substantially over recent decades, posing a threat to future water resources in the Peruvian Ancash region. A crucial step to better understand the evolution of these glaciers under changing conditions is to establish robust reconstructions of their past response to climate fluctuations. Such reconstructions are limited in the tropical Andes, which inhibits our understanding of the climatic drivers of tropical glacier length and surface mass balance changes. The relative importance of temperature versus precipitation rate changes on glacier length changes is therefore still debated in the region. Here, we present 42 cosmogenic 10Be exposure ages from moraine boulder samples, establishing for the first time a comprehensive chronology for Late-glacial, Holocene and Neoglacial advances of four distinct Cordillera Blanca mountain glaciers. We use this chronology to constrain a series of moraine-matching numerical model-run simulations conducted for each dated glacier advance using a spatially-distributed ice-flow model coupled with a positive degree-day surface mass balance parameterisation. These simulations aim at modelling and estimating former three-dimensional glacier geometries, equilibrium line altitudes, surface mass balance properties and their evolution through time. This analysis also enables us to use glacier surface mass balance as a proxy for past atmospheric temperature and precipitation variations at the time of the reconstructed glacier advances. This new, multi-method glacier reconstruction enables, for the Cordillera Blanca: 1) novel glacio-geomorphological interpretations, 2) an improved understanding of glacier extent, surface mass balance and volume change during the Late-glacial, Holocene and Neoglacial phases of advance, and 3) new estimations of paleoclimate conditions required for the reconstructed glacier events to occur.   

How to cite: Leger, T., Hein, A., Goldberg, D., and Fabel, D.: Late-glacial to Neoglacial evolution of glacier extent and surface mass balance in the Cordillera Blanca, Peruvian Andes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4999, https://doi.org/10.5194/egusphere-egu22-4999, 2022.

17:34–17:44
|
EGU22-2237
|
ECS
|
solicited
|
Highlight
|
On-site presentation
Loic Piret, Sebastien bertrand, and Fernando Torrejón

Proglacial lake sediments are widely recognised as accurate and high-resolution archives of climate and glacier variability. Sediments deposited in proglacial lakes are frequently varved, which offers the possibility to generate precisely-dated records, and their basal ages are often used to constrain deglaciation histories. It is often assumed that lake sedimentation starts immediately after deglaciation. With this in mind, we studied the onset of lake sedimentation in a recently deglaciated lake (Calluqueo Lake, Chilean Patagonia) to investigate the possible delay between proglacial lake formation and establishment of a continuous sediment record. Calluqueo Lake is a 3.5 km long lake composed of a large 220 m deep proximal basin, separated from a smaller 50 m deep distal basin by a 40 m deep sill. The lake is bordered by steep lateral moraines that contain large boulders. Aerial images and historical data show that Calluqueo Glacier entirely covered the lake basin until 1941. Since then, it rapidly receded until it became land-based in 1985. Side Scan sonar images and grab sampling shows that the sediment cover is limited to the small distal basin, which was entirely deglaciated by 1978. By comparison, no sediment was found in the deepest proximal basin although it has been ice free for at least three decades. Varve counting of sediments deposited in the distal basin shows that the stratigraphic record starts in 1996 ± 4 CE, i.e., that the first 20 – 50 years of the glacier’s retreat are not represented in the sediments of Calluqueo Lake. We hypothesize that the fine-grained sediments that are discharged into the lake immediately after its formation first start accumulating between the large boulders that compose the ablation moraine on the lake floor. The continuous stratigraphic record only starts forming after the coarse moraine deposits are buried under fine-grained particles. Our results have important implications for the use of proglacial lake sediments in paleoclimate and paleoenvironmental research. They suggest that proglacial lake sediment records lack the first 20 – 50 years of sedimentation. Although this delay may be negligible for reconstructions of deglaciation histories based on basal radiocarbon ages, it becomes significant for the use of lake sediment records from recently deglaciated environments.

How to cite: Piret, L., bertrand, S., and Torrejón, F.: Multidecadal Delay Between Deglaciation and Formation of a Proglacial Lake Sediment Record, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2237, https://doi.org/10.5194/egusphere-egu22-2237, 2022.

17:44–17:50
|
EGU22-2054
|
ECS
|
Virtual presentation
Franziska Temme, David Farías-Barahona, Thorsten Seehaus, Tobias Sauter, Ricardo Jaña, Jorge Arigony-Neto, Inti Gonzalez, Christoph Schneider, and Johannes Fürst

Together with the Northern and the Southern Patagonian Icefield, the Cordillera Darwin Icefield (CDI) in Tierra del Fuego experienced strong ice loss during the last decades. In some areas the observed glacier retreat contrasts with findings of recent surface mass balance studies, which implies that the observed losses are partly caused by dynamic adjustments. However, the difficult accessibility of Patagonian glaciers and the harsh conditions result in scarce observational data of glacier mass balances, especially for the CDI. In the westernmost region of the CDI, Monte Sarmiento is located. It hosts an 83 km2 icefield, with Schiaparelli Glacier being the largest glacier, terminating in a proglacial lake.

We focus on reproducing the local meteorological conditions using statistical downscaling of atmospheric reanalysis data to the study site as well as a linear model of orographic precipitation. Subsequently, we concentrate on a best representation of the surface mass balance (SMB) conditions on the local glaciers. For this purpose, we apply four melt models of different complexity: i) a positive degree-day model, ii) a simplified energy balance model using potential insolation, iii) a simplified energy balance model using the actual insolation (accounting for cloud cover, shading effects and diffuse radiation) and iv) a fully-fledged surface energy balance model. For the latter, we rely on the “COupled Snowpack and Ice surface energy and mass balance model in PYthon” (COSIPY). These models are calibrated on Schiaparelli Glacier (24.3 km2), which is the largest and best-studied glacier of the Monte Sarmiento Massif. Observational records comprise in-situ stake, thickness and meteorological measurements as well as remotely sensed elevation changes and flow velocities. After the melt model calibration, we apply them to other adjacent glacier basins and assess their performances against geodetic mass changes. This way, we want to answer the question if it is feasible to apply SMB models, calibrated for one single glacier, to surrounding glaciated areas under these unique climatic conditions. If a single-site calibration showed poor transferability properties, further remotely sensed observables will be considered in the calibration. This way we also hope to answer the question, which melt model can best reproduce the spatial variability in remotely sensed specific mass balances over a larger region.

How to cite: Temme, F., Farías-Barahona, D., Seehaus, T., Sauter, T., Jaña, R., Arigony-Neto, J., Gonzalez, I., Schneider, C., and Fürst, J.: Simulating the surface mass balance at the Monte Sarmiento Massif, Cordillera Darwin, Chile, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2054, https://doi.org/10.5194/egusphere-egu22-2054, 2022.

17:50–17:56
|
EGU22-9793
|
ECS
|
Virtual presentation
Andrés Castillo, Matthias Prange, Jorjo Bernales, Franco Retamal-Ramírez, Michael Schulz, and Irina Rogozhina

Glacial geomorphological and geochronological studies suggest that the Patagonian Ice Sheet (PIS) stretched from 38°S to 55°S during the Marine Isotope Stages (MIS) 2-3. While its western margin reached the Pacific Ocean, the easternmost sectors of the PIS were characterized by terrestrial lobes that fed large paleo glacial lakes after its maximum extension towards the end of the MIS 3. An ice-marginal stabilization occurred throughout the global Last Glacial Maximum followed by a rapid deglaciation after 18,000 yr before present.

Here we present an ensemble of transient numerical simulations of the PIS that have been carried out to provide information on its thickness and extents through the MIS 3 and MIS 2. Our aim here is to determine the range of climate conditions that matches the field-derived ice sheet geometries and the timing of local deglaciation, while bracketing the spread in possible ice volumes and sea level contributions originating from uncertainties in the internal parameters and external forcings. The model ensemble makes use of the new higher-order version of the ice sheet model SICOPOLIS forced by combination of present-day atmospheric conditions from the ERA5 reanalysis and outputs from the Paleoclimate Modeling Intercomparison Project (PMIP) and new Community Earth System Model (CESM) experiments. Our results indicate that the regional climate conditions required to reproduce a realistic growth and demise of the PIS through the Late Quaternary are not captured by coarse-resolution global climate models, implying the necessity of high spatial-resolution regional modeling. Our results also suggest that in order to realistically simulate the evolution of the PIS in agreement with geological archives, the MIS3 should have witnessed colder regional temperatures in and around Patagonia than those shown by global climate models for the MIS 2.

How to cite: Castillo, A., Prange, M., Bernales, J., Retamal-Ramírez, F., Schulz, M., and Rogozhina, I.: Numerical reconstructions of the Patagonian Ice Sheet: Growth and demise through the Late Quaternary, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9793, https://doi.org/10.5194/egusphere-egu22-9793, 2022.

17:56–18:02
|
EGU22-6505
|
ECS
|
On-site presentation
Maximillian Van Wyk de Vries, Emi Ito, Mark Shapley, Guido Brignone, Matias Romero, and Andrew D. Wickert

Proglacial lakes provide valuable records of paleoclimate, volcanism, and glaciation. We present results from spatially extensive coring of Lago Argentino, a 1500 km2 proglacial lake on the eastern margin of the Southern Patagonian Icefield (SPI). We recovered forty-seven sediment cores from water depths up to 600 m. Detailed analysis of this sediment reveals annual laminations – known as varves – which we use to build a high-resolution age-depth model for each core.

In this presentation, we discuss the insight gained into varve formation mechanisms, paleoclimate, and glacier change in the Lago Argentino basin of the Southern Patagonian Icefield. Firstly, we show that varves form by three distinct mechanisms across Lago Argentino (~west to east): a seasonal cycle in glacial sediment influx, a seasonal cycle in lake mixing, and a seasonal cycle in fluvial sediment influx. Second, we examine the evidence for recent glacier fluctuations across Lago Argentino. We find evidence that glaciers were locally larger early in the last millennium than during the Little Ice Age. Finally, we examine the periodicity of sediment mass accumulation rate and find dominant decadal to centennial periodicities (35, 80, 150 and 200 years). We relate periodicities in sediment accumulation to periodicities in known climatic drivers, specifically the Southern Annular Mode. These results provide new insight into multiannual glacial change and sedimentation dynamics in a complex glacio-lacustrine system and highlight the value of proglacial lake records for understanding present-day glacier change.

How to cite: Van Wyk de Vries, M., Ito, E., Shapley, M., Brignone, G., Romero, M., and Wickert, A. D.: Insight into glacier evolution, proglacial lake dynamics, and paleoclimate from Lago Argentino, Patagonia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6505, https://doi.org/10.5194/egusphere-egu22-6505, 2022.

18:02–18:08
|
EGU22-10361
|
Presentation form not yet defined
Esteban Sagredo, Scott Reynhout, Michael Kaplan, Juan Aravena, Paola Araya, Brian Luckman, Roseanne Schwartz, and Joerg Schaefer

A well-resolved glacial chronology is crucial to compare sequences of glacial/climate events within and between regions, and thus, to unravel mechanisms underlying past climate changes. Important efforts have been made towards understanding the Holocene climate evolution of the Southern Andes; however, the timing, patterns and causes of glacial fluctuations during this period remain elusive. Advances in surface exposure dating techniques, together with the establishment of a Patagonian 10Be production rate, have opened new possibilities for establishing high-resolution glacial chronologies at centennial/decadal scale. Here we present a new comprehensive Holocene moraine chronology from Mt. San Lorenzo (47°S) in central Patagonia, Southern Hemisphere. Twenty-four new 10Be ages, together with three published ages, indicate that the Río Tranquilo glacier approached its Holocene maximum position sometime, or possibly on multiple occasions, between 9860 ± 180 and 6730 ± 130 yr. This event(s) was followed by a sequence of slightly smaller advances at 5750 ± 220, 4290 ± 100 (?), 3490 ± 140, 1440 ± 60, between 670 ± 20 and 430 ± 20, and at 390 ± 10 yr ago. By comparing our results with other glacier chronologies from central and southern Patagonia, we explore the role of the Southern Westerly Winds as a pacemaker of the Holocene glacier fluctuation in southern South America. 

How to cite: Sagredo, E., Reynhout, S., Kaplan, M., Aravena, J., Araya, P., Luckman, B., Schwartz, R., and Schaefer, J.: Holocene history of Rio Tranquilo Glacier, Monte San Lorenzo (47°S), Central Patagonia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10361, https://doi.org/10.5194/egusphere-egu22-10361, 2022.

18:08–18:14
|
EGU22-10632
|
ECS
|
Presentation form not yet defined
Emma Cooper, Varyl Thorndycraft, Bethan Davies, Adrian Palmer, and Juan-Luis García

The former Patagonian Ice Sheet (PIS) expanded and contracted multiple times during the Quaternary, preserving a well-defined geomorphological and sedimentological record of ice extent and dynamics. Influenced by both regional (e.g. Southern Westerly Winds) and interhemispheric climate forcing mechanisms, reconstructions of PIS extent and dynamics through time may yield unique insights into Southern Hemisphere (palaeo-)climate and (palaeo-)glacier dynamics.

An increasing number of palaeoglaciological reconstructions in Patagonia have highlighted spatial asynchrony in the timing of local glacial maxima and deglaciation. This offset in the timing of ice advance/retreat implies that dynamic controls, such as topography or calving mechanisms, played a part in regulating the structure and pace of deglaciation. Assessing the role of these mechanisms is complicated by a general lack of glacial landsystems work in Patagonia, particularly north of the Northern Patagonian Icefield (46 – 47.5 °S).

Here we aim to understand the timing, structure, and style of deglaciation in the Rio Cisnes valley, an eastern outlet glacier of the former Patagonian Ice Sheet. We combine glacial geomorphological mapping, field sedimentology, Uncrewed Aerial Vehicle (UAV) photogrammetry, and a new chronology based on cosmogenic nuclide surface-exposure age dating. These data informed a refined deglacial ice and palaeolake reconstruction. The new 10Be exposure ages constrain the timing of palaeolake level drop to ~16 ka, which indicates that icefield outlet glaciers were retreating back from their zone of confluence in the Cisnes valley into their respective valleys by this time, leaving the main Cisnes valley ice free.

How to cite: Cooper, E., Thorndycraft, V., Davies, B., Palmer, A., and García, J.-L.: Deglaciation dynamics of the Rio Cisnes palaeo-outlet glacier (~45°S), former Patagonian Ice Sheet, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10632, https://doi.org/10.5194/egusphere-egu22-10632, 2022.

18:14–18:20
|
EGU22-13508
|
Virtual presentation
Mario Veloso-Alarcón, Gazis Iason-Zois, Alessa Geiger, Bertrand Sebastien, and Cristián Rodrigo

The glacial history of Patagonia has been built from paleoclimate records found at the margin of the former Patagonian Ice-sheet. However, current deglaciation models of Patagonia still have spatio-temporal gaps to be filled. In this direction, the study of the submerged paleo-climate records at the Patagonian Fjord system and pro-glacial lakes could fill these gaps and enhance our knowledge on deglaciation in Patagonia. However, the exploration of such remote areas is hindered by logistic challenges and rough weather conditions.

In November of 2018 we collected the first high-resolution swath multibeam echosounder (MBES) bathymetry of Senos Icy and Glacier, the southern section of Canal Gajardo and Estero Portaluppi, which are fjords located at the flanks of Gran Campo Nevado. In this work, we present this new bathymetry and its first geomorphological interpretation. The analysis revealed a heterogeneous seafloor with geomorphological features related to glacial dynamics. The data interpretation is supplemented by shallow sub-bottom profiles that have been also acquired during that survey. We think that such information is the baseline for future exploration of these fjords focused on the already identified submerged glacial bedforms and their chronology.  

How to cite: Veloso-Alarcón, M., Iason-Zois, G., Geiger, A., Sebastien, B., and Rodrigo, C.: Advances on submarine geomorphology at the Fjord system of Gran Campo Nevado (~52°S), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13508, https://doi.org/10.5194/egusphere-egu22-13508, 2022.

18:20–18:30