Crevasse density, orientation and temporal variability at Narsap Sermia, Greenland

Mass loss from iceberg calving at marine-terminating glaciers is one of the largest and most poorly constrained contributors to sea-level rise. However, our understanding of the processes controlling ice fracturing and crevasse evolution is incomplete. Here, we use Gabor filter banks to automatically map crevasse density and orientation through time on a ~150 km2 terminus region of Narsap Sermia, an outlet glacier of the southwest Greenland ice sheet. We find that Narsap Sermia is dominated by transverse (flow-perpendicular) crevasses near the ice front and longitudinal (flow-aligned) crevasses across its central region. Measured crevasse orientation varies on sub-annual timescales by more than 45$^\circ$ in response to seasonal velocity changes, and also on multi-annual timescales in response to broader dynamic changes and glacier retreat. Our results show a gradual up-glacier propagation of the zone of flow-transverse crevassing coincident with frontal retreat and acceleration occurring in 2020/21, in addition to sub-annual crevasse changes primarily in transition zones between longitudinal to transverse crevasse orientation. This provides new insight into the dynamics of crevassing at large marine-terminating glaciers and a potential approach for the rapid identification of glacier dynamic change from a single pair of satellite images

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

Proglacial lakes, whose numbers have been growing around the world, may drive accelerated glacier retreat and provide valuable records of past glacier and climatic changes. Despite their importance, few studies have investigated the sedimentary properties and processes acting within large proglacial lakes. Lago Argentino (LArg) is a 1,500 km2 ice-contact lake on the eastern flank of the Southern Patagonian Icefield. Here, we describe the results from a detailed analysis of 47 sediment cores obtained throughout this lake basin, supplemented with remotely sensed data. We show that: (a) LArg exhibits a seasonal variation in sediment properties (varves); (b) varve formation results from three distinct processes, driven by seasonal changes in glacial sediment input, seasonal changes in fluvial sediment input, and seasonal variations in lake mixing; and (c) distance from glacier calving fronts provides the first-order control on sediment grain size and accumulation rate. Our findings highlight the exceptional preservation of annual laminations within proglacial lakes, their potential for reconstructing past glacier changes, and their relevance for forecasting future glacier–lake interactions.Fil: Van Wyk de Vries, Maximillian. University of Minnesota; Estados UnidosFil: Ito, Emi. University of Minnesota; Estados UnidosFil: Shapley, Mark. University of Minnesota; Estados UnidosFil: Brignone, Guido. Universidad Nacional de Córdoba; ArgentinaFil: Romero, Matias. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaFil: Wickert, Andrew D.. German Research Centre for Geosciences; Alemania. University of Minnesota; Estados UnidosFil: Miller, Louis H.. Macalester College; Estados UnidosFil: MacGregor, Kelly R.. Macalester College; Estados Unido

Northeastern Patagonian glacier advances (43°S) reflect northward migration of the Southern Westerlies towards the end of the last glaciation

International audienceThe last glacial termination was a key event during Earth’s Quaternary history that was associated with rapid, high-magnitude environmental and climatic change. Identifying its trigger mechanisms is critical for understanding Earth’s modern climate system over millennial timescales. It has been proposed that latitudinal shifts of the Southern Hemisphere Westerly Wind belt and the coupled Subtropical Front are important components of the changes leading to global deglaciation, making them essential to investigate and reconstruct empirically. The Patagonian Andes are part of the only continental landmass that fully intersects the Southern Westerly Winds, and thus present an opportunity to study their former latitudinal migrations through time and to constrain southern mid-latitude palaeo-climates. Here we use a combination of geomorphological mapping, terrestrial cosmogenic nuclide exposure dating and glacial numerical modelling to reconstruct the late-Last Glacial Maximum (LGM) behaviour and surface mass balance of two mountain glaciers of northeastern Patagonia (43°S, 71°W), the El Loro and Río Comisario palaeo-glaciers. In both valleys, we find geomorphological evidence of glacier advances that occurred after the retreat of the main ice-sheet outlet glacier from its LGM margins. We date the outermost moraine in the El Loro valley to 18.0 ± 1.15 ka. Moreover, a series of moraine-matching simulations were run for both glaciers using a spatially-distributed ice-flow model coupled with a positive degree-day surface mass balance parameterisation. Following a correction for cumulative local surface uplift resulting from glacial isostatic adjustment since ∼18 ka, which we estimate to be ∼130 m, the glacier model suggests that regional mean annual temperatures were between 1.9 and 2.8°C lower than present at around 18.0 ± 1.15 ka, while precipitation was between ∼50 and ∼380% higher than today. Our findings support the proposed equatorward migration of the precipitation-bearing Southern Westerly Wind belt towards the end of the LGM, between ∼19.5 and ∼18 ka, which caused more humid conditions towards the eastern margins of the northern Patagonian Ice Sheet a few centuries ahead of widespread deglaciation across the cordiller

Dynamics and physical parameters of the Lastarria debris avalanche, Central Andes

Volcanic debris avalanches are extremely destructive phenomena, with the potential to travel many kilometers from their source region, either as rockslides or as mass flows. Given that they may even be triggered at inactive volcanoes, their hazard is often underestimated. Understanding the dynamics of such mass movements is essential for evaluating and mitigating hazards. A number of case studies have been carried out around the world, but there is still a need for further studies of flow-dominated avalanches, which remain poorly constrained. These studies would have high educational value, providing striking examples to teach decision makers and at-risk populations about the hazard. In this study, we investigate the 7500 cal. year B.P. Lastarria debris avalanche. It is a 7 km-long deposit, with exceptional preservation of both the flow structures and the collapse scar. Detailed fieldwork, morphometric mapping of over 600 surface features, and numerical modelling was carried out to constrain the avalanche's trigger and flow parameters. Numerical models and field scaling relationships are in good agreement, suggesting maximum velocities of 210 to 270 km h(-1), negligible basal friction, low cohesion (50 kPa) and an intermediate friction coefficient. Structures are dominantly oriented parallel to transport direction, suggesting minimal influence from a smooth paleotopography. Lastarria provides an example of a shallow flank failure, initiated along strati graphic planes, that allowed low strength pyroclastic strata to disaggregate rapidly and then quickly accelerate to flow as a granular material at high velocity beyond the base of the volcano. Overall, Lastarria provides excellent constraints on granular avalanche initiation and flow, which are valuable for hazard assessments and for the study of less well-preserved flow deposits elsewhere. The question of which precursory signs may warn of such a flank failure remains open, and is important to address in future studies.Department of Geological sciences from Universidad Catolica del Norte (UCN) UNESCO Geosciences programme 692 French National Research Agency (ANR) 16-IDEX-0001 CAP 20-2

Dynamics and physical parameters of the Lastarria debris avalanche, Central Andes

Volcanic debris avalanches are extremely destructive phenomena, with the potential to travel many kilometers from their source region, either as rockslides or as mass flows. Given that they may even be triggered at inactive volcanoes, their hazard is often underestimated. Understanding the dynamics of such mass movements is essential for evaluating and mitigating hazards. A number of case studies have been carried out around the world, but there is still a need for further studies of flow-dominated avalanches, which remain poorly constrained. These studies would have high educational value, providing striking examples to teach decision makers and at-risk populations about the hazard. In this study, we investigate the 7500 cal. year B.P. Lastarria debris avalanche. It is a 7 km-long deposit, with exceptional preservation of both the flow structures and the collapse scar. Detailed fieldwork, morphometric mapping of over 600 surface features, and numerical modelling was carried out to constrain the avalanche's trigger and flow parameters. Numerical models and field scaling relationships are in good agreement, suggesting maximum velocities of 210 to 270 km h(-1), negligible basal friction, low cohesion (50 kPa) and an intermediate friction coefficient. Structures are dominantly oriented parallel to transport direction, suggesting minimal influence from a smooth paleotopography. Lastarria provides an example of a shallow flank failure, initiated along strati graphic planes, that allowed low strength pyroclastic strata to disaggregate rapidly and then quickly accelerate to flow as a granular material at high velocity beyond the base of the volcano. Overall, Lastarria provides excellent constraints on granular avalanche initiation and flow, which are valuable for hazard assessments and for the study of less well-preserved flow deposits elsewhere. The question of which precursory signs may warn of such a flank failure remains open, and is important to address in future studies.Department of Geological sciences from Universidad Catolica del Norte (UCN) UNESCO Geosciences programme 692 French National Research Agency (ANR) 16-IDEX-0001 CAP 20-2

Crevasse density, orientation and temporal variability at Narsap Sermia, Greenland

Abstract Mass loss from iceberg calving at marine-terminating glaciers is one of the largest and most poorly constrained contributors to sea-level rise. However, our understanding of the processes controlling ice fracturing and crevasse evolution is incomplete. Here, we use Gabor filter banks to automatically map crevasse density and orientation through time on a ~150 km2 terminus region of Narsap Sermia, an outlet glacier of the southwest Greenland ice sheet. We find that Narsap Sermia is dominated by transverse (flow-perpendicular) crevasses near the ice front and longitudinal (flow-aligned) crevasses across its central region. Measured crevasse orientation varies on sub-annual timescales by more than 45 $^\circ$ in response to seasonal velocity changes, and also on multi-annual timescales in response to broader dynamic changes and glacier retreat. Our results show a gradual up-glacier propagation of the zone of flow-transverse crevassing coincident with frontal retreat and acceleration occurring in 2020/21, in addition to sub-annual crevasse changes primarily in transition zones between longitudinal to transverse crevasse orientation. This provides new insight into the dynamics of crevassing at large marine-terminating glaciers and a potential approach for the rapid identification of glacier dynamic change from a single pair of satellite images.</jats:p

Glacier thickness maps for Ecuador and Colombia

Upload associated with Scientific Data submission: Glacier thickness and ice volume of the inner tropical Andes. The dataset includes: -Ice velocity maps for all 11 glacier regions (5 in Ecuador and 6 in Colombia) -Ice thickness maps for all 11 glacier regions generated using the 6 different thickness calculation methods -Multi-model ensemble mean glacier thickness maps for all 11 glacier regions -Basin-divided ice volumes for each glacier region, with a 1 km, 5 km, and 20 km buffer -Results of a full parameter sensitivity test for the thickness calculation All data are saved in 32-bit floating-point geotiff format. The data are freely available under the Creative Commons Attribution Licence, CC BY 4.0. The feature-tracking code used to derive ice velocities, GIV, is available on github and Zenodo (https://doi.org/10.5281/zenodo.4904544). All other code, including Google Earth Engine download scripts and the ice-thickness inversion code is available on zenodo (https://doi.org/10.5281/zenodo.6323069)

Increasing rate of 21st century volume loss of the Patagonian Icefields measured from proglacial river discharge

Abstract The Northern and Southern Patagonian Icefields are rapidly losing volume, with current volume loss rates greater than 20 km3 a−1. However, details of the spatial and temporal distribution of their volume loss remain uncertain. We evaluate the rate of 21st-century glacier volume loss using the hydrological balance of four glacierised Patagonian river basins. We isolate the streamflow contribution from changes in ice volume and evaluate whether the rate of volume loss has decreased, increased, or remained constant. Out of 11 glacierised sub-basins, seven exhibit significant increases in the rate of ice volume loss, with a 2006–2019 time integrated anomaly in the rate of glacier volume loss of 135 ± 50 km3. This anomaly in the rate of glacier-volume-loss is spatially heterogeneous, varying from a 7.06 ± 1.69 m a−1 increase in ice loss to a 3.18 ± 1.48 m a−1 decrease in ice loss. Greatest increases in the rate of ice loss are found in the early spring and late summer, suggesting a prolonging of the melt season. Our results highlight increasing, and in some cases accelerating, rates of volume loss of Patagonia's lake-terminating glaciers, with a 2006–2019 anomaly in the rate of glacier volume loss contributing an additional 0.027 ± 0.01 mm a−1 of global mean sea-level rise.</jats:p