Browsing by Author "Fernandez, Hans"

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    De-icing landsystem model for the Universidad Glacier (34° S) in the Central Andes of Chile during the past ∼660 years
    (2022) Fernandez, Hans; Garcia, Juan-Luis; Nussbaumer, Samuel U.; Janine Geiger, Alessa; Gartner-Roer, Isabelle; Perez, Francia; Tikhomirov, Dmitry; Christl, Marcus; Egli, Markus
    Reconstructing latest Holocene (< 1000 years) glacial landscape development in the Central Andes of Chile (30-35 degrees S) is key for understanding the response of the cryosphere during periods of negative glacier mass balance, such as the current one. The excellently preserved glacial landscape produced during the latest ice advance and retreat cycle is of particular interest for examining the detailed response of glaciers to deglaciation. To establish a conceptual model of glacier behavior under warm and dry climatic conditions, we reconstructed and dated the recent glacial history of the Universidad Glacier (34 degrees S) through detailed geomorphological mapping and Be-10 cosmogenic surface exposure dating. Our mapping describes a landsystem that spans from the current ice front to similar to 3 km down-valley, where a mosaic of glacial landforms includes mounded relief; sinkholes; debris -filled stripes; moraine belts; flutings; and a prominent basal till plain. Our Be-10 ages suggest that the Universidad Glacier has fluctuated in its forefield since the 13th - 15th centuries CE. We propose that the glacier evolved from a clean glacier to a debris-covered glacier, to an ice-cored moraine, and finally, to a massive dead-ice topography. This deglacial evolution intermittent and potentially reset by multiple standstills and/or re-advances during the overall retreat. The implication is that phases of active ice were followed by stagnation associated with progressive melting of dead ice under the supraglacial debris layer. Similar geomorphic features and processes are recorded in the present-day Universidad Glacier ablation zone, denoting a recurrent reconditioning over time analogous to the glacier's evolution during the latest Holocene.(C) 2022 Elsevier B.V. All rights reserved.
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    The Last Glacial Maximum and Deglacial History of the Seno Skyring Ice Lobe (52°S), Southern Patagonia
    (2022) Lira, Maria-Paz; Garcia, Juan-Luis; Bentley, Michael J.; Jamieson, Stewart S. R.; Darvill, Christopher M.; Hein, Andrew S.; Fernandez, Hans; Rodes, Angel; Fabel, Derek; Smedley, Rachel K.; Binnie, Steven A.
    There are still many uncertainties about the climatic forcing that drove the glacier fluctuations of the Patagonian Ice Sheet (PIS, 38-55 degrees S) during the last glacial period. A key source of uncertainty is the asynchrony of ice lobe fluctuations between the northern, central, and southern PIS. To fully understand the regional trends requires careful mapping and extensive geochronological studies. This paper presents geomorphological and geochronological reconstructions of the glacial and deglacial landforms formed during the last glacial period at the Seno Skyring lobe, southernmost Patagonia (52 degrees S, 71 degrees W). We present a detailed geomorphological map, where we identify two moraine systems. The outer and older is named Laguna Blanca (LB) and the inner Rio Verde (RV). The LB moraines were built subaerially, whereas parts of the RV were deposited subaqueously under the palaeo lake Laguna Blanca, which developed during deglaciation. We conducted surface exposure Be-10 dating methods on boulder samples collected from LB and RV glacial margins. The moraine LB III and LB IV formed at 26.3 +/- 2.3 ka (n = 5) and 24.3 +/- 0.9 ka (n = 3), respectively. For the inner RV moraine, we obtained an age of 18.7 +/- 1.5 ka (n = 6). For the palaeo Laguna Blanca evolution, we performed Be-10 exposure ages on shoreline berms and optically stimulated luminesce dating to constrain the lake levels, and Be-10 depth profile dating on an outwash deposit formed by a partial lake drainage event, which occurred at 22 +/- 3 ka. For the RV moraine deglaciation, we performed radiocarbon dating of basal sediments in a peat bog, which indicates that the glacier retreated from the terminal RV moraine by at least c. 16.4 cal kyr BP. Our moraine geochronology shows an asynchrony in the maximum extents and a different pattern of ice advances between neighbouring lobes in southern Patagonia. We speculate that this may be due, at least in part, to the interaction between topography and the precipitation carried by the southern westerly wind belt. However, we found broad synchrony of glacial readvances contemporaneous with the RV moraine.