Regina Reber

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Reber

First Name

Regina

ORCID

0000-0003-1660-5613

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Publications 1 - 4 of 4

LGM Glaciations in the Northeastern Anatolian Mountains: New Insights
Reber, Regina; Akçar, Naki; Tikhomirov, Dmitry; et al. (2022)
Geosciences
Barhal Valley belongs to the Çoruh Valley System in the Kaçkar Mountains of northeastern Anatolia. This 13 km long valley is located to the south of the main weather divide and to the east of Mt. Kaçkar, with the highest peak of the mountain range being 3932 m. Today, source of an average yearly precipitation of 2000 mm of moisture is the Black Sea, situated approximately 40 km to the north of the study site. Glaciers of the Last Glacial Maximum (LGM) descended directly from Mt. Kaçkar and reached an altitude of ca. 1850 m a.s.l. (above sea level). In this study, we are exploring whether the position of Barhal Valley to the south of the main weather divide and its east–west orientation have an influence on the existence and expansion of paleoglaciers. Here, we present 32 new cosmogenic 36Cl dates on erratic boulders from the Çoruh Valley System. We reconstructed three geomorphologically well-contained glacier advances in the Barhal Valley, namely at 34.0 ± 2.3 ka, 22.2 ± 2.6 ka, and 18.3 ± 1.7 ka within the time window of the global LGM. Field evidence shows that the glacier of the 18.3 ± 1.7 ka advance disappeared rapidly and that by the latest time, at 15.6 ± 1.8 ka, the upper cirques were ice-free. No evidence for Lateglacial glacier fluctuations was found, and the Neoglacial activity is restricted to the cirques with rock glaciers. A range of 2700 to 3000 m for the Equilibrium Line Altitude (ELA) at the LGM was reported based on modeling of the glacial morphology. We determined that the most likely position of the LGM ELA in the Çoruh Valley System was at 2900 m a.s.l. We suggest an alternative moisture source to the direct transport from the Black Sea for the ice accumulation in the Eastern Black See Mountains. The shift of the Polar Front and of the Siberian High Pressure System to the south during the LGM resulted in the domination of easterly airflow to the Caucasus and Kaçkar Mountains with moisture from expanded lakes in central–western Siberia and from the enlarged Aral-and Caspian Seas.
Timing of retreat of the Reuss Glacier (Switzerland) at the end of the Last Glacial Maximum
Reber, Regina; Akçar, Naki; Ivy-Ochs, Susan; et al. (2014)
Swiss Journal of Geosciences
We used cosmogenic 10Be and 36Cl to establish the timing of the onset of deglaciation after the Last Glacial Maximum of the Reuss Glacier, one of the piedmont lobes of the Alpine ice cap that reached the northern Alpine foreland in Switzerland. In this study, we sampled erratic boulders both at the frontal position in the foreland (Lenzburg and Wohlen, canton Aargau) and at the lateral Alpine border position (Seeboden moraine, Rigi, canton Schwyz). The minimum age for the beginning of retreat is 22.2 ± 1.0 ka at the frontal (terminal) position and 20.4 ± 1.0 ka at the lateral position. These ages are directly comparable with exposure ages from the other piedmont lobes in the northern Alpine foreland. Our data from the mountain called Rigi, do not support the hypothesis that boulders located external to the Seeboden moraine were deposited prior to the last glacial cycle. We present a first exposure age from an erratic boulder in a retreat position in the Alpine foreland. The Reuss Glacier was approximately 12 km behind the maximal extent no later than at 18.6 ± 0.9 ka.
Overdeepenings in the Swiss plateau: U-shaped geometries underlain by inner gorges
Bandou, Dimitri; Schlunegger, Fritz; Kissling, Eduard; et al. (2023)
Swiss Journal of Geosciences
We investigated the mechanisms leading to the formation of tunnel valleys in the Swiss foreland near Bern. We proceeded through producing 3D maps of the bedrock topography based on drillhole information and a new gravimetric survey combined with modelling. In this context, the combination of information about the densities of the sedimentary fill and of the bedrock, together with published borehole data and the results of gravity surveys along 11 profiles across the valleys, served as input for the application of our 3D gravity modelling software referred to as PRISMA. This ultimately allowed us to model the gravity effect of the Quaternary fill of the overdeepenings and to produce cross-sectional geometries of these troughs. The results show that 2–3 km upstream of the city of Bern, the overdeepenings are approximately 3 km wide. They are characterized by steep to oversteepened lateral flanks and a wide flat base, which we consider as a U-shaped cross-sectional geometry. There, the maximum residual gravity anomaly ranges between − 3 to − 4 mGal for the Aare valley, which is the main overdeepening of the region. Modelling shows that this corresponds to a depression, which reaches a depth of c. 300 m a.s.l. Farther downstream approaching Bern, the erosional trough narrows by c. 1 km, and the base gets shallower by c. 100 m as revealed by drillings. This is supported by the results of our gravity surveys, which disclose a lower maximum gravity effect of c. − 0.8 to − 1.3 mGal. Interestingly, in the Bern city area, these shallow troughs with maximum gravity anomalies ranging from − 1.4 to − 1.8 mGal are underlain by one or multiple inner gorges, which are at least 100 m deep (based on drilling information) and only a few tens of meters wide (disclosed by gravity modelling). At the downstream end of the Bern area, we observe that the trough widens from 2 km at the northern border of Bern to c. 4 km approximately 2 km farther downstream, while the bottom still reaches c. 300 to 200 m a.s.l. Our gravity survey implies that this change is associated with an increase in the maximum residual anomaly, reaching values of − 2.5 mGal. Interestingly, the overdeepening’s cross-sectional geometry in this area has steeply dipping flanks converging to a narrow base, which we consider as V-shaped. We attribute this shape to erosion by water either underneath or at the snout of a glacier, forming a gorge. This narrow bedrock depression was subsequently widened by glacial carving. In this context, strong glacial erosion upstream of the Bern area appears to have overprinted these traces. In contrast, beneath the city of Bern and farther downstream these V-shaped features have been preserved. Available chronological data suggest that the formation of this gorge occurred prior to MIS 8 and possibly during the aftermath of one of the largest glaciations when large fluxes of meltwater resulted in the fluvial carving into the bedrock.
The Aare main overdeepening on the northern margin of the European Alps: basins, riegels, and slot canyons
Schlunegger, Fritz; Kissling, Eduard; Bandou, Dimitri Tibo; et al. (2024)
Earth Surface Dynamics
This work summarizes the results of an interdisciplinary project where we aimed to explore the origin of overdeepenings through a combination of a gravimetry survey, drillings, and dating. To this end, we focused on the Bern area, Switzerland, situated on the northern margin of the European Alps. This area experienced multiple advances of piedmont glaciers during the Quaternary glaciations, resulting in the carving of the main overdeepening of the Aare River valley (referred to as the Aare main overdeepening). This bedrock depression is tens of kilometres long and up to several hundreds of metres to a few kilometres wide. We found that, in the Bern area, the Aare main overdeepening is made up of two > 200 m deep troughs that are separated by a ca. 5 km long and up to 150 m high transverse rocky ridge, interpreted as a riegel. The basins and the riegel are overlain by a > 200 m and a ca. 100 m thick succession of Quaternary sediments, respectively. The bedrock itself is made up of a Late Oligocene to Early Miocene suite of consolidated clastic deposits, which are part of the Molasse foreland basin. In contrast, the Quaternary suite comprises a Middle Pleistocene to Holocene succession of unconsolidated glacio-lacustrine gravel, sand, and mud. A synthesis of published gravimetry data revealed that the upstream stoss side of the bedrock riegel is ca. 50 % flatter than the downstream lee side. In addition, information from > 100 deep drillings reaching depths > 50 m suggests that the bedrock riegel is dissected by an anastomosing network of slot canyons. Apparently, the slot canyons established the hydrological connection between the upstream and downstream basins during their formation. Based on published modelling results, we interpret that the riegels and canyons were formed through incision of subglacial meltwater during a glacier's decay state, when large volumes of meltwater were released. It appears that such a situation has repeatedly occurred since the Middle Pleistocene Transition approximately 800 ka, when large and erosive piedmont glaciers several hundreds of metres thick began to advance far into the foreland. This resulted in the deep carving of the inner-Alpine valleys and additionally in the formation of overdeepenings, riegels, and slot canyons on the plateau situated on the northern margin of the Alps.

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Regina Reber

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