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Earth Surface Dynamics An interactive open-access journal of the European Geosciences Union
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Volume 6, issue 3 | Copyright
Earth Surf. Dynam., 6, 809-828, 2018
https://doi.org/10.5194/esurf-6-809-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 26 Sep 2018

Research article | 26 Sep 2018

Glacial dynamics in pre-Alpine narrow valleys during the Last Glacial Maximum inferred by lowland fluvial records (northeast Italy)

Sandro Rossato1, Anna Carraro2, Giovanni Monegato2, Paolo Mozzi1, and Fabio Tateo2 Sandro Rossato et al.
  • 1Department of Geosciences, University of Padova, Padova, 35131, Italy
  • 2Institute of Geosciences and Earth Resources (IGG) – National Research Council (CNR), Padova, 35131, Italy

Abstract. During the Last Glacial Maximum (LGM), most of the major glaciated basins of the European Southern Alps had piedmont lobes with large outwash plains; only a few glaciers remained within the valley. Piedmont glaciers have left well-preserved terminal moraines, which allow for investigations to be carried out and inferences to be made regarding their evolution and chronology. Valley glaciers' remnants, on the contrary, are often scantly preserved, and changes can only be detected through correlations with glaciofluvial deposits in downstream alluvial basins. The Brenta glacial system's dynamics in the glacier's terminal tract have been inferred through a wide range of sediment analysis techniques on an alluvial stratigraphic record of the Brenta megafan (northeast Italy), and via the mapping of in-valley glacial/glaciofluvial remnants. Glaciers flowing across narrow gorges could possibly be slowed/blocked by such morphology, and glacial/sediment fluxes may then be diverted to lateral valleys. Moreover, narrow valleys may induce glaciers to bulge and form icefalls at their front, preventing the formation of terminal moraines. The Brenta Glacier was probably slowed/blocked by the narrow Valsugana Gorge downstream of Primolano and was effectively diverted eastwards across a wind gap (Canal La Menor Valley), joining the Cismon/Piave glaciers near Rocca and ending  ∼ 2km downstream. The Cismon and Piave catchments started to contribute to the Brenta system just after 27kacalBP until at least  ∼ 19.5kacalBP. After the glaciers collapsed, the Piave River once again flowed into its main valley, whilst the Cismon continued to merge with the Brenta.

This investigation shows that glacial catchments may vary significantly over time during a single glaciation in rugged Alpine terrains. Sand petrography and the chemical/mineralogical composition of sediments are powerful proxies for tracing such variations, as they propagate through the glacial and glaciofluvial systems and can be recognized in the alluvial stratigraphic record far downstream from the glacier front.

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Glaciations may induce significant changes in the catchments of major sedimentary systems over time, even during a single phase. The rugged morphology of Alpine valleys may slow, block or divert glacial tongues. This conclusion arises from reconstructions made regarding the dynamics of the Brenta glacial system (northeast Italy). These reconstructions included sediment analysis techniques on the related alluvial stratigraphic record and mapping of in-valley glacial/glaciofluvial remnants.
Glaciations may induce significant changes in the catchments of major sedimentary systems over...
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