Glacial dynamics in pre-Alpine narrow valleys during the Last Glacial Maximum inferred by lowland fluvial records (northeast Italy)
<p>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 investigatio...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2018-09-01
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| Series: | Earth Surface Dynamics |
| Online Access: | https://www.earth-surf-dynam.net/6/809/2018/esurf-6-809-2018.pdf |
| Summary: | <p>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
∼ 2 km downstream. The Cismon and Piave catchments started to
contribute to the Brenta system just after 27 ka cal BP until at least
∼ 19.5 ka cal BP. After the glaciers collapsed, the Piave River once
again flowed into its main valley, whilst the Cismon continued to merge with
the Brenta.</p><p>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.</p> |
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| ISSN: | 2196-6311 2196-632X |