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| Titel |
Mass-movement and flood-induced deposits in Lake Ledro, southern Alps, Italy: implications for Holocene palaeohydrology and natural hazards |
| VerfasserIn |
A. Simonneau, E. Chapron, B. Vanniere, S. B. Wirth, A. Gilli, C. Giovanni, F. S. Anselmetti, M. Desmet, M. Magny |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1814-9324
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| Digitales Dokument |
URL |
| Erschienen |
In: Climate of the Past ; 9, no. 2 ; Nr. 9, no. 2 (2013-03-21), S.825-840 |
| Datensatznummer |
250018022
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| Publikation (Nr.) |
 copernicus.org/cp-9-825-2013.pdf |
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| Zusammenfassung |
| High-resolution seismic profiles and sediment cores from Lake Ledro combined
with soil and riverbed samples from the lake's catchment area are used to
assess the recurrence of natural hazards (earthquakes and flood events) in
the southern Italian Alps during the Holocene. Two well-developed deltas and
a flat central basin are identified on seismic profiles in Lake Ledro. Lake
sediments have been finely laminated in the basin since 9000 cal. yr BP
and frequently interrupted by two types of sedimentary events (SEs):
light-coloured massive layers and dark-coloured graded beds. Optical analysis
(quantitative organic petrography) of the organic matter present in soil,
riverbed and lacustrine samples together with lake sediment bulk density and
grain-size analysis illustrate that light-coloured layers consist of a
mixture of lacustrine sediments and mainly contain algal particles similar to
the ones observed in background sediments. Light-coloured layers thicker than
1.5 cm in the main basin of Lake Ledro are synchronous to numerous coeval
mass-wasting deposits remoulding the slopes of the basin. They are
interpreted as subaquatic mass-movements triggered by historical and
pre-historical regional earthquakes dated to AD 2005, AD 1891, AD 1045 and
1260, 2545, 2595, 3350, 3815, 4740, 7190, 9185 and 11 495 cal. yr BP.
Dark-coloured SEs develop high-amplitude reflections in front of the deltas
and in the deep central basin. These beds are mainly made of terrestrial
organic matter (soils and lignocellulosic debris) and are interpreted as
resulting from intense hyperpycnal flood event. Mapping and quantifying the
amount of soil material accumulated in the Holocene hyperpycnal flood
deposits of the sequence allow estimating that the equivalent soil thickness
eroded over the catchment area reached up to 5 mm during the largest
Holocene flood events. Such significant soil erosion is interpreted as
resulting from the combination of heavy rainfall and snowmelt. The recurrence
of flash flood events during the Holocene was, however, not high enough to
affect pedogenesis processes and highlight several wet regional periods
during the Holocene. The Holocene period is divided into four phases of
environmental evolution. Over the first half of the Holocene, a progressive
stabilization of the soils present through the catchment of Lake Ledro was
associated with a progressive reforestation of the area and only interrupted
during the wet 8.2 event when the soil destabilization was
particularly important. Lower soil erosion was recorded during the
mid-Holocene climatic optimum (8000–4200 cal. yr BP) and associated with
higher algal production. Between 4200 and 3100 cal. yr BP, both wetter
climate and human activities within the drainage basin drastically increased
soil erosion rates. Finally, from 3100 cal. yr BP to the present-day, data
suggest increasing and changing human land use. |
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