1,721,025 research outputs found
Geomorfologia dell'Alto Adriatico: il contributo della missione oceanografica SomRISA09.
No full textOceanographic surveys are an important tool in the investigation of quaternary deposits and morphologies located on sea floors. Their importance and potentialities in geomorphologic applications are here discussed in details, taking as example the SomRISA09 survey (North Adriatic Sea, 28/04/2009 – 07/05/2009). During this survey, University of Padua and CNR-ISMAR worked together to realize the DEM of the north-Adriatic sea and to connect it to DTM of the Venetian plain, created by the Department of Geography (University of Padua). Thanks to this DEM it was possible to appreciate the good preservations status of the LGM deposits. Together with this project, the CNR-ISMAR runned some other analyses; the involved instrumentation is here described, pointing out their potentialities and limits
Inferring LGM sedimentary and climatic changes in the southern Eastern Alps foreland through the analysis of a 14C ages database (Brenta megafan, Italy)
No full textThe analysis of a database of radiocarbon ages is proposed as a tool for investigating major glaciofluvial systems of the Last Glacial Maximum (LGM) in the Alpine foreland, and their relations with glacier dynamics and climatic fluctuations. Our research concerns the Brenta megafan (NE Italy), where 110 radiocarbon dates integrate a robust regional stratigraphic and palaeoclimatic framework. Age-depth models allowed us to calculate sedimentation rates, while the time distribution of peat layers, which recurrently formed in this region during the LGM, were estimated through meta-analysis. The reliability of statistical results was carefully evaluated using Pearson and Spearman coefficients. Sedimentation rates in the Brenta megafan markedly fluctuated during LGM: ≈1.8 m/ka between 40 and 26.7 ka cal BP; ≈3 m/ka between 26.7 and 23.8 ka cal BP and ≈1.4 m/ka from 23.8 to 17.5 ka cal BP, when the distributary system deactivated due to fan-head trenching. This is evidence that sediment input and routing in the glaciofluvial distributary system was particularly efficient during the central part of LGM, when glaciers were stable at their outermost position. Meta-analysis indicates an increase in peat formation in correspondence with global (Heinrich Event 3 and/or the Greenland Interstadial 5.1 and 4 for the 30.5, 29.6 and 28.8 ka cal BP peaks) and regional (23.5 ka cal BP) wet events. Other peaks at 22.2, 21.8, 20.2 and 19 ka cal BP correlate with fluctuations of south-eastern Alpine glaciers. Significant peat formation continued until ≈18 ka cal BP, when the last peak occurred. A marked decrease in peat formation is recorded concomitantly with the onset of Heinrich Event 2 (i.e. the 26 ka cal BP trough). The good correspondence of sedimentary events in the Brenta glaciofluvial system with the dynamics of glaciers and glaciofluvial and lacustrine systems in the southern Eastern Alps suggests a common climatic forcing on the whole region during the LGM. Peat layer formation in the floodplain fens increased significantly in correspondence with glacier withdrawals and/or wetter climatic episodes, constituting a good proxy for climatic fluctuations during glacial periods. It also allows correlations across different continental environments and regions in the northern hemisphere
Evoluzione geomorfologica e paleoidrografica dell'alta pianura vicentina
Full text linkThis work concerns the Late Quaternary evolution of the Western Venetian Plain, with a focus on the relations between the glacial complexes hosted in the terminal valley tract of the Astico Valley and the piedmont fans. Three distinct glacial events have been identified during this work. Remote sensing, field survey, stratigraphic measurements and reconstructions, sand petrography, radiocarbon and dendrochronological datings and pollen analyses allowed to define an evolutionary model of the Venetian plain during the Middle and Late Pleistocene. The glacial phases were distinguished in the Astico Valley and were attributed to the LGM, the MIS 6 and to a generic glaciation of the Middle Pleistocene. Sand petrography analyses show that all these glacial deposits contain rock fragments that reached the Astico Valley through a transfluence of the Adige glacier. During LGM, this glacial stream entered the Valley from the North through the Carbonare saddle (1075 m a.s.l.), as it probably happened also in previous major glaciations. The chronostratigraphy of cores drilled near the towns of Sandrigo, Marano Vicentino, Vicenza and Villaverla, as well as the data gathered from the geoelectrical surveys realized near the town of Breganze, show that the outwash stream changed its way to the piedmont plain at the end of LGM, as a response to rapid glacial collapse. This switch led to the deactivation of the north-western sector of the plain (Thiene fan) in favour of the south-eastern one (Sandrigo fan), and it could be linked with the well-known post-LMG incision of the Brenta megafan, visible also in the two cores drilled near the town of Piazzola sul Brenta. In addition, some indications about the development of the Astico River and Brenta River during the Holocene are provided.
The lower Astico Valley proved to have preserved significant evidence of even minor glacial fluctuations, in response of subtle climatic changes, which may be difficult to distinguish in major Alpine glaciersLa tesi è incentrata sull'evoluzione geomorfologica e paleoidrografica della pianura vicentina (pianura Veneta occidentale), durante il Pleistocene superiore e l'Olocene, con una speciale attenzione alle relazioni tra i complessi glaciali presenti nella Valdastico e i conoidi pedemontani. La ricerca ha permesso di distinguere 3 diverse fasi glaciali, identificate a partire dai depositi rinvenuti nella media e bassa Valdastico. L'utilizzo di tecniche di telerilevamento, rilevamento sul terreno, misure, correlazioni e ricostruzioni stratigrafiche, analisi petrografiche delle sabbie, datazioni dendrocronologiche e al radiocarbonio e analisi polliniche hanno permesso di costruire un solido modello evolutivo dell'area durante il Pleistocene medio e superiore. L'ultima fase glaciale è stata ascritta all'LGM, quella intermedia al MIS 6, mentre nel caso di quella più antica si può indicare solo una generale attribuzione al Pleistocene medio. Le analisi petrografiche indicano una stretta correlazione tra la presenza di una transfluenza del ghiacciaio dell'Adige in Valdastico attraverso la sella delle Carbonare (1075 m s.l.m.) e l'esistenza di un ghiacciaio vallivo sviluppato all'interno di quest'ultima. La cronostratigrafia derivante dai carotaggi meccanici realizzati vicino agli abitati di Sandrigo, Marano Vicentino, Vicenza e Villaverla, così come i risultati ottenuti da sondaggi geoelettrici realizzati in prossimità di Breganze, indicano che l'Astico cambiò direzione di deflusso in pianura in relazione al rapido collasso glaciale avvenuto alla fine dell'LGM. Questo spostamento ha determinato l'attivazione della porzione sud-orientale della pianura vicentina (il conoide di Sandrigo) a scapito della parte nord-occidentale (conoide di Thiene). Tale evento può essere correlato con l'incisione post-LGM del megafan del Brenta, ben documentata in letteratura e i cui effetti sono visibili nei carotaggi di Piazzola sul Brenta. Sono stati individuate indicazioni anche circa l'evoluzione olocenica dell'Astico e del Brenta, che seguivano direzioni di deflusso più verso sud rispetto alle attuali.
La media e bassa Valdastico si è rivelata essere un'area di interesse per la comprensione della risposta dei sistemi sedimentari fluvioglaciali ai cicli glaciale/interglaciale pleistocenici, avendo peraltro dimostrato la possibilità di rinvenire depositi indicatori di variazioni climatiche di portata anche ridotta all'interno di vallate prealpine di dimensioni medio-piccol
Workshop report : the Tagliamento river basin : don't divorce the river from its basin
No full textThe Tagliamento River basin is characterized by a precarious equilibrium between its peculiar natural conditions and the human needs. The “Tagliamento River” working group at the “12th European Seminar on Geography of Water” has described the different conflicts concerning the basin, to try to point out some suggestions to improve its management
LGM glacial retreat in the Astico valley and mismatch with the Adige and Brenta glacial transfluences (NE Italy)
No full textValley glaciers can be fed by transfluence from major glaciers through a gap or a saddle. These glacial systems may be more sensitive to rapid climate changes, in terms of temperature and precipitation rates. Here we present a case study concerning the timing of deglaciation in a Prealpine glacial system connected to transfluences from the Adige glacier. Changes in the position of the end moraines, hosted in the terminal valley reach, are coupled with observation of the glaciofluvial sedimentation in the piedmont area, with special reference to the Astico system, providing new insights on the onset of the glacial decay at the end of LGM
Reconstructing extreme ..ooding events in the Venetian-Friulian Plain (NE Italy) through meta-analysis of a 14C database
No full text1. Introduction
The study of the sedimentary record of the past alluvial episodes can support the recognition of extreme events of flooding, back to several hundred or thousands of years (Ely et al., 1993; Knox, 1993; Maas et al., 2001).
These studies, among the others, opened the path to the comparison of river systems alteration at various scale, even if at the interhemispheric one (Macklin et al., 2012). The significant increase of dated fluvial units permits the application of meta-analysis techniques which request large datasets. The INQUA group denominated “Hydrological EXtreme Events in Changing Climate” try to explorer this research approach, applying the numerical method developed by Macklin et al. (2006; 2012) for producing probability-based reconstructions of Holocene and Pleistocene flooding periods.
As part of this group, we applied the method to the 14C dating database of the Venetian-Friulian plain, which is one of the largest datasets dealing with alluvial stratigraphy. The aim of the whole process is to identify a probabilistic valuation of periods characterized by an increase in the amount of flooding episodes.
2. Study region
The Venetian-Fiulian Plain extends for about 10,000 km2 along the South-eastern Alps and was formed by the activity of the main Alpine rivers that are not tributaries of Po River (Isonzo, Tagliamento, Piave, Brenta and Adige rivers).
The rainfall regime is bimodal, with a maximum during autumn and a secondary peak in spring; mean annual rainfall values are significantly higher than those of the Mediterranean and central Europe. Those elements, combined, may periodically cause extreme flood events in the plain.
3. Methodology
During the last 30 years a large amount of 14C datings has been performed in NE Italy on a widespread type of materials and fluvial units and part of these data have been already collected in a standardized database (e.g. Bondesan et al., 2004; Carton et al., 2009; Fontana et al., 2010).
A database of about 400 14C datings was compiled, comprehending published and unpublished realized both with the conventional and the AMS method. The whole dataset was organized following the instructions provided by Johnstone et al. (2006). In particular, for each dating it’s recorded its location, type of sample, stratigraphic position and the geological meaning of the fluvial unit from which the age was obtained. The following step seek to determine if the dated sample represented a “change after” date. This correspond to a variation in the depositional style and it is defined as a mark that lies immediately below a marked sedimentary discontinuity, identified by a reversal in the natural floodplain fining-up sedimentary sequence, or where a peat or soil associated with a period of floodplain stability is overlain by a minerogenic sediment unit (Macklin et al., 2012). It has been demonstrated that the occurrence of these types of stratigraphic breaks can indicate a general change of the climate conditions, expressed by a significant flood event or an increase in flood frequency/magnitude.
The various data were subdivided according to their uncalibrated age into Pleistocene and Holocene dates, in order to isolate homogeneous chronological/climate periods. 14C ages were calibrated using the IntCal09 calibration curve and then processed using OxCal 4.1 (Bronk-Ramsey, 2001) to produce cumulative probability function (CPF) plots. Distinct plot were obtained for the “change after” dates, which constitutes a probability distribution that is the best estimate for the chronological distribution of the items dated.
4. Results and perspectives
Here are descried some of the preliminary results of the work and possible directions for the future research. Almost half of the database consists of LGM datings carried out on peat or organic silt/clay collected in the distal sector of the Venetian-Friulian Plain with boreholes from the immediate subsoil up to 30 m of depth. These organic layers represent wetlands developed over wide areas comprised between fluvial ridges and periodically inundated by the fluctuating groundwater (Miola et al., 2006). The accumulation of organic material continued until the alluvial minerogenic supply prevailed on the fen organic deposition. When this change occurs, the peat level is incorporated into the stratigraphic record. So, dating the top of these level provide a certain “change after” date.
The flooding episodes were identified as those portions of the plot where the relative CPF exceeded the mean value obtained for the whole dataset. Those events were considered rounding the value to the nearest century, in order to avoid over-interpretations.
The method has been applied in detail to 2 distinct river systems: Tagliamento and Brenta. Those river, actually, constitute the most studied systems of the area and, in addition, the number of available radiocarbon datings is significantly larger if compared to other Mediterranean systems (see Fig. 1 for a representations of the available datings in the Brenta system).
In the Holocene the research evidence at least 2 periods of climate deterioration, during the second part of the Subboreal period (4500-3000 years BP) and the dark ages (ca 500-1000 AD), respectively. These intervals were partly already known as period of significant river systems alteration, testified by frequent avulsions of the Tagliamento, Brenta and Piave rivers.
It’s important to compare the results with other independents climate proxies, in order to clarify if the process is consistent with them and if it’s possible to identify some periods of climate deterioration not yet discovered in these part of Italy. It is possible also to compare the results among the various river basins, to point out if some difference occurs, due to geographical/geological conditions. Moreover, the meta-analyses of radiocarbon database allows an objective comparison with the results obtained in other European and extra-European regions
Meta-analysis of a Holocene 14C database for the detection of paleohydrological crisis in the Venetian–Friulian Plain (NE Italy)
No full textThe Venetian–Friulian Plain is the northernmost alluvial environment facing the Adriatic Sea and it represents the
transition from theMediterranean domain to the Alps and the temperate regions of central and eastern Europe.
The investigated area consists of the alluvial systems of Brenta, Piave and Tagliamento rivers, forming distinct
alluvial megafans fed bymountain basins of 1567, 3899 and 2580 km2, respectively. The database of radiocarbon
dates related to theHolocene alluvial evolution of the Venetian–Friulian Plain consists of 136 samples, 65 of them
classified as change-after dates. We analyzed statistically the database with the aim of detecting periods of enhanced
flooding activity. The individual calibration probability intervals of each radiocarbon age were summed,
producing a cumulative probability density function (CPDF) plot for each alluvial systemand for thewhole database.
Each change-after CPDF plot has been subtracted to its correspondent CPDF plot of the entire sub-dataset,
obtaining a relative cumulative probability function (RCPF) curve.
The analysis of these curves evidences that statistically significant information are available between about 8.5
and 0.8 ka cal BP. In particular, nine periods of enhanced flooding activity have been identified: 8.4–8.3, 7.5–
7.2, 6.9–6.2, 5.5–5.3, 4.7–4.5, 2.3–2.1, 1.9–1.7, 1.6–1.4 and 1.3–0.8 ka cal BP. In the interval 8.5–0.8 ka cal BP,
some sub-periods are not statistically significant because of the relatively fewchange-after dates available. Notably,
between 4.5 and 2.3 ka cal BP no interval has been recognized, even if some important flooding deposits are
documented in the stratigraphic and geomorphological record.
Meta-analyses revealed quite a good correlation of several flooding periods occurred in the study area with the
flooding record of the Lake Iseo (northern Italy), as well as with positive peaks in the Ice Rafted Debris (IRD)
curve for the North Atlantic, namely Bond events 1, 3, 4 and 5. Comparison with other flood sequences obtained
in Great Britain, Spain, Poland and Germany with the same statistical approach used in this work confirms the
presence of some common intervals. In particular, synchronous periods of hydrological crisis are recorded in
NE Italy and Great Britain at 7.5–7.3, 6.9–6.5, 6.3–6.2, 4.7–4.5, 2.3–2.1, 1.5–1.4, 1.3–1.1, 0.9–0.8 ka cal BP. Two
of them, 4.7–4.5 and 0.9–0.8 ka cal BP, occurred also in the Iberian Peninsula. These results suggest that during
the middle and late Holocene enhanced flooding activity in NE Italy is recurrently connected to events or phases
of climatic deterioration at regional and continental scale, with minor influence of local forcings
Conflitti d'acqua e di uomini nel bacino del Tagliamento: l'utilità di un approccio integrato tra geografia umana e fisica
No full textThis paper comes from a collaboration involving three PhD students of the Department of Geography, University of Padua. The main aims are i) to summarize the results emerged during the 12th European Seminar on Geography of Water (Udine, 28 June - 9 July 2009) within the working group dedicated to Tagliamento river basin; ii) to test a multidisciplinary approach that joins physical and human geography. After a physical and administrative overview of the area, the paper focuses on conflicts between different uses of basin resources (hydropower production, irrigation, industrial use of water, gravel extraction, tourism, recreational activities), and with the risk management related to the Tagliamento. Some general suggestions concerning feasible solutions to the conflicts has been pointed out: i.e. the need to increase local community involvement in public choices, coupled to a reinforcement of a catchment scale vision of the problems. The topics are too vast and complex to be entirely detailed here; but, the analysis has highlighted the potentialities of a successful interdisciplinary collaboration dealing with an issue that requires complementary skills, methods and approaches
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