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Alluvial Megafans of Europe: Morphologies, Architectures and Formation Phases
No full textAlluvial megafans are not very common in Europe and the use of this term is not diffuse in the continent because of the persistent habit of describing as "fans" event the huge divergent alluvial landforms (>1000 km2). Considering the megafans that are currently still recognizable in the topography, they can be found only in some of the alluvial areas facing the Alps and the Carpathian chain.
Along the southern Alps, megafans are present from Milan (central Po Plain) to the whole Venetian-Friulian Plain. The major landforms are the ones formed by Adda, Olona, Oglio, Adige, Brenta, Piave and Tagliamento rivers. All these systems experienced a strong depositional phase in the LGM (29-17.5 ka BP), when the Alpine glaciers stationed at the mouth of their valleys and the rivers played as glacial outwashes. Sedimentary starvation characterized all the megafans of northern Italy since Late Glacial. Thus, the Alpine megafans can be mainly considered as relict products of the last glaciation, mainly controlled by the climate forcings.
Megafans are documented also in the Little Hungarian Plain (Danube River near Bratislava and Rába River megafans; mainly fed by the Alps) and in the Great Hungarian Plain (e.g. megafans of Maros, Szamos and Timis rivers). The largest megafan is the one formed by the Maros River, which consists of two lobes covering an overall area of at least 7000 km2. The dated traces of braided and meandering channel belts testify a continuative activity until late Holocene. Compared to the Alpine ones, the megafans of the Great Hungarian Plain are fed by larger catchments, but these were not severely glaciated during LGM and sustained important depositional phases also in Late Glacial and after. In the Carpathian Basin the megafan evolution was strongly influenced by differential subsidence
Investigating evidences of Quaternary glaciations in the Prealpine environment of the Astico valley
Full text linkIn the Astico valley (Venetian Prealps) some glacial, fluvioglacial and glaciolacustrine deposits were found. They are attributed to a pre-LGM glacial advance which reached further out in the valley. Geomorphological and stratigraphic data support this hypothesis. It is also pointed out the presence of a tectonic guidance in the developing of the Astico fluvial network
Late-Quaternary Alluvial Megafans of Europe
No full textMegafans are huge alluvial landforms with a convex geometry, generated by the activity of an instable fluvial systems radiating from an apex. They have an extent that generally exceed 1000 km2 and are formed by a large and fine-dominated distal portion. According with reference literature, megafans can develop where large active mountain catchments can deliver their sedimentary supply to a wide facing plain. Considering these characteristics and the tectonic setting of continental Europe, megafans could be currently described in some of the alluvial areas existing along the Alps and the Carpathian chain. The adoption of the megafan concept has been rather delayed in Europe because of the strong and traditional use of the term “fan” also for describing the largest divergent alluvial landforms. Even in very recent literature, some huge alluvial systems with an extent of some thousands of km2, are described as “fan”, despite the gravelly portion stops in the first 20 km from the valley mouth.
This research was limited to the late-Quaternary megafans that are still recognizable in the topography, while the previous similar landforms that now are no more connected to the present landscape or are part of the stratigraphic record, have not been discussed. The work was carried out starting from the analysis of the specific literature and of the DTMs obtained by SRTM data or, when available, by other more detailed information. The morphometric results were compared with remote-sensed images and with the specific literature describing geomorphological, sedimentological, stratigraphic and geochronological data.
Along the southern Alps megafans are present from Milan (central Po Plain) to the whole Venetian-Friulian Plain. The major landforms are the ones formed by Tagliamento, Piave, Brenta, Adige, Oglio, Olona and Adda rivers. All these systems experienced a strong depositional phase in the LGM (29-17.5 ka BP), when the Alpine glaciers stationed at the mouth of their valleys and the rivers were their outwashes. In that period the megafans reached their maximum extent (e.g. Brenta 2600 km2, Adige 1600 km2, Tagliamento 1200 km2), coupled by a vertical aggradation of 15-30 m. During LGM the channels of Alpine rivers where unconfined in the apical portion of their megafans and gravels could be transported only for the first 15-25 km, while the distal sector was mainly formed by silt and clay. On the contrary, sedimentary starvation characterized all the megafans of northern Italy since the glaciers started to withdrawn. This setting led the rivers to down cut in their LGM deposits and to form incised valleys, even in the distal sector. Thus, during Late Glacial and early Holocene, gravels were conveyed along the incised valleys up to the present coast. A different context settled since about 8 ka BP, when the Adriatic Sea arrived at -10 -5 m below the present level and a new depositional phase started. This situation induced the progressive infilling of the incisions in the distal sector, that now are almost completely buried. According with their evolution history, the southern Alpine megafans can be mainly considered as relict products of the last glaciation, mainly controlled by the climate forcings.
In the Little Hungarian Plain (LHP), the Danube River formed different generations of Quaternary megafans. The present one has its apex near Bratislava, extends for at least 4000 km2 and mainly consists of sandy and fine deposits. This megafan experienced a major forming phase during LGM and Late Galcial, but the Danube supported some aggradation even in the late Holocene. Up to its entrance in the LHP, the Danube is mainly supplied by Alpine catchments, as the Rába River (Raab in German), that flows from the Austrian Eastern Prealps (Burgenland) and created a megafan of ca. 1600 km2 in the SW portion of the LHP. Rába megafan was mainly generated during the last glaciation but, between 25-15 ka BP, the river abandoned large sectors of the megafan surface.
In the Great Hungarian Plain (GHP), many fan-shaped alluvial systems are present, but only few of them can be currently described as megafans (e.g. Maros, Szamos and Timis rivers). The largest megafan in the Carpathian Basin is the one formed by the Maros River (Mures in Romanian), which is fed by the SE Carpathian and by the Apuseni Mountains. This megafan consists of a northern and a southern lobe that cover an area of 5000 and 2000 km2, respectively. Gravels can be found in the shallow subsoil up to 25 km from the apex. In the northern lobe, traces of braided and meandering channel belts have been dated through OSL and testify a continuative activity during Late Glacial and Holocene. The southern lobe was activated since about 2 ka BP. Compared with the southern Alpine ones, the megafans of the Carpathian Basin are fed by larger catchments, but these were not severely glaciated during LGM and sustained also important depositional phases in the Late Glacial and Holocene. In the GHP the planform and the development of the megafans was strongly influenced by differential subsidence
Seesaw longitudinal–transverse drainage patterns driven by Middle and Late Pleistocene climate cycles in the foreland basin of the south-eastern European Alps
No full textThe multi-proxy sediment provenance analysis of two sedimentary successions (GER1 core, 130 m long, and CB core, 103 m long) provides new data for detecting the temporal and spatial variations in fluvial drainage patterns and landscape evolution of the Venetian Plain (NE Italy) in relation to Middle–Late Pleistocene climate fluctuations. Detailed petrographic analyses, compared to present-day river signatures, highlight compositional variations of the sediments, providing crucial information for detecting the depositional histories of the two sites, which lie about 15 km apart, and considering a source-to-sink multi-source context. The successions span from a cold phase older than MIS 9/11 to MIS 1, and are chronostratigraphically well correlated from the MIS 7.3 marine transgression. Despite belonging to the same alluvial system since the Last Glacial Maximum, the GER1 and CB cores show different depositional histories during previous Marine Isotopic Stages, starting at least from MIS 8 (i.e., ca 300–250 ka). A glacial interval older than MIS 9/11, is encountered only within records of the GER1 core. Due to its composition and the particularly coarse grain size, it represents a key element for detecting the depositional dynamics of megafans during past climate oscillations. Conversely, the presence of sediments not fully ascribable to any of the present-day catchment suggests the existence of a trunk paleo-river, longitudinal to the foreland axis, flowing from west to east along the Po Plain and occasionally draining the Venetian Plain. A causal relationship between prograding mechanisms of transverse alluvial megafans and Pleistocene climate variations is detected, taking into account responses of local alluvial systems to glaciers' development, sediment yield from the orogenic hinterland, and sea-level lowstands and highstands. A focus on glacial termination phases allows identification of two additional incised valleys, established at the end of the pre-MIS 9/11 glaciation and of MIS 6
Seesaw longitudinal-transverse drainage patterns driven by Middle and Late Pleistocene climate cycles in the foreland basin of the south-eastern European Alps
No full textThe multi-proxy sediment provenance analysis of two sedimentary successions (GER1 core, 130 m long, and CB core, 103mlong) provides newdata for detecting the temporal and spatial variations in fluvial drainage patterns and landscape evolution of the Venetian Plain (NE Italy) in relation to Middle-Late Pleistocene climate fluctuations. Detailed petrographic analyses, compared to present-day river signatures, highlight compositional variations of the sediments, providing crucial information for detecting the depositional histories of the two sites, which lie about 15 km apart, and considering a source-to-sink multi-source context. The successions span from a cold phase older than MIS 9/11 to MIS 1, and are chronostratigraphically well correlated from the MIS 7.3 marine transgression. Despite belonging to the same alluvial system since the Last Glacial Maximum, the GER1 and CB cores show different depositional histories during previous Marine Isotopic Stages, starting at least from MIS 8 (i.e., ca 300-250 ka). A glacial interval older than MIS 9/11, is encountered only within records of the GER1 core. Due to its composition and the particularly coarse grain size, it represents a key element for detecting the depositional dynamics of megafans during past climate oscillations. Conversely, the presence of sediments not fully ascribable to any of the present-day catchment suggests the existence of a trunk paleo-river, longitudinal to the foreland axis, flowing from west to east along the Po Plain and occasionally draining the Venetian Plain. A causal relationship between prograding mechanisms of transverse alluvial megafans and Pleistocene climate variations is detected, taking into account responses of local alluvial systems to glaciers' development, sediment yield from the orogenic hinterland, and sea-level lowstands and highstands. A focus on glacial termination phases allows identification of two additional incised valleys, established at the end of the pre-MIS 9/11 glaciation and of MIS 6. (C) 2021 Elsevier B.V. All rights reserved
Remote sensing assessment of changes of surface parameters in response to prolonged drought in the arid zone of central Iran (Gavkhoni playa)
No full textRemotely-sensed normalized difference vegetation index (NDVI) and land surface temperature (LST) are significant indicators for evaluating the environmental consequences of climate changes in arid regions. Understanding of the relationship between these changes and land surface properties of the arid regions is important in land planning. The Gavkhoni playa is a closed basin in the arid zone of Iran that has recently undergone significant environmental changes due to decreasing precipitations. The objective of this study was to explore the spatiotemporal changes of its LST and NDVI before and after the drought event of 2014–2018. Through the application of an integrated method based on cellular fractal model and continuous wavelet transform (CWT), we investigated the relationship between variation of surface fractal dimension and distribution of LST and NDVI changes before and after the drought. The results indicated substantial changes in LST and NDVI values associated with the onset of drought conditions. Changes in the spatial distribution of LST and NDVI were particularly high in the central playa area, the western and southern sides of the playa, including the salt lake, the wetlands, and the clay flat. These areas correspond to the zone 4 of the fractal dimension map where extreme topographic anomaly and complexity. Wavelet analysis confirmed the relationship between the surface fractal dimension pattern and anomalies in LST and NDVI variations. The investigation highlighted the ability of the integrated application of the cellular fractal model and wavelet analysis to quantify the relationship between land surface properties and the spatial variation of LST and NDVI in changing environmental conditions
The diluvium aquarum: geologic evidence and geoarchaeological constrains of extreme floods in northern Italy during early Middle Ages
No full textBetween the second part of the sixth century and the seventh century, many regions of Europe have been characterized by dramatic changes in the hydrographic setting, probably related to a strong cooling phase (Büntgen et al., 2016; Helama et al., 2017). In the Mediterranean region the period following the collapse of the Roman Empire is described by many authors as an interval characterized by important alluvial processes (e.g. floods, river avulsions and alluvial aggradation in the mountain valleys), strongly contrasting with the general geomorphological stability of Roman Age and Late Antiquity. Some important chronicles of early Middle Ages report the occurrence of very high-magnitude floods, often described by ancient historians as diluvium (deluge), contributing to create a sort of myth around an out-of-scale event or a longer meteo-climatic phase (Cremonini et al., 2013).
In the framework of the INQUA project “EX-AQUA: Palaeohydrological Extreme Events, evidence and archives” (1623P), a review of the traces of early Medieval floods occurred in Northern Italy was carried out. The study considered new information and critically re-analyses previous available data, supplied by geomorphological, stratigraphic and geoarchaeological evidence, ancient documents and written sources.
In Northern Italy a fast and strong sedimentary phase occurred between 5th and 9th century AD, leading many large Alpine rivers to avulse. In the system of Tagliamento, thanks to recent geoarchaeological excavations and geochronological analyses, a major extreme event is clearly constrained between the second half of the 6th and the first part of the 7th century, when the river avulsed and destroyed the ancient city of Concordia Sagittaria (Fontana et al., 2019). This episode overlaps with the one reported by the Lombard historian Paolo Diacono, dated to 589 AD, which strongly damaged Verona and, downstream of this city, possibly triggered the avulsion phase of Adige River near the so-called “Rotta della Cucca”. Important fluvial changes affected also the Piave and Livenza rivers, while an avulsion channel of Brenta River started to form in the 6th century AD.
Notwithstanding, for some minor alluvial systems the detailed chronology supported by archaeological and radiocarbon chronology allows to detect the existence of earlier flooding units, formed since the 2nd and 3rd century AD. Recent data in the Alpine valley of Adige River, around the city of Trento, point to the occurrence of some important flood events in the alluvial cones of the major tributary creeks already during the 3rd century AD. However, in the same area the floor of Adige valley experienced a vertical aggradation only since the 4th and 5th century AD, with an enhanced rate of deposition between 6th and 10th century AD. A rather comparable chronology characterizes part of the alluvial cones of the main Apennine streams flowing towards the Po Plain (e.g. near Modena), which aggraded during early Medieval, but this trend started already in the 3rd century AD (Cremonini et al., 2013).
This research supports new data for comparing the palaeoflood record of early Middle Ages with palaeoclimatic proxies, with the aim of distinguishing global forcing factors from regional constrains and anthropogenic disturbance.
Büntgen et al. (2016) – Cooling and societal change during the Late Antique Little Ice Age from 536 to around 660 AD. Nature Geoscience 9, 231–237.
Helama S., Jones P., Briffa K. (2017) - Dark Ages Cold Period: a literature review and directions for future research. Holocene 27, 1600–1606.
Cremonini S., Labate D., Curina R. (2013) - The late-antiquity environmental crisis in Emilia region (Po river plain, Northern Italy): Geoarchaeological evidence and paleoclimatic considerations. Quaternary International, 316, 162.178.
Fontana A., Frassine M., Ronchi L. (2019) - Geomorphological and Geoarchaeological Evidence of the Medieval Deluge in the Tagliamento River (NE Italy). In: Herget J., Fontana A. (Eds), Palaeohydrology, Traces, Tracks and Trails of Extreme Events. Springer, 97-116
Bicuspid aortic valve: a literature review and its impact on sport activity.
No full textThe bicuspid aortic valve (BAV) is the most common congenital cardiac malformation. A literature search was performed using the key words 'bicuspid aortic valve', 'pathophysiology', 'exercise' and 'training'. BAV is the result of a complex developmental process where several genes seem to lead to abnormal valvulogenesis. Complications associated with BAV include aortic stenosis (AS) and regurgitation, infective endocarditis and aortic dilation and dissection. Moreover, BAV may be associated with other cardiovascular anomalies, mainly aortic coarctation. There is greater awareness of BAV in the young population who practice sport, with an increasing interest on the impact of regular and competitive exercise on athletes with BAV. The early identification of BAV through pre-participation screening is of paramount importance, and the justification of the more appropriate diagnostic methods is still an area of debate. A normally functioning BAV usually does not represent a limit for practising sport. The stress of regular and intense exercise on an abnormal aortic valve may favour its early deterioration and accelerate the development of complications. Therefore, athletes with BAV warrant regular follow-up, which should include echocardiographic assessment at least every year. The eligibility for participation and ability to continue to practise competitive sports in athletes with BAV cannot be generalized, but needs to be individualized depending on age, severity of lesions and type of sport. Further studies are required to elucidate the impact of physical training and competitive sports on the natural course of the BAV
The late Pleistocene.Holocene evolution of the Cellina and Neduna alluvial fans (Friuli, NW Italy)
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