Sull'utilizzabilità a scopo geofisico delle relazioni fra anomalie Eötvössiane e magnetiche

Riassunto Viene mostrato come sia possibile dare pratiche applicazioni alle formule diEötvös sulle relazioni fra anomalie gravimetriche e magnetiche, in modo da ricavare le proprietà magnetiche delle rocce che causano l'anomalia. Da ciò l'opportunità di eseguire sempre unitamente a misurazioni con la bilancia di torsione anche misure magnetiche.

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Summary It is shown how is possible to give pratical applications toEötvös' formulas on relations between gravitational and magnetic anomalies, in such a way as to obtain informations on magnetic properties of rocks that cause the anomaly. It follows the opportunity of executing together with torsion balance measures, in as much as possible, also magnetic measurements.

     

Sulla costante fondamentale della formula ellissoidica internazionale per la gravita' normale

Riassunto Sulla base soprattutto delle numerose misure di gravità successive al 1930, dei nuovi valori compensati per le stazioni di riferimento e con opportune ipotesi per ridurre al minimo le cause di errore, che vengono esaminate e discusse, si procede al calcolo dig _e nelle due ipotesi diBouguer ed isostatica (h_c=–113,7 km). Il risultato è 978,043 nel sistema di Potsdam.

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Summary Principally, on the base of the numerous measures of gravity established after 1930, and of the new compensated values for the reference stations, and with suitable hypothesis to reduce to a minimum the causes of error, which are examined and discussed, it is calculated the value ofg _e in the two hypothesis ofBouguer and isostatical (h _c =–113,7 km). The result is 978,043 in Potsdam System.

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Zusammenfassung Auf Grund vor allem der zahlreichen nach 1930 ausgeführten Schweremessungen, der neuen kompensierten Werte fur die Hauptstationen, und durch geeignete Hypothesen um die Fehlerursachen, welche geprüft und erötert werden, zu reduzieren, wird esg _e in den beiden Hypothesen vonBouguer und der Isostasie (h _c =–113,7 km) berechnet. Das Resultat ist 978,043 im Potsdamer System.

     

Decoupled kinematics of two neighbouring permafrost creeping landforms in the Eastern Italian Alps

An overall acceleration of rock glacier displacement rates in the Alps has been observed in recent decades, with several cases of destabilization leading to potential geomorphological hazards. This behaviour has been attributed to the rising permafrost temperature, induced by atmospheric warming and regulated by thermo-hydrological processes. Landforms derived from the interaction of glacier remnants and permafrost are widespread in mountain areas, but are less studied and monitored than talus rock glaciers. This work presents a comparative study of a talus rock glacier and a glacial-permafrost composite landform (GPCL) in the Eastern Italian Alps. The two landforms are only 10 km apart, but have rather different elevation ranges and main slope aspects. The kinematics and ground thermal conditions were monitored from 2001 to 2015 along with geomorphological surveys, analyses of historical maps and remote sensing data. The dynamic behaviour of the rock glacier was similar to the majority of monitored rock glaciers in the Alps, with an acceleration after 2008 and a velocity peak in 2015. In contrast, the GPCL had a nearly unchanged displacement rate during the observation period. Statistical analyses of kinematic vs. nivo-meteorological variables revealed a dynamic decoupling of the two landforms after 2008 that corresponds with increased winter snow accumulation. Although the kinematics of both landforms respond to ground surface temperature variations, the collected evidence suggests a different reaction of ground surface temperature to variations in the precipitation regime. This different reaction is likely due to local topo-climatic conditions that affect snow redistribution by wind. The different reactions of the two systems to the same climatic forcing is likely a legacy of their different origins. GPCL dynamics result from interaction of permafrost and residual glacial dynamics that are associated with possible peculiarities in the internal/basal meltwater circulation, whose future response is uncertain and requires improved understanding. © 2019 John Wiley & Sons, Ltd. © 2019 John Wiley & Sons, Ltd.     

Delineation of saltwater intrusion zones using the time domain electromagnetic method: the Nabeul–Hammamet coastal aquifer case study (NE Tunisia)

The time domain electromagnetic method (TDEM) is applied to monitor, to delineate and to map the saltwater intrusion zones in the Mediterranean Plio‐Quaternary aquifer. Forty‐two TDEM soundings were carried out in the coastal plain of Nabeul–Hammamet region (NE Tunisia). TDEM resistivity data were correlated with the existing borehole logging data to assign them to a particular lithology and to provide information about the position of the freshwater–seawater transition zone. The geoelectric sections showing the vertical configuration of seawater intrusion, with the brackish‐salty‐saturated zones, have a resistivity ranging from ~0.1 to 5 Ω?m and are detected at a depth lower than 1.5 m. The salinized zones are located at Nabeul (Sidi Moussa, Sidi El Mahrsi, Al Gasba and Mrazgua) and at Hammamet (Touristic zone of Hammamet north and south, Baraket Essahel) and reached a distance of 4 km from the coastline, indicating a severe state for the aquifer in these zones. These TDEM results are confirmed by the increase of chloride concentration content in the analysed water samples of monitoring wells. Moreover, in the northeastern part, the presence of a saltwater front located far from the coast and along the NW–SE major surface fault can be explained by two hypothesis: (i) this fault seems to provide a conduit for seawater to move readily towards the water wells and (ii) the clay and gypsum infiltration of marine Messinian deposits through the fault plane leads to low resistivities. Finally, it comes out from this study that TDEM survey has successfully depicted salinized zones of this coastal aquifer. Copyright © 2012 John Wiley & Sons, Ltd.     

Multiple cosmogenic nuclides document complex Pleistocene exposure history of glacial drifts in Terra Nova Bay (northern Victoria Land, Antarctica)

Geomorphological and glacial geological surveys and multiple cosmogenic nuclide analyses (¹⁰Be, ²⁶Al, and ²¹Ne) allowed us to reconstruct the chronology of variations prior to the last glacial maximum of the East Antarctic Ice Sheet (EAIS) and valley glaciers in the Terra Nova Bay region. Glacially scoured coastal piedmonts with round-topped mountains occur below the highest local erosional trimline. They represent relict landscape features eroded by extensive ice overriding the whole coastal area before at least 6 Ma (pre-dating the build-up of the Mt. Melbourne volcanic field). Since then, summit surfaces were continuously exposed and well preserved under polar condition with negligible erosion rates on the order of 17 cm/Ma. Complex older drifts rest on deglaciated areas above the younger late-Pleistocene glacial drift and below the previously overridden summits. The combination of stable and radionuclide isotopes documents complex exposure histories with substantial periods of burial combined with minimal erosion. The areas below rounded summits were repeatedly exposed and buried by ice from local and outlet glaciers. The exposure ages of the older drift(s) indicate multiple Pleistocene glacial cycles, which did not significantly modify the pre-existing landscape.     

Natural and Anthropic Middle-term Variations in the Delta System at the Mouth of the Goro River (Po Delta, Italy)

Abstract. The modern delta system of the Po River is the result of an evolution strictly controlled by anthropic factors and mainly developed during a period of climatic deterioration (Little Ice Age 1550/1850).
At the beginning of the 17^th century the main branch of the Po River, Fornaci Po, was modified with the "Cut of Viro" in order to avoid landfill of the Venetian Lagoon. Simultaneously, the southernmost branch of Ariano, or Goro, was forced to flow southwards. Subsequent sedimentary variations, caused by changes in the climatic conditions, contributed to make the area supplied by the Goro Po River increasingly lagoonary. In the second half of the 19^th century (end of the Little Ice Age – L.I.A. –), the first coastal spits started to take shape and developed in different systems throughout the entire following century. Coastal spits turned out to produce in the original bay, a progressive closure towards the sea. The strong decrease in solid loads, characterising the second half of the 20^th century and mainly due to anthropic factors, marks the beginning of a new phase extending to the overall Po Delta system, in which the mouth layout is controlled by wave energy.     

Can Rock Composition Affect Sublittoral Epibenthic Communities?

Abstract. Biomineralogy, as the complex of interactions at different levels (cell, organism, species, and community) between organisms and minerals, may play a significant role in the spatial distribution and structure of marine communities. For instance, a negative influence of quartz has been underlined on the Mediterranean benthic communities, which show a species-poorer structure in quartz-rich environments. Excluding the role of quartz, the aim of this work is to verify whether the composition of various mineralogical substrata can affect a hard-bottom benthic community. In the Ligurian Sea, the Levanto area shows an astonishing complex of substrata with different petrographic characters: in a few kilometres, sandstones, serpentinites, gabbros, and basalts occur in geometric association. Consequently, this area represents a suitable frame for this type of study. Herein, algal photophilic assemblages growing on the four mineralogical substrata show significant differences in number of species and percentage cover or abundance. This suggests a significant influence of rock mineral composition on the hard bottom community. Therefore, rock composition must be taken into account for a better understanding of the processes at the basis of hard-bottom community development and diversity.     

Temporal variability of sedimentation rates and mobile fauna inside and outside a gorgonian garden

Paramuricea clavata (Cnidaria, Octocorallia) is an important ecosystem engineer of coralligenous assemblages increasingly threatened by anthropogenic activities and climate changes. As climate warming is predicted to continue in the coming years it is important to hypothesize future scenarios. Here we tested the influence of gorgonian colonies on sedimentation rates and vagile fauna trends, comparing sediments collected by traps inside and outside a gorgonian garden, in a coralligenous community of the Western Ligurian Sea, at 32 m depth, over a period of 1 year. The results indicated that sea fans created a sort of homeostatic effect on the surrounding habitat. We found evidence that where gorgonian colonies were present, the monthly fluctuations of sediments rate were lower than outside a garden. Gorgonian colonies also influenced the distribution of the associated vagile fauna; these organisms were generally more abundant inside than outside the garden. The data collected in this work appear to confirm the role of P. clavata as an ecosystem engineer, affecting biomass and variability of the surrounding habitat at both spatial and temporal scales.