Zur Geomorphogenie Anatoliens

Ohne Zusammenfassung     

The wave form of atmospherics

Summary The wave form of atmospherics recorded at a distance of some hundred km from the lightning stroke may be explained if the influence of propagation mechanism, excluding ionospheric reflection, is considered. The wave form results from the damping of higher frequencies, if propagation occurs about ground.

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Zusammenfassung Die Wellenform von atmosphärischen Störungen, die man in einer Entfernung von einigen hundert km vom Blitz registriert, kann erklärt werden, wenn man den Einfluss des Ausbreitungsmechanismus unter Ausschluss der Ionosphäre betrachtet. Die atmosphärische Störung verdankt ihre Form der frequenzabhängigen Ausbreitung entlang der Erdoberfläche, wobei die Dämpfung für hohe Frequenzen grösser ist als für niedere.

     

Solare Einflüsse auf das Verhalten des atmosphärischen Funkstörpegels bei Kurzwellen

Zusammenfassung Der zeitliche Gang der atmosph?tischen St?rungen ist zwei Einflüssen unterworfen: 1) Der zeitlichen und r?umlichen Verteilung der St?rquellen, 2) Den jeweiligen Ausbreitungsbedingungen des zu empfangenden Frequenzbandes. Die bei 5,5 MHz durchgeführten Messungen des atmosph?rischen St?rpegels zeigen den erwarteten Zusammenhang zwischen dem t?glichen Gang und dem Sonnenstand entsprechend den normalen Ausbreitungsbedingungen im 50 m Band. W?hrend M?gel-Dellinger Effekte nicht festgestellt werden konnten, ist die Nordlichtst?rung als Folge einer Korpuskularstrahlung der Sonne klar zu erkennen.

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Summary The temporal variation of atmospherics is subjected to two facts: 1) The temporal and local distribution of sources of atmospherics, 2) The present conditions of propagation with regard to the just received short-wave band. Measurements of atmospherics in 50 m-band proved the connection between atmospherics and solar-radiation corresponding to the normal conditions of short-wave propagation, showing a minimum at day and a maximum at night. Whilst the Dellinger-effect did not happen, atmospherics disappeard on account of aurora borealis and strong disturbance of the earth's magnetic field, in consequence of corpusculare-radiation of the sun. Monthly distribution of atmospherics in 50 m-band for 2 years measurements are given.

     

Subsidence due to crack closure and depressurization of hydrothermal systems: a case study from Mt Epomeo (Ischia Island,Italy)

Levelling surveys carried out between 1990 and 2003 on the Mt Epomeo resurgent block (Ischia Island) record negative dislocations on its northern and southern flanks with a maximum subsidence rate of 1.27 cm yr⁻¹. This deformation is not associated with the cooling, crystallization or lateral drainage of magma and cannot be explained by a pressure point or prolate ellipsoid source. Results from dislocation models and the available structural and geochemical information indicate that the subsidence is due to crack closure processes along two main ENE–WSW and E–W preexisting faults, which represent the preferred pathway of CO₂ degassing from the hydrothermal system located beneath Mt Epomeo. The monitoring of the dislocations and CO₂ flux along these faults could give useful information on the dynamics of the hydrothermal system.     

Monitoring, prediction, and early warning using ground-based radar interferometry

In order to define adequate prevention measures and to manage landslide emergencies, real-time monitoring is required. This paper presents two different applications of the remote sensing technique: the ground-based synthetic aperture radar interferometry, here proposed as a monitoring and early warning support for slope instability. Data acquisitions carried out through a ground-based synthetic aperture radar interferometer, operating in K_u band, installed in front of the observed slopes, are discussed. Two case studies, based on the use of the same apparatus (formerly developed by the Joint Research Center of the European Commission and by Ellegi-LiSALab srl), are reported: the first one concerns the monitoring of a large landslide, named Ruinon (Valfurva, Italy). The second one deals with the monitoring of the NW unstable slope in the Stromboli island aimed to implementing an early warning system. Acquired interferometric data are processed to provide displacements and velocity maps of the monitored area. The monitoring services ongoing on the Ruinon landslide and on Stromboli demonstrate the capability of this technique to operate in different operative settings (i.e., different phenomena and geological framework) and for different aims (monitoring for prevention, early warning, and emergency assessment). This methodology has also been proved by national and regional authorities of civil protection in order to provide a real-time monitoring for emergency management.     

Volcanic geomorphology and tectonics of the Aeolian archipelago (Southern Italy) based on integrated DEM data

The geomorphological and morphometric analysis of the sea floor topography surrounding the Aeolian Islands, South Tyrrhenian Sea, Italy, provides insights into the relationships between the volcanological evolution of the islands and their tectonic features. We constructed geomorphological maps of the submarine portions of the seven large edifices constituting the islands on the basis of a DEM with a 5 m resolution step. These maps include constructional and destructional landforms such as submarine volcanic vents located west of Lipari and north of Alicudi, and hummocky surfaces recognised north of Lipari and Salina. The latter landforms, together with the occurrence of large scars affecting the main edifices on land, suggest that sector collapses affected some islands. Geomorphological data indicate that the location of subaerial and submarine vents is strongly controlled by local tectonic structures striking WNW-ESE (Alicudi-Filicudi sector), NNW-SSE (Salina-Lipari-Vulcano sector) and NE-SW (Panarea-Stromboli sector). The islands can be divided into two groups on the basis of some morphometric parameters: a first group with a pancake-like shape, Dp/D (abrasion platform diameter/basal diameter) higher than 0.40 and H/D (total height/basal diameter) lower than 0.13, and a second group with a conical shape, characterised by Dp/D lower than 0.34 and H/D higher than 0.14. These ratios and other morphometric parameters reflect the different volcanological and structural evolution of the Aeolian Islands. The pancake-like shaped complexes have been created, in addition to their submarine stage, by extrusive and highly explosive activity, whereas the cone-shaped edifices have been characterised by effusive or moderate explosive activity.Editorial responsibility: C Kilburn     

Geochemistry of the Submarine Gaseous Emissions of Panarea (Aeolian Islands, Southern Italy): Magmatic vs. Hydrothermal Origin and Implications for Volcanic Surveillance

The marine sector surrounding Panarea Island (Aeolian Islands, South Italy) is affected by widespread submarine emissions of CO₂ -rich gases and thermal water discharges which have been known since the Roman Age. On November 3^rd, 2002 an anomalous degassing event affected the area, probably in response to a submarine explosion. The concentrations of minor reactive gases (CO, CH₄ and H₂) of samples collected in November and December, 2002 show drastic compositional changes when compared to previous samples collected from the same area in the 1980s. In particular the samples collected after the November 3^rd phenomenon display relative increases in H₂ and CO and a strong decrease in the CH₄ contents, while other gas species show no significant change. The interaction of the original gas with seawater explains the variable contents of CO₂, H₂S, N₂, Ar and He which characterize the different samples, but cannot explain the large variations of CO, CH₄ and H₂ which are instead compatible with changes in the redox, temperature and pressure conditions of the system. Two models, both implying an increasing input of magmatic fluids are compatible with the observed variations of minor reactive species. In the first one, the input of magmatic fluids drives the hydrothermal system towards atypical (more oxidizing) redox conditions, slowly pressurizing the system up to a critical state. In the second one, the hydrothermal system is flashed by the rising high-T volcanic fluid, suddenly released by a magmatic body at depth. The two models have different implications for volcanic surveillance and risk assessment: In the first case, the November 3^rd event may represent both the culmination of a relatively slow process which caused the overpressurization of the hydrothermal system and the beginning of a new phase of quiescence. The possible evolution of the second model is unforeseeable because it is mainly related to the thermal, baric and compositional state of the deep magmatic system that is poorly known.     

A critical appraisal of the Cayconi Formation, Crucero Basin, southeastern Peru

The Cayconi Formation of the Crucero Basin, Puno Department, southeastern Peru, has been described as a 800–1000 m sequence of Oligocene and Miocene fanglomerate and lacustrine sedimentary rocks, interlayered with mafic and silicic volcanic rocks, and unconformably overlying Paleozoic and Cretaceous successions. On the basis of new field and petrological investigations, key aspects of the stratigraphic relationships of the rocks comprising this formation, and hence the viability of this lithostratigraphic name, are questioned. Thus, several sedimentary units previously assigned to the Cayconi Formation are reinterpreted as Cretaceous or older. We further argue that the formational terminology fails to accomodate the great variety of volcanic rocks, which are, moreover, disposed in isolated eruptive fields. We therefore propose establishment of the Crucero Supergroup as a broad, yet flexible framework for lithostratigraphic subdivision of the Tertiary sequences of the Cordillera Oriental of southeastern Peru. This new nomenclature accomodates the voluminous two-mica ash flow tuffs (Macusani Volcanics) and associated rocks of the Quenamari Meseta, a succession excluded from the existing lithostratigraphic classification scheme. It also permits distinction between the petrogenetically-contrasted upper Oligocene — Lower Miocene and Middle Miocene — Upper Miocene volcanic suites, which dominate, respectively, the Picotani and Quenamari Groups comprising the proposed Crucero Supergroup. Finally, the economically important granitic/rhyolitic intrusive centers cogenetic with the volcanic rocks are readily assignable to intrusive lithodemes in each group.