136 research outputs found
Volcaniclastic debris flow occurrences in the Campania region (southern Italy) and their relation to Holocene - late Pleistocene pyroclastic fall deposits: implications for large scale hazard mapping
The Campania Region (Southern Italy) is characterized by the frequent occurrence of volcaniclastic
debris flows that produce damage to property and loss of life (more than 170 deaths between 1996
and 1999). Historical investigation allowed the identification of more than 500 events during the
last four centuries; in particular, more than half of these occurred in the last 100 years, causing
hundreds of deaths. The aim of this paper is to identify debris flow proneness and to quantify
hazard. To this end, we compared several elements such as the thickness distribution of pyroclastic
fall deposits from the last 18 ka of the Vesuvius and Phlegrean Fields volcanoes, the slopes of
relieves, and the historical record of volcaniclastic debris flows from AD 1500 to the present.
Results show that flow occurrence is not only a function of the cumulative thickness of past
pyroclastic fall deposits but also depends on the age of emplacement. Deposits younger than 10 ka
(Holocene eruptions) apparently increase the risk of debris flows, while those older than 10 ka (Late
Pleistocene eruptions) seem to play a less prominent role. This is probably in relation to different climatic conditions, and therefore different rates of erosion of pyroclastic falls between the
Holocene and the Late Pleistocene. Based on the above considerations, we compiled a large-scale
debris flow hazard map of the study area in which five main hazard zones are identified: very low,
low, moderate, high and very high
Observation of a One-Dimensional Spin-Orbit Gap in a Quantum Wire
Understanding the flow of spins in magnetic layered structures has enabled an
increase in data storage density in hard drives over the past decade of more
than two orders of magnitude1. Following this remarkable success, the field of
'spintronics' or spin-based electronics is moving beyond effects based on local
spin polarisation and is turning its attention to spin-orbit interaction (SOI)
effects, which hold promise for the production, detection and manipulation of
spin currents, allowing coherent transmission of information within a device.
While SOI-induced spin transport effects have been observed in two- and
three-dimensional samples, these have been subtle and elusive, often detected
only indirectly in electrical transport or else with more sophisticated
techniques. Here we present the first observation of a predicted 'spin-orbit
gap' in a one-dimensional sample, where counter-propagating spins, constituting
a spin current, are accompanied by a clear signal in the easily-measured linear
conductance of the system.Comment: 10 pages, 5 figures, supplementary informatio
GIS-assisted modelling for debris flow hazard assessment based on the events of May 1998 in the area of Sarno, Southern Italy. II: Velocity and Dynamic Pressure
The velocity and dynamic pressure of debris flows are critical determinants of the impact of these natural phenomena on infrastructure. Therefore, the prediction of these parameters is critical for hazard assessment and vulnerability analysis. We present here an approach to predict the velocity of debris flows on the basis of the energy line concept. First, we obtained empirically and field-based estimates of debris flow peak discharge, mean velocity at peak discharge and velocity, at channel bends and within the fans of ten of the debris flow events that occurred in May 1998 in the area of Sarno, Southern Italy. We used this data to calibrate regression models that enable the prediction of velocity as a function of the vertical distance between the energy line and the surface. Despite the complexity in morphology and behaviour of these flows, the statistical fits were good and the debris flow velocities can be predicted with an associated uncertainty of less than 30% and less than 3 m s-1. We wrote code in Visual Basic for Applications (VBA) that runs within ArcGIS® to implement the results of these calibrations and enable the automatic production of velocity and dynamic pressure maps. The collected data and resulting empirical models constitute a realistic basis for more complex numerical modelling. In addition, the GIS implementation constitutes a useful decision-support tool for real-time hazard mitigation. Copyright © 2008 John Wiley & Sons, Ltd
GIS-assisted modelling for debris flow hazard assessment based on the events of May 1998 in the area of Sarno, Southern Italy. Part I: Maximum run-out
Based on the debris flow events that occurred in May 1998 in the area of Sarno, Southern Italy, this
paper presents an approach to simulate debris flow maximum run-out. On the basis of the flow source
areas and an average thickness of 1.2 m of the scarps, we estimated debris flow volumes of the order
of 104 and 105 m3. Flow mobility ratios ( H/L) derived from the x,y,z coordinates of the lower-most
limit of the source areas (i.e. apex of the alluvial fan) and the distal limit of the flows ranged between
0.27 and 0.09. We performed regression analyses that showed a good correlation between the estimated
flow volumes and mobility ratios. This paper presents a methodology for predicting maximum
run-out of future debris flow events, based on the developed empirical relationship. We implemented
the equation that resulted from the calibration as a set of GIS-macros written in Visual Basic for Applications
(VBA) and running within ArcGIS. We carried out sensitivity analyses and observed that
hazard mapping with this methodology should attempt to delineate hazard zones with a minimum
horizontal resolution of 0.4 km. The developed procedure enables the rapid delineation of debris flow
maximum extent within reasonable levels of uncertainty, it incorporates sensitivities and it facilitates
hazard assessments via graphic-user interfaces and with modest computing resources
GIS-assisted modelling for debris flow hazard assessment based on the events of May 1998 in the area of Sarno, Southern Italy. Part II: Velocity and Dynamic Pressure
The velocity and dynamic pressure of debris flows are critical determinants of the impact of these natural phenomena on infrastructure. Therefore, the prediction of these parameters is critical for haz¬ard assessment and vulnerability analysis. We present here an approach to predict the velocity of de¬bris flows on the basis of the energy line concept. First, we obtained empirically- and field-based esti¬mates of debris flow peak discharge, mean velocity at peak discharge and velocity at channel bends and within the fans of ten of the debris flow events that occurred in May 1998 in the area of Sarno, Southern Italy. We used this data to calibrate regression models that enable the prediction of velocity as a function of the vertical distance between the energy line and the surface. Despite the complexity in morphology and behaviour of these flows, the statistical fits were good and the debris flow veloci¬ties can be predicted with an associated uncertainty of < 30% and < 3 m s-1. We wrote code in Visual Basic for Applications (VBA) that runs within ArcGIS ® to implement the results of these calibrations and enable the automatic production of velocity and dynamic pressure maps. The collected data and resulting empirical models constitute a realistic basis for more complex numerical modelling. In addi¬tion, the GIS-implementation constitutes a useful decision-support tool for real-time hazard mitigatio
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Age–depth model of the past 630 kyr for Lake Ohrid (FYROM/Albania) based on cyclostratigraphic analysis of downhole gamma ray data
Gamma ray (GR) fluctuations and potassium (K) values from downhole logging data obtained in the sediments of Lake Ohrid from 0 to 240 m below lake floor (b.l.f). correlate with fluctuations in δ18O values from the global benthic isotope stack LR04 (Lisiecki and Raymo, 2005). GR and K values are considered a reliable proxy to depict glacial-interglacial cycles, with high clastic input during cold and/or drier periods and high carbonate precipitation during warm and/or humid periods at Lake Ohrid. Spectral analysis was applied to investigate the climate signal and evolution over the length of the borehole. Linking downhole logging data with orbital cycles was used to estimate sedimentation rates and the effect of compaction was compensated for. Sedimentation rates increase on average by 14 % after decompaction of the sediment layers and the mean sedimentation rates shift from 45 cm kyr-1 between 0 and 110 m to 30 cm kyr-1 from 110 to 240 m b.l.f. Tuning of minima and maxima of gamma ray and potassium values versus LR04 extrema, in combination with eight independent tephrostratigraphical tie points, allows establishing of a robust age model for the downhole logging data over the past 630 kyr. © Author(s) 2015
Volcanic jets, plumes, and collapsing fountains: evidence from large-scale experiments, with particular emphasis on the entrainment rate
The source conditions of volcanic plumes and collapsing fountains are investigated by means of large-scale experiments. In the experiments, gas-particle jets issuing from a cylindrical conduit are forced into the atmosphere at different mass flow rates. Dense jets (high particle volumetric concentration, e.g., C 0 > 0.01) generate collapsing fountains, whose height scales with the squared exit velocity. This is consistent with Bernoulli's equation, which is a good approximation if air entrainment is negligible. In this case, kinetic energy is transformed into potential energy without any significant loss by friction with the atmosphere. The dense collapsing fountain, on hitting the ground, generates an intense shear flow similar to a pyroclastic density current. Dilute hot jets (low particle volumetric concentration, e.g., C 0 3). © 2014 Springer-Verlag Berlin Heidelberg
Sedimentological processes and environmental variability at Lake Ohrid (Macedonia, Albania) between 640 ka and present day
Lake Ohrid (FYROM, Albania) is thought to be more than 1.2 million years old and hosts more than 200 endemic species. As a target of the International Continental Scientific Drilling Program (ICDP), a successful deep drilling campaign was carried out within the scope of the Scientific Collaboration on Past Speciation Conditions in Lake Ohrid (SCOPSCO) project in 2013. Here, we present lithological, sedimentological, and (bio-)geochemical data from the upper 247.8 m of the overall 569 m long DEEP site sediment succession from the central part of the lake. According to an age model, which is based on nine tephra layers (1st order tie points), and on tuning of biogeochemical proxy data to orbital parameters (2nd order tie points) and to the global benthic isotope stack LR04 (3rd order tie points), respectively, the analyzed sediment sequence covers the last 640 ka
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The SCOPSCO drilling project recovers more than 1.2 million years of history from Lake Ohrid
The Scientific Collaboration on Past Speciation Conditions in Lake Ohrid (SCOPSCO) project is an international research initiative to study the influence of major geological and environmental events on the biological evolution of lake taxa. SCOPSCO drilling campaigns were carried out in 2011 and 2013. In 2011 we used gravity and piston coring at one of the five proposed drill sites, and in 2013 we undertook deep drilling with the Deep Lake Drilling System (DLDS) of Drilling, Observation and Sampling of the Earth's Continental Crust (DOSECC). In April and May 2013, a total of 2100 m sediments were recovered from four drill sites with water depths ranging from 125 to 260 m. The maximum drill depth was 569 m below the lake floor in the centre of the lake. By retrieving overlapping sediment sequences, 95% of the sediment succession was recovered. Initial data from borehole logging, core logging and geochemical measurements indicate that the sediment succession covers >1.2 million years (Ma) in a quasi-continuous sequence. These early findings suggest that the record from Lake Ohrid will substantially improve the knowledge of long-term environmental change and short-term geological events in the northeastern Mediterranean region, which forms the basis for improving understanding of the influence of major geological and environmental events on the biological evolution of endemic species
Observation of a One-Dimensional Spin-Orbit Gap in a Quantum Wire
Understanding the flow of spins in magnetic layered structures has enabled an
increase in data storage density in hard drives over the past decade of more
than two orders of magnitude1. Following this remarkable success, the field of
'spintronics' or spin-based electronics is moving beyond effects based on local
spin polarisation and is turning its attention to spin-orbit interaction (SOI)
effects, which hold promise for the production, detection and manipulation of
spin currents, allowing coherent transmission of information within a device.
While SOI-induced spin transport effects have been observed in two- and
three-dimensional samples, these have been subtle and elusive, often detected
only indirectly in electrical transport or else with more sophisticated
techniques. Here we present the first observation of a predicted 'spin-orbit
gap' in a one-dimensional sample, where counter-propagating spins, constituting
a spin current, are accompanied by a clear signal in the easily-measured linear
conductance of the system.Comment: 10 pages, 5 figures, supplementary informatio
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