Constructing the Tropics: Introduction   总被引：4，自引：2，他引：2  

Felix Driver  & Brenda S.A. Yeoh 《Singapore journal of tropical geography》2000,21(1):1-5

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Transient electromagnetic field in magneto-viscous medium     

Felix M. Kamenetsky  George M. Trigubovich 《Journal of Applied Geophysics》2011,75(2):373-378

When using Transient Geo-Electromagnetics (TEM) unusually slow decaying transients are sometimes observed in the absence of well-conductive objects. Many researchers explain this phenomenon by presence of material with magneto-viscous or superparamagnetic (SPM) properties. The analysis of electromagnetic (EM) field equations in conductive SPM medium is suggested in the present paper. It is shown that in a simplest case of small size single-domain magnetic particles with relative higher potential barrier energy, the SPM-medium is characterized by a very slow decaying exponential transient magnetic field, the level of which is much more as compared to that of due to non-magnetic medium of the same conductivity. This situation is traced up to the late transient time like 0.1 s and more. SPM and Induction fields are in the near zone additive. They depend in a different way on the superparamagnetic and electric properties of the SPM-medium. They also depend in different ways on the transient time and on the size of the transmitter–receiver configuration. These characteristics make it possible to recognize the presence of SPM-effect and to separate these fields.  相似文献   

Quantifying two-way influences between the Arctic and mid-latitudes through regionally increased CO2 concentrations in coupled climate simulations     

Semmler  Tido  Pithan  Felix  Jung  Thomas 《Climate Dynamics》2020,54(7):3307-3321

Climate Dynamics - In which direction is the influence larger: from the Arctic to the mid-latitudes or vice versa? To answer this question, CO2 concentrations have been regionally increased in...  相似文献   

Water for Life - By James L Westcoat, Jr and Gilbert F White     

Felix  P Amerasinghe 《The Geographical journal》2006,172(1):82-82

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A simple DEM assessment procedure for gully system analysis in the Lake Manyara area,northern Tanzania     

Maerker  Michael  Qu&#;n&#;herv&#;  Geraldine  Bachofer  Felix  Mori  Simone 《Natural Hazards》2015,76(1):235-257

Gully erosion is a major threat concerning landscape degradation in large areas along the northern Tanzanian Rift valley. It is the dominant erosion process producing large parts of the sediments that are effectively conducted into the river network. The study area is located in the Lake Manyara—Makuyuni River catchment, Arusha, northern Tanzania. During fieldwork, we measured topographic data of eight gully systems close to Makuyuni Town. The main focus of this study is to assess gully erosion dynamics using improved DEMs with original resolutions of 30 and 20 m, respectively. We assessed terrain characteristics to extract information on environmental drivers. To improve the DEM, we integrated information deduced from satellite images as well as from acquired GPS field data. Topographic indices such as Stream Power Index or Transport Capacity Index were derived from the re-interpolated DEM. To evaluate gully evolution, we assessed also the longitudinal slope profiles. Finally, the gully evolution phases of each gully were classified according to the concept proposed by Kosov et al. (Eksperimental’naya geomorfologiya, vol 3. Moscow University, Moskva, pp 113–140, 1978). The re-interpolated DEMs revealed a positive response especially for the more developed gullies. We show that the extraction of information on this spatial process scale based on “low-resolution” data is feasible with little additional fieldwork and image interpretation. In fact, areas identified as having a greater risk of gully erosion have been confirmed by observations and surveys carried out in the field.  相似文献   

Morphology and evolution of supraglacial hummocks on debris-covered Himalayan glaciers     

Oliver T. Bartlett  Felix S.L. Ng  Ann V. Rowan 《地球表面变化过程与地形》2021,46(3):525-539

Thick supraglacial debris layers often have an undulating, hummocky topography that influences the lateral transport of debris and meltwater and provides basins for supraglacial ponds. The role of ablation and other processes associated with supraglacial debris in giving rise to this hummocky topography is poorly understood. Characterizing hummocky topography is a first step towards understanding the feedbacks driving the evolution of debris-covered glacier surfaces and their potential impacts on mass balance, hydrology and glacier dynamics. Here we undertake a geomorphological assessment of the hummocky topography on five debris-covered glaciers in the Everest region of the central Himalaya. We characterize supraglacial hummocks through statistical analyses of their vertical relief and horizontal geometry. Our results establish supraglacial hummocks as a distinct landform. We find that a typical hummock has an elongation ratio of 1.1:1 in the direction of ice flow, length of 214 ± 109 m and width of 192 ± 88 m. Hummocky topography has a greater amplitude across-glacier (15.4 ± 10.9 m) compared to along the glacier flow line (12.6 ± 8.3 m). Consequently, hummock slopes are steeper in the across-glacier direction (8.7 ± 4.3°) than in the direction of ice flow (5.6 ± 4.0°). Longer, wider and higher-amplitude hummocks are found on larger glaciers. We postulate that directional anisotropy in the hummock topography arises because, while the pattern of differential ablation driving topography evolution is moderated by processes including the gravitational redistribution of debris across the glacier surface, it also inherits an orientation preference from the distribution of englacial debris in the underlying ice. Our morphometric data inform future efforts to model these interactions, which should account for additional factors such as the genesis of supraglacial ponds and ice cliffs and their impact on differential ablation.  相似文献   

Geochemical evidence for melting of carbonated peridotite on Santa Maria Island, Azores     

Christoph Beier  João Mata  Ferdinand Stöckhert  Nadine Mattielli  Philipp A. Brandl  Pedro Madureira  Felix S. Genske  Sofia Martins  José Madeira  Karsten M. Haase 《Contributions to Mineralogy and Petrology》2013,165(5):823-841

The islands of the Azores archipelago emerge from an oceanic plateau built on lithosphere increasing in age with distance from the Mid-Atlantic Ridge from 10 to 45 Ma. Here, we present the first comprehensive major and trace element and Sr–Nd–Pb isotope data from Santa Maria, the easternmost island of the archipelago, along with published data from the other Azores islands situated much closer to the Mid-Atlantic Ridge axis. We can show that the distinctively more variable and more enriched trace element ratios at Santa Maria combined with a relatively small range in Sr–Nd–Pb isotope ratios are the result of low degrees of partial melting of a common Azores mantle plume source underneath thicker lithosphere. This implies that melt extraction processes and melting dynamics may be able to better preserve the trace element mantle source variability underneath thicker lithosphere. These conclusions may apply widely for oceanic melts erupted on relatively thick lithosphere. In addition, lower Ti/Sm and K/La ratios and SiO₂ contents of Santa Maria lavas imply melting of a carbonated peridotite source. Mixing of variable portions of deep small-degree carbonated peridotite melts and shallow volatile-free garnet peridotite could explain the geochemical variability underneath Santa Maria in agreement with the volatile-rich nature of the Azores mantle source. However, Santa Maria is the Azores island where the CO₂-rich nature of the mantle source is more evident, reflecting a combination of a smaller extent of partial melting and the positioning at the edge of the tilted Azores mantle plume.  相似文献   

Recent effects of tidal and hydro‐meteorological changes on coastal plains near the mouth of the Amazon River     

José Tasso Felix Guimarães  Marcelo Cancela Lisboa Cohen  Marlon Carlos França  Luiz Carlos Ruiz Pessenda  Eduardo de Jesus Souza  Afonso César Rodrigues Nogueira  Ronnie Alves 《地球表面变化过程与地形》2013,38(13):1535-1549

The goal of this work was to understand the main hydrodynamic processes acting on tidal flats of the coast of Amapá near the mouth of the Amazon River, and how they change over the short term (~ 20 years). The analysis of morphological and geobotanical units was carried out by applying processing and interpretation methods to optical and synthetic aperture radar (SAR) images, combined with data on water salinity, maximum flood height, sedimentary facies data, rainfall and river discharge. The temporal analysis of morphological and geobotanical units suggests the relative stabilization of savannah, ‘várzea’ and mangrove areas during the drier period and increasing tidal amplitude between 1987 to 1997. The wetter period and decreasing tidal amplitude between 1997 to 2008 led to an increase in the area of ‘várzea’ and lakes over savannah, and the expansion of mangroves mainly over the inundated field and tidal mud/mixed flats. Therefore, the decrease in rainfall index during the drier period is well‐correlated with the reduction of the Calçoene River discharge and jointly with increasing tidal amplitude favored the increase of migration rate of the mud bank and erosion profile along the littoral. It was followed by the increase of the Calçoene River discharge and jointly with decreasing tidal amplitude during the wetter period, favoring the development of mangroves on muddy substrates near the coastline. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

The Purpose and Age of Underwater Walls in the Bay of Elaia of Western Turkey: A Multidisciplinary Approach     

Martin Seeliger  Dominik Brill  Stefan Feuser  Melanie Bartz  Ercan Erkul  Daniel Kelterbaum  Andreas Vtt  Christina Klein  Felix Pirson  Helmut Brückner 《Geoarchaeology》2014,29(2):138-155

Pergamum (modern: Bergama) was operating an important harbour used by military forces and merchants at the city of Elaia during Hellenistic and Roman Imperial times. Harbour‐related facilities such as warehouses, breakwaters and wharfs document the importance of this harbour site not only for the Pergamenians. This paper focuses on the purpose and age of six submerged wall structures situated approximately 1 km south of the ancient closed harbour basin of Elaia. Geoelectric cross‐sections and semi‐aquatic coring near these walls failed to detect any solid basement under the walls which excludes their possible use as breakwaters or wharfs. Instead, the walls were most likely delineating and separating evaporation ponds of salt works, which compares well with similar structures from other periods and places around the Mediterranean. Combined OSL and ¹⁴C‐dating determined the construction age of the installation between the 4th and 6th centuries A.D. Subsequent (re‐)uses are likely and are in agreement with findings from archaeological surveys.  相似文献   

Towards a science of past disasters     

Felix Riede 《Natural Hazards》2014,71(1):335-362

It is widely recognised that natural disasters emerge in the interplay between extreme geophysical events and the human communities affected by them. Whilst detailed natural scientific knowledge of a given event is critical in understanding its impacts, an equally thorough understanding of the affected communities, their economies, ecologies, religious structures, and how all of these have developed over time is arguably as important. Many extreme events leave methodologically convenient traces in the geological and archaeological records in the form of discrete stratigraphic layers often associated with both accurate and precise dates. This paper focuses on volcanic eruptions and draws on matched case studies to illustrate the usefulness of a two-step, quasi case–control comparative method for examining vulnerability and impacts in the near- and far-fields of these eruptions. Although issues of data resolution often plague the study of past disasters, these limitations are counterbalanced by the access to unique long-term information on societies and their material expressions of livelihood, as well as a similarly long-term perspective on the critical magnitude/frequency relationship of the geophysical trigger(s) in question. By drawing together aspects of contemporary Disaster Risk Reduction research, archaeology, and volcanology, this paper sketches out a methodological roadmap for a science of past disasters that aims to be relevant for not only understanding vulnerabilities and impacts in the deep past, but for also better understanding vulnerability in the present.  相似文献