Tectonics of the Aegean block: Rotation, side arc collision and crustal extension     

Yair Rotstein 《Tectonophysics》1985,117(1-2)

A new tectonic model for the Aegean block is outlined in an effort to explain the widespread extension observed in this region. A key element in this model is the concept of “side arc collision” This term is used to describe the interaction of subducted oceanic lithosphere with continental lithosphere in a subduction arc in which oblique subduction occurs. In the Hellenic arc side arc collision is proposed for the northeast corner near Rhodes. The collision involves subducted African lithosphere, moving to the northeast almost parallel to the arc, with the continental mass of southwest Turkey. It affects the motion of the Anatolian-Aegean plate complex, but is not similar to continental collision since it occurs mostly at depth and involves only little, if any, of the shallow and rigid part of the continental lithosphere. The model assumes that Anatolia and the Aegean are part of one plate complex which undergoes counterclockwise rotation; if it were not for the side arc collision near Rhodes, the two blocks would exhibit similar deformation and might, in effect, be indistinguishable. At present, however, free and undisturbed rotation is possible only for the Anatolian block (excluding western Anatolia) where the motion is accommodated by subduction along the Cyprean arc. Further west the side arc collision inhibits this rotation along the subduction front. Still further west, undisturbed subduction along the central and western parts of the Hellenic arc is again possible and is well documented. On the other side of the Anatolian-Aegean plate complex, relatively free motion occurs along the North Anatolian fault zone including in the Aegean Sea. The combination of this motion in the north with the local obstruction of the rotation near Rhodes, must create a torque and a new pattern of rotation for the western part of the plate complex, thus creating a separate Aegean block. Since, however, the two blocks are not separated by a plate boundary, the Aegean block cannot move freely according to the new torque. Effective motion of the Aegean block relative to Europe and Anatolia, particularly in the north, is achieved through extension of the crust (lithosphere?). Thus the greatest amount of deformation (extension) is observed along the suture zone between the two blocks and, in particular, in the northeastern part of the Aegean block where motion relative to Anatolia must be greatest.  相似文献   

Linking frequency of rainstorms,runoff generation and sediment transport across hyperarid talus-pediment slopes     

Yuval Shmilovitz  Efrat Morin  Yair Rinat  Itai Haviv  Genadi Carmi  Amit Mushkin  Yehouda Enzel 《地球表面变化过程与地形》2020,45(7):1644-1659

Documenting hillslope response to hydroclimatic forcing is crucial to our understanding of landscape evolution. The evolution of talus-pediment sequences (talus flatirons) in arid areas was often linked to climatic cycles, although the physical processes that may account for such a link remain obscure. Our approach is to integrate field measurements, remote sensing of rainfall and modeling to link between storm frequency, runoff, erosion and sediment transport. We present a quantitative hydrometeorological analysis of rainstorms, their geomorphic impact and their potential role in the evolution of hyperarid talus-pediment slopes in the Negev desert, Israel. Rainstorm properties were defined based on intensity–duration–frequency curves and using a rainfall simulator, artificial rainstorms were executed in the field. Then, the obtained measured experimental results were up-scaled to the entire slope length using a fully distributed hydrological model. In addition, natural storms and their hydro-geomorphic impacts were monitored using X-band radar and time-lapse cameras. These integrated analyses constrain the rainfall threshold for local runoff generation at rain intensity of 14 to 22 mm h^-1 for a duration of five minutes and provide a high-resolution characterization of small-scale runoff-generating rain cells. The current frequency of such runoff-producing rainstorms is ~1–3 per year. However, extending this local value into the full extent of hillslope runoff indicates that it occurs only under rainstorms with ≥ 100-years return interval, or 1% annual exceedance probability. Sheetwash efficiency rises with downslope distance; beyond a threshold distance of ~100 m, runoff during rainstorms with such annual exceedance probability are capable of transporting surface clasts. The erosion efficiency of these discrete rare events highlights their potential importance in shaping the landscape of arid regions. Our results support the hypothesis that a shift in the properties and frequency of extreme events can trigger significant geomorphic transitions in areas that remained hyperarid during the entire Quaternary. © 2020 John Wiley & Sons, Ltd.  相似文献   

Optical observations of transient luminous events associated with winter thunderstorms near the coast of Israel   总被引：1，自引：0，他引：1  

Yoav Yair  Colin Price  Michal Ganot  Eran Greenberg  Roy Yaniv  Baruch Ziv  Yosef Sherez  Adam Devir  Jo'zsef Br  Gabriella Stori 《Atmospheric Research》2009,91(2-4):529-537

We report the results of two observation campaigns conducted during the Northern Hemisphere winters of 2005–6 and 2006–7 aiming to detect transient luminous events (TLEs) above winter thunderstorms in the vicinity of Israel and the eastern coastline of the Mediterranean Sea. In 10 out of 31 different observation nights we detected 66 events: 56 sprites and 10 Elves. The detection ranges varied from 250 to 450 km. Sprites were found to be produced by active cells with a vertical dimension of 5–9 km and cloud top temperature ~ − 40 °C, embedded in a much larger matrix of stratiform precipitating cloudiness. This configuration closely resembles the conditions for winter sprites in the Hokuriku region of Japan. Synchronized with the optical observations, ELF data were recorded at two observation stations in Israel and Hungary in order to qualify and quantify parameters of the parent lightning discharge associated with the TLEs. These stations are located 500 km and 2100 km respectively from the Eastern Mediterranean Sea, where most TLEs occur. Among the optically observed TLE events, we found that all the ELF signals were produced solely by positive cloud-to-ground flashes (+ CGs), most of which were recorded in Israel (88%) and Hungary (77%). Calculation of the Charge Moment Change showed average values of 1400 ± 600 C km, with some extreme events exceeding 3500 C km. The average time delay between the ELF transient of the parent + CG and the observed sprites was 55 ms, with shorter delays for column sprites (42 ± 34 ms) compared to carrot sprites (68 ± 34). Furthermore, based on the ELF data, there were no early identifiable precursors to TLE occurrence in the regional lightning activity. From the spatial formation of the observed columniform sprites, we propose that columniform sprites are sometimes arranged in a 3-dimensional circular pattern, thus mapping the instantaneous electric field in the mesosphere.  相似文献   

Impact of gully incision on hillslope hydrology     

Xing Chen  Mukesh Kumar  Daniel deB Richter  Yair Mau 《水文研究》2020,34(19):3848-3866

The Southern U.S. Piedmont ranging from Virginia to Georgia underwent severe gully erosion over a century of farming mainly for cotton (1800s–1930s). Although tree succession blanketed much of this region by the middle 20th century, gully erosion still occurs, especially during wet seasons. While many studies on gully erosion have focused on soil loss, soil carbon exchange, and stormwater response, the impacts on soil moisture, groundwater, and transpiration remain under-studied. Using a newly developed 2D hydrologic model, this study analyzes the impacts of gully erosion on hillslope hydrologic states and fluxes. Results indicate that increases in gully incision lead to reduction in groundwater table, root zone soil moisture, and transpiration. These reductions show seasonal variations, but the season when the reduction is maximum differs among the hydrologic variables. Spatially, the impacts are generally the greatest near the toe of the hillslope and reduce further away from it, although the reductions are sometimes non-monotonic. Overall, the impacts are larger for shallow gully depths and diminish as the incision goes deeper. Lastly, the extent of impacts on a heterogeneous hillslope is found to be very different with respect to a homogeneous surrogate made of dominant soil properties. These results show that through gully erosion, the landscape not only loses soil but also a large amount of water from the subsurface. The magnitude of water loss is, however, dependent on hydrogeologic and topographic configuration of the hillslope. The results will facilitate (a) mapping of relative susceptibility of landscapes to gullying, (b) understanding of the impacts of stream manipulations such as due to dredging on hillslope eco-hydrology, (c) prioritization of mitigation measures to prevent gullying, and (d) design of observation campaigns to assess the impacts of gullying on hydrologic response.  相似文献   

The Kerguelen Province revisited: Additional constraints on the early development of the Southeast Indian Ocean     

Rotstein  Yair  Munschy  Marc  Bernard  Armelle 《Marine Geophysical Researches》2001,22(2):81-100

The Kerguelen Province, consisting of two oceanic plateaus (Kerguelen, Broken Ridge) and three basins (Enderby, Labuan and Diamantina), covers a large area of ocean floor in the southeast Indian Ocean. As very few magnetic anomalies have been identified in this area and only a few basement ages from the Kerguelen Plateau are known, reconstruction models of the Kerguelen Province are not well constrained. In an effort to gain more understanding about the evolution of this area, we have used satellite gravity to identify additional fracture zones. As they are likely to be associated with high frequency and low amplitude gravity anomalies, we have computed the vertical derivative map instead of the regular satellite gravity map. Using this approach, we have identified a series of fracture zones in the Enderby Basin, which are aligned with the Mesozoic fracture zones in the Perth Basin and converge to the Kerguelen Fracture Zone. In the conjugate Bay of Bengal, we traced an equivalent pattern of fracture zones which, together, better constrain the early evolution of this part of the Indian Ocean. Synthesis of these images and the other available data from the Kerguelen Province, suggests that the spreading of India from both Australia and Antarctica is closely related. Spreading between the three continents appears to have begun about the same time, in the early Cretaceous and thus, the accretion of some parts of the Kerguelen Province must have occurred before the onset of the quiet magnetic period at 118 Ma. At about 96–99 Ma, when the spreading direction in the Indian Ocean had changed into a N-S direction, it also took place throughout the Kerguelen Province. We find that previously proposed slow spreading in the Diamantina Zone and Labuan Basins, between 96–99 Ma and the initiation of the Southeast Indian Ridge at 43 Ma, could not have taken place. Furthermore, we suggest that there is growing evidence that the same is true for spreading in the eastward continuation of the Diamantina Zone and Labuan Basin, between Australia and Antarctica. Initiation of spreading in this area is likely to be contemporaneous with the spreading in the Kerguelen Province and, thus, older than 96–99 Ma. This revised version was published online in November 2006 with corrections to the Cover Date.  相似文献   

Production and transport of phytoplankton biomass over the continental shelf of the new york bight     

Thomas C. Malone  Thomas S. Hopkins  Paul G. Falkowski  Terry E. Whitledge 《Continental Shelf Research》1983,1(4)

Seasonal and event scale variations in the distribution and growth of phytoplankton in different hydrographic regions of the continental shelf are compared and evaluated in terms of floristic composition and the evolution of density and nutrient structure across the shelf. Annual cycles of phytoplankton biomass inshore of the 1000-m isobath are characterized by a March maximum and a July minimum. Cross-shelf biomass gradients usually increase in an offshore direction, a phenomenon that is most pronounced during March and April when biomass is high, diatoms dominate, and growth rate is light limited. This is a consequence of the combined effects of growth along the stratified side of the shelf-break front and offshore transport of biomass produced nearshore. We estimate that about 90% of the diatom biomass produced during the February to April bloom period (35% of annual production) is exported from shelf to slope water. Similar but less-pronounced gradients develop during summer due to the development of a chlorophyll maximum layer below the pycnocline where growth rate is also light limited. Production and loss are more tightly coupled under these conditions and about 9% of the biomass produced during May to October appears to be exported (5% of annual production). Export during the diatom bloom period is balanced mainly by nitrate inputs from the Gulf of Maine and adjacent slope water while summer export may be balanced by anthropogenic nitrogen input. The latter could be coupled with biomass export by ammonium remineralization and nitrification in the cold pool of the mid-shelf region. In general, export is greatest when diatoms dominate, growth is light limited, and biomass distributions are physically forced. Export is lowest when nanoplankton dominate, growth is nitrogen limited, and biomass distributions are controlled by grazing.The shelf-break front plays a key role, influencing patterns of phytoplankton growth, biomass distributions, and shelf export. During the diatom bloom period, the development of stratification in nutrient-rich offshore water between storm events results in high growth rates and biomass near the surface on the shelf side of the front. Under these conditions, biomass accumulates in the mid-shelf region on a time scale of days to weeks. Export occurs during wind events with net export from the shelf occurring on a time scale of weeks to months. Blooms also develop along the shelf side of the front during summer but below the pycnocline. Most of the summer export of biomass probably takes place here with accumulation and export occurring on a time scale of hours to days. While this export is small compared to export during the diatom bloom period, it may be critical to the prevention of anoxic events such as that of 1976.  相似文献   

Advertent/inadvertent changes in the spatial distribution of rainfall in the central coastal plain of Israel   总被引：1，自引：0，他引：1  

Yair Goldreich 《Climatic change》1987,11(3):361-373

Analysis of recent rainfall normals reveals an unusual spatial pattern where the rainfall increases with the distance from the sea over the central coastal plain of Israel. Applying a multiple regression technique separately to rainfall amounts for the two randomized experiments of cloud seeding of seeded days and not seeded days, leads to the conclusion that the inadvertent influence of recent urbanization processes along the coastal plain are the cause of this phenomenon, rather than the advertent artificial cloud seeding. The seeding effect at the target area, on the other hand, seems to increase the inhomogeneity of the spatial structure of the rainfall distribution.  相似文献   

Spatial distribution of surface properties,runoff generation and landscape development in the Zin Valley Badlands,northern Negev,Israel     

Nikolaus J. Kuhn  Aaron Yair  Milica Kasanin Grubin 《地球表面变化过程与地形》2004,29(11):1417-1430

In?ltration tests, soil mapping and soil property analysis were used to assess the effect of within‐storm rainfall conditions on spatial patterns of surface characteristics relevant for runoff generation, continuity and erosion in the Zin Valley Badlands. Runoff and erosion differ strongly between ridges and slopes. Soils at both locations are susceptible to sealing, but on the sideslopes deep desiccation cracks inhibit continuous ?ow, even during high magnitude rainstorms. The discontinuous nature of runoff has a feedback on surface conditions. Erosion on the ridges maintains shallow soils prone to sealing while in?ltration and deposition on the sideslopes enhance soil depth, a prerequisite for stable desiccation cracks. Some runoff generated on the ridges is transmitted to the valley via rills. On straight sideslopes, rills are single and often discontinuous, indicating limited frequency of continuous runoff. Along concave valley heads, rill systems are well integrated and continuous, concentrating runoff and reducing in?ltration losses along slopes. The longitudinal, V‐shaped valley morphology of small catchments in the Zin Valley Badlands re?ects the long‐term effect of different erosion rates in valley heads and on sideslopes. Over time, valley incision lengthened the sideslopes, reducing the portion of annual rainfall that was runoff‐effective. Once sideslopes reached a critical length that inhibited frequent continuous ?ow, a colluvium with an increased in?ltration capacity developed, reducing runoff frequency even further. Consequently, erosion on the valley sideslopes decreased. Continuous ?ow from ridges to the valley channel remained more common in integrated rill systems in concavities and valley heads, leading to more erosion and retreat of the valley heads. The spatial patterns of runoff and erosion in the Zin Valley Badlands demonstrate that landscape development is strongly affected by processes that lead to differentiation of soil properties on hillslopes with uniform lithology. The patterns of surface characteristics and their role in landscape development are strongly dependent on rainfall conditions, highlighting the need for geomorphologists to identify the dynamic spatial and temporal scales relevant for landscape development. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

Geochemical characteristics from tests of four modern planktonic foraminiferal species in the Indonesian Throughflow region and their implications     

Peng Zhang  Rina Zuraida  Yair Rosenthal  Ann Holbourn  Wolfgang Kuhnt  Jian Xu 《地学前缘(英文版)》2019,10(2):505-516

Test geochemistry of planktonic foraminifera is an indispensable tool in reconstructing past ocean hydrological changes. It is essential to investigate region-specific implications of test geochemistry,although those established from other regions can be broadly applied. In this study, characteristics of6180 and Mg/Ca from tests of four planktonic foraminiferal species, Globigerinoides ruber sensu stricto(s.s.), Globigerinoides sacculifer, Pulleniatina obliquiloculata and Neogloboquadrina dutertrei, from 60 coretop sediment samples retrieved from the Indonesian Throughflow(ITF) region were studied. These geochemical data were compared with modern hydrographic profiles in order to assess their relations and to investigate potential implications of test geochemical parameters in reconstructing past oceanographic change in the ITF region. Calcification depths of these four species were first estimated based on comparison between measured test δ180 and predicted calcite δ¹⁸O that was calculated from modern temperature and salinity. The results indicate that G. ruber s.s. and G. sacculifer calcify within the mixedlayer at 0-50 m and 20-75 m, respectively, whereas P. obliquiloculata and N. dutertrei calcify within the thermocline at around 75 to 125 m. A combined study of excess Mg/Ca(difference between measured and predicted Mg/Ca) and salinity suggests that salinity exerts a negligible impact on test Mg/Ca of these foraminiferal species in the ITF region. Comparison of test Mg/Ca-derived temperatures with temperature profiles of the upper 200 m of the water column from the seas of the ITF region also indicate calcification depths of these species, which match well with the above estimations using test δ¹⁸O. It further indicates that G. sacculifer may be more sensitive in reflecting changes in the depth of the mixedlayer, highlighting a potential use of Mg/Ca temperature difference between G. ruber s.s. and G. sacculifer in reconstructing the depth of the mixed-layer in the ITF region.  相似文献   

Trace metals distribution pattern in floodplain sediments of a lowland river in relation to contemporary valley bottom morphodynamics          下载免费PDF全文

Ewa Falkowska  Tomasz Falkowski 《地球表面变化过程与地形》2015,40(7):876-887

The distribution of trace metals in alluvial sediments depends on their natural background concentrations, and on the dynamics of contemporary depositional and erosional (mainly flood‐induced) processes. Geological and geochemical investigations were carried out in the valley of Vistula River near Magnuszew (central Poland). Sediment samples were collected from a depth of 35 cm and comprise sediments of all defined geomorphological features. Identification and geological interpretation of the morphodynamic sediment features was supported by aerial photographs and high‐resolution satellite images. These studies revealed that the distribution of trace metals is closely linked to the morphogenesis of the alluvial floodplain. The highest concentrations of Cu, Co, Zn, V, Cr and Ni were observed in crevasse‐splays deposits. By contrast, Sr, Pb and As were concentrated in deposits which fill oxbow lakes (partly infilled with organic deposits). The lowest concentrations of trace metals were detected in flood sediments deposited within erosional troughs. The geomorphological and sedimentological history of the fluvial features explains the pattern of heavy metal distribution on the current floodplain surface. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献