Consideration of human influences is crucial to understanding the coastal sediment supply and associated shoreline responses prior to undertaking coastal hazard management studies. Observation of the widening of some selected Indian beaches, especially over the last 6 decades, is of significance. From this perspective, Miramar Beach, Goa, India, was studied using three ground-penetrating radar shallow subsurface profiles (4 m depth). Based on a series of depositional siliciclastic packages, six progradational packages were recognised, which were interrupted by sharp erosional boundaries. These erosional boundaries represent transgressive phases of the shoreline migration. It was observed that the shoreline migration is coupled with the deposition and erosion of sediments, and this is supported by the historical admiralty charts. The optically simulated luminescence dating of the sediments collected at the first progradation period reveals that the age corresponds to the years 1952–1957, which also corroborates the information provided by the local populace. In the past 6 decades, the shoreline growth has been rapid because of the heavy sediment influx from the Mandovi River caused by increased mining activities (since the 1950s) in upstream areas. Since the 1950s, the shoreline has prograded rapidly, building a beach from ~40 to ~280 m wide (average rate of 4 m/year) in response to enhanced sediment supply from the Mandovi River created by mining activities upstream. Superimposed on this overall regressive trend is a series of deposition and erosion cycles. Perhaps, if a similar trend continues, then there will possibly be a further widening of the beach in the future. A close monitoring network is needed to understand the causes of the cycles in shoreline position and to predict their future behaviour. The present investigation on the nature of the coastal response to anthropogenic activities in a river basin as well as the role of short-time cycles on shoreline behaviour in the last 6 decades could be an ideal reference study and motivate the search for similar areas along other coastal locations. 相似文献
Apatite fission track (AFT) and (U–Th)/He data from the High Atlas have been obtained for the first time to constrain the tectono‐thermal evolution of the central part of the chain. Results from Palaeozoic basement massifs indicate long residence at low temperatures, consistently with their original location out of the deepest Mesozoic rift troughs and indicating minor exhumation. The best rocks for extracting the Alpine history of the Atlas Mountains are Jurassic intrusives, which yield AFT ages centred on c. 80 Ma; thermal models based on AFT data and constrained by (U–Th)/He suggest that these ages are included in a slow cooling trend from intrusion age to c. 50 Ma ago that we attribute to post‐rift thermal relaxation. This is followed by a stability period of c. 30 Ma and then by a final exhumational cooling until present exposure. Eocene intrusives yield AFT ages similar to those of Rb–Sr and K–Ar suggesting rapid emplacement in the uppermost crust. 相似文献
High spatial resolution spectroscopy at 8–13 μm with T-ReCS on Gemini-S has revealed striking variations in the mid-infrared emission and absorption in the nucleus of the Circinus galaxy (hereafter Circinus) on subarcsecond scales. The core of Circinus is compact and obscured by a substantial column of cool silicate dust. Weak extended emission to the east and west coincides with the coronal line region and arises from featureless dust grains which are probably heated by line emission in the coronal emission zone. The extended emission on the east side of the nucleus displays a much deeper silicate absorption than that on the west, indicating significant columns of cool material along the line of sight and corresponding to an additional extinction of AV ∼ 25 mag . Emission bands from aromatic hydrocarbons are not subject to this additional extinction, are relatively weak in the core and in the coronal line region, and are much more spatially extended than the continuum dust emission; they presumably arise in the circumnuclear star-forming regions. These data are interpreted in terms of an inclined disc-like structure around the nucleus extending over tens of parsecs and possibly related to the inner disc found from observations of water masers by Greenhill et al.. 相似文献
In this paper, a novelty-free software to assess an efficient CIPW Norm (± 0.006 wt.% in differences between input and output data) is presented. The package is available in the official repository for user-contributed R packages (CRAN: Comprehensive R Archive Network). The software is able to handle big data sets and considers minor and trace element compositions. The algorithm can calculate odd minerals in igneous rocks, such as cancrinite and calcite, adjust the Fe+3/Fe+2 ratio in different standard approaches, and recalculate the compositions of the rocks in an anhydrous basis (100 ± 0.003 wt.% volatile-free adjusted). Furthermore, the package calculates several petrological parameters, and the graphical outputs are displayed following IUGS scheme standards. The prime aspect of shinyNORRRM is the symbiosis of native R functions with the R package’s shiny (Web Application Framework for R) to run the norm in a user-friendly interface. shinyNORRRM can be executed in any operating system and requires no previous programming knowledge, thus promising to be the universal computational program in this matter. The output data are printed in the standard comma-separated values (*.csv) format, which is highly compatible with general spreadsheet editors. In this work, the algorithm of our program is validated using already compiled whole-rock geochemical databases.
Natural Hazards - The Hindu Kush Himalayan region is extremely susceptible to periodic monsoon floods. Early warning systems with the ability to predict floods in advance can benefit tens of... 相似文献
Natural Hazards - We expand on existing probabilistic tsunami hazard analysis (PTHA) approaches by presenting a methodology wherein the epistemic uncertainties associated with tsunami timing,... 相似文献
Climate Dynamics - We investigate the global distribution of hourly precipitation and its connections with the El Niño–Southern Oscillation (ENSO) using both satellite precipitation... 相似文献