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21.
Climate is one of the most of influential natural factors on society and economy. One of the consequences of climate anomalies is the emergence of diseases and epidemics, especially in agrarian societies. The current concern with long-term climate change and its measurable consequences on health and disease gives new relevance to the question of how agrarian societies fared during sharp droughts and other climatic hardships, especially those subject to the disruptive processes of colonization. Not many studies have been done in Latin America that relate climate, epidemics and mortality from a historical perspective. This paper explores the association between climatic anomalies, epidemic events, and native demographic decline in the Alto Peru region in the highlands of Bolivia, in the late eighteenth and early nineteenth century. Studies of historic climatology indicate that adverse climate events became more frequent in the southern areas of South America during these centuries. There were extreme oscillations in precipitation, especially beginning in the 1750’s which significantly impacted the largest group of people in late colonial Alto Peru: the indigenous population, whose vulnerability increased in face of local climatic anomalies and the resulting epidemiological risk. Both the quantitative and the qualitative analysis show associations between climatic and epidemic events. 相似文献
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We test for the existence of long-term trends in 25- to 50-year long series of monthly rainfall, average river discharges, and minimum air temperatures in Colombia. The Empirical Mode Decomposition method is used as a mathematical filter to decompose a given time series into a finite number of intrinsic mode functions, assuming the coexistence of different frequency oscillatory modes in the series, and that the residual captures the likely existing long-term trends. The Mann-Kendall test for autocorrelated data is used to assess the statistical significance of the identified trends, and the Sen test is used to quantify their magnitudes. Results show that 62 % of river discharge series exhibit significant decreasing trends between 0.01-1.92 m 3 s ?1 per year, which are highly consistent downstream albeit with different ratios between the trend magnitudes and mean discharges. Most minimum temperature series (87 %) exhibit increasing trends (0.01-0.08 °Cyr ?1). Results for precipitation series are inconclusive owing to the mixing between increasing trends (41 %, between 0.1-7.0 mm yr ?1) and decreasing trends (44 %, between 0.1-7.4 mm yr ?1), with no clear-cut geographical pattern, except for the increasing trend identified along the Pacific region, consistent with the increasing trend identified in the strength of the Chocó low-level wind jet off the Pacific coast of Colombia, an important moisture source of continental precipitation. Our results contribute to discerning between signals of climate change and climate variability in tropical South America. 相似文献
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Alkali basalts of Pliocene age are the last episode of volcanism in the SE Spain Volcanic Province, postdating a complex series of Miocene calc-alkaline to ultrapotassic rocks. This volcanism is represented by small outcrops and vents NW of Cartagena that has been interpreted as a volcanic episode similar to the contemporaneous monogenetic alkaline basaltic volcanism of the Iberian Peninsula and Western/Central Europe. However, their geochemical signature is characterised by relatively higher 87Sr/86Sr ratios as well as distinct trace element anomalies which, at different scale, are only found in the spatially related calc-alkaline to ultrapotassic volcanism. Quantitative modelling of these data demonstrate that the geochemical signature of the Pliocene alkali basalts of Cartagena can be explained by the interaction between primitive melts generated from a sublithospheric mantle source similar to that identified for other volcanic regions of Spain, and liquids derived from the overlying lithospheric mantle. This interaction implies that the alkali basalts show some geochemical features only observed in mantle lithosphere-derived melts (e.g. Sr isotope enrichment and Th–U–Pb positive anomalies), while retaining an overall geochemical signature similar to other Iberian basalts (e.g. Rb–K negative anomalies). This model also implies that beneath the SEVP, enriched (metasomatized) portions were still present within the lithospheric mantle after the Miocene magmatic episodes. 相似文献
24.
Javier Almendros Jesús M. Ibez Enrique Carmona Daria Zandomeneghi 《Journal of Volcanology and Geothermal Research》2007,160(3-4):285-299
We analyze data from three seismic antennas deployed in Las Cañadas caldera (Tenerife) during May–July 2004. The period selected for the analysis (May 12–31, 2004) constitutes one of the most active seismic episodes reported in the area, except for the precursory seismicity accompanying historical eruptions. Most seismic signals recorded by the antennas were volcano-tectonic (VT) earthquakes. They usually exhibited low magnitudes, although some of them were large enough to be felt at nearby villages. A few long-period (LP) events, generally associated with the presence of volcanic fluids in the medium, were also detected. Furthermore, we detected the appearance of a continuous tremor that started on May 18 and lasted for several weeks, at least until the end of the recording period. It is the first time that volcanic tremor has been reported at Teide volcano. This tremor was a small-amplitude, narrow-band signal with central frequency in the range 1–6 Hz. It was detected at the three antennas located in Las Cañadas caldera. We applied the zero-lag cross-correlation (ZLCC) method to estimate the propagation parameters (back-azimuth and apparent slowness) of the recorded signals. For VT earthquakes, we also determined the S–P times and source locations. Our results indicate that at the beginning of the analyzed period most earthquakes clustered in a deep volume below the northwest flank of Teide volcano. The similarity of the propagation parameters obtained for LP events and these early VT earthquakes suggests that LP events might also originate within the source volume of the VT cluster. During the last two weeks of May, VT earthquakes were generally shallower, and spread all over Las Cañadas caldera. Finally, the analysis of the tremor wavefield points to the presence of multiple, low-energy sources acting simultaneously. We propose a model to explain the pattern of seismicity observed at Teide volcano. The process started in early April with a deep magma injection under the northwest flank of Teide volcano, related to a basaltic magma chamber inferred by geological and geophysical studies. The stress changes associated with the injection produced the deep VT cluster. In turn, the occurrence of earthquakes permitted an enhanced supply of fresh magmatic gases toward the surface. This gas flow induced the generation of LP events. The gases permeated the volcanic edifice, producing lubrication of pre-existing fractures and thus favoring the occurrence of VT earthquakes. On May 18, the flow front reached the shallow aquifer located under Las Cañadas caldera. The induced instability constituted the driving mechanism of the observed tremor. 相似文献
25.
Facundo?CarmonaEmail author Raúl?Rivas Eduardo?Kruse 《Theoretical and Applied Climatology》2017,128(1-2):89-102
Heatwave intensity and frequency are predicted to increase in the coming years, and this will bear adverse consequences to the environmental well-being and the socio-economic fabric in urbanized areas. The hazardous combination of increased heat storage and reduced water retention capacities of the land surface make the urban areas warmer than the surrounding rural areas in what is commonly known as the urban heat island (UHI) effect. The primary motives of this study are to quantify the interaction of this city-scale UHI with synoptic-scale heatwave episodes and to analyze the factors that mediate this interaction. A modified version of the Weather Research and Forecasting model (WRF) is utilized to simulate two heatwave episodes in New York City. The land surface scheme in the default WRF model is modified to better represent the surface to atmosphere exchanges over urban areas. Our results indicate that during the heatwave episodes, the daily-averaged UHI in NYC increased by 1.5 K. Furthermore, most of this amplification occurs in the mid-afternoon period when the temperatures peak. Wind direction and urban-rural contrasts in available energy and moisture availability are found to have significant and systematic effects on the UHI, but wind speed plays a secondary role. 相似文献
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One restriction of landscape studies is that land use and cover change is often regarded as irreversible. A highly dynamic landscape in southern Chile was selected to show that forest cover change involves a series of complex transitions and trajectories. Using Landsat images from 1976, 1985, 1999 and 2007 an in-depth analysis of the transition matrix was conducted to separate random and systematic transitions which were grouped into trajectories using a pixel-history approach. Main trajectories were linked to fragmentation indices and farming systems through cluster analysis. Of the 247 trajectories identified, old growth forest persistence comprised 22% of the landscape, whereas deforestation trajectories comprised 20.9% and were mostly composed of changes from old growth forest to shrubland (13.9%). Trajectories of forest degradation from old growth to secondary forest comprised 19.7% of the landscape. The periods 1976-1985 and 1999-2007 concentrated the most systematic deforestation and degradation transitions. In turn, random transitions predominated between 1985 and 1999, probably in response to economic factors that acted suddenly on the landscape during the 80’s, such as the woodchip export and aquaculture booms. A close relationship between landscape fragmentation and the proportion of systematic transitions and farming systems was found; specifically, the highest entropy indices occurred in clusters which exhibited the lowest proportion of systematic transitions and the highest proportion (>70%) of peasant agricultural systems. Understanding the complexity of forest cover change trajectories is relevant for improving the prediction of possible landscape evolutions and establishing landscape management priorities. 相似文献
28.
José Ignacio Manteca José Ángel López García Roberto Oyarzun Carlos Carmona 《Mineralium Deposita》2014,49(6):777-783
Between 1957 and 1990, the Peñarroya Mining and Metallurgical Company (SMMPE) disposed about 60 million tonnes of tailings materials directly to the Mediterranean Sea. A substantial part of it (12.5 Mt) was dragged back by the sea currents progressively infilling the Portman Bay (Murcia, SE Spain), thus making the shoreline advance between 500 and 600 m seaward. The Roberto froth flotation plant processed mineral from manto-type deposits belonging to the Sierra de Cartagena-La Unión lead-zinc district. One of the mineral assemblages present in these deposits comprises greenalite, magnetite, sulfides, carbonates, and silica. Despite that magnetite recovery was undertaken by SMMPE between 1959 and 1967, we estimate that magnetite contained in the tailings hosts a substantial resource that could be as large as 2.3 Mt of iron ore. The ore contains magnetite ± hematite ± siderite. Tidal waves and sea currents led to gravimetric classification of the tailings material, with concentration of the dense iron oxides in the sandy fractions, eventually forming a coastal placer iron deposit. A major problem for magnetic separation is the intimate intergrowth between magnetite, hematite, and siderite. Besides, the sands contain large concentrations of Pb (0.27 %), Zn (0.72 %), and As (559 ppm). 相似文献
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The arrangement of sediment couplets preserved in Thalassinoides shafts suggests that tides regulated the passive filling of these trace fossils and, thus, represent tubular tidalites. The thickness variation in individual layers and couplets implies a mixed diurnal, semi‐diurnal tidal signature where packages of either thick‐layered or thin‐layered couplets alternate. Calcarenitic sediment accumulated when tidal current velocity was too high to allow deposition of mud, whereas a marly mud layer is interpreted to have formed during more tranquil times of a tidal cycle (in particular, low‐tide slack water). The tidal record within the burrows covers a few weeks and the corresponding spring–neap cycles. The fill of the Thalassinoides shafts is the only known record to decipher the tidal signature from otherwise totally bioturbated sediments. These deposits accumulated in a lower‐shoreface to upper‐offshore setting during the late Miocene on a shallow shelf extending from the Atlantic Ocean to the west into northern Patagonia. The fill of all investigated burrows started around spring tide and, thus, the behaviour of the burrow producers – probably crustaceans – is speculated to have been affected by tides or the high water level because all studied burrows became abandoned around the same period of a tidal cycle. 相似文献