Ubinas: the evolution of the historically most active volcano in southern Peru     

Jean-Claude Thouret  Marco Rivera  Gerhard Wörner  Marie-Christine Gerbe  Anthony Finizola  Michel Fornari  Katherine Gonzales 《Bulletin of Volcanology》2005,67(6):557-589

Ubinas volcano has had 23 degassing and ashfall episodes since A.D. 1550, making it the historically most active volcano in southern Peru. Based on fieldwork, on interpretation of aerial photographs and satellite images, and on radiometric ages, the eruptive history of Ubinas is divided into two major periods. Ubinas I (Middle Pleistocene >376 ka) is characterized by lava flow activity that formed the lower part of the edifice. This edifice collapsed and resulted in a debris-avalanche deposit distributed as far as 12 km downstream the Rio Ubinas. Non-welded ignimbrites were erupted subsequently and ponded to a thickness of 150 m as far as 7 km south of the summit. These eruptions probably left a small collapse caldera on the summit of Ubinas I. A 100-m-thick sequence of ash-and-pumice flow deposits followed, filling paleo-valleys 6 km from the summit. Ubinas II, 376 ky to present comprises several stages. The summit cone was built by andesite and dacite flows between 376 and 142 ky. A series of domes grew on the southern flank and the largest one was dated at 250 ky; block-and-ash flow deposits from these domes filled the upper Rio Ubinas valley 10 km to the south. The summit caldera was formed between 25 and 9.7 ky. Ash-flow deposits and two Plinian deposits reflect explosive eruptions of more differentiated magmas. A debris-avalanche deposit (about 1.2 km³) formed hummocks at the base of the 1,000-m-high, fractured and unstable south flank before 3.6 ka. Countless explosive events took place inside the summit caldera during the last 9.7 ky. The last Plinian eruption, dated A.D.1000–1160, produced an andesitic pumice-fall deposit, which achieved a thickness of 25 cm 40 km SE of the summit. Minor eruptions since then show phreatomagmatic characteristics and a wide range in composition (mafic to rhyolitic): the events reported since A.D. 1550 include many degassing episodes, four moderate (VEI 2–3) eruptions, and one VEI 3 eruption in A.D. 1667. Ubinas erupted high-K, calc-alkaline magmas (SiO₂=56 to 71%). Magmatic processes include fractional crystallization and mixing of deeply derived mafic andesites in a shallow magma chamber. Parent magmas have been relatively homogeneous through time but reflect variable conditions of deep-crustal assimilation, as shown in the large variations in Sr/Y and LREE/HREE. Depleted HREE and Y values in some lavas, mostly late mafic rocks, suggest contamination of magmas near the base of the >60-km-thick continental crust. The most recently erupted products (mostly scoria) show a wide range in composition and a trend towards more mafic magmas.Recent eruptions indicate that Ubinas poses a severe threat to at least 5,000 people living in the valley of the Rio Ubinas, and within a 15-km radius of the summit. The threat includes thick tephra falls, phreatomagmatic ejecta, failure of the unstable south flank with subsequent debris avalanches, rain-triggered lahars, and pyroclastic flows. Should Plinian eruptions of the size of the Holocene events recur at Ubinas, tephra fall would affect about one million people living in the Arequipa area 60 km west of the summit.Editorial responsibility: D Dingwell  相似文献   

The solar causes of major geomagnetic storms     

S. Bravo  A. L. Rivera 《Annales Geophysicae》1994,12(2-3):113-120

In this paper we reanalyse the set of ten major geomagnetic storms which occurred between August 1978 and December 1979. We relate them to the characteristics of the solar wind disturbances which caused them and the solar sources of such disturbances as tracked by means of interplanetary scintillation. It seems to us that the shock causing the sudden commencement and the plasma behind it with an important long-lasting B_z south component (B_z  相似文献   

Sedimentary facies,fossil distribution and depositional setting of the late Ediacaran Tamengo Formation (Brazil)     

Kamilla Borges Amorim  Jhon Willy Lopes Afonso  Juliana de Moraes Leme  Cleber Quidute Clemente Diniz  Laura Carolina Montenegro Rivera  Juan Camilo Gómez-Gutiérrez  Paulo César Boggiani  Ricardo Ivan Ferreira Trindade 《Sedimentology》2020,67(7):3422-3450

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A principal component analysis approach to assess CHIRPS precipitation dataset for the study of climate variability of the La Plata Basin,Southern South America     

Cerón  Wilmar Loaiza  Molina-Carpio  Jorge  Ayes Rivera  Irma  Andreoli  Rita Valeria  Kayano  Mary Toshie  Canchala  Teresita 《Natural Hazards》2020,103(1):767-783

Natural Hazards - This article assesses the consistency of the satellite precipitation estimate CHIRPS v.2 to describe the spatiotemporal rainfall variability in the La Plata Basin (LPB), the...  相似文献   

Seasonal variation of particulate heavy metals in the Lower Paraíba do Sul River, R.J., Brazil     

C. E. V. Carvalho  A. R. C. Ovalle  C. E. Rezende  M. M. Molisani  M. S. M. B. Salomão  L. D. Lacerda 《Environmental Geology》1999,37(4):297-302

 Temporal and spatial variability of particulate metal concentrations (Cu, Cr, Zn, Mn and Fe) were investigated in the lower drainage basin of the Paraíba do Sul River. The results showed that the spatial variability was not important for all the studied metals, however, temporal variations seems to be considerable. In general, two distinct behaviors were observed for particulate heavy metals: (1) metal concentration increase together with water flow (Fe and Cu) and (2) concentration decrease with increasing water flux (Zn, Cr and Mn). The Fe and Cu behavior is probably due to the strong association of these metals with surface runoff, although their sources seem to be distinct. Iron probably originates from the regional soils rich in iron oxides, and Cu is possibly associated to the large-scale use of copper fungicides in the sugar cane plantations. The opposite trend observed for Zn, Cr and Mn probably reflects the importance of the industrial and urban effluents as a secondary source of these elements for the system. Their behavior is probably associated with the dilution effect caused by the input of a suspended matter poor in these metals originated from the surface runoff during the rainy season. Received: 4 March 1998 · Accepted: 30 June 1998  相似文献   

Microphytobenthic primary production as C uptake in sublittoral sediments of the Gulf of Trieste (northern Adriatic Sea): Methodological aspects and data analyses     

Tamara Cibic  Oriana Blasutto  Nicoletta Burba  Serena Fonda Umani 《Estuarine, Coastal and Shelf Science》2008

From January 2003 to December 2004 microphytobenthic primary production was estimated both from in situ (MPPs) and in the laboratory (MPPp) ¹⁴C-incubation of slurries collected in a coastal site of the Gulf of Trieste (northern Adriatic Sea). MPPs values varied from −7.54 ± 3.12 to 34.59 ± 7.66 mg C m⁻² h⁻¹ over the whole period. The lowest MPPs were observed in November 2003 and August 2004, while the highest MPPs in July 2003 and May 2004, in correspondence with high PAR at the bottom. Significant correlations between MPPs and the microphytobenthic biomass (BIOM) (r = 0.75, p < 0.001), between MPPs and PAR at the bottom (r = 0.54, p < 0.01) and between MPPs and OXY (r = 0.50, p < 0.05) were revealed. MPPp values were higher than MPPs ones in 15 out of 23 observations, with the highest MPPp recorded in July 2003. At 17 m depth a seasonal pattern of sampling months was revealed by the cluster analysis. The role of abiotic parameters in determining this seasonal pattern was highlighted by the PCA, with the first axis correlated with MPPs and PAR, and the second one with temperature. Applying the fuzzy sets it resulted that spring months showed a higher degree of membership with MPPs, summer months with temperature and autumn–winter months with OXY. The microphytobenthic community did not seem to be photosynthetically active throughout the study period. From August–September to December low or negative MPPs values were recorded. We infer that during these months a shift from the autotrophic to heterotrophic metabolism of the benthic microalgae occurred in correspondence with low PAR and/or high temperature at the bottom. Despite the progressive lowering of the trophy of the study area occurred during the last 20 years, we found higher primary production values than those estimated two decades earlier.  相似文献   

Forecasting monthly precipitation in Central Chile: a self-organizing map approach using filtered sea surface temperature   总被引：1，自引：0，他引：1  

Diego Rivera  Mario Lillo  Cintia B. Uvo  Max Billib  José Luis Arumí 《Theoretical and Applied Climatology》2012,107(1-2):1-13

Western South America is subject to considerable inter-annual variability due to El Ni?o–Southern Oscillation (ENSO) so forecasting inter-annual variations associated with ENSO would provide an opportunity to tailor management decisions more appropriately to the season. On one hand, the self-organizing maps (SOM) method is a suitable technique to explore the association between sea surface temperature and precipitation fields. On the other hand, Wavelet transform is a filtering technique, which allows the identification of relevant frequencies in signals, and also allows localization on time. Taking advantage of both methods, we present a method to forecast monthly precipitation using the SOM trained with filtered SST anomalies. The use of the SOM to forecast precipitation for Chillan showed good agreement between forecasted and measured values, with correlation coefficients (r ²) ranging from 0.72 to 0.91, making the combined use filtered SST fields and SOM a suitable tool to assist water management, for example in agricultural water management. The method can be easily tailored to be applied in other stations or to other variables.  相似文献   

Uncertainty in a monthly water balance model using the generalized likelihood uncertainty estimation methodology     

Rivera  Diego  Rivas  Yessica  Godoy  Alex 《Journal of Earth System Science》2015,124(1):49-59

Journal of Earth System Science - Hydrological models are simplified representations of natural processes and subject to errors. Uncertainty bounds are a commonly used way to assess the impact of...  相似文献   

A review of remote sensing methods for glacier mass balance determination   总被引：3，自引：2，他引：1  

Jonathan L. Bamber  Andres Rivera   《Global and Planetary Change》2007,59(1-4):138

Airborne and satellite remote sensing is the only practical approach for deriving a wide area, regional assessment of glacier mass balance. A number of remote sensing approaches are possible for inferring the mass balance from some sort of proxy estimate. Here, we review the key methods relevant, in particular to Andean glaciers, discussing their strengths and weaknesses, and data sets that could be more fully exploited. We also consider future satellite missions that will provide advances in our observational capabilities. The methods discussed include observation of elevation changes, estimation of ice flux, repeat measurement of changes in spatial extent, snowline elevation and accumulation–ablation area ratio estimation. The methods are illustrated utilising a comprehensive review of results obtained from a number of studies of South American glaciers, focusing specifically on the Patagonian Icefields. In particular, we present some new results from Glaciar Chico, Southern Patagonian Icefield, Chile, where a variety of different satellite and in-situ data have been combined to estimate mass balance using a geodetic or elevation change approach over about a 25 yr period.  相似文献   

Identifiability analysis: towards constrained equifinality and reduced uncertainty in a conceptual model     

Enrique Muñoz  Diego Rivera  Fernando Vergara  Pedro Tume  José Luis Arumí 《水文科学杂志》2013,58(9):1690-1703

Abstract

Different sets of parameters and conceptualizations of a basin can give equally good results in terms of predefined objective functions. Therefore, a need exists to tackle equifinality and quantify the uncertainty bands of a model. In this paper we use the concepts of equifinality, identifiability and uncertainty to propose a simple method aimed at constraining the equifinal parameters and reducing the uncertainty bands of model outputs, and obtaining physically possible and reasonable models. Additionally, the uncertainty of equifinal solutions is quantified to estimate the amount by which output uncertainty can be reduced by knowing how to discard most of the equifinal solutions of a model. As a study case, a conceptual model of the Chillán basin in Chile is carried out. From the study it is concluded that using identifiability analysis makes it possible to constrain equifinal solutions with reduced uncertainty and realistic models, resulting in a framework that can be recommended to practitioners, especially due to the simplicity of the method.  相似文献