The Quetzalapa Pumice: a voluminous late Pleistocene rhyolite deposit in the eastern Trans-Mexican Volcanic Belt

The study area is located in the east part of the Trans-Mexican Volcanic Belt, in the Las Cumbres Volcanic Complex (LCVC) which lies between two large stratovolcanoes: Pico de Orizaba (5700 m a.s.l.) to the south, and Cofre de Perote (4200 m a.s.l.) to the NNE. The most conspicuous structure of the LCVC is a 4-km-diameter circular crater with a dacitic dome in the center, which constitutes the remains of a destroyed stratovolcano.The Quetzalapa Pumice (QP) was produced by a plinian eruption that was dated by the ¹⁴C method at 20 000 yr. BP. The eruptive sequence consists predominantly of pumice fall deposits and scarce intra-plinian pyroclastic flow deposits, which crop out on the west flank of the LCVC. The absence of post-plinian ignimbrite deposits is striking.The deposits are well sorted, clast-supported with reverse grading at the base, with a medium to high accessory lithics content. The maximum average thickness of the deposit in the proximal areas is about 15 m and has been divided into three members: the Basal Member (BM), 2 m thick with four submembers (BMf₁, BMf₂, BMf₃, and BMafl), the Intermediate Member (IM), 10 m thick with two submembers (IMpf and IMaf), and the Upper Member (UM), 3 m thick with four submembers (UMpl, UMsdf, UMwaf, and UMpls).The predominant component of the fall deposits is a white, highly vesiculated pumice with 71% SiO₂ content. Plagioclase is the most abundant mineral followed by 1–3-mm-long biotite phenocrysts. The accessory lithics are lavas mostly of andesitic composition. Their abundance increases toward the uppermost levels of the sequence.We calculate a minimum volume of 8.4 km³ (2.22 km³ dense rock equivalent), for the entire QP deposit. Isopach and isopleth maps show that the IM deposit has an elongated distribution with a NNE–SSW direction, whereas the UM deposit has a circular distribution.We estimate a maximum eruptive column height for the IM of 20 km. Field studies and isopach and isopleth maps indicate that the eruptive column was affected by a strong wind.Previous studies located the QP source in the Las Cumbres crater. However, based on the isopach and isopleth distribution, and the lack of pumice fall deposits inside the Las Cumbres crater, we consider that the QP emission center is located on the west flank of the LCVC, and was buried by its own pumice fall deposits. It coincides with an explosion crater called La Capilla formed during the closing phase of the QP eruption.A ‘pumice fountain’ model is proposed to explain the observed sequence of deposits. According to this model, the material was emitted through a ‘hose-type’ conduit during a monogenetic eruption of rhyolitic composition. This kind of volcanic activity is not extensively reported in the literature.     

A generalized zero-lag cross-correlation approach for Rapid Earthquake Localization (REL): the example of the Istanbul Megacity Rapid Response System

A seismic antenna approach based on the generalized zero-lag cross-correlation method for rapid earthquake localization is proposed. This method is intended to be applied primarily for early warning, whenever the epicentre-to-target distances guarantee enough lead-time, rapid response purposes, and for those circumstances when a seismogenic area is not directly accessible with seismic stations or/and a network of instruments is concentrated within the area to be warned. The procedure we propose aims to provide useful information for magnitude determination and shake-maps generation. Indeed, it relies only on the first P-wave triggered arrivals from seismic stations, and is designed to work in real-time for the localization of events occurring outside of the network, that is, under conditions that might be detrimental to standard localization approaches. The procedure can by summarized by a few preliminary pre-seismic and real-time co-seismic steps. In the pre-seismic time-frame, for the cases where a large and dense network exists, waiting for all stations to trigger could dramatically reduce the available lead-time for the warning. Therefore, in such cases, the network could profitably be divided into sub-arrays, while also taking advantage of available earthquake recordings or simulated data sets. During the co-seismic time-frame, the main operations are: (1) individual on-site triggering by the P-wave of the seismic stations (e.g. by a STA/LTA algorithm); (2) real-time communication of key parameters (e.g. P-wave arrival time, and signal quality) to a main centre by SMS/WLAN; (3) setup of a pseudo data set, composed by a Gaussian function centred at the P-time, and with a bell width that can be set up proportional to the trigger signal-to-noise ratio (SNR); (4) calculation of a coherency map for the sub-array with triggered stations (preliminary sub-array location); and (5) stacking of coherency maps from the different sub-arrays (final location). By the stack of coherency maps estimated by the different sub-arrays in the last step of the procedure, the epicentral area’s location may be better constrained. This innovative approach for rapid localization was applied to both synthetic data, and real observations of two small earthquakes that occurred in the Marmara Sea, Turkey, which were recorded by the Istanbul Earthquake Rapid Response System.     

The eutrophication history of a tropical water supply reservoir in Brazil

Guarapiranga Reservoir is the second most important public water supply in São Paulo, Brazil and has been eutrophic for several decades. We inferred the major ecological shifts for the period 1919–2010 related to multiple stressors (forest flooding, hydrological change, use of algicide and eutrophication), using geochemistry (TOC, TN, TP, C/N, δ¹⁵N, δ¹³C) and diatom assemblages in a short (75-cm) sediment core. Thirty-two diatom species were abundant in the core and stratigraphically constrained incremental sum of squares analysis enabled identification of three diatom zones and four subzones, i.e. depths at which marked changes in species composition occurred. Early diatom assemblages were dominated by benthic, oligotrophic taxa, mainly Eunotia, influenced by flooded vegetation after dam construction. A shift to dominance by a planktonic species (Eunotia tukanorum) occurred ca. 1932, during the period of initial physical disturbance and early use of the water body as a public water supply. Diatoms and geochemical variables show that the reservoir was oligotrophic from ~1919 to 1947. Eutrophication began ~1975 and by the early 1980s the reservoir had become eutrophic, in response to an explosive increase in human population in the watershed. Severe cultural eutrophication has persisted since ~1990. Higher concentrations of copper in the sediments, beginning in 1991, reflect the increased use of copper sulfate to control cyanobacteria blooms and provide a chronological marker. Higher δ¹⁵N values in recent sediments indicate greater sewage inputs and low C/N values reflect the predominant contribution of algae to sediment organic matter. Eutrophic taxa Cyclotella meneghiniana and Nitzschia sp. dominate recent diatom assemblages, along with Aulacoseira granulata, a species that is tolerant of copper sulfate. Diatom assemblages reflect multiple stressors, however, geochemical information provides a better understanding of the early phase of the reservoir. Paleolimnologically documented trophic state changes in this important drinking water supply are largely attributable to increased urbanization of the drainage basin and inputs of sewage. Management efforts should focus on mitigating this nutrient source.     

Locally weighted linear combination in a vector geographic information system

Weighted linear combination is a multi-criteria decision analysis technique that can be used by decision-makers to select an optimal location from a collection of alternative locations. Its local form takes into account the range of attribute values within a user-defined neighbourhood in accordance with the range-sensitivity principle. This research explores locally weighted linear combination in a vector-based geographic information system. A custom application in ArcGIS 10 allows the user to select a neighbourhood definition from a standard set including contiguity, distance, and k-nearest neighbours, for which local weights are generated. A case study on vulnerability to heat-related illness in Toronto is used to illustrate the technique. The impact of local weighting on the heat vulnerability index is examined using visual analysis of the spatial patterns of heat vulnerability under the global and local approaches, as well as the sensitivity of the local approach to the selected neighbourhood definition. A trade-off analysis of the local weights is also presented. The combination of socio-demographic and environmental determinants in a locally weighted index results in patterns of heat vulnerability that could support targeted hot weather response at a micro-geographic level within urban neighbourhoods.     

Wave observation in the marginal ice zone with the TerraSAR-X satellite

This article investigates the penetration of ocean waves into the marginal ice zone (MIZ), observed by satellite, and likewise provides a basis for the future cross-validation of respective models. To this end, synthetic aperture radar images from the TerraSAR-X satellite (TS-X) and numerical simulations of the European Centre for Medium-Range Weather Forecasts (ECMWF) are used. The focus is an event of swell waves, developed during a storm passage in the Atlantic, penetrating deeply into the MIZ off the coast of Eastern Greenland in February 2013. The TS-X scene which is the basis for this investigation extends from the ice-free open ocean to solid ice. The variation of the peak wavelength is analysed and potential sources of variability are discussed. We find an increase in wavelength which is consistent with the spatial dispersion of deep water waves, even within the ice-covered region.     

Astrodynamical Space Test of Relativity Using Optical Devices I (ASTROD I)—A class-M fundamental physics mission proposal for Cosmic Vision 2015–2025

ASTROD I is a planned interplanetary space mission with multiple goals. The primary aims are: to test general relativity with an improvement in sensitivity of over three orders of magnitude, improving our understanding of gravity and aiding the development of a new quantum gravity theory; to measure key solar system parameters with increased accuracy, advancing solar physics and our knowledge of the solar system; and to measure the time rate of change of the gravitational constant with an order of magnitude improvement and the anomalous Pioneer acceleration, thereby probing dark matter and dark energy gravitationally. It is an international project, with major contributions from Europe and China and is envisaged as the first in a series of ASTROD missions. ASTROD I will consist of one spacecraft carrying a telescope, four lasers, two event timers and a clock. Two-way, two-wavelength laser pulse ranging will be used between the spacecraft in a solar orbit and deep space laser stations on Earth, to achieve the ASTROD I goals. A second mission, ASTROD (ASTROD II) is envisaged as a three-spacecraft mission which would test General Relativity to 1 ppb, enable detection of solar g-modes, measure the solar Lense–Thirring effect to 10 ppm, and probe gravitational waves at frequencies below the LISA bandwidth. In the third phase (ASTROD III or Super-ASTROD), larger orbits could be implemented to map the outer solar system and to probe primordial gravitational-waves at frequencies below the ASTROD II bandwidth.

Wind-Direction Effects on Urban-Type Flows

Practically all extant work on flows over obstacle arrays, whether laboratory experiments or numerical modelling, is for cases where the oncoming wind is normal to salient faces of the obstacles. In the field, however, this is rarely the case. Here, simulations of flows at various directions over arrays of cubes representing typical urban canopy regions are presented and discussed. The computations are of both direct numerical simulation and large-eddy simulation type. Attention is concentrated on the differences in the mean flow within the canopy region arising from the different wind directions and the consequent effects on global properties such as the total surface drag, which can change very significantly—by up to a factor of three in some circumstances. It is shown that for a given Reynolds number the typical viscous forces are generally a rather larger fraction of the pressure forces (principally the drag) for non-normal than for normal wind directions and that, dependent on the surface morphology, the average flow direction deep within the canopy can be largely independent of the oncoming wind direction. Even for regular arrays of regular obstacles, a wind direction not normal to the obstacle faces can in general generate a lateral lift force (in the direction normal to the oncoming flow). The results demonstrate this and it is shown how computations in a finite domain with the oncoming flow generated by an appropriate forcing term (e.g. a pressure gradient) then lead inevitably to an oncoming wind direction aloft that is not aligned with the forcing term vector.     

Mechanism of calcrete formation in the Lower Cretaceous (Neocomian) fluvial deposits,northeastern Iran based on petrographic,geochemical data

The Kopet-Dagh basin of northeastern Iran was formed during the Middle Triassic orogeny. From Jurassic through Miocene time, sedimentation was relatively continuous in this basin. The Shurijeh Formation (Neocomian), which consists of red bed siliciclastic sediments that were deposited in fluvial depositional settings, crops out in the southeastern part of the Kopet-Dagh basin. In addition to clastic lithofacies, non-clastic facies in the form of calcrete paleosols, were identified in this formation. The calcrete host rocks are mainly sandstone, pebbly sandstone. The calcrete in middle unit in the Shurijeh Formation consists of, from bottom to top: incipient calcrete, nodular calcrete, massive calcrete horizons. The maturity pattern of these calcrete gradationally increases from bottom to top in this unit. Lack of organo-sedimentary structure (mainly plant roots), diversity of calcite fabric, suggest that the studied calcretes have a multi-phase development: a short vadose phase followed by a long phreatic phase. These calcretes are neither pedogenic nor groundwater calcretes. Petrographic studies show that they are composed of micritic textures with a variety of calcite fabrics, microsparitic/sparitic veins, displacive, replacive fabrics, quartz, hematite grains. Cathodoluminescence images, trace elemental analysis (Fe, Mn increased, Na, Sr decreased) of calcrete samples show the effects of meteoric waters during the calcrete formation when water tables were variable. In this study, we conclude that evaporation, degassing of carbon dioxide are the two main factors in the formation of non-pedogenic or groundwater calcrete. The sources of carbonate were probably parent materials, surface waters, ground waters, eolian dusts, numerous outcrops of limestones that have been exposed in the source area during Neocomian time.