Sierra Negra Research Articles

Upper Givetian and Frasnian (Middle and Upper Devonian) conodonts from Ampriú (Aragonian Pyrenees, Spain): global correlations and palaeogeographic relations

Abstract: This report describes for the first time a part of the Middle and Upper Devonian conodont sequence of the Sierra Negra Subfacies in the Aragonian Pyrenees (Spain), establishing the basis for further sound correlations both across the distinct Pyrenean facies and subfacies and on other relevant world areas. The description of 20 conodont taxa and their stratigraphical distribution permits recognition of two separate time intervals. The older one corresponds to the lower Upper Givetian (Middle Devonian), hermanni to cristatus ectypus zones. The younger interval is uppermost Lower Frasnian to lower Middle Frasnian (Upper Devonian) and is equivalent to MN4–MN6 zones. The combination of litho‐ and conodont biofacies supports the distinction between the Sierra Negra and Renanué Subfacies. Conodont biofacies for the studied interval are partially close to the ones from the Compte Subfacies, but lithofacies are clearly different. This faunal similarity fosters accurate correlation between subfacies and stimulates further research aiming at Devonian Pyrenean basin(s) reconstruction. Additionally, this faunal sequence permits direct comparison with regions located in northern Gondwana and in the Russian platform for part of the interval. Comparison with Laurasia, mainly with the Northwest Territories of Canada and the north‐western United States, is also provided. Some taxa are also common with eastern and central Asia (China, Siberia, Tadzhikistan, Afghanistan), Australia and western USA (Nevada).

Fumarole/plume and diffuse CO2 emission from Sierra Negra caldera, Galapagos archipelago

Measurements of visible and diffuse gas emission were conducted in 2006 at the summit of Sierra Negra volcano, Galapagos, with the aim to better characterize degassing after the 2005 eruption. A total SO2 emission of 11 ± 2 t day−1 was derived from miniature differential optical absorption spectrometer (mini-DOAS) ground-based measurements of the plume emanating from the Mini Azufral fumarolic area, the most important site of visible degassing at Sierra Negra volcano. Using a portable multigas system, the H2S/SO2, CO2/SO2, and H2O/SO2 molar ratios in the Mina Azufral plume emissions were found to be 0.41, 52.2, and 867.9, respectively. The corresponding H2O, CO2, and H2S emission rates were 562, 394, and 3 t day−1, respectively. The total output of diffuse CO2 emissions from the summit of Sierra Negra volcano was 990 ± 85 t day−1, with 605 t day−1 being released by a deep source. The diffuse-to-plume CO2 emission ratio was about 1.5. Mina Azufral fumaroles released gasses containing 73.6 mol% of H2O; the main noncondensable components amounted to 97.4 mol% CO2, 1.5 mol% SO2, 0.6 mol% H2S, and 0.35 mol% N2. The higher H2S/SO2 ratio values found in 2006 as compared to those reported before the 2005 eruption reveal a significant hydrothermal contribution to the fumarolic emissions. 3He/4He ratios measured at Mina Azufral fumarolic discharges showed values of 17.88 ± 0.25 RA, indicating a mid-ocean ridge basalts (MORB) and a Galapagos plume contribution of 53 and 47 %, respectively.

The HAWC observatory

The High Altitude Water Cherenkov (HAWC) observatory is a new very high energy water Cherenkov gamma ray telescope, now under construction at 4100m altitude at Sierra Negra, Mexico. Due to its increased altitude, larger surface area and improved design, HAWC will be about 15 times more sensitive than its predecessor, Milagro. With its wide field of view and high duty factor, HAWC will be an excellent instrument for the studies of diffuse gamma ray emission, the high energy spectra of Galactic gamma ray sources, and transient emission from extragalactic objects such as GRBs and AGN, as well as surveying a large fraction of the VHE sky.

Localidades adicionales en la distribución geográfica de la pava cojolita (Penelope purpurascens) en Puebla y Oaxaca, México

Reportamos localidades adicionales para la pava cojolita (Penelope purpurascens) en la Sierra Norte y Sierra Negra, Puebla, y en la Sierra de Juárez, Oaxaca. Estos registros están basados en imágenes de fototrampeo, observaciones directas e indirectas (individuo cautivo, patas, plumas), grabaciones de vocalizaciones e información oral de cazadores experimentados. Presentamos los primeros registros fotográficos de esta especie que complementan el conocimiento sobre su distribución geográfica en Puebla y Oaxaca.

Four new species of the genus Pseudocellus (Arachnida: Ricinulei: Ricinoididae) from Mexico

Four new species of ricinuleids are described: Pseudocellus chankin from caves and surface collections in southern Mexico (Chiapas & Tabasco) and Guatemala (Petén); Pseudocellus jarocho from a single surface collection in Veracruz, México; Pseudocellus oztotl, a troglobitic and troglomorphic species from Cueva de Las Tres Quimeras in the Sierra Negra, Puebla, Mexico; and Pseudocellus platnicki, also troglobitic and troglomorphic, known from a single cave in Coahuila, Mexico. The number of known species in the genus increases to 24, and Mexican species to 14. An identification key for adult males of the species found in Mexico and southern USA is provided.

Prospects for GRB detection with HAWC scalers

The High Altitude Water Cherenkov (HAWC) experiment is a high energy gamma ray observatory which is currently under construction in the Sierra Negra, Mexico, at an altitude of 4100 m. It will detect gamma-ray induced atmospheric particle showers on the ground. The water Cherenkov particle detection technique allows for full day observations of a large fraction of the sky. HAWC is the successor of Milagro. Because of the higher altitude, size and improved detector design, the sensitivity of HAWC will be ≈15× higher than the sensitivity of Milagro. Besides a triggered data acquisition system (DAQ) searching for individual air shower events, a scaler DAQ counting all signals in the HAWC photomultiplier tubes (PMTs) above a fixed threshold is available. The large sky coverage of about 1.5 sr and high duty cycle of HAWC increases its detection potential for transient sources like gamma ray bursts (GRBs). The sensitive energy range of the scaler DAQ overlaps at low energies with the energy range of the Large Area Telescope (LAT) aboard the Fermi satellite. We demonstrate that GRBs with a high energy spectral component ( E γ ≳ 30 GeV) seen by the LAT are also visible for the HAWC scaler DAQ. The properties of the GRB spectra at high energies provide information about e ±-pair attenuation inside of GRB jets, extra-galactic background light (EBL) absorption and the maximum energy to which particles can be accelerated in GRBs.

Insights into the Galápagos plume from uranium-series isotopes of recently erupted basalts

Uranium-series isotopes (238U-230Th-226Ra-210Pb), major element, trace element, and Sr-Nd isotopic data are presented for recent (<60 years old) Galapagos archipelago basalts. Volcanic rocks from all centers studied (Fernandina, Cerro Azul, Sierra Negra, and Wolf Volcano) display 230Th excesses (4%–15%) and steep rare earth element (REE) patterns indicative of residual garnet during partial melting of their mantle source. Rare earth element modeling suggests that only a few percent of garnet is involved. Correlations between (238U/232Th), radiogenic isotopes and Nb/Zr ratio suggest that the U/Th ratio of these Galapagos volcanic rocks is primarily controlled by geochemical source variations and not fractionation during partial melting. The lowest (230Th/238U) ratio is not observed at Fernandina (the supposed center of the plume) but at the more geochemically “depleted” Wolf Volcano, further to the north. Small radium excesses are observed for all samples with (226Ra/230Th) ranging from 1.107 to 1.614. The 226Ra-230Th disequilibria do not correlate with other uranium-series parent-daughter nuclide pairs or geochemical data, suggesting modification at shallow levels on timescales relevant to the half-life of 226Ra (1600 years). The combination of 226Ra and 210Pb excesses is inconsistent with interaction of magma with cumulate material unless decoupling of 210Pb (or an intermediate daughter, such as 222Rn) occurs prior to modification of Ra-Th disequilibria. An intriguing correlation of (210Pb/226Ra)0 with Nb/Zr and radiogenic isotopes requires further investigation but suggests possible control via magmatic degassing and accumulation that may somehow be related to source heterogeneities.

Deformation Time-Series Generation in Areas Characterized by Large Displacement Dynamics: The SAR Amplitude Pixel-Offset SBAS Technique

We exploit the amplitude information of a sequence of synthetic aperture radar (SAR) images, acquired at different times, in order to generate displacement time-series in areas characterized by large and/or rapid deformation, the size of which is on the order of the image's pixel dimensions. We follow the same rationale of the Small BAseline Subset (SBAS) differential SAR interferometry (DInSAR) approach, by coupling the available SAR images into pairs characterized by a small separation between the acquisition orbits. We exploit the amplitudes of the selected image pairs in order to calculate the relative across-track (range) and along-track (azimuth) pixel-offsets (PO). Finally, we apply the SBAS inversion strategy to retrieve the range and azimuth displacement time-series. This approach, referred to as pixel-offset (PO-) SBAS technique, has been applied to a set of 25 ENVISAT SAR observations of the Sierra Negra caldera, Galapagos Islands, spanning the 2003-2007 time interval. The retrieved deformation time-series show the capability of the technique to detect and measure the large displacements affecting the inner part of the caldera that, in correspondence to the October 2005 eruption, reached several meters. Moreover, by comparing the PO-SBAS results to continuous GPS measurements, we estimate that the accuracy of the PO-SBAS time-series is on the order of 1/30th of a pixel for both range and azimuth directions.

Composição, estrutura e similaridade florística da Floresta Atlântica, na Serra Negra, Rio Preto - MG

Resumo A Serra Negra, no município de Rio Preto (MG), estende-se por uma região com fisionomias florestais serranas da Mantiqueira e campos altimontanos, entre as elevações do maciço do Itatiaia (RJ, SP e MG) e da Serra do Ibitipoca (MG). Com o objetivo de investigar o comportamento das variáveis comunitárias da flora arbórea em condições diferentes de altitude e alagamento, determinou-se a composição florística, estrutura e similaridade entre três fragmentos de floresta (aluvial, montana e nebular) e a suas relações florísticas com estudos da região. Foram amostrados 2.572 indivíduos, identificados em 194 espécies, distribuídas em 59 famílias e 118 gêneros. As famílias com maior riqueza foram Myrtaceae (30 espécies), Lauraceae (20), Melastomataceae (17) e Fabaceae (13). Os três tipos de vegetação estudados, associados a diferentes condições ambientais, diferem entre si em sua composição e estrutura. A floresta aluvial revelou-se com reduzida diversidade, baixa estatura e alta dominância ecológica. A floresta nebular destacou-se por apresentar elementos típicos de altitude em detrimento de espécies freqüentes na região abaixo da escarpa da serra, onde a diversidade foi maior. A flora arbórea da Serra Negra, formada pelo conjunto das áreas estudadas, apresenta um conjunto considerável de elementos com distribuição característica de ambientes montanhosos do Sudeste do Brasil.

Description of a4 -channel FPGA-controlled ADC-based DAQ system for general purpose PMT signals

We describe a general purpose data acquisition system for PMT signals. Hardware-wise it consists of a 4-channel ADC daughter board, an FPGA mother board, a GPS receiver and an atmospheric pressure sensor and a temperature sensor. The four ADC channels simultaneously sample PMT input signals with a sampling rate of 100MS/s. We have evaluated the noise of our system obtaining less than -48.6dB. This DAQ system includes a firmware suitable for pulse processing in cosmic rays applications. In particular, we describe in detail the way in which this system can be used during the commissioning and early operation phases of the High Altitude Water Cherenkov Observatory (HAWC) currently under construction at Sierra Negra in Mexico.

A new species of night lizard of the genus Lepidophyma (Squamata: Xantusiidae) from southern Puebla, México

A new species of Lepidophyma is described from the Sierra Negra in southern Puebla. This new species is known only from the type locality and is characterized by a combination of several characters (number of dorsal scales, total of femoral pores, number of lateral tubercles, number the dorsal interwhorls separated the whorls, number of the paravertebral rows, number of the toe lamellae and number of gulars). It lives between rocks in remnants of Tropical Evergreen Forest. The description of this new species increases the number of species in the genus to 19.

The capabilities of the calculated approach for the astroclimatic assessment in radioastronomy

The work is dedicated to calculation of daily variability of monthly averaged full vertical at-mospheric absorption for six well-known moun- tain locations of sub-millimeter wave band ra-diotelescopes obtained with usage of chosen by authors models combination. Test locations we- re defined as follows: Chajnantor plateau in the Atacama mountain desert (Chile), Hanle (India), South Pole (Antarctic), Mauna Kea (Hawaii, USA), Sierra Negra (Puebla, Mexico) and El Leoncito (Argentine). The data of these calculations were compared with the data of long term radiometric observations of other authors. Se- arching for new alternative places to complement existing sub-millimeter telescopes locations was attempted too.

Geant4 simulation of the solar neutron telescope at Sierra Negra, Mexico

The solar neutron telescope (SNT) at Sierra Negra (19.0°N, 97.3°W and 4580 m.a.s.l) is part of a worldwide network of similar detectors (Valdés-Galicia et al., (2004) [1]). This SNT has an area of 4 m 2; it is composed by four 1 m×1 m×30 cm plastic scintillators (Sci). The Telescope is completely surrounded by anti-coincidence proportional counters (PRCs) to separate charged particles from the neutron flux. In order to discard photon background it is shielded on its sides by 10 mm thick iron plates and on its top by 5 mm lead plates. It is capable of registering four different channels corresponding to four energy deposition thresholds: E>30, >60, >90 and >120 MeV. The arrival direction of neutrons is determined by gondolas of PRCs in electronic coincidence, four layers of these gondolas orthogonally located underneath the SNT, two in the NS direction and two in the EW direction. We present here simulations of the detector response to neutrons, protons, electrons and gammas in range of energies from 100 to 1000 MeV. We report on the detector efficiency and on its angular resolution for particles impinging the device with different zenith angles. The simulation code was written using the Geant4 package (Agostinelli et al., (2003) [2]), taking into account all relevant physical processes.

Weather at Sierra Negra: 7.3-yr statistics and a new method to estimate the temporal fraction of cloud cover

Sierra Negra, one of the highest peaks in central Mexico, is the site of the Large Millimeter Telescope. We describe the first results of a comprehensive analysis of the weather data measured in situ from October 2000 to February 2008 to be used as a reference for future activity in the site. We compare the data from two different stations at the summit considering the accuracy of both instruments. We analysed the diurnal, seasonal and annual cycles for all the parameters. The thermal stability is remarkably good, crucial for a good performance of the telescopes. From the solar radiation data we developed a new method to estimate the fraction of time when the sky is clear of clouds. We show that our measurements are consistent with a warm standard atmosphere model. The conditions at the site are benign and stable given its altitude, showing that Sierra Negra is a extremely good site for millimeter and high energy observations.

Physics of ion acceleration in the solar flare on 2005 September 7 determines γ-ray and neutron production

Relativistic neutrons were observed by the neutron monitors at Mt. Chacaltaya and Mexico City and by the solar neutron telescopes at Chacaltaya and Mt. Sierra Negra in association with an X17.0 flare on 2005 September 7. The neutron signal continued for more than 20 min with high statistical significance. Intense emissions of γ -rays were also registered by INTEGRAL, and during the decay phase by RHESSI. We analyzed these data using the solar-flare magnetic-loop transport and interaction model of Hua et al. [Hua, X.-M., Kozlovsky, B., Lingenfelter, R.E. et al. Angular and energy-dependent neutron emission from solar flare magnetic loops, Astrophys. J. Suppl. Ser. 140, 563–579, 2002], and found that the model could successfully fit the data with intermediate values of loop magnetic convergence and pitch-angle scattering parameters. These results indicate that solar neutrons were produced at the same time as the γ -ray line emission and that ions were continuously accelerated at the emission site.

Estimating the altitude of volcanic sulfur dioxide plumes from space borne hyper‐spectral UV measurements

The altitude of volcanic sulfur dioxide (SO2) plumes determines the transport and atmospheric residence time of derived sulfate aerosol, and hence their impacts on the environment and climate. Knowledge of the altitude of fresh eruption clouds is also very important in aviation safety to avoid flying through ash clouds and for forecasting of plume drift. In this paper, we demonstrate the altitude dependence of the spectral response in the backscattered ultraviolet (BUV) radiance when a SO2 absorption layer is added to an ozone‐laden atmosphere. The distinctive spectral response serves as the physical basis for simultaneous SO2 loading and altitude retrievals, which can improve the characterization of volcanic emissions. We accomplish this by extending the recently developed Iterative Spectral Fitting (ISF) algorithm to include effective plume altitude determination when performing simultaneous ozone and SO2 retrievals. The extended ISF algorithm is applied to hyper‐spectral Ozone Monitoring Instrument (OMI) measurements of two volcanic eruptions: Sierra Negra in October 2005 and Jebel al Tair in September 2007. The results show for the first time that a wide range of SO2 plume altitudes can be estimated directly from hyper‐spectral BUV radiance measurements.

A multi-sensor comparison of sulphur dioxide emissions from the 2005 eruption of Sierra Negra volcano, Galápagos Islands

Sulphur dioxide retrievals of three satellite-based sensors (the Total Ozone Mapping Spectrometer, the Ozone Monitoring Instrument and the Moderate Resolution Imaging Spectroradiometer) were performed on the volcanic cloud from the Sierra Negra, Galápagos Islands eruption of October 22 to October 30, 2005. Near-coincidental plume acquisitions on 23 October from each of the sensors were compared spatially on a pixel-by-pixel basis in order to assess the level of agreement between the retrievals. The variation in pixel size and shape between sensors was accounted for by resampling MODIS data to the geometry of the UV sensors. It was found that correlations between retrievals were wide ranging with estimates of total tonnage ranging from 60 kt up to 1800 kt. Spatial comparisons show variation according to plume altitude and overpass time and are compounded by interference from other volcanic species as well as individual instrument error. The comparison of these sensors provides an insight into the relative merits of each method and illustrates the usefulness of a holistic approach to satellite remote sensing of sulphur dioxide. This will permit the development of more robust retrieval schemes and therefore increasingly reliable estimations of volcanic SO 2 emissions.

Improving retrieval of volcanic sulfur dioxide from backscattered UV satellite observations

Existing algorithms that use satellite measurements of solar backscattered ultraviolet (BUV) radiances to retrieve sulfur dioxide (SO2) vertical columns underestimate the large SO2 amounts encountered in fresh volcanic eruption clouds. To eliminate this underestimation we have developed a new technique, named the Iterative Spectral Fitting (ISF) algorithm, for accurate retrieval of SO2 vertical columns in the full range of volcanic emissions. The ISF algorithm is applied to Ozone Monitoring Instrument (OMI) BUV measurements of the Sierra Negra eruption (Galàpagos Islands, Ecuador) in October 2005. The results represent major improvements over the operational OMI SO2 products. Based on the ISF data, we report the largest SO2 vertical column amount (&gt;1000 Dobson Units (DU), where 1 DU = 2.69 × 1016 molecules/cm2) ever observed by a space borne instrument, implying that very high concentrations of SO2 can occur in the lower troposphere during effusive eruptions.

Measurements of SO2 profiles in volcanic plumes from the NASA Tropospheric Emission Spectrometer (TES)

Satellite measurements are now recognized as a key element for the early detection and characterization of volcanic eruptions, in particular in the context of aircraft routing. A common tracer of volcanic plumes is sulfur dioxide (SO2), which so far has been measured by ultraviolet‐visible (UV‐vis) instruments and multispectral infrared (IR) sounders. Here we report the first SO2 vertical profile retrieved from high spectral resolution thermal infrared nadir radiance spectra and we provide information on both the quantity of gas emitted and its altitude. From the radiance spectra provided by the Tropospheric Emission Spectrometer (TES) aboard the NASA AURA satellite, and owing to the ∼0.1 cm−1 (apodized) spectral resolution, elevated levels of SO2 were measured following volcanic eruptions occurring in 2005 (Manam, Sierra Negra) and 2006 (Rabaul, Nyamuragira). Column values are found to be in good agreement with the data provided by Ozone Mapping Instrument (OMI), a UV‐vis instrument also onboard the AURA satellite.

4D gravity changes associated with the 2005 eruption of Sierra Negra volcano, Galápagos

Sierra Negra volcano, the most voluminous shield volcano in the Galápagos archipelago and one of the largest basaltic calderas in the world, erupted on October 22, 2005 after more than [Formula: see text] of quiescence. GPS and satellite radar interferometry (InSAR) monitoring of the deformation of the caldera floor in the months prior to the eruption documented extraordinary inflation rates [Formula: see text]. The total amount of uplift recorded since monitoring began in 1992 approached [Formula: see text] at the center of the caldera over the eight days of the eruption the caldera floor deflated a maximum of 5 m and subsquently renewed its inflation, but at a decelerating rate. To gain insight into the nature of the subsurface mass/density changes associated with the deformation, gravity measurements performed in 2005, 2006, and 2007 are compared to previous measurements from 2001-2002 when the volcano underwent a period of minor deflation and magma withdrawal.The residual gravity decrease between 2001-2002 and 2005 is among the largest ever recorded atan active volcano (−950 μGal) and suggests that inflation was accompanied by a relative density decrease in the magmatic system. Forward modeling of the residual gravity data in 4D (from 2002 to 2005) gives an estimate of the amount of vesiculation in the shallow sill required to explain the observed gravity variations. Geochemical constraints from melt inclusion and satellite remote-sensing data allow us to estimate the pre-eruptive gas content of the magma and place constraints on the thickness of the gas-rich sill necessary to produce the gravity anomalies observed. Results suggest that reasonable sill thicknesses [Formula: see text] and bubble contents (10–50 volume %) can explain the large decrease in residual gravity prior to eruption. Following the eruption (2006 and 2007), the deformation and gravity patterns suggest re-equilibration of the pressure regime in the shallow magma system via a renewed influx of relatively gas-poor magma into the shallow parts of the system.