scholarly journals Tephra fallout from the long-lasting Tungurahua eruptive cycle (1999-2014): Variations through eruptive style transition and deposition processes

2017 ◽  
Vol 45 (1) ◽  
pp. 47 ◽  
Author(s):  
Jorge Eduardo Bustillos A. ◽  
Jorge Eduardo Romero ◽  
Alicia Guevara C. ◽  
Juan Díaz-Alvarado
Keyword(s):  
Grain Size ◽  
Grain Size Analysis ◽  
Size Analysis ◽  
Density Currents ◽  
Tephra Fall ◽  
X Ray ◽  
Eruptive Cycle ◽  
Grain Size Distributions ◽  
Deposition Processes ◽  
Glass Shards

The Tungurahua volcano (Northern Andean Volcanic Zone) has been erupting since 1999, with at least four eruptive phases up to present. Although a dozen of research focuses in tephra fall deposits during this period, none of them cover the full eruptive cycle. We investigated the eruptive mechanisms and tephra fall deposition processes at Tungurahua between 1999 and 2014, through systematic analyses of tephra samples collected westward of the volcano using mechanical sieving grain size analysis, lithology, scanning electron microscopy, X-Ray fluorescence and X-Ray diffraction. Tephra is compounded by varying amounts of scoria (black and brown), lithics, hydrothermally altered fragments, pumice, glass shards and free crystals. Textural analyses of juvenile grains (scoria, pumice and glass shards) revealed a diversity of features concerning to their vesicularity, shape and surface/perimeter. Initially, tephra was characterized by hydrothermally altered fragments related to a phreatic phase which then evolved to a pure magmatic activity with Strombolian eruptions. A homogeneous andesitic composition was observed between 1999 and 2003; however silicarich compositions occurred later in 2006. Similarly, the mineral assemblage contained plagioclase, pyroxene and olivine, but magnetite and akermanite were then included during 2006, thus indicating the eruption of a new, probably mixed magma. As consequence, Plinian activity occurred in August 2006. Further activity in 2007 ejected notable amounts (40-65%) of recycled material during Vulcanian eruptions. New eruptions occurred between 2008 and 2010, and juvenile ash revealed the interplay between brittle and ductile fragmentation through ash explosions, jetting events and Strombolian activity. The activity between 2010 and 2012 incorporated hydrothermally altered material at time that eruptive silences became longer and frequent, thus suggesting the development of a sporadic hydrothermal system. Finally, between 2013 and 2014 a series of Vulcanian events occurred. Observed grain size distributions allow us to propose three different processes occurring during tephra deposition: 1) deposition of multiple ash plumes, 2) contributions from elutriated pyroclastic density currents or grain size mixing due to major eruptions, and 3) the aggregation of particles due to rain and/or lighting. From mineralogy and grain size we infer that exposition to ash may produce acute human health effects.

scholarly journals A Comparison of Grain Size Measurements in Al-Cu Thin Films: Imaging Vs. Diffraction Techniques

2002 ◽  
Vol 10 (6) ◽  
pp. 5-9 ◽  
Author(s):  
L.M. Gignac ◽  
C.E. Murray ◽  
K.P. Rodbell ◽  
M. Gribelyuk
Keyword(s):  
Grain Size ◽  
Measurement Techniques ◽  
Measurement Range ◽  
Grain Size Analysis ◽  
Size Analysis ◽  
Analysis Methodology ◽  
Grain Structures ◽  
Grain Size Distributions ◽  
Major Factors ◽  
Microscopy Techniques

Numerous microscopy techniques, based on both imaging and diffraction, exist for the measurement of grain size distributions in polycrystalline thin-film samples. The accuracy of each technique is affected by three major factors: the effective resolution of the instrument relative to the characteristic grain size, the detection of the grain size through the thickness of the film, and the recognition of boundaries between adjacent grains during post-processing. When the instrument resolution is primarily considered, the measurement technique has a practical grain size measurement range, see Fig. 1 for a comparison of ranges for several measurement techniques. In bulk metallurgy grain size analysis, methodology has been developed to represent 3-dimensionai grain structures from measurements taken on 2-dimensional images.

scholarly journals GRAINet: mapping grain size distributions in river beds from UAV images with convolutional neural networks

2021 ◽  
Vol 25 (5) ◽  
pp. 2567-2597
Author(s):  
Nico Lang ◽  
Andrea Irniger ◽  
Agnieszka Rozniak ◽  
Roni Hunziker ◽  
Jan Dirk Wegner ◽  
...  
Keyword(s):  
Grain Size ◽  
Training Data ◽  
Grain Size Analysis ◽  
Training Dataset ◽  
Size Analysis ◽  
Size Distributions ◽  
Mean Diameter ◽  
Grain Size Distributions ◽  
Gravel Bars ◽  
Uav Images

Abstract. Grain size analysis is the key to understand the sediment dynamics of river systems. We propose GRAINet, a data-driven approach to analyze grain size distributions of entire gravel bars based on georeferenced UAV images. A convolutional neural network is trained to regress grain size distributions as well as the characteristic mean diameter from raw images. GRAINet allows for the holistic analysis of entire gravel bars, resulting in (i) high-resolution estimates and maps of the spatial grain size distribution at large scale and (ii) robust grading curves for entire gravel bars. To collect an extensive training dataset of 1491 samples, we introduce digital line sampling as a new annotation strategy. Our evaluation on 25 gravel bars along six different rivers in Switzerland yields high accuracy: the resulting maps of mean diameters have a mean absolute error (MAE) of 1.1 cm, with no bias. Robust grading curves for entire gravel bars can be extracted if representative training data are available. At the gravel bar level the MAE of the predicted mean diameter is even reduced to 0.3 cm, for bars with mean diameters ranging from 1.3 to 29.3 cm. Extensive experiments were carried out to study the quality of the digital line samples, the generalization capability of GRAINet to new locations, the model performance with respect to human labeling noise, the limitations of the current model, and the potential of GRAINet to analyze images with low resolutions.

scholarly journals Influence of α-Bi2O3 chemical prehistory on the morphology of the obtaining basic bismuth succinate

2021 ◽  
Vol 340 ◽  
pp. 01020
Author(s):  
Liubov Afonina ◽  
Evgeniya Timakova
Keyword(s):  
Electron Microscopy ◽  
Particle Size ◽  
Grain Size ◽  
Grain Size Analysis ◽  
Size Analysis ◽  
Medical Applications ◽  
Antibacterial Drug ◽  
Chemical Analyses ◽  
Monoclinic Modification ◽  
X Ray

The antibacterial drug, basic bismuth succinate of the composition Ñ2Í4(ÑÎÎBiO)2 is shown to obtain expediently by the interaction of bismuth oxide α-Bi2O3 with a succinic acid solution. Using the method of electron microscopy the influence of the chemical prehistory of obtaining the precursor, monoclinic modification of α-Bi2O3, on the morphological features of basic bismuth succinate synthesized from it has been investigated. The composition of Ñ2Í4(ÑÎÎBiO)2 was confirmed by the data of X-ray phase and chemical analyses. Based on the data of grain size analysis, the particle size of the obtained samples of basic bismuth succinate was estimated and the conditions for the synthesis of fine-crystalline C2H4(COOBiO)2, which is necessary for medical applications, were selected.

scholarly journals Investigation of Particle Size Distribution for Fine-Grained Soil Using a Grain Size Analysis Equipment Automated by X-ray Method

2000 ◽  
Vol 40 (2) ◽  
pp. 127-133
Author(s):  
Yukio Furukawa ◽  
Tatsushi Fujita ◽  
Tadayuki Kunihiro ◽  
Hisashi Tsuchiya ◽  
Yukio Saito
Keyword(s):  
Particle Size ◽  
Grain Size ◽  
Particle Size Distribution ◽  
Size Distribution ◽  
Grain Size Analysis ◽  
Size Analysis ◽  
Ray Method ◽  
X Ray ◽  
Fine Grained ◽  
Fine Grained Soil

High-resolution records of grain-size and depositional environment correlated to the Homo erectus Nariokotome Boy site, West Turkana, Kenya

2021 ◽  
Author(s):  
Conner O'Reilly ◽  
Catherine C. Beck ◽  
Jeroen H. van der Lubbe ◽  
Craig S. Feibel ◽  
Bruce Wegter ◽  
...  
Keyword(s):  
Grain Size ◽  
High Resolution ◽  
Homo Erectus ◽  
Eastern Africa ◽  
Coarse Grained ◽  
Grain Size Analysis ◽  
Size Analysis ◽  
Sedimentary Sequences ◽  
Grain Size Distributions ◽  
Material Grain Size

<p>The Turkana Basin in northern Kenya contains a robust record of hominin fossils, including Nariokotome Boy (discovered from the NK3 site), the most complete H. erectus specimen found to date. Understanding the paleoenvironmental context in which hominins such as H. erectus evolved has been an objective of decades of research in eastern Africa. Here, we present a study using grain size analyses to infer the paleoenvironmental conditions responsible for the deposition of the sedimentary sequences directly associated with NK3. We resampled a ~14 m interval at from the West Turkana Kaitio (WTK13) core, collected as part of the Hominin Sites and Paleolakes Drilling Project. This interval ties directly to the outcrop where Nariokotome Boy was recovered. By sampling continuously at 0.5 cm intervals (~7 yrs/sample), we document the paleoenvironment in ultra high-resolution (i.e. a scale relevant to a hominin life) that directly correlates to the NK3 site. Over 350 sediment samples were pre-treated to remove carbonate, biogenic silica, and other organic material from detrital material. Grain size distributions were measured on a Malvern Mastersizer 3000 using wet suspension. Based on these analyses, the interval was dominated by silt, which was further investigated using end-member modeling. A four end-member solution explained on average 99% of the population variability. The bottom of the interval was more coarse-grained, with an abrupt fining transition at 38.83 meter below surface (mbsf), which corresponds with the transition out of a tuffaceous interval (Natoo tuff) and into a pedogenically modified interval. This correlation is significant as the top of this tuff is the surface upon which Nariokotome Boy was recovered. Previous facies and grain size analyses revealed and quantified Turkana’s dynamic lake level history. However, our grain size analysis provides unprecedented resolution for the paleoenvironment during which Nariokotome Boy lived. Our 0.5 cm sampling resolution enables us to quantify depositional changes on a scale comparable with previous descriptive facies analyses and to refine transitions between paleosols, fluvial deposits, and lacustrine deposition at the interface of these three paleoenvironments enabling us to reconstruct a dynamic lakeshore environment during the lifetime of the Nariokotome Boy.</p>

Stratigraphic effects of tubificids in freshwater sediments: a kinetic study based on X-ray images and grain-size analysis

2006 ◽  
Vol 30 (2) ◽  
pp. 228-237 ◽  
Author(s):  
Aurélie Ciutat ◽  
Olivier Weber ◽  
Magali Gérino ◽  
Alain Boudou
Keyword(s):  
Grain Size ◽  
Kinetic Study ◽  
Grain Size Analysis ◽  
Size Analysis ◽  
Freshwater Sediments ◽  
X Ray

Soil Particle Size Analysis Using X-Ray Absorption

1996 ◽  
Vol 1548 (1) ◽  
pp. 51-59 ◽  
Author(s):  
Stanley J. Vitton ◽  
Carl C. Nesbitt ◽  
Leon Y. Sadler
Keyword(s):  
Particle Size ◽  
Grain Size ◽  
Size Range ◽  
Particle Size Analysis ◽  
Size Analysis ◽  
Size Distributions ◽  
X Ray ◽  
Grain Size Distributions ◽  
X Ray Absorption ◽  
Representative Samples

The hydrometer method is the standard method of grain size analysis used in geotechnical engineering. Although the hydrometer method provides accurate grain size distributions and is relatively easy to conduct, it takes a minimum of 2 days to complete and is subject to operator error. In studies where small-magnitude changes or more rapid results are required, an alternative method to hydrometer testing is to use an automated particle size analysis instrument employing X-ray absorption. This technique passes a finely collated X-ray beam through a suspension of settling particle in a fluid. Because the intensity of the X-ray is directly related to the percentage mass of soil in a suspension, Stokes' law can be used to calculate the grain size distribution of a soil assuming an equivalent particle diameter for the soil grains. X-ray absorption has been found to produce accurate grain size distributions in the 75 μm to 1 μm size range when sample preparation adheres to AASHTO T88-90 specifications and suspension concentrations are approximately 2 percent by volume. Testing for particles sizes down to 1 μm takes approximately 20 min per sample. Technical concerns remaining involve obtaining representative samples of the soil in the 75 μm, to 1 μm size range suspension for testing. One method being evaluated is injection flow analysis, which is an inexpensive method of obtaining representative samples used with a variety of inorganic, industrial, and environmental materials in which direct sampling of fluid is required.

scholarly journals Grain-Size Distribution and Structural Characteristics of Varved Sediments from Lake Żabińskie (Northeastern Poland)

Quaternary ◽  
2019 ◽  
Vol 2 (1) ◽  
pp. 8 ◽  
Author(s):  
Maurycy Żarczyński ◽  
Jacek Szmańda ◽  
Wojciech Tylmann
Keyword(s):  
Particle Size ◽  
Grain Size ◽  
Layer Thickness ◽  
Grain Size Analysis ◽  
Size Analysis ◽  
Size Distributions ◽  
Particle Size Distributions ◽  
Grain Size Distributions ◽  
Northeastern Poland ◽  
Size Data

Typically, the description of varve microfacies is based on microscopic sedimentary structures, while standard grain-size analysis is commonly applied with lower resolution. Studies involving a direct comparison of varve microfacies and particle-size distributions, common for clastic environments, are scarce for biogenic varves. In this study, we analyzed nine-year resolution grain-size data from Lake Żabińskie (northeastern Poland) to detect differences between varve microfacies. Six varve microfacies were differentiated using grain-size distributions and sedimentological attributes (calcite layer thickness, dark layer thickness, mass accumulation rate). However, changes in particle-size distributions between different varve types are relatively small and indicate a similar source for the material deposited. Decomposition of grain-size distributions with the end-member approach allows recognition of relative changes for the deposition of allochthonous (mineral) and autochthonous (carbonates, (hydr)oxides) components. Grain-size data suggest that sources of allochthonous material remained constant, while varve formation was controlled mostly by in-lake processes.

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