Abrasion in pyroclastic flows     

A. Freundt  H. -U. Schmincke 《International Journal of Earth Sciences》1992,81(2):383-389

The relative size of glass rims coating crystals in the matrix ash provides a semi-quantitative measure of abrasion of ash grains in pyroclastic flows. Median abrasion indices (= area_crystal / area_{glass rim}) are 8.4 to 18.5 in Laacher See pyroclastic flow units but only 4 to 6.3 in assocciated fallout, showing stronger abrasion of ash particles in the pyroclastic flows. All pyroclasts undergo strong attrition in the vent but clasts in pyroclastic flows undergo a second major phase of abrasion during high-energy near-vent flow. Abrasion of ash particles is weaker during lower-energy higher-strength motion further downstream, suggesting that high contents of fine ash in distal deposits are due to diminishing elutriation rather than high rate of attrition.

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Zusammenfassung Die relative Größe von Glassäumen um Kristalle in der Matrix-Asche kann als semi-quantitatives Maß für den Abrieb von Aschepartikeln in pyroklastischen Strömen benutzt werden. Median-Werte des Abriebs-Index (= Fläche_kristall / Fläche_Glassaum) betragen 8,4 bis 18,5 in pyroklastischen Fließeinheiten am Laacher See. Abriebs-Indices stratigraphisch assoziierter Bims-Fallablagerungen liegen bei nur 4 bis 6,3; dies belegt einen höheren Abrieb von Aschepartikeln in den pyroklastischen Strömen. Alle Pyroklasten erfahren gemeinsam starken Abrieb im Schlot, aber Partikel in pyroklastischen Strömen durchlaufen eine zweite Phase starken Abriebs während des hochenergetischen Transports im schlotnahen Bereich. Bei niedriger-energetischem Fließen mit wachsender Bingham-Festigkeit weiter talabwärts wird der Partikelabrieb schwächer. Hohe Gehalte an feiner Asche in distalen Fließeinheiten sind also eher auf schwächer werdende Elutriierung als auf stärkeren Abrieb zurückzuführen.

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Résumé La dimension relative des enduits vitreux qui enrobent les cristaux dans les dépôts de cendres volcaniques peut être utilisée comme mesure semiquantitative de l'abrasion des particules dans les courants pyroclastiques. Au Laacher See les indices d'abrasion (surface du cristal/surface de l'enduit vitreux) sont de 8,4 à 18,5 dans les coulées pyroclastiques et seulement de 4 à 6,3 dans les sédiments formés par retombée, qui leur sont interstratifiés; les particules de cendre ont donc subi une abrasion plus forte dans les coulées. Tous les pyroclastes subissent une forte abrasion dans le cratère; mais dans les coulées pyroclastiques, ils subissent une deuxième action d'abrasion au cours de leur transport en milieu de haute énergie, à proximité du cratère. Dans les conditions de plus basse énergie qui régnent plus en aval, l'abrasion est moins forte; on en déduit que la forte teneur en fines dans les dépôts distaux résulte d'une diminution de l'élutriation plutôt que d'une forte action d'abrasion.

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Discharge experiments simulating chemical evolution on the surface of Titan     

Kristof Plankensteiner  Bernd M. Rode  Tomas Mikoviny  Armin Hansel  Georg Fischer  Helmut O. Rucker 《Icarus》2007,187(2):616-619

Saturn's moon Titan has been considered as one of the few places in our Solar System, where atmospheric and surface conditions could have produced organic compounds essential as precursors for an evolution of life. The Cassini-Huygens mission has provided new data on Titan's atmosphere and surface, which enabled us to simulate the chemical processes occurring under these conditions. Possible lightning events on Titan cannot only produce higher hydrocarbons, but also allow surface water ice to participate in the reaction scenario, resulting in CHO, CHN, and CHON compounds including several molecules relevant for the formation of amino acids and nucleic acids.  相似文献   

FORSAT: a 3D forest monitoring system for cover mapping and volumetric 3D change detection     

Efstratios Stylianidis  Daniela Poli  Martin Hofer  Armin Gruen  Victor Sanchez Martin 《International Journal of Digital Earth》2020,13(8):854-885

ABSTRACT

A 3D forest monitoring system, called FORSAT (a satellite very high resolution image processing platform for forest assessment), was developed for the extraction of 3D geometric forest information from very high resolution (VHR) satellite imagery and the automatic 3D change detection. FORSAT is composed of two complementary tasks: (1) the geometric and radiometric processing of satellite optical imagery and digital surface model (DSM) reconstruction by using a precise and robust image matching approach specially designed for VHR satellite imagery, (2) 3D surface comparison for change detection. It allows the users to import DSMs, align them using an advanced 3D surface matching approach and calculate the 3D differences and volume changes (together with precision values) between epochs. FORSAT is a single source and flexible forest information solution, allowing expert and non-expert remote sensing users to monitor forests in three and four (time) dimensions. The geometric resolution and thematic content of VHR optical imagery are sufficient for many forest information needs such as deforestation, clear-cut and fire severity mapping. The capacity and benefits of FORSAT, as a forest information system contributing to the sustainable forest management, have been tested and validated in case studies located in Austria, Switzerland and Spain.  相似文献   

A study to explain the emission of nitric oxide from a marsh soil   总被引：1，自引：0，他引：1  

Armin Remde  Jörg Ludwig  Franz X. Meixner  Ralf Conrad 《Journal of Atmospheric Chemistry》1993,17(3):249-275

In the period 18–21 September 1989, soil NO emission was studied at Halvergate Marshes, Norfolk (U.K.) within the framework of the BIATEX-LOVENOX joint field experiment. Using a dynamic chamber technique, 186 measurements at four plots were performed showing a net NO flux of 7.2–14.6×10^–12 kgN m^–2 s^–1. Soil samples from a soil profile (1.0 m) at a representative site and from the uppermost layer (0.1 m) of each of the four plots were sent to the laboratory for (a) detailed physical and chemical soil analysis, (b) determination of NO production rates, NO uptake rate constants, and NO compensation mixing ratios, and (c) characterization of the microbial processes involved. A diffusive model (Galbally and Johansson, 1989) was applied to the laboratory results to infer NO fluxes of the individual soil samples. When we compared these fluxes with those measured in the field, we found agreement within a factor 2–4. Furthermore, laboratory studies showed, that NO was produced and consumed only in the upper soil layer (0–0.1 m depth) and that the NO production and consumption activities observed in the Halvergate marsh soil were most probably due to the anaerobic metabolism of denitrifying bacteria operating in anaerobic microniches within the generally aerobic soil.  相似文献   

Different age response of zircon and monazite during the tectono-metamorphic evolution of a high grade paragneiss from the Ruhla Crystalline Complex,central Germany   总被引：5，自引：0，他引：5  

Armin?ZehEmail author  Ian?S.?Williams  Helene?Br?tz  Ian?L.?Millar 《Contributions to Mineralogy and Petrology》2003,145(6):691-706

Results of TIMS, SIMS and SEM analyses show that zircon and monazite in a high-grade paragneiss of the Ruhla Crystalline Complex, central Germany, were formed and/or altered during different stages of a tectono-metamorphic history between Early Devonian and Permian times. Detrital zircon cores of >460 Ma place an older limit on the age of anatexis, and show that the paragneiss sequence contains rocks at least as young as early Cambrian. Metamorphic zircon growth commenced at ~365 Ma, peaking at ~360–355 Ma at the same time that granite dykes were emplaced. In contrast, monazite in the paragneiss preserves little record of the metamorphic peak. Most monazite grains grew or were recrystallised in the Lower Carboniferous at ~339 Ma, contemporaneous with the emplacement of voluminous diorite and granite bodies. These intrusions and related tectonics caused some of the high-U zircon overgrowths to undergo moderate to severe Pb loss. A second Pb loss event, between 300 and 280 Ma, can be related to Late Carboniferous/Early Permian large-scale block faulting.Editorial responsibility: J. Hoefs  相似文献   

The formation of high-grade ignimbrites, I: Experiments on high- and low-concentration transport systems containing sticky particles     

Armin Freundt 《Bulletin of Volcanology》1998,59(6):414-435

 High-grade ignimbrites are thought to be deposited by pyroclastic flows at temperatures exceeding minimum welding temperature or even solidus temperature. Corresponding pyroclastic-flow particles range from plastic to partially liquid and are able to aggregate or coalesce. This contrasts with particles in pyroclastic flows producing unwelded ignimbrite, which are capable of elastic grain interactions. The low aspect ratio and great areal extent of high-grade ignimbrites requires transport in a particulate state either by (a) high-concentration mass flow facilitated by fluidizing gas reducing internal friction, or by (b) expanded turbulent flow of low but downward increasing concentration. This paper presents experiments designed to investigate the effects of plastic to liquid particles on these two contrasting transport mechanisms. Gas fluidization experiments using polyethyleneglycole (PEG) powders heated above minimum sintering (T_ms) and melting (T_m) temperatures cover a wide range of fluidization velocities (U_mf>U_a>0.6·U_t) but are always in the bubbly fluidization regime similar to fluidized ignimbrite ash, where particle volume concentration outside the bubbles is high (≈10^–1). When the powders reach a critical temperature T_m≥T≥T_ms, defluidization by catastrophic particle aggregation immediately commences in both stationary and laterally moving fluidized beds as well as in experiments using mixtures of high- and low-T_m (≥30 wt.%) PEG powders, when T≥T_ms of the lower-T_m powder. This indicates that extended particulate transport at T≥T_ms is not possible at such high particle concentrations. In the turbulent flow experiments, liquid sprays of molten PEG or water, vertically injected into a high-Re (>10⁴) horizontal air flow, form a low-concentration (10^–5 to 10^–4) turbulent suspension current. Proximal formation of partially coalesced aggregates, which settle faster than individual particles, causes the measured downstream decay of sedimentation rate to be steeper than predicted by theory of single solid-particle sedimentation from turbulent suspensions. As particles become finer downstream and coalescence efficiency decreases in response to cooling, more distally formed aggregates become too small and rare to modify sedimentation-rate decay from that of suspension flows containing solid particles. The key difference between the two transport systems is particle concentration, C. Since particle collision rate R_coll∝C², collision rates in fluidized beds are so high that all particles immediately aggregate when coalescence efficiency (1≥E_coal≥0) is larger than 10^-3. Low-concentration suspensions, on the other hand, require much higher values of E_coal for significant aggregation to occur. Dilute pyroclastic flows will have higher particle volume fractions (≈10^–3) than the experimental currents, but then viscous pyroclasts should have lower coalescence efficiencies than PEG droplets. Experimental results thus support an expanded turbulent transport mechanism of pyroclastic flows generating extensive high-grade ignimbrite sheets. Received: 28 August 1996 / Accepted: 3 December 1997  相似文献   

Book review     

Joseph C. Loon  Armin Gruen 《Journal of Geodesy》1984,58(4):XII-XV

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Assessing streams in Germany with benthic invertebrates: Development of a multimetric invertebrate based assessment system   总被引：3，自引：0，他引：3  

Jürgen Bhmer  Claudia Rawer-Jost  Armin Zenker  Carolin Meier  Christian K. Feld  Regina Biss  Daniel Hering 《Limnologica》2004,34(4):416-432

The main aim of the study was to develop a multimetric assessment system for macroinvertebrate communities of small and mid-sized streams in Germany in accordance with the Water Framework Directive of the European Union. The system should be applicable by water authorities, capable of distinguishing between different impacts, and specifically adapted to all types of small and mid-sized rivers in Germany. An assessment system has been developed consisting of two modules based on the established indices for saprobic degradation and acidity, and a third module covering general degradation. For the third module a new multimetric index (MMI) was developed and tested using preclassifications for stream hydromorphological degradation, land use and general impairment as impact measures. More information on sampling method, season and the type of dominating human impairment allowed to further analyse the index' capabilities and sensitivity. It performed well in all seasons and detected all types of impairment except acidity. The usefulness of the impact measures used in this study is discussed with regard to the development of a multimetric index. The comparison of the new index with other indices showed that it is especially sensitive in detecting macroinvertebrate community responses to hydromorphological degradation and pollution such as the German AQEM index, while IBI 12 and Renkonen's similarity more reflect general community shifts caused by any type of disturbance. The new assessment system will be proposed for future use by state agencies for nationwide monitoring in the context of the Water Framework Directive implementation.  相似文献   

Geochemical characteristics and Sr‐Nd‐Hf isotope compositions of Late Triassic post‐collisional A‐type granites in Sarudik,SW Sumatra,Indonesia     

Haikun Zhang  Peng Hu  Liang Cao  Armin Tampubolon  Asui Liu  Xiang Cheng  Mingguo Zhan  Luozhong Pan  Yu Dai  Beihong Pan 《Island Arc》2020,29(1)

Late Triassic A‐type granites are identified in this study in Sarudik, SW Sumatra. We present new data on zircon U–Pb geochronology, whole‐rock major and trace elements and Sr‐Nd‐Hf isotope geochemistry, aiming to study their petrogenesis and tectonic implications. LA‐ICP‐MS U–Pb dating of zircon separated from one biotite monzogranite sample yields a concordia age of 222.6 ±1.0 Ma, indicating a Late Triassic magmatic event. The studied granites are classified as weakly peralumious, high‐K calc‐alkaline granites. They exhibit high SiO₂, K₂O + Na₂O, FeO/(FeO + MgO) and Ga/Al ratios and low Al₂O₃, CaO, MgO, P₂O₅ and TiO₂ contents, with enrichment of Rb, Th and U and depletion of Ba, Sr, P and Eu, showing the features of A‐type granites. The granites have zircon ε_Hf(t) values from ?4.6 to ?0.4 and whole‐rock ε_Nd(t) values from ?5.51 to ?4.98, with Mesoproterozoic T_DM2 ages (1278–1544 Ma) for both Hf and Nd isotopes. Geochemical and isotopic data suggest that the source of these A‐type granites is the Mesoproterozoic continental crust, without significant incorporation of mantle‐derived component, and their formation is controlled by subsequent fractional crystallization. The Sarudik A‐type granites are further assigned to A2‐type formed in post‐collisional environment. Combined with previous knowledge on the western SE Asia tectonic evolution, we conclude that the formation of the Late Triassic A‐type granites is related to the post‐collisional extension induced by the crustal thickening, gravitational collapse, and asthenosphere upwelling following the collision between the Sibumasu and the East Malaya Block.  相似文献   

Grain crushing in geoscience materials-Key issues on crushing response,measurement and modeling:Review and preface     

Yang Xiao  Chandrakant SDesai  Ali Daouadji  Armin WStuedlein  Hanlong Liu  Hossam Abuel-Naga 《地学前缘(英文版)》2020,(2):363-374

Grain crushing is commonly encountered in deep foundation engineering,high rockfill dam engineering,railway engineering,mining engineering,coastal engineering,petroleum engineering,and other geoscience application.Grain crushing is affected by fundamental soil characteristics,such as their mineral strength,grain size and distribution,grain shape,density and specimen size,and also by external factors including stress magnitude and path,loading rate and duration,degree of saturation,temperature and geochemical environment.Crushable material becomes a series of different materials with the change in its grading during grain crushing,resulting in a decrease in strength and dilatancy and an increase in compressibility.Effects of grain crushing on strength,dilatancy,deformation and failure mechanisms have been extensively investigated through laboratory testing,discrete element method(DEM)modelling,Weibull statistics,and constitutive modelling within the framework of the extended crushing-dependent critical state theory or the energy-based theory.Eleven papers summarized in this review article for this special issue addressed the above issues in grain crushing through the advanced testing and modelling.  相似文献