An automatic procedure to forecast tephra fallout     

A. Folch  C. Cavazzoni  A. Costa  G. Macedonio 《Journal of Volcanology and Geothermal Research》2008

Tephra fallout constitutes a serious threat to communities around active volcanoes. Reliable short-term forecasts represent a valuable aid for scientists and civil authorities to mitigate the effects of fallout on the surrounding areas during an episode of crisis. We present a platform-independent automatic procedure with the aim to daily forecast transport and deposition of volcanic particles. The procedure builds on a series of programs and interfaces that automate the data flow and the execution and subsequent postprocess of fallout models. Firstly, the procedure downloads regional meteorological forecasts for the area and time interval of interest, filters and converts data from its native format, and runs the CALMET diagnostic model to obtain the wind field and other micro-meteorological variables on a finer local-scale 3-D grid defined by the user. Secondly, it assesses the distribution of mass along the eruptive column, commonly by means of the radial averaged buoyant plume equations depending on the prognostic wind field and on the conditions at the vent (granulometry, mass eruption rate, etc). All these data serve as input for the fallout models. The initial version of the procedure includes only two Eulerian models, HAZMAP and FALL3D, the latter available as serial and parallel implementations. However, the procedure is designed to incorporate easily other models in a near future with minor modifications on the model source code. The last step is to postprocess the outcomes of models to obtain maps written in standard file formats. These maps contain plots of relevant quantities such as predicted ground load, expected deposit thickness and, for the case of or 3-D models, concentration on air or flight safety concentration thresholds.  相似文献   

土壤颗粒组成影响137Cs含量的初步实验结果   总被引：15，自引：6，他引：9  

严平  高尚玉  董光荣 《中国沙漠》2002,22(2):150-153

放射性核素¹³⁷Cs作为人类核试验的产物,以其独特的理化性质而成为研究土壤侵蚀和泥沙沉积一种良好的示踪源。在¹³⁷Cs的再分配过程中,土壤颗粒组成是影响土壤¹³⁷Cs的重要因子。一般认为,土壤中的¹³⁷Cs活度主要与粘粘含量有关,但这要取决于原生沉积物的颗粒组成。通过选取共和盆地主要的三种土壤类型,采集0~30cm的混合样品,进行入工筛分,测定不同粒径成分的¹³⁷Cs含量。初步实验表明,砂质土的¹³⁷Cs活度与平均粒径之间呈负指数关系,0.01~0.1mm组分对¹³⁷Cs含量的影响最为显著;壤质土的¹³⁷Cs活度主要与粗粉砂(0.01~0.05mm)含量有关,与137Cs活度主要与原生沉积物的颗粒特性和粒度有关.¹³⁷Cs一旦被原生沉积物颗粒吸附,在以后的土壤颗粒再分配过程中,是很难被置换掉的。  相似文献   

Statistically coherent approach involving log-ratio transformation of geochemical data enabled tephra correlations of two late Pleistocene tephra from the eastern Adriatic shelf     

《Quaternary Geochronology》2023

Tephrostratigraphic correlations commonly rely on geochemical composition supported by additional constraints (e.g., multiple stratigraphically ordered tephra, geochronological-stratigraphical constraints, and isotopic determinations), which provide key clues to restrict the number of possible candidates and disambiguate the correlation of a specific tephra among compositionally similar volcanic sources/tephra. However, such additional data may not be available or acquirable, leaving the geochemical data as sole, but challenging viable approach. In this study, two geochronologically poorly constrained late Pleistocene tephra from the eastern Adriatic –from a sand profile on Mljet Island (M-53/2) and from a marine sediment core from Pirovac Bay (PROS 721)– were correlated to known eruptions using only geochemical data (major and trace elements of glass shards), which were treated using both log ratio transformed and raw data. After the statistical treatment of the geochemical data using bivariate plots, linear discrimination analyses and selbal algorithm, the tephra M-53/2 and PROS 721 were suitably correlated with the widespread tephra generated during the Campi Flegrei eruptions of Massereia del Monte (Y-3 marine tephra, 29.0 ± 0.8 ka) and Neapolitan Yellow Tuff (14.5 ± 0.4 ka), respectively. This study showed that the correlation was hardly tenable when using the raw data, as opposed to compositional approach, which yielded satisfactory results. As a consequence, the distribution of Massereia del Monte/Y-3 tephra extended far toward the northeast, while a better chronological model, for reconstructing the paleoenvironmental changes at the Pirovac Bay location and the Holocene sea-level dynamics, could be obtained.  相似文献   

Using tephrostratigraphy and cryptotephrostratigraphy to re-evaluate and improve the Middle Pleistocene age model for marine sequences in northeast Japan (Chikyu C9001C)     

《Quaternary Geochronology》2017

We refine the tephrostratigraphy and cryptotephrostratigraphy of the Middle Pleistocene deep-sea sediments in the C9001C cores and reconstruct the age model of the cores to provide a standard stratigraphy for the NW Pacific Ocean area. In the lower half of the cores (corresponding to marine isotopic stages [MISs] 9–18), we newly identify nine concentrations (spikes) of glass shards (numbered G17–G25 from top to bottom) below sixteen previously reported spikes (numbered G1–G16) in the upper half of the cores (MISs 1–9). We correlated two spikes (both cryptotephras) with known widespread tephras: G18 with Naruohama-IV (MIS 10d; 357 ka) and G19 with Kasamori 5 (MIS 12b–c; 434–458 ka). Although the two cryptotephra spikes cannot be distinguished by the major- and trace-element compositions of glass shards, these correlations are based upon their stratigraphic occurrence within separate glacial periods (MISs 10 and 12) as indicated by the δ¹⁸O stratigraphy of the C9001C sequence. Based on the stratigraphic positions of the Naruohama-IV and Kasamori 5 tephras, we assign the sediment units corresponding to MISs 10, 11, and 12, and revise the previous assignment of core segments corresponding to MISs 7, 8, and 9. The resulting tephra-based age model is consistent with the last occurrence of Proboscia curvirostris, but it is inconsistent with the first occurrence of Emiliania huxleyi. According to the new age model, the sedimentation rate during MISs 18–2 has ranged from 0.21 m/ky (during MIS 17) to 0.74 m/ky (during MISs 8 and 9), however, the sedimentation rate was never as high as the rate of 1.1 m/ky indicated by an earlier age model.  相似文献   

Compositions of glass in proximal tephras from eruptions in the Azores archipelago and their links with distal sites in Ireland     

《Quaternary Geochronology》2017

The Azores archipelago is one of the most active volcanic areas in the North Atlantic region, with approximately 30 eruptions during the last 600 years. The geochemical composition of associated tephra-derived glass is, however, not well characterized. This study presents major element compositions of glass shards from five major eruptives on the Azores: a trachybasaltic eruptive on the island of Faial (Capelinhos AD, 1957) and four explosive trachytic eruptives on the island of São Miguel (Fogo A c. 5600 cal yrs. BP, Sete Cidades c. AD 1440, Fogo AD 1563 and Furnas AD 1630). The major element compositions suggest that tephras from three active stratovolcanoes on São Miguel, Sete Cidades, Fogo and Furnas, can be distinguished from one another using bi-plots of FeO_tot vs. TiO₂ and FeO_tot vs. CaO. Late Holocene tephras found on Ireland have previously been attributed to eruptions occurring on Jan Mayen but possess a strong geochemical similarity to proximal tephras from the Azores, especially those from the Furnas volcano. The similarity of the proximal tephras on São Miguel, especially Furnas AD 1563 and Furnas AD 1630 and distal tephras in Ireland is demonstrated by strong similarity coefficients (>0.95) and the closeness of major element composition. The dominant wind direction over the Azores is favourable for tephra dispersal to western Europe and we suggest that at least three tephras found in Ireland were erupted from the Furnas volcano, and that trachytic tephras erupted from explosive eruptions on São Miguel have a potential to contribute to the construction of a European-wide tephrostratigraphic framework.  相似文献   

Deglaciation and volcano-seismic activity in Northern Iceland: Holocene and early Eemian     

《Geodinamica Acta》2013,26(1):81-100

The North Volcanic Zone of Iceland was unglaciated during most interglacials. Subsequently, the region was covered by the Weichselian ice cap. A widespread interglacial complex, the Sy?ra Formation, has been mapped in this zone. It covers probably O.I.S.5e, 5d and 5c. Its formation and preservation are discussed in terms of rift and volcanism activity, in interrelations with the former deglaciation. A topographic bulge, presumed of glacio-isostatic origin, limited the downstream drainage of the Jökulsa a Fjolum river enabling the interglacial sedimentation and the excavation of one of the canyons of Dettifoss. Effusive volcanic activity in the rift is important prior to the Sy?ra 4 unit in association with an early abrupt event (SY2: Sy?ra ash), related to a phreato-magmatic eruption at the eastern hyaloclastite ridge or from the Askja volcano and to jökulhlaup events. It corresponds probably to ash Zone B as defined by Sejrup et al., (1989) on the Northern Iceland shelf. The previous activity of hyaloclastite ridge is recorded during the Marine Isotope Stage 6 (MIS 6 = Saalian) and its deglaciation, a younger effusive event is dated at 80 ka. The Interglacial paleo-seismic region is similar to the present one; during deglaciation, the seismic zone is widened, up to 60 km to the East. Continuous micro-seismicity related to dyke intrusion and effusive or phreato-magmatic eruptions develop at the onset of deglaciation. It is discrete during the full interglacials, and most intense during pyroclastic eruptions. A comparison with the Late Glacial/Holocene deglaciation is provided in the same region.  相似文献   

The effects of fire and tephra deposition on forest vegetation in the Central Cascades, Oregon     

Colin J. Long  Mitchell J. Power 《Quaternary Research》2011,75(1):151-158

High-resolution charcoal and pollen analyses were used to reconstruct a 12,000-yr-long fire and vegetation history of the Tumalo Lake watershed and to examine the short-term effects that tephra deposition have on forest composition and fire regime. The record suggests that, from 12,000 to 9200 cal yr BP, the watershed was dominated by an open Pinus forest with Artemisia as a common understory species. Fire episodes occurred on average every 115 yr. Beginning around 9200 cal yr BP, and continuing to the present, Abies became more common while Artemisia declined, suggesting the development of a closed forest structure and a decrease in the frequency of fire episodes, occurring on average every 160 yr. High-resolution pollen analyses before and after the emplacement of three distinct tephra deposits in the watershed suggest that nonarboreal species were most affected by tephra events and that recovery of the vegetation community to previous conditions took between 40 and 100 yr. Changes in forest composition were not associated with tephra depositional events or changes in fire-episode frequency, implying that the regional climate is the more important control on long-term forest composition and structure of the vegetation in the Cascade Range.  相似文献   

火山灰年代学:原理与应用   总被引：1，自引：0，他引：1  

陈宣谕  徐义刚  Martin MENZIES 《岩石学报》2014,30(12):3491-3500

火山灰(2mm)等时标志层是火山灰年代学研究的基础。火山灰地层的直接或间接测年依赖于火山灰中存在合适的原生矿物(如:透长石、锆石、磷灰石)或外来物质(如:炭化木)。然而大多数火山灰沉积层,尤其是远源火山灰,其主要由岩浆源碎屑构成,开展测年显得十分困难。利用火山玻璃(岩浆)的地球化学,是一种被广泛应用的替代性方法。火山玻璃作为岩浆源物质普遍出现在各类近源、远源可见火山灰层和显微火山灰中,其主量、微量元素含量和特定的同位素组成能被电子、激光和离子探针技术准确测定。近源-远源玻璃化学成分的相互匹配,使得火山灰等时标志层得以在时间和空间上相互关联,构成有力的地层学工具,用以同步各类环境、考古和火山活动记录。近源火山沉积和远源火山灰层中的年龄信息得以实现交叉验证和整合。远源海洋、湖泊沉积中的相对年龄信息(氧同位素地层学,年纹层年代学)也为揭示火山活动、古环境变化和考古学事件的时间顺序提供了可能。火山灰年代学在地球科学中应用广泛,尤其是对于第四纪研究,其在同步各类记录从而评估火山活动、气候/环境变化和人类演化/迁移的因果关系中具有至关重要的作用。  相似文献   

当代火山喷发碎屑堆积物的研究进展及其主要类型   总被引：6，自引：0，他引：6  

刘祥 《世界地质》1996,15(1):1-6

火山喷发碎屑堆积物主要分为：火山喷发空中降落堆积物、火山碎屑、流状堆积物、火山泥流堆积物和火山基浪堆积物。简述了这些火山碎屑堆积物的成因及主要特征。  相似文献   

Identification of the Fugloyarbanki tephra in the NGRIP ice core: a key tie‐point for marine and ice‐core sequences during the last glacial period     

S. M. Davies  S. Wastegård  T. L. Rasmussen  A. Svensson  S. J. Johnsen  J. P. Steffensen  K. K. Andersen 《第四纪科学杂志》2008,23(5):409-414

A visible tephra horizon in the NGRIP ice core has been identified by geochemical analysis as the Fugloyarbanki Tephra, a widespread marker horizon in marine cores from the Faroe Islands area and the northern North Atlantic. An age of 26 740 ± 390 yr b2k (1σ uncertainty) is derived for this tephra according to the new Greenland Ice Core Chronology (GICC05) based on multi‐parameter counting of annual layers. Detection of this tephra for the first time within the NGRIP ice core provides a key tie‐point between marine and ice‐core records during the transition between MIS 3 and 2. Identification of this volcanic event within the Greenland records demonstrates the future potential of using tephrochronology to precisely correlate palaeoarchives in widely separated localities that span the last glacial period, as well as providing a potential method for examining the extent of the radiocarbon marine reservoir effect at this time. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献