长白山天池火山千年大喷发空降碎屑物的数值模拟   总被引：4，自引：1，他引：4  

于红梅  许建东  赵谊 《地震地质》2007,29(3):522-534

文中以Suzuki火山灰扩散数学模型为基础,考虑了空气参数随海拔高度的变化和不同大小的颗粒由于内含气泡数量的不同而造成的密度不同,计算了不同尺寸颗粒的最终沉降速度和沉降时间。并对喷发柱扩散概率浓度的计算公式进行了修正,对长白山天池火山千年大喷发空降碎屑物的空间分布进行了数值模拟。模拟时根据风速随高度的变化应用3个模型:1)固定风速30m/s;2)风速从地球表面线性增加到对流层顶部,在平流层的速度为对流层顶部风速的0.75倍(又称MW1模型);3)风速在对流层与MW1相同,但是从对流层顶部到20km高处风速线性减小,20km高度以上的风速为对流层顶部的10%(又称MW2模型)。通过与前人的结果进行比较,说明了模型的合理性,最后分析了模拟结果与前人结果之间存在差异的原因  相似文献   

Individual glass shard trace element analyses confirm that all known Toba tephra reported from India is from the c. 75‐ka Youngest Toba eruption          下载免费PDF全文

NICHOLAS J. G. PEARCE  JOHN A. WESTGATE  EMMA GATTI  JINNAPPA N. PATTAN  GOPAL PARTHIBAN  HEMA ACHYUTHAN 《第四纪科学杂志》2014,29(8):729-734

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Tephrochronology of recent events in the Andean Range (northern Patagonia): spatial distribution and provenance of lacustrine ash layers in the Nahuel Huapi National Park     

Romina Daga  Sergio Ribeiro Guevara  M. Lidia Sánchez  María Arribére 《第四纪科学杂志》2010,25(7):1113-1123

Tephrochronology is a powerful tool for dating sedimentary sequences, especially in Patagonia, where a large number of active volcanoes have produced frequent historical eruptions. Short lacustrine sedimentary sequences were extracted from the lakes Moreno Oeste and Ton?ek (Nahuel Huapi National Park). Seventeen volcanic ash layers were identified in both cores, ²¹⁰Pb and ¹³⁷Cs were used for dating techniques, and historical volcanic records were employed for correlation. White pumice and glass shards from the tephras were characterised by measuring major and trace element contents by instrumental neutron activation analysis. Two volcanic sources – the Cordón Caulle and the Calbuco volcanoes – were recognised as the prevailing systems that impacted the area in the past 800–1000 a. The Calbuco volcano was mainly responsible for the nine tephras identified in the Lake Ton?ek sequence. Four of these nine tephras also contained material from the Cordón Caulle complex, and could be interpreted as composite tephras or possible reworked ones. The Calbuco volcano showed predominant influences in the Lake Moreno Oeste sequence. Six of the eight tephras identified in such a sequence were from the Calbuco volcano, and three of these six contained material from the Cordón Caulle complex. The other two were from the Cordón Caulle complex, with contributions from the Calbuco volcano in one of them. These findings show that the high frequency of volcanic events in the study region demands an accurate characterisation of the products generated by each source, as well as an evaluation of their spatial distribution, to obtain a consistent framework for dating recent environmental changes. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Proximal–distal fall deposit correlation of VEI-5 tephra (Towada-Chuseri) from Towada volcano,northeast Japan     

Daisuke Ishimura  Reona Hiramine 《第四纪科学杂志》2020,35(1-2):334-348

A tephra layer offers an isochronous surface in sediments, thus serving as a key bed and/or an age marker. Recent high-resolution sediment research (e.g. varved sediments) has revealed optically invisible tephra fingerprints and provided high-precision tephra ages. However, a tephra-based correlation cannot succeed without detailed knowledge of the tephra characteristics in a proximal area to correlate with tephra in high-resolution sediments in remote areas. Here we documented the detailed characteristics of Towada-Chuseri (To-Cu) tephra, which is associated with the Middle Holocene volcanic explosivity index 5 eruption of Towada volcano, northeast Japan. We used To-Cu tephra samples to achieve the proximal–distal correlation of three members: Chuseri pumice (Cu), Kanegasawa pumice (Kn) and Utarube ash (Ut). These distal occurrences correlate with proximal To-Cu tephra based on volcanic glass morphology and refractive index, as well as on major element composition of volcanic glass shards. Refractive indices allow the preliminary correlation of each member, and major element composition helps in distinguishing Ut from the other members. Glass morphology provides additional support. These correlations reveal that To-Cu, especially Cu, covered central to northeast Japan while confirming that To-Cu is the representative tephra in the Middle Holocene of the Tohoku region.  相似文献   

Machine learning classifiers for attributing tephra to source volcanoes: an evaluation of methods for Alaska tephras     

Matthew S. M. Bolton  Britta J. L. Jensen  Kristi Wallace  Nore Praet  David Fortin  Darrell Kaufman  Marc De Batist 《第四纪科学杂志》2020,35(1-2):81-92

Glass composition-based correlations of volcanic ash (tephra) traditionally rely on extensive manual plotting. Many previous statistical methods for testing correlations are limited by using geochemical means, masking diagnostic variability. We suggest that machine learning classifiers can expedite correlation, quickly narrowing the list of likely candidates using well-trained models. Eruptives from Alaska's Aleutian Arc-Alaska Peninsula and Wrangell volcanic field were used as a test environment for 11 supervised classification algorithms, trained on nearly 2000 electron probe microanalysis measurements of glass major oxides, representing 10 volcanic sources. Artificial neural networks and random forests were consistently among the top-performing learners (accuracy and kappa > 0.96). Their combination as an average ensemble effectively improves their performance. Using this combined model on tephras from Eklutna Lake, south-central Alaska, showed that predictions match traditional methods and can speed correlation. Although classifiers are useful tools, they should aid expert analysis, not replace it. The Eklutna Lake tephras are mostly from Redoubt Volcano. Besides tephras from known Holocene-active sources, Holocene tephra geochemically consistent with Pleistocene Emmons Lake Volcanic Center (Dawson tephra), but from a yet unknown source, is evident. These tephras are mostly anchored by a highly resolved varved chronology and represent new important regional stratigraphic markers.  相似文献   

Feldspar composition as an efficient tool for tephra identification: a case study from Holocene and Lateglacial lacustrine sequences (Jura,France)          下载免费PDF全文

GWÉNOLÉ JOUANNIC  ANNE‐VÉRONIQUE WALTER‐SIMONNET  GILLES BOSSUET  CAROLE BEGEOT  ANNE‐LISE DEVELLE 《第四纪科学杂志》2015,30(6):569-583

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鄂霍次克海东南部OS03-1岩心重矿物分布特征及物质来源     

王昆山  石学法  吴永华  邹建军  姜晓黎 《海洋学报》2014,36(5):177-185

对鄂霍次克海东南部科学院隆起区OS03-1岩心碎屑重矿物及火山灰层进行了详细分析。岩心重矿物以紫苏辉石、绿帘石和普通角闪石为主,特征矿物为钛磁铁矿和普通辉石,矿物特征表明本岩心的物质主要来源于冰筏搬运(陆源)和火山喷发。陆源物质大部分来源于鄂霍次克海西部和北部地区,少量来自堪察加半岛冰川携带沉积物;火山物质则来源于堪察加半岛和千岛群岛的火山喷发产物。在岩心中识别出3个火山灰层,各种证据表明火山灰层1与已知的K2火山灰层相同,形成年代为26ka BP;火山灰层3具有明显火山物质与陆源物质混合特征,而火山灰层2则只能通过碎屑矿物的含量特征来判定,外在颜色不明显,已经明显的被陆源物质所稀释。研究表明,碎屑矿物组分参数可以有效地指示物质来源,也是识别火山灰层存在(特别是被陆源物质稀释)的可靠指标。  相似文献   

New Holocene tephras and a proxy climate record from a blanket mire in northern Skye,Scotland     

P. G. Langdon  K. E. Barber 《第四纪科学杂志》2001,16(8):753-759

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Holocene vegetation and volcanic activity,Auckland Isthmus,New Zealand     

Rewi M. Newnham  David J. Lowe 《第四纪科学杂志》1991,6(3):177-193

A 12 000 to 4000 yr BP pollen and tephra-bearing profile from Auckland, New Zealand, provides insights into the vegetation history and evidence for early Holocene volcanic activity in this area centred on the Mount Wellington basaltic volcano. Possibly 500 yr separated initial scoriaceous ash deposition (ca. 9500 yr ago) and subsequent major lava flows (ca. 9000 yr ago) from Mount Wellington. The local vegelation, topography, and drainage patterns were substantially modified during this time, and damming by the lava flows resulted in the formation of Lake Waiatarua in a shallow valley head ca. 9000 yr ago. Diatom evidence indicates that this lake was initially deep (> 5 m) but was shallowing around 4000 yr ago. In contrast to the Mount Wellington eruptions, tephra deposition resulting from distant rhyolitic volcanic activity of the central North Island and Mayor Island has had little effect on the Auckland vegetation during this time interval (12 000–4000 yr ago). Between ca. 12 000 and 10 000 yr ago, conifer-angiosperm forest was the predominant vegetation cover on Auckland Isthmus, but during the early Holocene, forest dominated by Metrosideros expanded, probably on to fresh volcanic surfaces resulting from the Mount Wellington eruptions. At this time, swamp forest communities developed in Waiatarua valley basin, and included species indicative of moist, mild, relatively frost-free climates. Some taxa show histories consistent with other records from the northern New Zealand region, including the rise of Ascarina lucida ca. 11 000 to 9000 yr ago, and its subsequent decline, and the expansion of Agathis australis (kauri) forest communities from ca. 6000 yr ago. Taken together the history of local and regional vegetation points to a mild, moist and weakly seasonal early Holocene climate, which subsequently became drier with greater seasonal temperature extremes.  相似文献   

Depositional process of the Byk-E tephra bed in the Chiba section,central Japan: A marker bed defining the Global Boundary Stratotype Section and Point for the Chibanian Stage     

Yasufumi Satoguchi  Yoshihiro Takeshita  Hiroomi Nakazato  Yusuke Suganuma 《Island Arc》2021,30(1):e12432

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