张家口中生代火山盆地火山喷发对古气候的影响

本文在详细地研究了张家口中生代火山盆地火山喷发物的基础上,利用岩石学及大气环境化学的基本原理,提出了一套系统估算火山喷出气体及气溶胶总量的程序与方法,并对张家口中生代火山喷出气体的种类、总量及气溶胶总量进行了估算;分析了火山硫化物气体转化为火山硫酸盐气溶胶的光化学过程及可能途径。在分别研究了本区火山喷发导致的“阳伞效应”与“温室效应”的基础上,探讨了该区火山喷发对地表温度的综合影响。初步结果表明：张家口中生代火山盆地火山喷发向当时大气圈中输送了约９．９６×１０１０ｋｇ的硫酸盐气溶胶,它们能导致当时北半球范围内太阳总幅射率降低０．８１％～３．６０％,最终造成地表温度下降约０．８１℃～３．６℃。     

A new 40Ar/39Ar eruption age for the Mount Widderin volcano,Newer Volcanic Province,Australia, with implications for eruption frequency in the region

The Mount Widderin shield volcano is located near Skipton, western Victoria, in the Western Plains subprovince of the monogenetic Pliocene–Holocene Newer Volcanic Province (NVP). Radiometric ages for lavas in the Hamilton–Skipton–Derrinallum area are few, owing to limited suitable outcrop for K–Ar or ⁴⁰Ar/³⁹Ar geochronology studies. Existing age constraints for flows in this area have been inferred from Regolith Landform Units (RLUs), complemented by a small number of K–Ar studies on ≥1 Ma flows. Although the RLU approach provides a valuable overview of relative eruption ages across the NVP, it is of limited use in eruption frequency studies. Additional radio-isotopic ages are required to refine age ranges for individual RLUs, and to validate previous assignment of individual flows to specific RLUs. We report a new, high-precision ⁴⁰Ar/³⁹Ar age of 389 ± 8 ka (2σ) for a Mount Widderin basalt sample. Based on this age and geomorphic observations, we propose that both the Widderin and Elephant lava flows be reassigned from the Eccles RLU to the Rouse RLU. We use the 389 ± 8 ka (2σ) age for Widderin, along with published K–Ar ages, to anchor a stratigraphic sequence of 15 individual flows in the Hamilton–Skipton–Derrinallum area, demonstrating that intermittent volcanism has occurred in this area from ≥3 Ma to ≤0.389 Ma. Within the limits of available data for the NVP, this time span of volcanic activity is second only to that of the Melbourne area. We consider the significance of the Widderin eruption age, in conjunction with published age constraints for maars and scoria cones of the Western Plains subprovince, building on previous studies that have focused solely on lava flow ages. The inclusion of the additional data weakens the argument for a decrease in volcanic activity after ca 0.9 Ma as implied by published ages for lava flows only. Additional detailed combined geochronology–geomorphology studies of lavas, scoria cones and maars in strategically selected small areas are advocated to better understand eruption frequency across the NVP.     

Was the lethal eruption of Lake Nyos related to a double CO2/H2O density inversion?

The 1986 lethal eruption of Lake Nyos (Cameroon) was caused by a sudden inversion between deep, CO₂-loaded bottom lake waters and denser, gas-free surface waters. A deep CO₂ source has been found in fluid inclusions which occur predominantly in clinopyroxenes from lherzolitic mantle xenoliths, brought to the surface by the last erupted alkali basalts. P–T conditions of CO₂ trapping correspond to a gas density equal (or higher) than that of liquid water. It is suggested that this dense CO₂, found in many ultrabasic mantle xenoliths worldwide, has accumulated at km depth, below a column of descending lake water. It may remain in a stable state for a long period, as long as the temperature is above the density inversion temperature for pure H₂O/CO₂ systems. At an estimated depth of about 3 km, cooling by descending waters (to about 30 °C) induces a density inversion for the upper part of the CO₂ reservoir. This causes a constant, regular upstream of low-density CO₂ which, in its turn, feeds the shallower lake density inversion.     

Understanding the 2007-2008 eruption of Anak Krakatau Volcano by combining remote sensing technique and seismic data

One of the most violent volcanic eruptions in recorded history is the Krakatau eruption on August 27, 1883. This caldera-forming eruption destroyed two thirds of the Krakatau volcanic island in the Sunda Strait resulting in the remaining three small islands later known as the Krakatau complex. From 1927 to 1929, eruptions in the center of Krakatau complex have produced a new volcano named Anak Krakatau, which continuously builds its body through eruptions until now. One eruption event took place between 2007 and 2008 with several eruptions that lasted in total from the end of October 2007 to August 2008. Eruptions were characterized by Strombolian activity with ash columns 1 km high, as well as pyroclastic and lava flows. We monitored the ground deformation of Anak Krakatau Volcano by interfering PALSAR data from June 2007 to February 2009. The result of InSAR technique shows a complex pattern of ground deformation. Inflation up to 4 cm, together with subsidence around the crater, was measured for almost three months before the eruption with a volume increase of approximately 1 × 10⁶ m³. After the eruption, the southwest side of the volcanic cone subsided by 18 cm, whereas the northeast side of the cone uplifted 12 cm in almost two years. The observed ground deformation after the eruption can be explained by 4 m of tensile opening along a dipping rectangular tensile dislocation buried in an elastic half-space, approximately 400 m below sea level.     

The impact of the Laacher See Tephra on terrestrial and aquatic ecosystems in the Black Forest,southern germany

Late-glacial lake sediments containing the Laacher See Tephra (LST, 11000 yr BP) have been analysed for pollen and diatoms at two sites (Hirschenmoor, Rotmeer) in the montane belt of the Black Forest (southern Germany) in order to detect the possible impact of this major volcanic eruption on terrestrial and aquatic biota. The pollen assemblages at both sites show a minor increase in grasses and sedges following the tephra deposition, whereas the pollen of aquatic macrophytes do not show any consistent pattern. Partial redundancy analysis and Monte Carlo permutation tests suggest, however, that the LST had no statistically significant effect either on the terrestrial or aquatic pollen assemblages at either site when the effects of time and climatic change are allowed for statistically. The diatom assemblages at both sites changed after the deposition of the LST and diatominferred pH estimates suggest a short but non-significant excursion towards lower values. Multivariate analyses of the diatom data indicate a statistically significant impact of the deposition of the LST and associated changes in sediment lithology on the diatom assemblages when the effects of climatic change and time are allowed for statistically. However, owing to the interaction between tephra and lithology it is not possible to conclude if the diatom changes were caused by the deposition of the LST or by lithological changes.     

Explosive volcanic eruptions - VI. Ejecta dispersal in plinian eruptions: the control of eruption conditions and atmospheric properties

Summary. A simple model is developed to relate the maximum down-wind and cross-wind ranges of pyroclasts forming a plinian airfall deposit to the dynamic processes in the eruption cloud from which they fall and the atmospheric wind conditions in the area. The eruption cloud dynamics are in turn related to the eruptive conditions in the vent (vent radius, exsolved magmatic volatile weight fraction, velocity with which material passes through the vent, and mass eruption rate), some or all of which can be deduced if the appropriate field measurements can be made. Some aspects of the stability of convecting volcanic eruption clouds are investigated, and the effects on eruption cloud height of the local atmospheric temperature profile and the value adopted for the entrainment constant (which relates the horizontal flow speed of atmospheric air entering the column to the vertical rise speed of the column material) are explored. It is confirmed that eruption-cloud rise height and pyroclast dispersal are mainly controlled by the mass eruption rate (per unit length of active fissure in the case of linear vents) and, hence, the heat input rate to the cloud; but a significant subsidiary dependence on the amount of exsolved magma volatiles is also found. The eruption cloud model is validated by application to observed historic eruptions, and its use in the analysis of palaeo-eruptions is discussed.     

火山学研究进展

从火山学和火山动力学，统计研究，火山灾害以及火山活动对全球气候变化的影响回顾了近年火山学研究的主要进展。     

五大连池老黑山火烧山火山喷发物及形成的物理过程

以当代火山物理的观点和思路对黑龙江省五大连池老黑山火烧山进行了研究。在旧锥锥体上部发现滞后角砾岩，在其下部坡脚发现有涌浪（ｓｕｒｇｅ）堆积物的存在，对形成过程和机制做了一些解释。     

新托尔巴奇克火山研究综述

位于堪察加半岛的新托尔巴奇克山是世界上有史以来仅遥六个大裂隙喷发的火山之一，也是迄今对喷发研究得最为详尽的三个火山之一。本文从喷发活动、玄武岩、气体成分与升华物，喷发区地球物理特征，喷发预报，地震，形变及喷发机制等方面综合论述了该火山的观测观察成果，并指出这些成果对我国火山研究有重要的借鉴意义。     

Environmental assessment of 1991 Hudson volcano eruption ashfall effects on southern Patagonia region,Argentina

The August 1991 eruption of the Hudson volcano in the southern Andean volcanic zone affected an area of 1000 km in radius to the east in the Argentine Patagonic meseta. The thickness of ash ranged from 20 cm in the Andean area to less than 1 mm in the Atlantic coast zone. Wind storms reactivated the ash deposits, together with terrigenous material, more than one year after the eruption. In order to assess the potential risk of the ash, analyses of concentration, size, mineralogical composition, toxic elements, and irritating effects of gases were performed. In all samples, the percentage of particles of the 2-to 5-m range is below the toxic threshold level. Trace elements are below the toxic threshold concentration for humans and animals. The major impact of the ashfall was on sheep herds; about one third of them were lost in the areas close to the volcano. Soil incorporated the ash layers, and a fast recovery of orchards was reported two years later. Rivers were loaded with sediment in the immediate aftermath, but one year later returned to previous conditions. Along the shores of the Buenos Aires Lake, a fresh tephra layer can be distinguished.