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.     

Magma contamination by direct wall rock interaction: constraints from xenoliths from the walls of a carbonate-hosted magma chamber (Vesuvius 1944 eruption)

During the 1944 eruption of Vesuvius different types of xenoliths were ejected. They represent fragments of the walls of a low volume (<0.5 km³) shallow (3–4 km depth) magma chamber. The study of these xenoliths enables us to estimate the amount of contamination occurring at the boundary of a high-T alkaline magma chamber hosted in carbonate rocks. The process of contamination of the magma by carbonates can be modelled, using isotopic and chemical data, as a mixing between magma and marbles. Mass exchanges occur at the boundary between the crystallizing magma and marble wall rocks, where endoskarn forms. The contamination of the solidification front of the chamber is very limited. The solidification front and the skarn shell effectively isolate the interior of the magma chamber from new inputs of contaminants from the carbonate wall rocks. Therefore, the main volume of magma, hosted in the magma chamber, did not undergo any significant mass exchange with the wall rocks.     

The 26.5 ka Oruanui eruption, New Zealand: an introduction and overview

The 26.5 ka Oruanui eruption, from Taupo volcano in the central North Island of New Zealand, is the largest known ‘wet’ eruption, generating 430 km³ of fall deposits, 320 km³ of pyroclastic density–current (PDC) deposits (mostly ignimbrite) and 420 km³ of primary intracaldera material, equivalent to 530 km³ of magma. Erupted magma is >99% rhyolite and <1% relatively mafic compositions (52.3–63.3% SiO₂). The latter vary in abundance at different stratigraphic levels from 0.1 to 4 wt%, defining three ‘spikes’ that are used to correlate fall and coeval PDC activity. The eruption is divided into 10 phases on the basis of nine mappable fall units and a tenth, poorly preserved but volumetrically dominant fall unit. Fall units 1–9 individually range from 0.8 to 85 km³ and unit 10, by subtraction, is 265 km³; all fall deposits are of wide (plinian) to extremely wide dispersal. Fall deposits show a wide range of depositional states, from dry to water saturated, reflecting varied pyroclast:water ratios. Multiple bedding and normal grading in the fall deposits show the first third of the eruption was very spasmodic; short-lived but intense bursts of activity were separated by time breaks from zero up to several weeks to months. PDC activity occurred throughout the eruption. Both dilute and concentrated currents are inferred to have been present from deposit characteristics, with the latter being volumetrically dominant (>90%). PDC deposits range from mm- to cm-thick ultra-thin veneers enclosed within fall material to >200 m-thick ignimbrite in proximal areas. The farthest travelled (90 km), most energetic PDCs (velocities >100 m s⁻¹) occurred during phase 8, but the most voluminous PDC deposits were emplaced during phase 10. Grain size variations in the PDC deposits are complex, with changes seen vertically in thick, proximal accumulations being greater than those seen laterally from near-source to most-distal deposits. Modern Lake Taupo partly infills the caldera generated during this eruption; a 140 km² structural collapse area is concealed beneath the lake, while the lake outline reflects coeval peripheral and volcano–tectonic collapse. Early eruption phases saw shifting vent positions; development of the caldera to its maximum extent (indicated by lithic lag breccias) occurred during phase 10. The Oruanui eruption shows many unusual features; its episodic nature, wide range of depositional conditions in fall deposits of very wide dispersal, and complex interplay of fall and PDC activity.     

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.     

长白山全新世以来的火山喷发活动与森林火灾研究

采用同位素年代测定等方法,探讨了长白山一万年以来火山活动的期次、规模及森林火灾。     

Cone-building block-and-ash flows: the Senyama volcanic products of O’e Takayama volcano,SW Japan

The Senyama volcanic products of the late Pliocene to early Pleistocene O’e Takayama volcano overlie a 100-m-thick, late Pliocene coastal quartz-sandstone and are intruded by an early Pleistocene dacite dome. The Senyama volcanic products are the remains of a cone that retains a basal part 1.5 km across and 150–250 m high from the substrate. The cone comprises dacite block-and-ash flow deposits and minor base-surge deposits occur at the base. Single beds of the block-and-ash flow deposits are 1–16 m thick and dip inward 20–40° at the base of the cone and inward or outward 10–20° at the summit. Juvenile fragments in the block-and-ash flow deposits are non- to poorly vesicular and commonly have curviplanar surfaces and prismatic joints extending inward from the surfaces, which imply quenching and brittle fracturing of dacite lava. They are variably hydrothermally altered. Nevertheless, juvenile blocks appear to retain a uniform direction of the magnetization vector residual during thermal demagnetization between 280°C and 625°C. At the time of the eruption, the well-sorted sand of the substrate was at the coast and a good aquifer that facilitated explosive interaction of water and the ascending dacite lava. The mechanism of the explosion perhaps involved thermal contraction cracking of the dacite lava, water-inflow into the interior of the lava, and explosive expansion of the water. Initial phreatomagmatic explosions opened the vent. Succeeding phreatomagmatic or phreatomagmatic–vulcanian explosions produced block-and-ash flow deposits around the vent. Hydrothermal silver-ore deposits and manganese-oxide deposits occur in the Senyama volcanic products and the underlying sandstone, respectively. They could represent post-eruptive activity of the hydrothermal system developed in and around the cone.