五大连池新期火山锥体结构及喷发过程

五大连池新期火山（1719～1921年喷发）包括老黑山和火烧山两座火山。火山由富钾玄武质熔岩盾和锥体组成,造盾喷溢与造锥喷发交替进行。老黑山形成相对较早,喷发规模大,锥体结构复杂,为两期形成的复式套叠锥,晚期锥体中心为漏斗状火山口,火山喷发过程可分为5个阶段。火烧山为一单锥,锥体中心发育破火口,火山活动经历了3个阶段。     

火山爆发对新疆太阳辐射和气温的影响

本文利用１９６１－１９９３年新疆１６个气象站气温资料和８个日射站的辐射资料，分析了火山爆发指数ＶＥＩ≥４级的９次强火山爆发对新疆太阳直接辐射和气温的影响。分析结果表明，强火山爆发后的１－２年中，新疆的太阳直接辐射有明显减少，年平均气温和季节平均气温都有不同程度的下降，北疆秋季气温下降的一致性和幅度最明显。同时分析证实了１９９２－１９９３年新疆夏、秋季的低温与１９９１年６月菲律宾ＶＥＩ６级的Ｐｉｎａ     

中国东北晚全新世火山爆发最新的一次活跃期

中国东北晚全新世火山活动十分强烈,1200 AD±的一次活跃期及其所产生的地质灾害已被很好地研究.根据历史记载、热释光测年和¹⁴C测年等资料,在1720 AD±存在最新的一次活跃期.确证这一活跃期的存在并开展火山地质灾害调查与研究,对探索火山活动节律和火山地质灾害预警等均有重要的理论和实际意义.     

Volcanic ash and tsunami record of the Minoan Late Bronze Age Eruption (Santorini) in a distal setting,southwestern Turkey

We present the volcanic ash and tsunami record of the Minoan Late Bronze Age Eruption of Santorini (LBAES) in a distal setting in southwestern Turkey. In one of the drilled cores at the Letoon Hellenic antique site on Eşençay Delta, we encountered a 4 cm thick tephra deposit underlain by 46 cm thick tsunami-deposited sand (tsunamite), and an organic-rich layer that we ¹⁴C dated to 3295 ± 30 bp or 1633 bc. The relationship between Santorini distal volcanic ash and underlying tsunamite is described and interpreted. LBAES occurred in four main phases: (1) plinian; (2) phreatomagmatic; (3) phreatomagmatic with mudflows; and (4) ignimbritic flows and co-ignimbrite tephra falls. In this study, we aim to understand which eruptive phases generate distal ash during the Minoan eruptive sequence by examining the 3D surface morphology of ash formed by different fragmentation processes. To that end, we used numerous statistical multivariates, 3D fractal dimension of roughness, and a new textural parameter of surface area-3D/plotted area-2D to characterise the eruption dynamics. Based on ash surface morphologies and the calculated statistical parameters, we propose that that distal ash is represented by a single layer composed of well-mixed (coarse to fine) magmatic and phreatomagmatic ash.     

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.     

汶川大地震震中喷发气、石的“爆烈式泥火山”场景——兼讨论地震的超临界水流体退相爆发成因

经多次现场核实,5．12汶川地震震中实为：有巨量喷发气、石的“爆烈式泥火山”伴大地震一巨量黑烟喷发和成千万m^3灰砂夹巨石千米抛射,同时引发烈度Ⅺ级的Ms8．0大地震。震中的此场景显然不能用传统构造运动成因自圆其说。汶川大地震只能是地内超临界水流体（简称SCW）退相爆发成因：地震带地下（10-20）km深处,汇聚了巨量SCW（H2O-CO2-空气-CH体系）流体,当其首先上窜到震中莲花心沟下方,减压至临界点（Pc=22．1Mpa）时,瞬间爆发退相,放出能量巨大和体积膨胀千倍的气体,爆发炸碎孕震库上方围岩,造成龙门山断裂带瞬间释放能量,形成大地震。     

Impacts of explosive volcanism on distal alluvial sedimentation: Examples from the Pliocene–Holocene volcaniclastic successions of Japan

Volcanic activities can create cataclysmic hazards to surrounding environments and human life not only during the eruption but also by hydrologic remobilisation (lahar) processes after the cessation of eruptive activity. Although there are many studies dealing with the assessment and mitigation of volcanic hazards, these are mostly concentrated on primary eruptive processes in areas proximal to active volcanoes. However, the influence of volcaniclastic resedimentation may surpass the impacts of primary eruptive activity in terms of both extent and persistence, and can ultimately result in severe hazards in downstream areas.Examination of the volcaniclastic successions of non-marine Pliocene–Holocene sedimentary basins in Japan has revealed hydrological volcaniclastic sedimentation in fluvial and lacustrine environments hundreds of kilometres from the inferred source volcano. Impacts on these distal and often spatially separated basins included drastic changes in depositional systems caused by sudden massive influxes of remobilised pyroclastic material. Typical volcaniclastic beds comprise centimetre- to decimetre-thick primary pyroclastic fall deposits overlain by metre- to 10s of metres-thick resedimented volcaniclastic deposits, intercalated in sedimentary successions of non-volcanic provenance. The relatively low component of primary pyroclastic fall deposits in the volcaniclastic beds suggests that: 1) potential volcanic hazards would be underestimated on the basis of primary pyroclastic fall events alone; and 2) the majority of resedimented material was likely derived from erosion of non-welded pyroclastic flow deposits in catchment areas rather than remobilisation of local fallout deposits from surrounding hillslopes.The nature, distribution and sequence of facies developed by distal volcaniclastic sediments reflect the influence of: 1) proximity to ignimbrite, but not directly with the distance to the eruptive centre; 2) ignimbrite nature (non-welded or welded) and volume; 3) temporal changes in sediment flux from the source area; 4) the physiography and drainage patterns of the source area and the receiving basin, and any intervening areas; and 5) the formation of ephemeral dam-lakes and intra-caldera lakes whose potential catastrophic failure can impact distal areas. Models of the styles and timing of distal volcaniclastic resedimentation are thus more complicated than those developed for proximal settings of stratovolcanoes and their volcaniclastic aprons and hence present different challenges for hazard assessment and mitigation.     

Intra-crater deposits of the Toga tuff ring, Oga Peninsula, NE Japan

The Toga tuff ring is a large, dissected tuff ring located on the modern shoreline of the Oga Peninsula, NE Japan. The crater measures 2 km by 2.4 km and the inner crater walls are inclined inward at 40–50° to form a funnel shape. Intra-crater beds are mainly composed of platy or blocky, non- to variably vesicular glass shards and pumice lapilli of K-rich rhyolite composition and dip inward at 10°–30° or less. A gravity model suggests they fill the downward-tapering conduit to a depth of 548 m below sea level. Fission-track dates from the intra-crater deposits indicate the age of the Toga tuff ring is ca. 420 ka, likely corresponding to a stage of global sea-level fall, MIS 12. Subsequent sea-level rise and marine transgression is inferred to have resulted in erosion of almost the entire outer tuff ring by post-eruptive wave action.The intra-crater deposit`s are exposed over a thickness of 50 m in the deeply incised crater floor. They comprise mainly monomictic tephra of phreatomagmatic origin and are similar in grain-size distribution and sedimentary structures to relatively high and low density turbidites, although the constituents, sparse block-sag structures, and multiple fluid-escape dikes suggest that they are the subaqueous equivalents of high- and low-density pyroclastic currents with similar grain-sizes and degree of grain-size sorting. Marine diatom frustules sparsely contained in the deposits suggest that the crater was likely open to the sea, enabling rapid access of seawater to the vent. Pyroclasts ejected through the water flowed back into the crater to form eruption-fed oscillatory or circular turbidity currents and were repeatedly recycled and variably abraded by subsequent explosions, while many juvenile pumice lapilli and ash grains were carried beyond the crater rim to form relatively dilute pyroclastic currents. The Toga example suggests that primary deposits emplaced in crater lakes are well sorted, graded and stratified with polymodal flow directions, sparse block-sags, and vesicular and fragile fragments that are more or less abraded by repeated explosions and recycling.     

缅甸硅化木(“树化玉”)的成因

近年,中国宝玉石和观赏石市场上出现了一种十分受人青睐的玉石品种——缅甸“树化玉”(硅化木),媒体广告对其宣传有加,给人们带来无限商机。但对其成因环境之说却十分离谱。现试图避开商业炒作的市场环境,拟从地质科学的角度,以地质事实为依据,揭示缅甸树化玉(硅化木)形成的奥秘。