近53a珠峰地区气温降水变化特征分析

利用聂拉木和定日国家气象观测站1967~2019年月气温和降水资料,开展了珠穆朗玛峰（简称珠峰）地区季、年气温和降水变化特征分析及变化趋势检验。结果表明：近53a珠峰地区季、年平均气温呈显著升高趋势,冬季增温幅度最大,年平均气温在1997年之前为波动下降而1997年之后则是波动增加,进入21世纪后气温升高愈发明显且在冬季尤为突出;珠峰地区1967~2019年降水量呈波动变化但变化趋势不显著;珠峰地区气温和降水体现出较强的局地性差异,其南、北坡气温和降水呈现出不同的变化特征。     

Pre- and post-drill comparison of the Mount Elbert gas hydrate prospect, Alaska North Slope

In 2006, the United States Geological Survey (USGS) completed a detailed analysis and interpretation of available 2-D and 3-D seismic data, along with seismic modeling and correlation with specially processed downhole well log data for identifying potential gas hydrate accumulations on the North Slope of Alaska. A methodology was developed for identifying sub-permafrost gas hydrate prospects within the gas hydrate stability zone in the Milne Point area. The study revealed a total of 14 gas hydrate prospects in this area.In order to validate the gas hydrate prospecting protocol of the USGS and to acquire critical reservoir data needed to develop a longer-term production testing program, a stratigraphic test well was drilled at the Mount Elbert prospect in the Milne Point area in early 2007. The drilling confirmed the presence of two prominent gas-hydrate-bearing units in the Mount Elbert prospect, and high quality well logs and core data were acquired. The post-drill results indicate pre-drill predictions of the reservoir thickness and the gas-hydrate saturations based on seismic and existing well data were 90% accurate for the upper unit (hydrate unit D) and 70% accurate for the lower unit (hydrate unit C), confirming the validity of the USGS approach to gas hydrate prospecting. The Mount Elbert prospect is the first gas hydrate accumulation on the North Slope of Alaska identified primarily on the basis of seismic attribute analysis and specially processed downhole log data. Post-drill well log data enabled a better constraint of the elastic model and the development of an improved approach to the gas hydrate prospecting using seismic attributes.     

First recorded eruption of Mount Belinda volcano (Montagu Island), South Sandwich Islands

The MODVOLC satellite monitoring system has revealed the first recorded eruption of Mount Belinda volcano, on Montagu Island in the remote South Sandwich Islands. Here we present some initial qualitative observations gleaned from a collection of satellite imagery covering the eruption, including MODIS, Landsat 7 ETM+, ASTER, and RADARSAT-1 data. MODVOLC thermal alerts indicate that the eruption started sometime between 12 September and 20 October 2001, with low-intensity subaerial explosive activity from the islands summit peak, Mount Belinda. By January 2002 a small lava flow had been emplaced near the summit, and activity subsequently increased to some of the highest observed levels in August 2002. Observations from passing ships in February and March 2003 provided the first visual confirmation of the eruption. ASTER images obtained in August 2003 show that the eruption at Mount Belinda entered a new phase around this time, with fresh lava effusion into the surrounding icefield. MODIS radiance trends also suggest that the overall activity level increased significantly after July 2003. Thermal anomalies continued to be observed in MODIS imagery in early 2004, indicating a prolonged low-intensity eruption and the likely establishment of a persistent summit lava lake, similar to that observed on neighboring Saunders Island in 2001. Our new observations also indicate that lava lake activity continues on Saunders Island.Editorial responsibility: J. Gilbert     

Seismic image of the Mount Spurr magmatic system

 The three-dimensional P-wave velocity structure of Mount Spurr is determined to depths of 10 km by tomographic inversion of 3,754 first-arriving P-wave times from local earthquakes recorded by a permanent network of 11 seismographs. Results show a prominent low-velocity zone extending from the surface to 3–4 km below sea level beneath the southeastern flank of Crater Peak, spatially coincident with a geothermal system. P-wave velocities in this low-velocity zone are approximately 20% slower than those in the shallow crystalline basement rocks. Beneath Crater Peak an approximately 3-km-wide zone of relative low velocities correlates with a near-vertical band of seismicity, suggestive of a magmatic conduit. No large low-velocity zone indicative of a magma chamber occurs within the upper 10 km of the crust. These observations are consistent with petrologic and geochemical studies suggesting that Crater Peak magmas originate in the lower crust or upper mantle and have a short residence time in the shallow crust. Earthquakes relocated using the three-dimensional velocity structure correlate well with surface geology and other geophysical observations; thus, they provide additional constraints on the kinematics of the Mount Spurr magmatic system. Received: 4 December 1997 / Accepted: 27 February 1998     

Directed blasts and blast-generated pyroclastic density currents: a comparison of the Bezymianny 1956, Mount St Helens 1980, and Soufrière Hills,Montserrat 1997 eruptions and deposits

We compare eruptive dynamics, effects and deposits of the Bezymianny 1956 (BZ), Mount St Helens 1980 (MSH), and Soufrière Hills volcano, Montserrat 1997 (SHV) eruptions, the key events of which included powerful directed blasts. Each blast subsequently generated a high-energy stratified pyroclastic density current (PDC) with a high speed at onset. The blasts were triggered by rapid unloading of an extruding or intruding shallow magma body (lava dome and/or cryptodome) of andesitic or dacitic composition. The unloading was caused by sector failures of the volcanic edifices, with respective volumes for BZ, MSH, and SHV c. 0.5, 2.5, and 0.05 km³. The blasts devastated approximately elliptical areas, axial directions of which coincided with the directions of sector failures. We separate the transient directed blast phenomenon into three main parts, the burst phase, the collapse phase, and the PDC phase. In the burst phase the pressurized mixture is driven by initial kinetic energy and expands rapidly into the atmosphere, with much of the expansion having an initially lateral component. The erupted material fails to mix with sufficient air to form a buoyant column, but in the collapse phase, falls beyond the source as an inclined fountain, and thereafter generates a PDC moving parallel to the ground surface. It is possible for the burst phase to comprise an overpressured jet, which requires injection of momentum from an orifice; however some exploding sources may have different geometry and a jet is not necessarily formed. A major unresolved question is whether the preponderance of strong damage observed in the volcanic blasts should be attributed to shock waves within an overpressured jet, or alternatively to dynamic pressures and shocks within the energetic collapse and PDC phases. Internal shock structures related to unsteady flow and compressibility effects can occur in each phase. We withhold judgment about published shock models as a primary explanation for the damage sustained at MSH until modern 3D numerical modeling is accomplished, but argue that much of the damage observed in directed blasts can be reasonably interpreted to have been caused by high dynamic pressures and clast impact loading by an inclined collapsing fountain and stratified PDC. This view is reinforced by recent modeling cited for SHV. In distal and peripheral regions, solids concentration, maximum particle size, current speed, and dynamic pressure are diminished, resulting in lesser damage and enhanced influence by local topography on the PDC. Despite the different scales of the blasts (devastated areas were respectively 500, 600, and >10 km² for BZ, MSH, and SHV), and some complexity involving retrogressive slide blocks and clusters of explosions, their pyroclastic deposits demonstrate strong similarity. Juvenile material composes >50% of the deposits, implying for the blasts a dominantly magmatic mechanism although hydrothermal explosions also occurred. The character of the magma fragmented by explosions (highly viscous, phenocryst-rich, variable microlite content) determined the bimodal distributions of juvenile clast density and vesicularity. Thickness of the deposits fluctuates in proximal areas but in general decreases with distance from the crater, and laterally from the axial region. The proximal stratigraphy of the blast deposits comprises four layers named A, B, C, D from bottom to top. Layer A is represented by very poorly sorted debris with admixtures of vegetation and soil, with a strongly erosive ground contact; its appearance varies at different sites due to different ground conditions at the time of the blasts. The layer reflects intense turbulent boundary shear between the basal part of the energetic head of the PDC and the substrate. Layer B exhibits relatively well-sorted fines-depleted debris with some charred plant fragments; its deposition occurred by rapid suspension sedimentation in rapidly waning, high-concentration conditions. Layer C is mainly a poorly sorted massive layer enriched by fines with its uppermost part laminated, created by rapid sedimentation under moderate-concentration, weakly tractive conditions, with the uppermost laminated part reflecting a dilute depositional regime with grain-by-grain traction deposition. By analogy to laboratory experiments, mixing at the flow head of the PDC created a turbulent dilute wake above the body of a gravity current, with layer B deposited by the flow body and layer C by the wake. The uppermost layer D of fines and accretionary lapilli is an ash fallout deposit of the finest particles from the high-rising buoyant thermal plume derived from the sediment-depleted pyroclastic density current. The strong similarity among these eruptions and their deposits suggests that these cases represent similar source, transport and depositional phenomena.     

航磁资料在澳大利亚昆士兰州艾萨山选区成矿预测中的应用

高精度航磁测量相对简单,获得的信息丰富,是开展大面积成矿预测的有利工具。澳大利亚艾萨山选区地质资料较少,地面物探工作开展较难。利用高精度航磁资料,对该地区航磁数据进行了处理与解释,推断出断裂构造及岩体分布。结合区域成矿地质、构造环境和金属矿床时空分布特点,识别出成矿有利地区的航磁异常特征,划分了有利航磁异常分布带。在航磁有利异常分布图的基础上,结合矿床、矿点位置情况,进一步圈定出成矿远景区,为该地区成矿预测工作提供了依据。     

珠峰地区雨季对流层大气的特征分析

利用2007年7月中国科学院珠穆朗玛峰综合观测站的边界层塔、无线电探空和风温廓线仪观测资料,分析了珠穆朗玛峰地区雨季低层大气风温湿等特征.珠峰地区雨季近地层风速、风向、温度等有明显的日变化.近地层风的日变化有两个很明显的阶段,00:00～14:30受谷风的影响而刮偏北风,14:30～24:00受冰川风的影响以偏南风为主.白天的冰川风比夜间的谷风要强些.中午13:30在600m以下存在强水平风速垂直切变,这可能是珠峰地区发生降雨的重要原因之一.低空急流在夏季比较常见.对流层平均降温率为0.685K/100m.低层大气的相对湿度一般有两个峰值高度,最大值在4000m以下,第二峰值高度不固定,到16000m以后相对湿度超不过10%.各层大气的风速风向差别较大.     

Evolution of Mount Cameroon volcanism: Geochemistry,mineral chemistry and radiogenic isotopes (Pb,Sr, Nd)

Mount Cameroon volcano has erupted several times in the 20th Century with documented eruptions in 1909, 1922, 1954, 1959, 1982, 1999 and 2000. Evidence of historic volcanism is represented by several older lava flows and lahar deposits around the flanks of the volcano. This study aims to assess the evolution of Mount Cameroon volcanism through its eruptive history via interpretation of mineralogical, whole rock geochemical and Pb, Sr, Nd isotope data generated from historic and recent lava flows. In this study, samples were collected from the 1959, 1982, 1999 and 2000 eruptions and from several historic eruption sites with unknown eruption dates.Evaluation of major and trace element data demonstrates that Mount Cameroon is geotectonically associated with within-plate Ocean Island Basalt Settings. More than 90% of the studied historic lavas (n ​= ​29) classify as tephrites and basanites whereas the modern lavas (n ​= ​38) are predominantly trachybasalts, demonstrating evolution from primitive to evolved lavas over time typically in response to fractional crystallization. Petrographically, the lavas are porphyritic with main mineral phases being olivine, clinopyroxene, plagioclase feldspars and Fe–Ti–Cr oxides. The 1982 lavas are predominantly aphyric and dominated by lath-shaped flow-aligned plagioclase in the groundmass. Olivine chemistry shows variable forsterite compositions from Fo_60–89. Clinopyroxenes vary from diopside through augite to titanaugite with chemical composition ranges from Wo₄₅En₃₂Fs₇ to Wo₅₁En₄₇Fs₁₇. Plagioclase feldspars vary from labradorite (An_56–70) to bytownite (An_80–87). For the Fe–Ti–Cr oxides, calculated ulvöspinel component shows a wide variation from ulv_38–87. CIPW-normative classification on the Di-Ol-Hy-Qz-Ne system shows that all Mount Cameroon lavas are nepheline-normative (Ne ranges from 4.20 wt.% to 11.45 ​wt.%).Radiogenic isotope data demonstrate that Mount Cameroon lavas are HIMU (or high μ ​= ​²³⁸U/²⁰⁴Pb), characterized by ²⁰⁶Pb/²⁰⁴Pb ​= ​20.19–20.46, ²⁰⁷Pb/²⁰⁴Pb ​= ​15.63–15.69, ²⁰⁸Pb/²⁰⁴Pb ​= ​40.01–40.30, ⁸⁷Sr/⁸⁶Sr ​= ​0.70322–0.70339 (ε_Sr ​= ​−21.37 to −18.96) and ¹⁴³Nd/¹⁴⁴Nd ​= ​0.51276–0.51285 (ε_Nd ​= ​+2.29 to +4.05). The historic lavas show stronger HIMU signature relative to the modern lavas, suggesting evolution towards less HIMU signatures over time. This study has revealed that Mount Cameroon volcanism has evolved from primitive magmas characterized by stronger HIMU signatures with high ^206/204Pb and ^208/204Pb isotopes, low SiO₂ and high Mg, Ni, Cr content towards lower HIMU signatures with relatively higher SiO₂, lower Mg, Cr and Ni compositions. The geochemical and isotopic changes, which account for the evolution of magmatism on Mount Cameroon occur over long periods of time because all the modern lavas erupted within the last 100 years are isotopically homogeneous, with very limited variation in SiO₂ compositions.     

Strong seasonality in sand loading and resulting feedbacks on sediment transport,bed texture,and channel planform at Mount Pinatubo,Philippines

Declining sand inputs to a channel with bimodal bed sediment can lead to degradation, armoring, and reduced bedload transport rates. Where sand loading is episodic, channels may alternate between high‐sand and low‐sand conditions, with ensuing responses in bed texture and bedload transport rates. The effects of episodic sand loading are explored through flow, grain size, and bedload transport measurements on the Pasig‐Potrero River, a sediment‐rich channel draining Mount Pinatubo, Philippines. Sand loading on the Pasig‐Potrero River is highly seasonal, and channel adjustments between seasons are dramatic. In the rainy season, inputs from sand‐rich 1991 eruption deposits lead to active, sand‐bedded, braided channels. In the dry season, many precipitation‐driven sand sources are cut off, leading to incision, armoring, and significantly lower bedload transport rates. This seasonal transition offers an excellent opportunity to examine models of degradation, incision, and armoring as well as the effectiveness of sediment transport models that explicitly encapsulate the importance of sand on transport rates. During the fall 2009 seasonal transition, 7·6 km of channel incised and armored, carving a 2–3 m deep channel on the upper alluvial fan. Bedload transport rates measured in the August 2009 rainy season were over four orders of magnitude greater than gravel‐bedded dry‐season channels surveyed in January 2010, despite having similar shear stress and unit discharge conditions. Within dry‐season incised channels, bed armoring is rapid, leading to an abrupt gravel‐sand transition. Bedload transport rates adjust more slowly, creating a lag between armoring and commensurate reductions in transport. Seasonal channel incision occurred in steps, aided by lateral migration into sand‐rich banks. These lateral sand inputs may increase armor layer mobility, renewing incision, and forming terraces within the incised seasonal channel. The seasonal incised channel is currently being reset by precipitation‐driven sand loading during the next rainy season, and the cycle begins again. Copyright © 2012 John Wiley & Sons, Ltd.     

泰安市岩盐资源开发利用与保护工作探析

随着岩盐资源开发强度逐年加大,开发利用保护任务日渐繁重,由于岩盐独特开采方法和工艺,应探索相应的监管措施和手段。通过对大汶口岩盐资源赋存特点和开发利用现状分析,指出其开发过程中存在的问题,就岩盐开采方法和工艺的监管措施和手段进行探索,提出开发利用和保护建议,从而有利于促进加强岩盐资源的开发利用和保护工作。