Modeling of Stress Changes at Mayon Volcano,Philippines     

K. F. Tiampo  J. Fernández  T. Hayes  G. Jentzsch 《Pure and Applied Geophysics》2007,164(4):819-835

In this paper, we analyze the stress change associated with the inverted volcanic source models at Mayon volcano, Philippines, where there are gravity changes without significant deformation after the 1993 eruption. We detail the applicable data and the associated inversion techniques and models prior to calculating the appropriate stress changes. It is determined that the stress change associated with the central magmatic source produces compressional stress changes at a secondary source to the northwest, prompting a change in the local water storage in the underlying fractured rock.  相似文献   

The November 2002 eruption at Piton de la Fournaise volcano,La Réunion Island: ground deformation,seismicity, and pit crater collapse     

Marc-Antoine Longpré  Thomas Staudacher  John Stix 《Bulletin of Volcanology》2007,69(5):511-525

An eruption on the eastern flank of Piton de la Fournaise volcano started on 16 November, 2002 after 10 months of quiescence. After a relatively constant level of activity during the first 13 days of the eruption, lava discharge, volcanic tremor and seismicity increased from 29 November to 3 December. Lava effusion suddenly ceased on 3 December while shallow earthquakes beneath the Dolomieu summit crater were still recorded at a rate of about one per minute. This unusual activity continued and increased in intensity over the next three weeks, ending with the formation of a pit crater within Dolomieu. Based on ground deformation, measured by rapid-static and continuous GPS and an extensometer, seismic data, and lava effusion patterns, the eruptive period is divided into five stages: 1) slow summit inflation and sporadic seismicity; 2) rapid summit inflation and a short seismic crisis; 3) rapid flank inflation, onset of summit deflation, sporadic seismicity, accompanied by stable effusion; 4) flank inflation, coupled with summit deflation, intense seismicity, and increased lava effusion; and finally 5) little deflation, intense shallow seismicity, and the end of lava effusion. We propose a model in which the pre-intrusive inflation of Stage 1 in the months preceding the eruption was caused by a magma body located near sea level. The magma reservoir was the source of an intrusion rising under the summit during Stage 2. In Stage 3, the magma ponded at a shallow level in the edifice while the lateral injection of a radial dike reached the surface on the eastern flank of the basaltic volcano, causing lava effusion. Pressure decrease in the magmatic plumbing system followed, resulting in upward migration of a collapse front, forming a subterranean column of debris by faulting and stoping. This caused intense shallow seismicity, increase in discharge of lava and volcanic tremor at the lateral vent in Stage 4 and, eventually the formation of a pit crater in Stage 5.  相似文献   

萨热阔布—铁米尔铁矿区金铅锌成矿系列   总被引：11，自引：4，他引：11       下载免费PDF全文

马忠美  仇银江等 《地质与勘探》2001,37(4):23-26

萨热阔布－铁米尔特金铅锌多金属矿床受下泥盆统康布铁堡组上亚组第二岩性段含酸性火山碎屑岩的泥质沉积和化学沉积层控制，铁铅锌金矿床的成因类型与火山气液喷流沉积改造型。在时间和空间分布上有明显的规律性：在成矿时序上有先铁铜、后铅锌、最后为金矿；在空间分布规律上，铁铜矿床产于喷口附近，金产于火山沉积洼地的边缘的火山斜坡上，铅锌产于沉积洼地之中。  相似文献   

泥浆含砂率对桩基质量的影响     

宋明智  许谷星 《江西地质》2001,15(4):301-304

本文通过对泥浆中颗粒的沉降特性分析，从量上得出泥浆性能对泥浆中颗粒的悬浮携渣能力。泥浆是一流变性的流体，对泥浆性能的把握，应综合考虑，而不偏向于某个指标。提出了在实践中对泥浆的正确使用和泥浆性能取用的建议。  相似文献   

The Llullaillaco volcano, northwest Argentina: construction by Pleistocene volcanism and destruction by sector collapse     

J. P. Richards  M. Villeneuve 《Journal of Volcanology and Geothermal Research》2001,105(1-2)

Llullaillaco is one of a chain of Quaternary stratovolcanoes that defines the present Andean Central Volcanic Zone (CVZ), and marks the border between Chile and Argentina/Bolivia. The current edifice is constructed from a series of thick dacitic lava flows, forming the second tallest active volcano in the world (6739 m). K–Ar and new biotite laser ⁴⁰Ar/³⁹Ar step-heating dates indicate that the volcano was constructed during the Pleistocene (≤1.5 Ma), with a youngest date of 0.048±0.012 Ma being recorded for a fresh dacite flow that descends the southern flank. Additional ⁴⁰Ar/³⁹Ar measurements for andesitic and dacitic lava flows from the surrounding volcanic terrain yield dates of between 11.94±0.13 Ma and 5.48±0.07 Ma, corresponding to an extended period of Miocene volcanism which defines much of the landscape in this region. Major- and trace-element compositions of lavas from Llullaillaco are typical of Miocene–Pleistocene volcanic rocks from the western margin of the CVZ, and are related to relatively shallow-dipping subduction of the Nazca plate beneath northern Chile and Argentina.Oversteepening of the edifice by stacking of thick, viscous, dacitic lava flows resulted in collapse of its southeastern flank to form a large volcanic debris avalanche. Biotite ⁴⁰Ar/³⁹Ar dating of lava blocks from the avalanche deposit indicate that collapse occurred at or after 0.15 Ma, and may have been triggered by extrusion of a dacitic flow similar to the one dated at 0.048±0.012 Ma. The avalanche deposits are exceptionally well preserved due to the arid climate, and prominent levées, longitudinal ridges, and megablocks up to 20-m diameter are observed.The avalanche descended 2.8 km vertically, and bifurcated around an older volcano, Cerro Rosado, before debouching onto the salt flats of Salina de Llullaillaco. The north and south limbs of the avalanche traveled 25 and 23 km, respectively, and together cover an area of approximately 165 km². Estimates of deposit volume are hampered by a lack of thickness information except at the edges, but it is likely to be between 1 and 2 km³. Equivalent coefficients of friction of 0.11 and 0.12, and excess travel distances of 20.5 and 18.5 km, are calculated for the north and south limbs, respectively. The avalanche ascended 400 m where it broke against the western flank of Cerro Rosado, and a minimum flow velocity of 90 m s⁻¹ can be calculated at this point; lower velocities of 45 m s⁻¹ are calculated where distal toes ascend 200 m slopes.It is suggested that the remaining precipitous edifice has a high probability for further avalanche collapse in the event of renewed volcanism.  相似文献   

Magmatic gas scrubbing: implications for volcano monitoring   总被引：1，自引：0，他引：1  

R. B. Symonds  T. M. Gerlach  M. H. Reed 《Journal of Volcanology and Geothermal Research》2001,108(1-4)

Despite the abundance of SO_2(g) in magmatic gases, precursory increases in magmatic SO_2(g) are not always observed prior to volcanic eruption, probably because many terrestrial volcanoes contain abundant groundwater or surface water that scrubs magmatic gases until a dry pathway to the atmosphere is established. To better understand scrubbing and its implications for volcano monitoring, we model thermochemically the reaction of magmatic gases with water. First, we inject a 915°C magmatic gas from Merapi volcano into 25°C air-saturated water (ASW) over a wide range of gas/water mass ratios from 0.0002 to 100 and at a total pressure of 0.1 MPa. Then we model closed-system cooling of the magmatic gas, magmatic gas-ASW mixing at 5.0 MPa, runs with varied temperature and composition of the ASW, a case with a wide range of magmatic–gas compositions, and a reaction of a magmatic gas–ASW mixture with rock. The modeling predicts gas and water compositions, and, in one case, alteration assemblages for a wide range of scrubbing conditions; these results can be compared directly with samples from degassing volcanoes. The modeling suggests that CO_2(g) is the main species to monitor when scrubbing exists; another candidate is H₂S_(g), but it can be affected by reactions with aqueous ferrous iron. In contrast, scrubbing by water will prevent significant SO_2(g) and most HCl_(g) emissions until dry pathways are established, except for moderate HCl_(g) degassing from pH<0.5 hydrothermal waters. Furthermore, it appears that scrubbing will prevent much, if any, SO_2(g) degassing from long-resident boiling hydrothermal systems. Several processes can also decrease or increase H_2(g) emissions during scrubbing making H_2(g) a poor choice to detect changes in magma degassing.We applied the model results to interpret field observations and emission rate data from four eruptions: (1) Crater Peak on Mount Spurr (1992) where, except for a short post-eruptive period, scrubbing appears to have drastically diminished pre-, inter-, and post-eruptive SO_2(g) emissions, but had much less impact on CO_2(g) emissions. (2) Mount St. Helens where scrubbing of SO_2(g) was important prior to and three weeks after the 18 May 1980 eruption. Scrubbing was also active during a period of unrest in the summer of 1998. (3) Mount Pinatubo where early drying out prevented SO_2(g) scrubbing before the climactic 15 June 1991 eruption. (4) The ongoing eruption at Popocatépetl in an arid region of Mexico where there is little evidence of scrubbing.In most eruptive cycles, the impact of scrubbing will be greater during pre- and post-eruptive periods than during the main eruptive and intense passive degassing stages. Therefore, we recommend monitoring the following gases: CO_2(g) and H₂S_(g) in precursory stages; CO_2(g), H₂S_(g), SO_2(g), HCl_(g), and HF_(g) in eruptive and intense passive degassing stages; and CO_2(g) and H₂S_(g) again in the declining stages. CO_2(g) is clearly the main candidate for early emission rate monitoring, although significant early increases in the intensity and geographic distribution of H₂S_(g) emissions should be taken as an important sign of volcanic unrest and a potential precursor. Owing to the difficulty of extracting SO_2(g) from hydrothermal waters, the emergence of >100 t/d (tons per day) of SO_2(g) in addition to CO_2(g) and H₂S_(g) should be taken as a criterion of magma intrusion. Finally, the modeling suggests that the interpretation of gas-ratio data requires a case-by-case evaluation since ratio changes can often be produced by several mechanisms; nevertheless, several gas ratios may provide useful indices for monitoring the drying out of gas pathways.  相似文献   

成槽作业中泥浆的护壁作用分析   总被引：1，自引：0，他引：1       下载免费PDF全文

李小青  潘鸿宝 《探矿工程》2001,(4):21-23

根据土层的物理力学性质、地下水位分析护壁泥浆对地下连续墙槽壁稳定性的影响，导出槽壁稳定性数学模型公式，并提出相应的护壁措施，防止槽壁的坍塌。  相似文献   

国内外泥浆材料的现状及发展趋势   总被引：7，自引：0，他引：7       下载免费PDF全文

何远信 《探矿工程》2001,(5):47-49

系统介绍了泥浆材料的现状及发展趋势，重点叙述了水基泥浆、油基泥浆及合成基泥浆这3大类泥浆材料的现状及发展趋势。  相似文献   

“科钻一井”一开泥浆技术          下载免费PDF全文

陈小明李传武  孙德宇李发东　和昔 《探矿工程》2001,(6):63-64

“科钻一井”一开井段采用了钠膨润土-高粘CMC泥浆体系，视漏失情况添加GD-Ⅲ随钻堵漏剂，满足了施工携带岩屑和堵漏防漏要求。介绍了该井一开井段的泥浆技术，并对泥浆成本进行了分析。  相似文献   

长白山天池火山密码破译势在必行     

金东淳  李范熙  崔钟燮 《地震地磁观测与研究》1996,(4)

长白山天池火山是中新世以来多次喷发并造成严重灾害的火山。通过十几年的火山地质及火山地震监测研究认为长白山天池火山近期不会马上喷发，但它是一座具有潜在喷发危险性的活动火山，并提出建立长白山火山观测站的重要意义，讨论了天地火山密码的破译需要调动各方面有利因素和有利条件。  相似文献