Influence of volcanic activity on spring water chemistry at Popocatepetl Volcano, Mexico     

A. L. Martin-Del Pozzo  F. Aceves  R. Espinasa  A. Aguayo  S. Inguaggiato  P. Morales  E. Cienfuegos 《Chemical Geology》2002,190(1-4):207-229

The results of the 7 years (1994–2000) of monthly monitoring of spring water before and during eruptions show response to volcanic activity. Low salinity and temperature characterize most of the springs, which are located on the flanks of Popocatepetl Volcano. The pH ranges from 5.8 to 7.8 and temperature from 3 to 36 °C. Oxygen and hydrogen isotopic data show that the water is of meteoric origin, but SO₄²⁻, Cl⁻, F⁻, HCO₃⁻, B, and SO₄²⁻/Cl⁻ variations precede main eruptive activity, which is considered linked to influx of magmatic gases and acid fluids that react with sublimates and host rock and mix with the large water system. Na⁺, Ca²⁺, SiO₂ and Mg²⁺ concentrations in the water also increased before eruptive activity. The computed partial pressure of CO₂ in equilibrium with spring waters shows values higher than air-saturated water (ASW), with the highest values up to 0.73 bar of pCO₂. Boron is detected in the water only preceding the larger eruptions. When present, boron concentration is normally under health standard limits, but in two cases the concentration was slightly above. Other components are within health standard limits, except for F⁻ in one spring.  相似文献   

Mechanisms of crustal uplift and subsidence at the Yellowstone caldera,Wyoming     

Daniel Dzurisin  Kenneth M. Yamashita  Jack W. Kleinman 《Bulletin of Volcanology》1994,56(4):261-270

Leveling surveys in 1923, 1976, and each year from 1983 to 1993 have shown that the east-central part of the Yellowstone caldera, near the base of the Sour Creek resurgent dome, rose at an average rate of 14±1 mm/year from 1923 to 1976 and 22±1 mm/year from 1976 to 1984. In contrast, no detectable movement occurred in the same area from 1984 to 1985 (-2±5 mm/year), and from 1985 to 1993 the area subsided at an average rate of 19±1 mm/year. We conclude that uplift from 1923 to 1984 was caused by: (1) pressurization of the deep hydrothermal system by fluids released from a crystallizing body of rhyolite magma beneath the caldera, then trapped beneath a self-sealed zone near the base of the hydrothermal system; and (2) aseismic intrusions of magma into the lower part of the sub-caldera magma body. Subsidence since 1985 is attributed to: (1) depressurization and fluid loss from the deep hydrothermal system, and (2) sagging of the caldera floor in response to regional crustal extension. Future intrusions might trigger renewed eruptive activity at Yellowstone, but most intrusions at large silicic calderas seem to be accommodated without eruptions. Overpressurization of the deep hydrothermal system could conceivably result in a phreatic or phreatomagmatic eruption, but this hazard is mitigated by episodic rupturing of the self-sealed zone during shallow earthquake swarms. Historical ground movements, although rapid by most geologic standards, seem to be typical of inter-eruption periods at large, mature, silicic magma systems like Yellowstone. The greatest short-term hazards posed by continuing unrest in the Yellowstone region are: (1) moderate to large earthquakes (magnitude 5.5–7.5), with a recurrence interval of a few decdes; and (2) small hydrothermal explosions, most of which affect only a small area (<0.01 km²), with a recurrence interval of a few years.  相似文献   

Implications for the thermal regime of acoustic noise measurements in Crater Lake,Mount Ruapehu,New Zealand     

J. Vandemeulebrouck  A. W. Hurst  N. Poussielgue 《Bulletin of Volcanology》1994,56(6-7):493-501

Hydrophone measurements of acoustic noise levels in the Crater Lake of Mount Ruapehu, New Zealand were made on 18 January 1991 from an inflatable rubber boat on the lake. The greatest sound pressures were recorded in the 1–10 Hz band, with sound levels generally decreasing about 20 dB per decade from 10 Hz to 80 kHz. The low frequency noise did not have an obvious relationship to the tremor observed at a seismic station within 1 km of the lake. The comparatively low levels of middle and high frequency sound meant that at the time of measurement, direct steam input did not make a significant contribution to the heating of Crater Lake. This is consistent with the earlier conclusion that during the last decade a major part of the heat input of Crater Lake has come from lake water that was heated below the lake and recycled back into the lake.  相似文献   

Active skarn formation beneath Lascar Volcano, northern Chile: a petrographic and geochemical study of xenoliths in eruption products   总被引：4，自引：0，他引：4  

S. J. MATTHEWS  R. A. MARQUILLAS  A. J. KEMP  F. K. GRANGE  & M. C. GARDEWEG 《Journal of Metamorphic Geology》1996,14(4):509-530

Calcsilicate xenoliths occur in large numbers in some lavas and pyroclastic flows of Lascar Volcano. Their whole-rock major element and REE compositions indicate that the protolith was the Upper Cretaceous Yacoraite Formation, which crops out extensively in NW Argentina. The whole-rock major element compositions of the xenoliths fall into specific groups suggesting a strong geochemical zonation in the skarn zone. Three geochemical zones have been identified; (1) an outer metamorphic zone rich in wollastonite; (2) a middle zone rich in pyroxene and garnet; (3) an inner zone rich in pyroxene and magnetite. The two innermost zones have developed from the wollastonite zone by infiltration of metasomatic fluids rich in Fe, Mn, Mg, Ti and Al. Whole-rock REE patterns have not changed significantly during prograde metamorphism and metasomatism, indicating REE immobility in the altering fluids. Retrograde alteration by acid-sulphate fluids produced anhydrite skarns and secondary calcite and wilkeite veins in the wollastonite zone. The carbon and oxygen isotopic compositions of this calcite indicate that it formed by Rayleigh crystallization from a low-temperature (<200 °C) fluid containing dissolved H₂CO₃. The calculated δ¹⁸O of the water in this fluid suggests a magmatic origin whereas the calculated δ¹³C of the dissolved carbonate is consistent with derivation from rocks of the Yacoraite Formation at 350 °C. It is suggested that the magmatic acid-sulphate fluid was responsible for leaching carbonate from the surrounding carbonate rocks and redepositing it in the skarn zone. REEs were mobilized during the retrograde acid-sulphate and acid-carbonate alteration. A negative Ce anomaly associated with this carbonate and sulphate indicates high oxygen fugacities in the mineralizing fluids.  相似文献   

Thermal monitoring of Lascar Volcano, Chile, using infrared data from the along-track scanning radiometer: a 1992–1995 time series     

M. J. Wooster  D. A. Rothery 《Bulletin of Volcanology》1997,58(7):566-579

 Lascar Volcano (22°22'S, 67°44'W) is the most active volcano of the central Andes of northern Chile. Activity since 1984 has been characterised by periods of lava dome growth and decay within the active crater, punctuated by explosive eruptions. We present herein a technique for monitoring the high-temperature activity within the active crater using frequent measurements of emitted shortwave infrared (SWIR) radiation made by the spaceborne along-track scanning radiometer (ATSR). The ATSR is an instrument of low spatial resolution (pixels 1 km across) that shares certain characteristics with the MODIS instrument, planned for use as a volcano monitoring tool in the NASA EOS Volcanology Project. We present a comprehensive time series of over 60 cloud- and plume-free nighttime ATSR observations for 1992–1995, a period during which Lascar experienced its largest historical eruption. Variations in short wavelength infrared flux relate directly to changes in high-temperature surfaces within the active crater. From these data, interpretations can be made that supplement published field reports and that can document the presence and status of the lava dome during periods where direct, ground-based, observations are lacking. Our data agree with less frequent information collected from sensors with high spatial resolution, such as the Landsat thematic mapper (Oppenheimer et al. 1993) and are consistent with field observations and models that relate subsidence of the dome to subsequent explosive eruptions (Matthews et al., 1997). Most obviously, Lascar's major April 1993 eruption follows a period in which the magnitude of emitted shortwave infrared radiation fell by 90%. At this time subsidence of the 1991–1992 lava dome was reported by field observers and this subsidence is believed to have impeded the escape of hot volatiles and ultimately triggered the eruption (Smithsonian Institution 1993a). Extrapolating beyond the period for which field observations of the summit are available, our data show that the vulcanian eruption of 20 July 1995 occurred after a period of gradual increase in short wavelength infrared flux throughout 1994 and a more rapid flux decline during 1995. We attribute this additional, otherwise undocumented, cycle of increasing and decreasing SWIR radiance as most likely representing variations in degassing through fumaroles contained within the summit crater. Alternatively, it may reflect a cycle of dome growth and decay. The explosive eruption of 17 December 1993 appears to have followed a similar, but shorter, variation in SWIR flux, and we conclude that large explosive eruptions are more likely when the 1.6-μm signal has fallen from a high to a low level. The ATSR instrument offers low-cost data at high temporal resolution. Despite the low spatial detail of the measurements, ATSR-type instruments can provide data that relate directly to the status of Lascar's lava dome and other high-temperature surfaces. We suggest that such data can therefore assist with predictions of eruptive behaviour, deduced from application of physical models of lava dome development at this and similar volcanoes. Received: 1 October 1996 / Accepted: 13 January 1997  相似文献   

长白山天池火山区大地电磁测深初步观测   总被引：24，自引：7，他引：24       下载免费PDF全文

汤吉  刘铁胜 《地震地质》1997,19(2):69-170

在长白山火山区沿着两条剖面进行了１５个测点的大地电磁测深观测，对地磁感应矢量和地下电性分布维数特征进行了分析，并使用阻抗张量分解和二维自动反演等新技术对资料进行了解释。结果表明，火山区及其周围地区的地下电性结构具有二维特征，但在火山口及其附近地下存在局部三维异常体，异常体埋深约１２ｋｍ，初步推测可能是火山岩浆囊  相似文献   

Updating channel morphology in digital elevation models: lahar assessment for Tenenepanco-Huiloac Gorge, Popocatépetl volcano, Mexico     

Esperanza Muñoz-Salinas  C. S. Renschler  D. Palacios  L. M. Namikawa 《Natural Hazards》2008,45(2):309-320

In contrast to dramatic flow regime changes by less frequent large-scale volcanic eruptions, those caused by more frequent small-scale processes in volcanic landscapes may also drastically change the direction and dynamics of flow in a drainage system formed solely by fluvial processes. During such periods of channel morphology change, it is necessary to frequently update channel flow parameters to assess preventive measures for civil protection purposes. Often aerial photography is impracticable, since parts of the channels are covered by dense vegetation, while total station and laser topographic surveys are often too slow and costly, particularly during a high frequency of events. This article introduces and validates a new methodology for updating the representation of channel morphology in Digital Elevation Models (DEM) used specifically for assessing the dangers of frequently occurring lahars along gorges in volcanic landscapes during eruptive and non-eruptive periods. The updating of channel cross-sections was achieved by inserting more detailed representative profiles of homogeneous channel sectors in DEMs derived from existing less detailed topographic maps. The channel profiles were surveyed along the thalweg in equidistant points according to Universal Transverse Mercator (UTM) (x,y) coordinates and elevation derived from the existing DEM. The proposed technique was applied at Tenenepanco-Huiloac Gorge on Popocatépetl volcano, Mexico, in an area affected by major lahars during the volcano’s most recent eruptive period from 1994 to 2005. The proposed method can reduce the cost and person-hours of a regular channel topographic survey dramatically and the enhanced DEM can determine volume parameters and flood zones associated with the 1 July 1997 and 21 January 2001 lahars, respectively. In addition, the updated DEM with better channel representation allowed a more realistic fluid flow and lahar simulation with the process-based TITAN2D model.  相似文献   

Imaging of V_p, V_s, and Poisson’s ratio anomalies beneath Kyushu, southwest Japan: Implications for volcanism and forearc mantle wedge serpentinization     

Mohamed K. Salah  Tetsuzo Seno 《Journal of Asian Earth Sciences》2008,31(4-6):404-428

We determine detailed 3-D V_p and V_s structures of the crust and uppermost mantle beneath the Kyushu Island, southwest Japan, using a large number of arrival times from local earthquakes. From the obtained V_p and V_s models, we further calculate Poisson’s ratio images beneath the study area. By using this large data set, we successfully image the 3-D seismic velocity and Poisson’s ratio structures beneath Kyushu down to a depth of 150 km with a more reliable spatial resolution than previous studies. Our results show very clear low V_p and low V_s anomalies in the crust and uppermost mantle beneath the northern volcanoes, such as Abu, Kujyu and Unzen. Low-velocity anomalies are seen in the mantle beneath most other volcanoes. In contrast, there are no significant low-velocity anomalies in the crust or in the upper mantle between Aso and Kirishima. The subducting Philippine Sea slab is imaged generally as a high-velocity anomaly down to a depth of 150 km with some patches of normal to low seismic wave velocities. The Poisson’s ratio is almost normal beneath most volcanoes. The crustal seismicity is distributed in both the high- and low-velocity zones, but most distinctly in the low Poisson’s ratio zone. A high Poisson’s ratio region is found in the forearc crustal wedge above the slab in the junction area with Shikoku and Honshu; this high Poisson’s ratio could be caused by fluid-filled cracks induced by dehydration from the Philippine Sea slab. The Poisson’s ratio is normal to low in the forearc mantle in middle-south Kyushu. This is consistent with the absence of low-frequency tremors, and may indicate that dehydration from the subducting crust is not vigorous in this region.  相似文献   

Geology and geochemical evaluation of Taftan Volcano, Sistan and Baluchestan Province, southeast of Iran     

H. Biabangard  A. Moradian 《中国地球化学学报》2008,27(4):356-369

At a glance of its stratighraphy, the Taftan Volcano can be classified as three groups： pre-, syn- and post-volcanic deposits. The pre-volcanic deposits consist mostly of flysch facies and colored mélange complex. The syn-volcanic deposits are mainly the product of the Taftan Volcano which is mostly composed of pyroclastic and lava flows from the main body of this volcano. The post-volcanic deposits are mostly epiclastic and reworked materials from the Taftan Volcano due to its erosion and weathering. Major and trace elements, and Sr/Rb isotopic compositions determined on whole-rock samples from the Taftan Volcano showed that the volcano was formed at the continental margin. The whole-rock isotopic composition of the Taftan Volcano showed a feature of strong enrichment with ^87Sr/^86Sr=0.705326-0.705921. Geochronological samples of the Tartan Volcano determined by the ^40K/^40Ar method gave an age range of 6.95±0.72 to 0.71±0.03 Ma. The rare-earth element patterns are characterized by high LREE and nearly strongly linear patterns for MREE to HREE, suggesting that distinctive minerals such as olivine and pyroxene crystallized in the early magmatic stage and then were involved in reaction between the lower crust and residual magma. The integrated isotope and trace element systematics and tectonic structure beneath the Taftan Volcano suggested the lower-crust assimilation by the primary magma. The primary magma had generated from a heterogeneous mantle source and a secondary petrogenetical process. This magma could have been affected by the subduction of the Oman Sea undemeath the continental Eurasia plate.  相似文献   

Volcanogenic dark matter and mass extinctions     

Samar Abbas  Afsar Abbas 《Astroparticle Physics》1998,8(4):317-320

The passage of the Earth through dense clumps of dark matter, the presence of which is predicted by certain cosmologies, would produce large quantities of heat in the interior of this planet through the capture and subsequent annihilation of dark matter particles. This heat would lead to large-scale volcanism which could in turn have caused mass extinctions. The periodicity of such volcanic outbursts agrees with the frequency of paleontological mass extinctions as well as the observed periodicity in the occurrence of the largest flood basalt provinces on the globe.  相似文献