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1.
Sheridan Michael F. Hubbard Bernard Carrasco-núñez Gerardo Siebe Claus 《Natural Hazards》2004,33(2):209-221
Volcán Citlaltépetl (Pico de Orizaba) with an elevation of 5,675 m is the highest volcano in North America. Its most recent catastrophic events involved the production of pyroclastic flows that erupted approximately 4,000, 8,500, and 13,000 years ago. The distribution of mapped deposits from these eruptions gives an approximate guide to the extent of products from potential future eruptions. Because the topography of this volcano is constantly changing computer simulations were made on the present topography using three computer algorithms: energy cone, FLOW2D, and FLOW3D. The Heim Coefficient (), used as a code parameter for frictional sliding in all our algorithms, is the ratio of the assumed drop in elevation (H) divided by the lateral extent of the mapped deposits (L). The viscosity parameter for the FLOW2D and FLOW3D codes was adjusted so that the paths of the flows mimicked those inferred from the mapped deposits. We modeled two categories of pyroclastic flows modeled for the level I and level II events. Level I pyroclastic flows correspond to small but more frequent block-and-ash flows that remain on the main cone. Level II flows correspond to more widespread flows from catastrophic eruptions with an approximate 4,000-year repose period. We developed hazard maps from simulations based on a National Imagery and Mapping Agency (NIMA) DTED-1 DEM with a 90 m grid and a vertical accuracy of ±30 m. Because realistic visualization is an important aid to understanding the risks related to volcanic hazards we present the DEM as modeled by FLOW3D. The model shows that the pyroclastic flows extend for much greater distances to the east of the volcano summit where the topographic relief is nearly 4,300 m. This study was used to plot hazard zones for pyroclastic flows in the official hazard map that was published recently. 相似文献
2.
Servando De la Cruz-Reyna Izumi Yokoyama Alicia Martínez-Bringas Esteban Ramos 《Bulletin of Volcanology》2008,70(6):753-767
Popocatépetl Volcano is located in the central Mexican Volcanic Belt, within a densely populated region inhabited by over
20 million people. The eruptive history of this volcano indicates that it is capable of producing a wide range of eruptions,
including Plinian events. After nearly 70 years of quiescence, Popocatépetl reawakened in December 21, 1994. The eruptive
activity has continued up until the date of this submission and has been characterized by a succession of lava dome growth-and-destruction
episodes, similar to events that have apparently been typical for Popocatépetl since the fourteenth century. In this regime,
the episodes of effusive and moderately explosive activity alternate with long periods of almost total quiescence. In this
paper we analyze five years of volcano-tectonic seismicity preceding the initial eruption of the current episode. The evolution
of the V-T seismicity shows four distinct stages, which we interpret in terms of the internal processes which precede an eruption
after a long period of quiescence. The thermal effects of a magma intrusion at depth, the fracturing related to the slow development
of magma-related fluid pathways, the concentration of stress causing a protracted acceleration of this process, and a final
relaxation or redistribution of the stress shortly before the initial eruption are reflected in the rates of V-T seismic energy
release. A hindsight analysis of this activity shows that the acceleration of the seismicity in the third stage asymptotically
forecast the time of the eruption. The total seismic energy release needed to produce an eruption after a long period of quiescence
is related to the volume of rock that must be fractured so imposing a characteristic threshold limit for polygenetic volcanoes,
limit that was reached by Popocatépetl before the eruption. 相似文献
3.
M. A. Armienta S. De la Cruz-Reyna J. L. Macías 《Journal of Volcanology and Geothermal Research》2000,97(1-4)
Three crater lakes from Mexican volcanoes were sampled and analyzed at various dates to determine their chemical characteristics. Strong differences were observed in the chemistry among the three lakes: Nevado de Toluca, considered as dormant, El Chichón at a post-eruptive stage, and Popocatépetl at a pre-eruptive stage. Not surprisingly, no influence of volcanic activity was found at the Nevado de Toluca volcano, while the other volcanoes showed a correlation between the changing level of activity and the evolution of chemical trends. Low pHs (<3.0) were measured in the water from the active volcanoes, while a pH of 5.6 was measured at the Nevado de Toluca Sun lake. Changes with time were observed at Popocatépetl and El Chichón. Concentrations of volcanic-gas derived species like Cl−, SO42− and F− decreased irregularly at El Chichón from 1983 until 1997. Major cations concentrations also diminished at El Chichón. A 100% increase in the SO42− content was measured at Popocatépetl between 1985 and 1994. An increase in the Mg/Cl ratio between 1992 (Mg/Cl=0.085) and 1994 (Mg/Cl=0.177) was observed at Popocatépetl, before the disappearance of the crater lake in 1994. It is concluded that chemical analysis of crater lakes may provide a useful additional tool for active-volcano monitoring. 相似文献
4.
The Citlaltépetl Ignimbrite records one of the largest explosive events during the Holocene activity of Citlaltépetl Volcano
(Pico de Orizaba). Multiple pyroclastic flow units, a fall deposit, and some lahar units were emplaced between 8500–9000 y
B.P. as a result of repetitive but discrete explosive events. The whole ignimbrite resulted from discrete fluctuations in
eruptive intensity that decreased with time. The initial pyroclastic flow pulse was by far the most violent and widespread
event, and its deposits show conspicuous variations in structure and texture that could be associated with different mechanisms
of transport and emplacement. Subpopulation Sequential Fragmentation Transport (SFT) analyses were carried out in order to
determine the physical mechanisms that selectively concentrate or remove particles in the moving flows. We suggest that lateral
and temporal changes in the flow rheology, in which fluidization, yield strength, entrainment of atmospheric air, and sedimentation
played a dominant role in flow propagation and emplacement, may imprint a unique signature in the grain-size spectra. The
lowermost unit of the Citlaltépetl Ignimbrite can be envisaged by a model in which progressive aggradation near the vent became
replaced by en masse emplacement farther outward.
Received: 24 March 1998 / Accepted: 9 October 1998 相似文献
5.
Using pattern recognition techniques, we formulate a simple prediction rule for a retrospective prediction of the three last largest eruptions of the Popocatépetl, Mexico, volcano that occurred on 23 April–30 June 1997 (Eruption 1; VEI ~ 2–3); 11 December 2000–23 January 2001 (Eruption 2; VEI ~ 3–4) and 7 June–4 September 2002 (Eruption 3; explosive dome extrusion and destruction phase). Times of Increased Probability (TIP) were estimated from the seismicity recorded by the local seismic network from 1 January 1995 to 31 December 2005. A TIP is issued when a cluster of seismic events occurs under our algorithm considerations in a temporal window several days (or weeks) prior to large volcanic activity providing sufficient time to organize an effective alert strategy. The best predictions of the three analyzed eruptions were obtained when averaging seismicity rate over a 5-day window with a threshold value of 12 events and declaring an alarm for 45 days. A TIP was issued about six weeks before Eruption 1. TIPs were detected about one and four weeks before Eruptions 2 and 3, respectively. According to our objectives, in all cases, the observed TIPs would have allowed the development of an effective civil protection strategy. Although, under our model considerations the three eruptive events were successfully predicted, one false alarm was also issued by our algorithm. An analysis of the epicentral and depth distribution of the local seismicity used by our prediction rule reveals that successful TIPs were issued from microearthquakes that took place below and towards SE of the crater. On the contrary, the seismicity that issued the observed false alarm was concentrated below the summit of the volcano. We conclude that recording of precursory seismicity below and SE of the crater together with detection of TIPs as described here, could become an important tool to predict future large eruptions at Popocatépetl. Although our model worked well for events that occurred in the past, it is necessary to verify the real capability of the model for future eruptive events. 相似文献
6.
ESPERANZA MUÑOZ‐SALINAS MIGUEL CASTILLO‐RODRÍGUEZ VLAD MANEA MARINA MANEA DAVID PALACIOS 《Geografiska Annaler: Series A, Physical Geography》2010,92(3):311-328
Lahars are hazardous events that can cause serious damage to people who live close to volcanic areas; several were registered at different times in the last century, such as at Mt St Helens (USA) in 1980, Nevado del Ruiz (Colombia) in 1985 and Mt Pinatubo (Philippines) in 1990. Risk maps are currently used by decision‐makers to help them plan to mitigate the hazard‐risk of lahars. Risk maps are acquired based on a series of tenets that take into account the distribution and chronology of past lahar deposits, and basically two approaches have been used: (1) The use of Flow Simulation Software (FSS), which simulates flows along channels in a Digital Elevation Model and (2) The Geochronological Method (GM), in which the mapping is based on the evaluation of lahar magnitude and frequency. This study addresses the production of a lahar risk map using the two approaches (FSS and GM) for a study area located at Popocatépetl volcano – Central Mexico. Santiago Xalitzintla, a town located on the northern flank of Popocatépetl volcano, where volcanic activity in recent centuries has triggered numerous lahars that have endangered local inhabitants, has been used for the case study. Results from FSS did not provide satisfactory findings because they were not consistent with lahar sediment observations made during fieldwork. By contrast, the GM produced results consistent with these observations, and therefore we use them to assess the hazard and produce the risk map for the study area. 相似文献
7.
Inclusions of quenched silicate liquid in igneous phenocryst phases represent important windows into the pre-eruption chemistry of volcanic rocks. Melt inclusions are subject to a variety of potential modifications after entrapment, which obscure the connection between final inclusion composition, and entrapment conditions. We concentrate on the effects of post-entrapment crystallization (PEC) in the cooling inclusion. PEC is neither an isobaric nor an isochoric process. Pressure decreases between 2 and 27 bars per degree of cooling, depending on the chemistry of melt and host and on the degree of PEC. In the equilibrium case, between about 50% and 65% of this pressure effect is due to thermal expansivity of the liquid, 10–35% from thermal expansivity of the host, and 5–40% from mass transfer between the inclusion and host. This complicates the application of simple element-partitioning schemes for back-calculating the effects of post-entrapment crystallization except in the simplest cases. We present a thermodynamic algorithm for PEC correction. This method is based on the self-consistent thermodynamic model set used in the MELTS software package. The algorithm moves backward through the PEC process, incrementally adding equilibrium crystal composition to the liquid while accounting for consequent variations in pressure and oxygen fugacity. Entrapment conditions are assumed to have been reached when the instantaneous liquidus solid composition most closely matches that of the bulk host crystal. Besides giving information on the degree of PEC and initial inclusion composition, the proposed algorithm can provide constraints on the pressure, temperature and oxygen fugacity at the time of entrapment. Olivine- and orthopyroxene-hosted inclusions from Popocatépetl, Mexico help constrain pre-eruption conditions for mixed magmas from recent eruptive products. Feldspar-hosted inclusions from Satsuma-Iwojima, Japan suggest that these magmas were substantially undersaturated with respect to supercritical vapor phase at the time of entrapment and underwent on the order of 29% post-entrapment crystallization. Quartz-hosted inclusions can potentially be employed in more silicic compositions, but this will require refinement of existing thermodynamic models. 相似文献
8.
D.?R.?ZimbelmanEmail author R.?J.?Watters I.?R.?Firth G.?N.?Breit G.?Carrasco-Nunez 《Bulletin of Volcanology》2004,66(1):66-79
Citlaltépetl volcano is the easternmost stratovolcano in the Trans-Mexican Volcanic Belt. Situated within 110 km of Veracruz, it has experienced two major collapse events and, subsequent to its last collapse, rebuilt a massive, symmetrical summit cone. To enhance hazard mitigation efforts we assess the stability of Citlaltépetl's summit cone, the area thought most likely to fail during a potential massive collapse event. Through geologic mapping, alteration mineralogy, geotechnical studies, and stability modeling we provide important constraints on the likelihood, location, and size of a potential collapse event. The volcano's summit cone is young, highly fractured, and hydrothermally altered. Fractures are most abundant within 5–20-m wide zones defined by multiple parallel to subparallel fractures. Alteration is most pervasive within the fracture systems and includes acid sulfate, advanced argillic, argillic, and silicification ranks. Fractured and altered rocks both have significantly reduced rock strengths, representing likely bounding surfaces for future collapse events. The fracture systems and altered rock masses occur non-uniformly, as an orthogonal set with N–S and E–W trends. Because these surfaces occur non-uniformly, hazards associated with collapse are unevenly distributed about the volcano. Depending on uncertainties in bounding surfaces, but constrained by detailed field studies, potential failure volumes are estimated to range between 0.04–0.5 km3. Stability modeling was used to assess potential edifice failure events. Modeled failure of the outer portion of the cone initially occurs as an "intact block" bounded by steeply dipping joints and outwardly dipping flow contacts. As collapse progresses, more of the inner cone fails and the outer "intact" block transforms into a collection of smaller blocks. Eventually, a steep face develops in the uppermost and central portion of the cone. This modeled failure morphology mimics collapse amphitheaters present at many of the world's stratovolcanoes that have experienced massive failure events.Editorial responsibility: H. Shinohara 相似文献
9.
Elemental, isotopic, and mineral compositions as well as rocktextures were examined in samples from Popocatépetl volcanoand immediately surrounding monogenetic scoria cones of theSierra Chichinautzin Volcanic Field, central Mexico. Magma generationis strongly linked to the active subduction regime to the south.Rocks range in composition from basalt to dacite, but Popocatépetlsamples are generally more evolved and have mineral compositionsand textures consistent with more complicated, multi-stage evolutionaryprocesses. High-Mg calc-alkaline and more alkaline primitivemagmas are present in the monogenetic cones. Systematic variationsin major and trace element compositions within the monogeneticsuite can mostly be explained by polybaric fractional crystallizationprocesses in small and short-lived magmatic systems. In contrast,Popocatépetl stratovolcano has produced homogeneous magmacompositions from a shallow, long-lived magma chamber that isperiodically replenished by primitive basaltic magmas. The currenteruption (1994–present) has produced silicic dome lavasand pumice clasts that display mingling of an evolved daciticcomponent with an olivine-bearing mafic component. The longevityof the magma chamber hosted in Cretaceous limestones has fosteredinteraction with these rocks as evidenced by the chemical andisotopic compositions of the different eruptive products, contact-metamorphosedxenoliths, and fumarolic gases. Popocatépetl volcanicproducts display a considerable range of 87Sr/86Sr (0·70397–0·70463)and Nd (+6·2 to +3·0) whereas Pb isotope ratiosare relatively homogeneous (206Pb/204Pb 18·61–18·70;207Pb/204Pb 15·56–15·60). KEY WORDS: Popocatépetl; Sierra Chichinautzin Volcanic Field; arc petrogenesis; radiogenic isotopes 相似文献
10.
Volcan Popocatepetl, Mexico. Petrology, Magma Mixing, and Immediate Sources of Volatiles for the 1994-Present Eruption 总被引：1，自引：0，他引：1
Volcán Popocatépetl has been the site of voluminousdegassing accompanied by minor eruptive activity from late 1994until the time of writing (August 2002). This contribution presentspetrological investigations of magma erupted in 1997 and 1998,including major-element and volatile (S, Cl, F, and H2O) datafrom glass inclusions and matrix glasses. Magma erupted fromPopocatépetl is a mixture of dacite (65 wt % SiO2, two-pyroxenes+ plagioclase + Fe–Ti oxides + apatite, 3 wt % H2O, P= 1·5 kbar, fO2 = NNO + 0·5 log units) and basalticandesite (53 wt % SiO2, olivine + two-pyroxenes, 3 wt % H2O,P = 1–4 kbar). Magma mixed at 4–6 km depth in proportionsbetween 45:55 and 85:15 wt % silicic:mafic magma. The pre-eruptivevolatile content of the basaltic andesite is 1980 ppm S, 1060ppm Cl, 950 ppm F, and 3·3 wt % H2O. The pre-eruptivevolatile content of the dacite is 130 ± 50 ppm S, 880± 70 ppm Cl, 570 ± 100 ppm F, and 2·9 ±0·2 wt % H2O. Degassing from 0·031 km3 of eruptedmagma accounts for only 0·7 wt % of the observed SO2emission. Circulation of magma in the volcanic conduit in thepresence of a modest bubble phase is a possible mechanism toexplain the high rates of degassing and limited magma productionat Popocatépetl. KEY WORDS: glass inclusions; igneous petrology; Mexico; Popocatépetl; volatiles 相似文献