Vanadium sublimates from the fumaroles of Izalco volcano, El Salvador

Prior to the recent discovery of high-temperature vanadium sublimates at the fumaroles of Izalco volcano, El Salvador, the only vanadium minerals known were those formed at low-temperature surface conditions. Six new vanadium compounds have already been discovered at Izalco volcano, and five of these have been elevated to mineral status. Two of the minerals are among the most vanadium-rich compounds known in nature.Field studies and studies of the crystal chemistry of the sublimate phases have allowed delineation of the conditions of exsolution of vanadium-bearing gases from the magma and conditions of sublimation of the vanadium compounds. A vanadium halogen or oxyhalogen gas phase was exsolved from a basaltic magma when the magma was 550 m below the summit crater. As the gas rose to the fumaroles and mixed with the atmosphere, the oxygen fugacity rose from that of the magma to at least 10^−3,5 bar. At the fumaroles, the vanadium compounds sublimated at various temperatures, but a minimum temperature of 760° can be determined for one of the phases based on geothermometry determined from phase relations in the system CuO-V₂O₅. The studies have demonstrated that a vanadium-bearing gas can segregate from a magma with normal basaltic concentrations of vanadium.     

The 2005 eruption of Ilamatepec (Santa Ana) volcano,El Salvador

We report the stratigraphic sequence of the 2005 eruption of Ilamatepec volcano together with sedimentological and chemical analyses of its products.Structural and textural characteristics of the deposits indicate that the eruption was driven by a small-volume rhyolitic intrusion at shallow levels, which resulted first in the collapse of the existing hydrothermally altered fan of previous deposits inside the crater lake, driving phreatic explosions with launching of blocks on ballistic trajectories; later the magma interacted with lake waters producing several hydromagmatic pyroclastic density currents (PDCs). These flows were energetic enough to knock down pine trees up to distances of 1.8 km from the crater in the E-NE sector of the volcano. Finally, ejection of ballistic blocks that landed on previously emplaced, wet pyroclastic density current deposits, caused the generation of a lahar that flowed down the steep eastern flank toward the El Jabillal gully. Subsequent lahars occurred as a result of intense rain caused by hurricane Stan.Radiocarbon ages on paleosols and charcoal fragments, separating previous volcanogenic sequences, indicate that similar eruptions have occurred more frequently in the past centuries, than previously thought.The new data confirms that Ilamatepec volcano is one of the most active volcanoes in El Salvador. Nevertheless, more detailed studies of the eruptive sequence of Ilamatepec volcano are mandatory to establish future eruptive patterns.     

萨尔瓦多地震

20 0 1年 1月 1 3日 (星期六 ) ,一次里氏 7.6级地震袭击了萨尔瓦多。这个小而人口稠密的中美洲国家 ( 6 2 0万居民居住在 2 .1万 km2 面积的土地上 )已经不止一次遭受如此命运了。自1 6世纪以来 ,圣萨尔瓦多首都已 1 1次被夷为废墟。在中美洲 ,萨尔瓦多并非是易受损害的唯一国家 ,1 972年尼加拉瓜地震和 1 976年危地马拉地震所造成的破坏就是证明。在第一次地震刚好一个月后 ,2月 1 3日又发生了第二次地震。这次地震被测定为里氏6 .6级 ,震中与第一次地震的不同 ,并在这个国家的中部和农村地区产生了一个新的破坏区域。紧接第一次地震之后…     

Tidal triggering of seismic and volcanic phenomena during the 1879–1880 eruption of Islas Quemadas volcano in El Salvador, Central America

The Islas Quemadas dome in Lake Ilopango, El Salvador, was extruded during December 1879 to March 1880. The eruption took place in six distinct periods, five of which began near fortnightly minima in the amplitude of the semidiurnal solid earth tide. An earthquake swarm preceded dome extrusion. Felt earthquakes were carefully recorded during a two-day period preceding a destructive main shock that occurred on December 27, 1879. During this foreshock sequence the periods of highest earthquake activity occurred at times of maxima and minima in semidiurnal solid-earth tide. The four largest earthquakes, including the main shock, occurred at maxima in the semidiurnal tide.     

Strahlungsmessungen mit dem Bellani-Kugelpyranometer in El Salvador (Mittelamerika)

Zusammenfassung Der Jahresverlauf der Zirkumglobalstrahlung in El Salvador wird in seiner Abhängigkeit vom Jahresgang der Sonnenhöhe, den Bewölkungs- und Trübungsverhältnissen diskutiert. Der Zusammenhang zwischen dem Strahlungsgenuss einer Kugel und einer horizontalen Fläche wird im Hinblick auf die jahreszeitlich wechselnde Sonnenhöhe untersucht; es zeigt sich, dass die Globalstrahlung mit befriedigender Genauigkeit aus Messungen der Zirkumglobalstrahlung zu bestimmen ist. Die Beziehung zwischen Zirkumglobalstrahlung und Sonnenscheindauer bzw. Bewölkungsverhältnissen wechselt jahreszeitlich, entsprechend den mittleren Sonnenhöhen, und gestattet, lückenhafte Messreihen der Zirkumglobalstrahlung nach Registrierungen der Sonnenscheindauer zu reduzieren.

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Summary The annual variation of circumglobal radiation in El Salvador, depending on the seasonal change of solar height, cloudiness and turbidity, is discussed. The relation between the radiation received on a sphere and a horizontal surface on the other hand, is examined with respect to seasonal change of solar height; global radiation is to be determined from measurements of circumglobal radiation with satisfactory accuracy. The relation between circumglobal radiation and sunshine duration or cloud conditions, changes throughout the year, according to mean solar height; uncomplete series of circumglobal radiation can be reduced after records of the duration of sunshine.

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Resumen El transcurso anual de la radiación circumglobal en El Salvador es discutido con referencia a la variación anual de la altura del Sol, la nubosidada y la turbiedad. La relación entre la cantidad de radiación recibida por una esfera y una superficie horizontal, por otra parte, es investigada con respecto al cambio estacional de la altura del sol; resulta que la radiación global es a determiner con satisfactoria exactitud. a base de mediciones de la radiación circunglobal. La relación entre radiación circunglobal y duración del brillo solar o nubosidad, respectivamente, varía segun la estación del año, correspondientemente a la altura media del sol; series cortos o incompletos de la radiación circunglobal pueden ser reducidas segun registros de la duración de la luz solar.

     

Geochemical trends of sequential lava flows from Meseta volcano, Guatemala

The Meseta and Fuego volcanoes closely overlap and collectively are known as the Fuego Volcanic Complex. Historic activity occurs exclusively at Fuego, the southern center, and consists of high-Al basalts. Meseta, the inactive northern center, is predominantly composed of basaltic andesites with minor basalt and andesite. A thick sequence of lava flows and dikes is exposed by a steep collapse escarpment on the east flank of Meseta. The upper 75% of the sequence was sampled from three interfingering stratigraphic sections consisting of 27, 10 and 4 lavas, respectively. Temporal geochemical trends of each section indicates a complex evolutionary history. A major trend toward more evolved compositions upward in the section is consistent with crystal fractionation. This trend is sharply interrupted by the youngest lavas which become distinctly more mafic in composition. Magma mixing is apparently the dominant magmatic evolution process that generated these lavas. The two trends have distinct Sr signatures that suggest a change in parental magma compositions. This abrupt change in composition is interpreted to signal high input rates of mafic magma into the subvolcanic magma chamber. These changes eventually led to sector collapse of Meseta volcano and deposition of the Escuintla debris avalanche. Eruptive activity then migrated to the Fuego volcano where historic activity is similar to that of Meseta immediately prior to its collapse.     

Ground-based thermal imaging of lava lakes at Erebus volcano,Antarctica

Mount Erebus, a large intraplate stratovolcano dominating Ross Island, Antarctica, hosts the world's only active phonolite lava lakes. The main manifestation of activity at Erebus volcano in December 2004 was as the presence of two convecting lava lakes within an inner crater. The long-lived Ray Lake, ~ 1400 m² in area, was the site of up to 10 small Strombolian eruptions per day. A new but short-lived, ~ 1000–1200 m² lake formed at Werner vent in December 2004 sourced by lava flowing from a crater formed in 1993 by a phreatic eruption. We measured the radiative heat flux from the two lakes in December 2004 using a compact infrared (IR) imaging camera. Daily thermal IR surveys from the Main Crater rim provide images of the lava lake surface temperatures and identify sites of upwelling and downwelling. The radiative heat outputs calculated for the Ray and Werner Lakes are 30–35 MW and 20 MW, respectively. We estimate that the magma flux needed to sustain the combined heat loss is ~ 250–710 kg s^− 1, that the minimum volume of the magma reservoir is 2 km³, and that the radius of the conduit feeding the Ray lake is ~ 2 m.     

Dynamics of a confined lava flow on Kilauea volcano,Hawaii

This paper presents a new method of analysing lava flow deposits which allows the velocity, discharge rate and rheological properties of channelled moving lavas to be calculated. The theory is applied to a lava flow which was erupted on Kilauea in July 1974. This flow came from a line of fissures on the edge of the caldera and was confined to a pre-existing gully within 50 m of leaving the vent. The lava drained onto the floor of the caldera when the activity stopped, but left wall and floor deposits which showed that the lava banked up as it flowed around each of the bends. Field surveys established the radius of curvature of each bend and the associated lava levels, and these data, together with related field and laboratory measurements, are used to study the rheology of the lava. The results show the flow to have been fast moving but still laminar, with a mean velocity of just over 8 m s^–1; the lava had a low or negligible yield strength and viscosities in the range 85–140 Pa s. An extension of the basic method is considered, and the possibility of supercritical flow discussed.     

Marine environmental impact due to mining activities of El Salvador copper mine,Chile

Marine environmental impact as a result of copper mine tailing dumping in the sea is studied at Chañaral (North of Chile). These dumpings, from the copper mine El Salvador, have hindered harbour activities, caused geomorphological coastal modifications and affected seriously marine coastal ecosystems and recreational activities. At the old dumping site, Chañaral Bay (1938–1974), nearly 150 million tons of fine sediments were accumulated. Tailing discharges at the new dumping site, Caleta Palito, about 8 km north of Chañaral Bay are accumulating approximately at the rate of 25 000 tons of fine sediments per day, plus unknown quantities of chemicals (Cu, As, CN^?). From January 1975 to July 1976, this site has received over 13 million tons of sediments which has caused deterioration of the marine coastal environment, reduction in light penetration and high mortalities among marine invertebrates, fishes and algae.     

The geochemistry of El Misti volcano,Peru fumaroles

El Misti is a 5822 m strato volcano in southern Peru. The mineralogy of the fumaroles is essentially sulfur, anhydrite, gypsum and ralstonite which are precipitated by acid vapors at 100°C–125°C. There are 2 to 6 parts per thousand chloride concentrations and several parts per million sodium, potassium, magnesium, calcium, iron and zinc concentrations in the condensed vapors. Elemental ratios indicate near complete leaching of the wall rock by the vapors. Arsenic and selenium are contaminants of the sulfur but are absent from the other minerals. Both the gypsum and anhydrite contain strontium and lead and show no tendency to fractionate these metals. The anhydrite alone contains significant thallium and bismuth. Bromine, strontium, thallium and lead are present in the ralstonite. The average δ D and δ O¹⁸ ratios from the fumarolic condensates are ?31.4 ‰ and +4.8 ‰ respectively. A marine contaminated heavy water source at depth is indicated as the parent water for the vapors.     

The earthquake sequence of May 1951 at Jucuapa, El Salvador

Three earthquakes that happened over two days in May 1951 caused extensive damage to villages in a small area of eastern El Salvador (Central America). Contemporary hypocentral solutions indicated focal depths, confirmed by re-calculations using available seismic data, of the order of 90 km, suggesting events associated with the subducted Cocos plate. Macroseismic observations strongly indicate that the earthquakes were of very shallow focus and this is supported by wave-form modeling and the appearance of seismograms recorded in Guatemala. A re-evaluation of the location and source characteristics for these events is presented, together with a fault plane solution and additional macroseismic evidence. The implications for seismic hazard and risk assessment in Central America, where shallow earthquakes of moderate magnitude, frequently occurring in clusters, pose the greatest threat to settlements which, like the area affected by these events, are concentrated along the axis of Quaternary volcanoes.     

The dynamics of a channel-fed lava flow on Pico Partido volcano, Lanzarote

A short length of channel on Pico Partido volcano, Lanzarote, provides us the opportunity to examine the dynamics of lava flowing in a channel that extends over a sudden break in slope. The 1–2-m-wide, 0.5–2-m-deep channel was built during the 1730–1736 eruptions on Lanzarote and exhibits a sinuous, well-formed channel over a steep (11° slope) 100-m-long proximal section. Over-flow units comprising smooth pahoehoe sheet flow, as well as evidence on the inner channel walls for multiple (at least 11) flow levels, attest to unsteady flow in the channel. In addition, superelevation is apparent at each of the six bends along the proximal channel section. Superelevation results from banking of the lava as it moves around the bend thus causing preferential construction of the outer bank. As a result, the channel profile at each bend is asymmetric with an outer bank that is higher than the inner bank. Analysis of superelevation indicates flow velocities of ~8 m s^–1. Our analysis of the superelevation features is based on an inertia-gravity balance, which we show is appropriate, even though the down-channel flow is in laminar flow. We use a viscosity-gravity balance model, together with the velocities calculated from superelevation, to obtain viscosities in the range 25–60 Pa s (assuming that the lava behaved as a Newtonian liquid). Estimated volume fluxes are in the range 7–12 m³ s^–1. An apparent down-flow increase in derived volume flux may have resulted from variable supply or bulking up of the flow due to vesiculation. Where the channel moves over a sharp break in slope and onto slopes of ~6°, the channel becomes less well defined and widens considerably. At the break of slope, an elongate ridge extends across the channel. We speculate that this ridge was formed as a result of a reduction in velocity immediately below the break of slope to allow deposition of entrained material or accretion of lava to the channel bed as a result of a change in flow regime or depth.     

Metal speciation and environmental impact on sandy beaches due to El Salvador copper mine, Chile

Several coastal rocky shores in northern Chile have been affected by the discharges of copper mine tailings. The present study aims to analyze the chemical speciation of heavy metals in relation to the diversity of sessile species in the rocky intertidal benthic community on the northern Chilean coast, which is influenced by the presence of copper mine tailings. In particular, the chemical forms of Cd, Cu, Fe, Mn, Ni, Pb and Zn in beach sediment samples collected in the area influenced by El Salvador mine tailings were studied using a sequential chemical extraction method. In general, all the elements present a maximum concentration in the area near the actual discharge point (Caleta Palito). With regard to Cu and Mn, the concentrations range between 7.2-985 and 746-22,739 microg/g respectively, being lower than background levels only in the control site of Caleta Zenteno. Moreover, the correlation coefficients highlight that Fe, Mn and Ni correlate significantly and positively in the studied area, showing a possible common, natural origin, whilst Cu shows a negative correlation with Fe, Mn and Ni. It could be possible that Cu has an anthropogenic origin, coming from mining activity in the area. Cd, Fe, Mn, Ni, Pb and Zn are mostly associated with the residual phase, whilst Cu presents a different speciation pattern, as resulted from selective extractions. In fact, Cu is highly associated with organic and exchangeable phases in contaminated localities, whilst it is mainly bound to the residual phase in control sites. Moreover, our results, compared to local biological diversity, showed that those sites characterized by the highest metal concentrations in bioavailable phase had the lowest biodiversity.     

Variational coupling of Plinian column models and data: Application to El Chichón volcano

Many efforts have been done in the modelling of Plinian columns. However, until now, the inverse problem of the reconstruction of a Plinian event from observed data has been only roughly tackled. This paper discusses the efficient variational data assimilation (VDA) that manages the optimization iterate sequence by means of gradient computations. Theoretical developments of VDA are presented for both the Woods equations and a generic system allowing for the modelling of the Navier–Stokes equations. Two- and three-dimensional unsteady Plinian models being based on the latters, VDA could be clearly performed on their differentiable subset of equations.     

2001年的萨尔瓦多:热带火山环境中的地震灾害及防灾

应萨尔瓦多驻墨西哥大使馆的邀请 ,在2 0 0 1年 1月 1 3日灾害性地震 ( MW=7.6)之后2个星期 ,我们访问了萨尔瓦多。我们一行人中曾有一位在这个国家研究过早期地震灾害( L omnitz and Schultz,1 966)。本文就是我们现场考察的结果。1　地震概况主震 ( MW=7.6)发生于当地时间 2 0 0 1年1月 1 3日星期六上午 1 1时 3 3分 ,震中位于萨尔瓦多南海岸 ( 1 2 .80°N,88.78°W) ,震源深度约 40 km。第 2次较大地震 ( MW=6.6)发生于 2 0 0 1年 2月 1 3日 ,震中位于内陆 1 3 .64°N88 .94°W处 ,震源深度 1 3 km。地震共导致1 1 0 0多人死亡 ,且…     

Three thousand years of flank and central vent eruptions of the San Salvador volcanic complex (El Salvador) and their effects on El Cambio archeological site: a review based on tephrostratigraphy

The volcanic events of the last 3,000?years at San Salvador volcanic complex are reviewed using detailed stratigraphic records exposed in new excavations between 2005 and 2007, at El Cambio archeological site (Zapotitán Valley, El Salvador), and in other outcrops on the northern and northwestern sectors of the complex. The sequences that overlie Tierra Blanca Joven (cal. 429?±?107?ad), from the Ilopango caldera, comprise the Loma Caldera (cal. 590?±?90?ad) and El Playón (1658?C1671) deposits and the San Andrés Tuff (cal. 1031?±?29?ad), related to El Boquerón Volcano. The surge deposits within the El Playón, San Andrés Tuff and overlying Talpetate II sequences indicate the significance of phreatomagmatic phases in both central vent and flank eruptions during the last 1,600?years. Newly identified volcanic deposits underlying Tierra Blanca Joven at El Cambio extend the stratigraphic record of the area to 3,000?years?bp. Paleosols interstratified with those deposits contain cultural artifacts which could be associated with the Middle Preclassic period (900?C400?bc). If correct, human occupation of the site during the Preclassic period was more intense than previously known and volcanic eruptions must have affected prehistoric settlements. The archeological findings provide information on how prehistoric populations dealt with volcanic hazards, thousands of years ago in the eastern Zapotitán Valley, where several housing projects are currently being developed. The new stratigraphic and volcanological data can be used as a basis for local and regional hazard assessment related to future secondary vent activity in the San Salvador Volcanic Complex.     

Gravity and seismicity analyses of the El Chichon volcano,Chiapas, Mexico

Subduction induced compressional stress, lateral displacement faults probably linked to the NW extension of the Polochic-Motagua fault system, and local magma emplacement create a complex geological setting for the El Chichon volcano.Gravity analysis reveals that the principal structures in the area correspond to synclines and anticlines. Downward continuation of the gravity field suggests the presence of magma emplacement SE of the volcano. This magmatic emplacement appears to be the principal cause of the truncation of the syncline in which the volcano lies.Analyses of earthquakes occurring after eruptions show that the vertical distribution of events is confined to a roughly cylindrical zone which correlates well with the region of magmatic emplacement inferred from the gravity analysis.Even though more than 350 km separate the volcano from the Middle American trench, the compressional stress regime reported for the area may correlate with subduction stress (N30°E). However, the strike direction for the principal faults in the zone, N60°W, permits us to postulate that the NW extension of the Polochic-Motagua fault system is implicated in the local tectonics of the El Chichon area.     

Magnetic petrology of the 1991–1995 dacite lava of Unzen volcano,Japan: Degree of oxidation and implications for the growth of lava domes

To understand the oxidation state and process of oxidation of lava domes, we carried out magnetic petrological analyses of lava samples obtained from domes and block-and-ash-flow deposits associated with the 1991–1995 eruption of Unzen volcano, Japan. As a result, we recognize three different types of magnetic petrology, each related to deuteric high-temperature oxidation during initial cooling. Type A oxides are characterized by homogenous titanomagnetite and titanohematite, indicating a low oxidation state and high titanomagnetite concentrations. Type B oxides are weakly exsolved and contain titanohematite laths and rutile lenses, indicating a higher oxidation state. Type C oxides, which represent the highest oxidation state, are completely exsolved and composed of Ti-poor titanomagnetite, titanohematite, rutile, and pseudobrookite, indicating high hematite concentrations. Some grains in Types A and B show indications of reduction, which was related to interaction with volcanic gases subsequent to high-temperature oxidation. In terms of geological occurrence, the oxidation processes probably differed for endogenous and exogenous domes. Endogenous dome lavas are oxidized concentrically and are classified into the three types according to their location within the dome: samples from the surface are strongly oxidized and classified as Type C, while the inner part is unoxidized and classified as Type A. Exogenous dome lavas are unoxidized and assigned to Type A. Some samples show signs of reduction, which may have occurred around fumaroles. We propose that location within the dome and the process of dome growth are the factors that control oxidation.     

Simulations of the 2004 lava flow at Etna volcano using the magflow cellular automata model

Since the mechanical properties of lava change over time, lava flows represent a challenge for physically based modeling. This change is ruled by a temperature field which needs to be modeled. MAGFLOW Cellular Automata (CA) model was developed for physically based simulations of lava flows in near real-time. We introduced an algorithm based on the Monte Carlo approach to solve the anisotropic problem. As transition rule of CA, a steady-state solution of Navier-Stokes equations was adopted in the case of isothermal laminar pressure-driven Bingham fluid. For the cooling mechanism, we consider only the radiative heat loss from the surface of the flow and the change of the temperature due to mixture of lavas between cells with different temperatures. The model was applied to reproduce a real lava flow that occurred during the 2004–2005 Etna eruption. The simulations were computed using three different empirical relationships between viscosity and temperature.     

Diversion of lava flows by aerial bombing — lessons from Mauna Loa volcano,Hawaii

Lava flows from Mauna Loa volcano can travel the long distances from source vents to populated areas of east Hawaii only if heat-insulating supply conduits (lava channels and/or lava tubes) are constructed and maintained, so as to channelize the flow and prevent heat loss during transport. Lava is commonly directed into such conduits by horseshoe-or lyre-shaped spatter cones-loose accumulations of partially welded scoria formed around principal vents during periods of high fountaining. These conduit systems commonly develop fragile areas amenable to artificial disruption by explosives during typical eruptions. If these conduits can be broken or blocked, lava supply to the threatening flow fronts will be cut off or reduced. Explosives were first suggested as a means to divert lava flows threatening Hilo, Hawaii during the eruption of 1881. They were first used in 1935, without significant success, when the Army Air Force bombed an active pahoehoe channel and tube system on Mauna Loa’s north flank. Channel walls of a Mauna Loa flow were also bombed in 1942, but again there were no significant effects. The locations of the 1935 and 1942 bomb impact areas were determined and are shown for the first time, and the bombing effects are documented. Three days after the 1942 bombing the spatter cone surrounding the principal vent partially collapsed by natural processes, and caused the main flow advancing on Hilo to cease movement. This suggested that spatter cones might be a suitable target for future lava diversion attempts. Because ordnance, tactics, and aircraft delivery systems have changed dramatically since 1942, the U.S. Air Force conducted extensive testing of large aerial bombs (to 900 kg) on prehistoric Mauna Loa lavas in 1975 and 1976, to evaluate applicability of the new systems to lava diversion. Thirty-six bombs were dropped on lava tubes, channels, and a spatter cone in the tests, and it was verified that spatter cones are especially fragile. Bomb crater size (to 30 m diameter) was found to be inversely related to target rock density, with the largest craters produced in the least dense, weakest rock. Bomb fuze time delays of 0.05 sec caused maximum disruption effects for the high impact velocities employed (250 to 275 m/sec). Modern aerial bombing has a substantial probability of success for diversion of lava from most expected types of eruptions on Mauna Loa’s Northeast Rift Zone, if Hilo is threatened and if Air Force assistance is requested. The techniques discussed in this paper may be applicable to other areas of the world threatened by fluid lava flows in the future.