Potential Flank-Collapse of Soufrière Volcano, Guadeloupe, Lesser Antilles? Numerical Simulation and Hazards     

Anne Le Friant  Georges Boudon  Jean-Christophe Komorowski  Philippe Heinrich  Michel P. Semet 《Natural Hazards》2006,39(3):381-393

The past history of recurrent flank collapses of la Soufrière volcano of Guadeloupe, its structure, its well-developed hydrothermal system and the current activity constitute factors that could promote a future flank collapse, particularly in the case of a significant increase of activity, with or without shallow magmatic input. To address the hazards associated with such a collapse, we model the emplacement of the debris avalanche generated by a flank-collapse event in 1,250 BC (3,100 years B.P.). We use a finite-difference grain-flow model solving mass and momentum conservation equations that are depth-averaged over the slide thickness, and a Coulomb-type friction law with a variable basal (minimum) friction angle. Using the parameter values determined from this simulation, we then simulate the debris avalanche which could be generated by a potential collapse of the present lava dome. We then discuss the region which could be affected by such a future collapse, and additional associated hazards of concern.  相似文献   

The Characteristics of Seismic Activity Before the Devastating Earthquake with M wg. 0 Off the West Coast of Northern Sumatra     

Xue Yan 《中国地震研究》2006,20(2):118-126

The characteristics of seismic activity in different time-spatial domain before the Mw9.0 earthquake were studied. The results are as follows ： ① The activity of the deep earthquakes in the north boundary zone of the Australian plate had been evidently strengthened since 1994, showing an increased frequency, magnitude and depth, especially in regards to the heterogeneous distribution of the earthquake depth （namely between 500km and 689km）. Meanwhile the shallow earthquakes of M ≥ 7.0 in the Sumatra island and its vicinity had been obviously strengthened too, and formed a strengthening area with a length of about 1000 km and width 300 km. ②The time distribution of global strong earthquakes with M≥ 7.0 shows that the character of anomalous seismic quiescence-activity one year before the Mw9.0 earthquake and during its active period, the strong earthquakes formed a seismic belt striking in NWW direction. At the same time, there is a seismic gap formed by earthquakes of M ≥ 5.0 in the epicenter and its neighboring region. ③ Two deep earthquakes of M ≥ 7.0 occurred in the west and in the east of the north boundary zone of the Australian plate half year ago. It is notable that one of them occurred in the Sumatra island where no deep earthquake with M ③ 6.0 has occurred in the past thirty years. ④The space distribution of moderate shocks occurring three days ago exhibited a NWW-strike seismic belt along the north boundary zone of the Australian plate. ⑤The activity of volcanoes distributed in the north boundary zone of the Australian plate had been strengthened in the past 4 years, especially several months before the occurrence of the Mw9.0 earthquake.  相似文献   

Increasing public awareness of natural hazards via the Internet     

Paula K. Dunbar 《Natural Hazards》2007,42(3):529-536

NOAA’s National Geophysical Data Center is using state-of-the-art Internet tools for natural hazards education, public outreach, and access to natural hazards data. For example, NGDC acquires, processes, and provides access to geologic hazards event data that are useful in natural hazards risk assessment and hazards-related research. In addition, a collection of natural hazards slides and a teacher’s guide on volcanoes are available online. NGDC also created an online “Kids Hazards Quiz” to test the user’s knowledge of disaster safety information. An online Natural Hazards Data Resources Directory provides access to information and links to organizations that provide natural hazards data and information. Expanded access to these data and information by the public and researchers can increase public awareness of natural hazards, improve hazards research, and ultimately reduce the devastating impacts of natural disasters.  相似文献   

Volcanic hazards zonation of the Nevado de Toluca Volcano,Central Mexico     

José Fernando Aceves Quesada  Ana Lillian Martin Del Pozzo  Jorge López Blanco 《Natural Hazards》2007,41(1):159-180

Nevado de Toluca Volcano (NTV), located in central Mexico, is a large stratovolcano, with an explosive history. The area is one of the most important developing centers (>2 millions) in Mexico and in the last 30 yrs large population growth and expansion have increased the potential risk in case of a reactivation of the volcano. As part of a study to assess volcanic risk, this paper presents the results of the volcanic hazard analysis for the NTV. A total of 150 stratigraphic sections were made in the field and three new ages were obtained. Eruptions from NTV produced a complex sequence of pyroclastic deposits that have affected the area at least 18 times during the last 100,000 yrs. Eight vulcanian, four plinian and one-ultraplinian eruptions as well as the destruction of at least three domes occurred in the last 42,000 yr BP as well as two sector collapses in the last 100,000 yrs. Isopach and isopleth maps for the main ulraplinian eruption were also made. The original cone height (5,080 m.a.s.l) was reconstructed through geomorphologic methods. The maximum distance calculated with the energy line for the block and ash flows was 41 km, 35 km for pumice flows and 45 km for debris avalanches. The dominant wind direction at altitudes of 20–30 km is to the east-northeast from November to March, west-northwest in April and west from May to October. Five hazards maps (block and ash flows, pumice flows, ash fall, debris avalanches, and lahars) were made for the NTV. The pyroclastic flows and lahars represent very high to medium hazard for Toluca, Villa Guerrero, Coatepec, Tianguistengo, Metepec, Tenango, Lerma and Zinacantepec. A new debris avalanche would probably affect the south and northeast because of active faulting (E–W and NW–SE) and existing topographic differences in height.  相似文献   

A 3D magnetic structure of Izu-Oshima Volcano and their changes after the eruption in 1986 as estimated from repeated airborne magnetic surveys     

Yoshio Ueda 《Journal of Volcanology and Geothermal Research》2007

A 3D magnetic inversion method using a conjugate gradient method (CG method) was developed for constructing 3D magnetization models of a volcanic edifice and applied to aeromagnetic anomalies of Izu-Oshima Volcano surveyed in 1986 and in 1997. The calculated results of the 1986 data show that the volcanic edifice of Izu-Oshima Volcano has a mean magnetization intensity ranging from 10.4 to 12.1 A/m. The derived 3D magnetic structure shows low magnetization zones beneath the west-northwest of the western caldera rim, beneath the west-southwest of Mt. Mihara and beneath Mt. Shiroishi. These features may be related with demagnetizations, reflecting a high thermal state due to magma activities in the 1986 eruption. The comparison between 3D magnetization models in 1986 and in 1997, indicates meaningful changes beneath the C-craters erupted in 1986, suggesting a recovery process of demagnetizations and a considerable decrease of magnetization intensities in the foot of Mt. Futago, indicative of demagnetizations. A derived magnetization model including Izu-Oshima Volcano and its surrounding sea areas clarifies the submerged volcanic edifices around Izu-Oshima Island, and suggests that the old volcanic edifices of Fudeshima, Gyojyanoiwaya, and Okata Volcanoes have been affected by eastward migrations due to massive intrusions of a dike-like structure inferred at the base of Izu-Oshima Volcano.  相似文献   

The millennium eruption of Hekla in February 2000     

Ármann Höskuldsson  Níels Óskarsson  Rikke Pedersen  Karl Grönvold  Kristín Vogfjörð  Rósa Ólafsdóttir 《Bulletin of Volcanology》2007,70(2):169-182

The 18th historic eruption of Hekla started on 26 February, 2000. It was a short-lived but intense event, emitting basaltic andesitic (55.5 wt% SiO₂) pyroclastic fragments and lava. During the course of the eruption, monitoring was done by both instruments and direct observations, together providing unique insight into the current activity of Hekla. During the 12-day eruption, a total of 0.189 km³ DRE of magma was emitted. The eruptive fissure split into five segments. The segments at the highest altitude were active during the first hours, while the segments at lower altitude continued throughout the eruption. The eruption started in a highly explosive manner giving rise to a Subplinian eruptive column and consequent basaltic pyroclastic flows fed by column collapses. After the explosive phase reached its maximum, the eruption went through three more phases, namely fire-fountaining, Strombolian bursts and lava effusion. In this paper, we describe the course of events of the eruption of Hekla and the origin of its magma, and then show that the discharge rate can be linked to different style of eruptive activity, which are controlled by fissure geometry. We also show that the eruption phases observed at Hekla can be linked with inferred magma chamber overpressure prior to the eruption.  相似文献   

Interpretation of 1992–1994 Gravity Changes around Mayon Volcano,Philippines, Using Point Sources     

A. G. Camacho  J. Fernández  M. Charco  K. F. Tiampo  G. Jentzsch 《Pure and Applied Geophysics》2007,164(4):733-749

Significant gravity changes observed around the Mayon Volcano (Philippines) between 1992 and 1994 at 26 stations are interpreted in terms of an increase of mass and pressure changes at several point sources modelled using a fast inversion process. This inversion approach attempts to fit gravity and elevation changes by combining a random search for the positions of the sources and a linear least-squares fit for the incremental mass, pressure and possible common regional values for gravity or elevation changes. Some stabilizer terms are included in the misfit function. Models with one and two sources were tested against the observed changes at Mayon. Models with only one-source give a best fit for a shallow source with a positive mass increment, horizontally displaced far from the summit. The study using two sources gives a best fit that is similar to the one-source model, but in addition indicates anomalous behavior at stations in the SW. Neglecting the stations located southward from a local fracture, the best-fitting model suggests one central positive mass change source, which is likely to be an intrusion of about 0.5 MU with a depth of about 5 km beneath the volcano. Standard deviation for the residuals ranges from 7–8 μGal for one-source models to 6–7 μGal for models with two sources. Both of the cases are below the error value of 9.4 μGal estimated for the gravity data, so that it is not possible to discriminate between both possible interpretations without additional information.  相似文献   

The Black Sea basins structure and history: New model based on new deep penetration regional seismic data. Part 1: Basins structure and fill     

《Marine and Petroleum Geology》2015

This work is based upon results of interpretation of about 8872 km-long regional seismic lines acquired in 2011 within the international project Geology Without Limits in the Black Sea. The seismic lines cover nearly the entire Black Sea Basins, including Russia, Turkey, Ukraine, Romania and Bulgaria sectors. A new map of acoustic basement relief and a new tectonic structure scheme are constructed for the Black Sea Basins. The basement of the Black Sea includes areas with oceanic crust and areas with highly rifted continental crust. A chain of buried seamounts, which were interpreted as submarine volcanoes of Late Cretaceous (Santonian to Campanian) age, has been identified to the north of the Turkish coast. On the Shatsky Ridge, probable volcanoes of Albian age have also been recognized. Synorogenic turbidite sequences of Paleocene, Eocene and Oligocene ages have been mapped. In the Cenozoic, numerous compressional and transpressional structures were formed in different parts of the Black Sea Basin. During the Pleistocene–Quaternary, turbidites, mass-transport deposits and leveed channels were formed in the distal part of the Danube Delta.  相似文献   

海拉尔盆地非典型沉积岩中柯绿泥石和钠板石组合的发现及其石油地质意义          下载免费PDF全文

要丹  刘财  张民志 《地球物理学进展》2006,21(3):949-956

柯绿泥石和钠板石为稀有矿物,在储集层中并不常见,而两者同时出现则很罕见.作者通过最近的海拉尔盆地特殊储层样品的X衍射试验分析和详细研究,发现1：1规则混合层矿物柯绿泥石和钠板石同时存在于海拉尔盆地含火山凝灰质蚀变储层或非储层的某些井段中,而且在一定范围内的岩石孔隙中可以大量持续出现,指出了本区柯绿泥石和钠板石的组合特征,结合该区地层水和微量元素地球化学特征以及重砂特征等研究了柯绿泥石和钠板石的成因矿物学意义和其它石油地质意义.海拉尔盆地柯绿泥石和钠板石在同一储层样品中的共生存在现象是世界范围内的首次发现和报道.  相似文献   

The 2005 eruption of Sierra Negra volcano,Galápagos,Ecuador     

Dennis J. Geist  Karen S. Harpp  Terry R. Naumann  Michael Poland  William W. Chadwick  Minard Hall  Erika Rader 《Bulletin of Volcanology》2008,70(6):655-673

Sierra Negra volcano began erupting on 22 October 2005, after a repose of 26 years. A plume of ash and steam more than 13 km high accompanied the initial phase of the eruption and was quickly followed by a ~2-km-long curtain of lava fountains. The eruptive fissure opened inside the north rim of the caldera, on the opposite side of the caldera from an active fault system that experienced an m_b 4.6 earthquake and ~84 cm of uplift on 16 April 2005. The main products of the eruption were an `a`a flow that ponded in the caldera and clastigenic lavas that flowed down the north flank. The `a`a flow grew in an unusual way. Once it had established most of its aerial extent, the interior of the flow was fed via a perched lava pond, causing inflation of the `a`a. This pressurized fluid interior then fed pahoehoe breakouts along the margins of the flow, many of which were subsequently overridden by `a`a, as the crust slowly spread from the center of the pond and tumbled over the pahoehoe. The curtain of lava fountains coalesced with time, and by day 4, only one vent was erupting. The effusion rate slowed from day 7 until the eruption’s end two days later on 30 October. Although the caldera floor had inflated by ~5 m since 1992, and the rate of inflation had accelerated since 2003, there was no transient deformation in the hours or days before the eruption. During the 8 days of the eruption, GPS and InSAR data show that the caldera floor deflated ~5 m, and the volcano contracted horizontally ~6 m. The total eruptive volume is estimated as being ~150×10⁶ m³. The opening-phase tephra is more evolved than the eruptive products that followed. The compositional variation of tephra and lava sampled over the course of the eruption is attributed to eruption from a zoned sill that lies 2.1 km beneath the caldera floor.  相似文献