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1.
The 2002 eruption of Nyiragongo volcano constitutes the most outstanding case ever of lava flow in a big town. It also represents one of the very rare cases of direct casualties from lava flows, which had high velocities of up to tens of kilometer per hour. As in the 1977 eruption, which is the only other eccentric eruption of the volcano in more than 100 years, lava flows were emitted from several vents along a N–S system of fractures extending for more than 10 km, from which they propagated mostly towards Lake Kivu and Goma, a town of about 500,000 inhabitants. We assessed the lava flow hazard on the entire volcano and in the towns of Goma (D.R.C.) and Gisenyi (Rwanda) through numerical simulations of probable lava flow paths. Lava flow paths are computed based on the steepest descent principle, modified by stochastically perturbing the topography to take into account the capability of lava flows to override topographic obstacles, fill topographic depressions, and spread over the topography. Code calibration and the definition of the expected lava flow length and vent opening probability distributions were done based on the 1977 and 2002 eruptions. The final lava flow hazard map shows that the eastern sector of Goma devastated in 2002 represents the area of highest hazard on the flanks of the volcano. The second highest hazard sector in Goma is the area of propagation of the western lava flow in 2002. The town of Gisenyi is subject to moderate to high hazard due to its proximity to the alignment of fractures active in 1977 and 2002. In a companion paper (Chirico et al., Bull Volcanol, in this issue, 2008) we use numerical simulations to investigate the possibility of reducing lava flow hazard through the construction of protective barriers, and formulate a proposal for the future development of the town of Goma.  相似文献   

2.
Mt. Nyiragongo is one of the most dangerous volcanoes in the world for the risk associated with the propagation of lava flows. In 2002 several vents opened along a huge system of fractures, pouring out lava which reached and destroyed a considerable part of Goma, a town of about 500,000 inhabitants on the shore of Lake Kivu. In a companion paper (Favalli et al. in Bull Volcanol, this issue, 2008) we employed numerical simulations of probable lava flow paths to evaluate the lava flow hazard on the flanks of the volcano, including the neighbouring towns of Goma (DRC) and Gisenyi (Rwanda). In this paper we use numerical simulations to investigate the possibility of significantly reducing the lava flow hazard in the city through the construction of protective barriers. These barriers are added to the DEM of the area as additional morphological elements, and their effect is evaluated by repeating numerical simulations with and without the presence of barriers. A parametric study on barrier location, size, shape and orientation led to the identification of barriers which maximize protection while minimizing their impact. This study shows that the highest hazard area corresponding to eastern Goma, which was largely destroyed by lava flows in 2002, cannot be effectively protected from future lava flows towards Lake Kivu and should be abandoned. On the contrary, the rest of the town can be sheltered from lava flows by means of two barriers that deviate or contain the lava within the East Goma sector. A proposal for the future development of the town is formulated, whereby “new” Goma is completely safe from the arrival of lava flows originating from vents outside its boundaries. The proposal minimizes the risk of further destruction in town due to future lava flows.  相似文献   

3.
Geological surveys, tephrostratigraphic study, and 40Ar/39Ar age determinations have allowed us to chronologically constrain the geological evolution of the lower NW flank of Etna volcano and to reconstruct the eruptive style of the Mt Barca flank eruption. This peripheral sector of the Mt Etna edifice, corresponding to the upper Simeto valley, was invaded by the Ellittico volcano lava flows between 41 and 29 ka ago when the Mt Barca eruption occurred. The vent of this flank eruption is located at about 15 km away from the summit craters, close to the town of Bronte. The Mt Barca eruption was characterized by a vigorous explosive activity that produced pyroclastic deposits dispersed eastward and minor effusive activity with the emission of a 1.1-km-long lava flow. Explosive activity was characterized by a phreatomagmatic phase followed by a magmatic one. The geological setting of this peripheral sector of the volcano favors the interaction between the rising magma and the shallow groundwater hosted in the volcanic pile resting on the impermeable sedimentary basement. This process produced phreatomagmatic activity in the first phase of the eruption, forming a pyroclastic fall deposit made of high-density, poorly vesicular scoria lapilli and lithic clasts. Conversely, during the second phase, a typical strombolian fall deposit formed. In terms of hazard assessment, the possible occurrence of this type of highly explosive flank eruption, at lower elevation in the densely inhabited areas, increases the volcanic risk in the Etnean region and widens the already known hazard scenario.  相似文献   

4.
The lava flow hazard is an important and frequent disaster for residents in the volcanic area. In this paper, we focus on the lava flow inundation hazard zoning based on the example case of the Ashikule volcano in Xinjiang, China. Firstly, the parameters of magma such as density, viscosity and temperature are calculated by the empirical formula of magma utilizing results of previous field geological survey and petrology analysis. Then, using the kinematic thermo-rheological model, we simulated the inundation area of lava flow from Ashi volcano at the effusion rates of 200m3/s and 500m3/s. The simulation results of Ashi volcano well coincide to the geological map and verify that the method and parameters are valid. Then the applied simulations were carried out to calculate the lava flow inundation area in future eruption at Ashi, Wuluke and Daheishan crater with different effusion rates. At last, according to the analysis of the applied simulation results and drawing lessons from the foreign disaster zoning method, the four-level hazard zoning was built and set with different colors. The first level with red color is the extra-dangerous zone that is always inundated in any eruption but only distributes near the lava spillway of the crater. The second level with orange color is the dangerous zone that is inundated in the medium scale eruption. The third level with yellow color is the sub-dangerous zone that is corresponding to the large eruption. The fourth level with blue color is the potential dangerous zone that is only inundated in the extra-large eruption. In addition, we put forward the suggestion to respond to and avoid the disaster in future. Although China has not been affected by the lava flow for nearly three hundred years, the prospective study in this paper will lay the foundation for the study of related disasters, and provide the reference for the major construction projects in the volcanic area.  相似文献   

5.
Longgang volcano cluster is 150km away from the Tianchi volcano, located in Jingyu and Huinan Counties, Jilin Province, China. It had a long active history and produced hundreds of volcanoes. The latest and largest eruption occurred between 1 500 and 1 600 years ago by Jinlongdingzi(JLDZ)volcano which had several eruptions in the history. This paper discusses the volcanic hazard types, and using the numerical simulations of lava flow obtained with the Volcflow model, proposes the hazard zonation of JLDZ volcano area. JLDZ volcano eruption type is sub-plinian, which produced a great mass of tephra fallout, covering an area of 260km2. The major types of volcanic hazards in JLDZ area are lava flow, tephra fallout and spatter deposits. Volcflow is developed by Kelfoun for the simulation of volcanic flows. The result of Volcflow shows that the flows are on the both sides of the previous lava flows which are low-lying areas now. According to the physical parameters of historical eruption and Volcflow, we propose the preliminary volcanic hazard zonation in JLDZ area. The air fall deposits are the most dangerous product in JLDZ. The highly dangerous region of spatter deposits is limited to a radius of about 2km around the volcano. The high risk area of tephra fallout is between 2km to 9km around the volcano, and between 9km to 14km is the moderate risk area. Out of 14km, it is the low risk area. Lava flow is controlled by topography. From Jinchuan Town to Houhe Village near the volcano is the low-lying area. If the volcano erupts, these areas will be in danger.  相似文献   

6.
The age of past lava flows is crucial information for evaluating the hazards and risks posed by effusive volcanoes, but traditional dating methods are expensive and time‐consuming. This study proposes an alternative statistical dating method based on remote sensing observations of tropical volcanoes by exploiting the relationship between lava flow age and vegetation cover. First, the factors controlling vegetation density on lava flows, represented by the normalized difference vegetation index (NDVI), were investigated. These factors were then integrated into pixel‐based multi‐variable regression models of lava flow age to derive lava flow age maps. The method was tested at a pixel scale on three tropical African volcanoes with considerable recent effusive activity: Nyamuragira (Democratic Republic of Congo), Mt Cameroon (Cameroon) and Karthala (the Comoros). Due to different climatic and topographic conditions, the parameters of the spatial modeling are volcano‐specific. Validation suggests that the obtained statistical models are robust and can thus be applied for estimating the age of unmodified undated lava flow surfaces for these volcanoes. When the models are applied to fully vegetated lava flows, the results should be interpreted with caution due to the saturation of NDVI. In order to improve the accuracy of the models, when available, spatial data on temperature and precipitation should be included to directly represent climatic variation. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

7.
Mount Cameroon is an active volcano located in the Gulf of Guinea, west of Central Africa. After the March–April 1999 eruption on the SW flank, another eruption of the volcano occurred in 2000. It took place from three sites on the southwest flank and near the summit. The first eruptive site was located 500 m to the southwest of the summit, at 3900 m altitude. Activity on this site was mainly explosive with no lava flow. The second site was located between 3220 and 3470 m altitude. Lava was emitted along NNE–SSE fissures from this site and flew towards Buea, the main city of the area, stopping ~ 4 km from the first houses. The last site was located in the south western flank at 2750 m altitude. The lava ejected from an old cone near the first 1999 eruptive site was divided into two branches, for a total length of around 1 km. The location of active volcanic cones in 1999 and 2000 seems to be linked to the local tectonics. The pre-eruptive period was characterized by a seismic swarm which may be a precursor recorded in March 2000 by an analogue seismic station. The main shock was a magnitude 3.2 event, and was felt by the population in Ekona town located on the eastern flank. It had a Modified Mercalli intensity of III–IV. When the eruption started, a temporary network of short period 3-component seismic stations was set up around the volcano to improve the monitoring of seismic activity. The co-eruptive period from late May to September was characterized by sequences of earthquake swarms, volcanic tremor and a family of earthquakes having similar waveform and appearing regularly in August and early September. Some of the earthquakes were felt by the population in Buea and its environments. The largest seismic event recorded had a magnitude of 4. During the post-eruptive period from mid-September to December, seismicity returned to its background level of 1–3 earthquakes per 3 days. Hypocenter locations reveal a linear narrow structure under the summit zone which could represent the magmatic conduit of the volcano. The frequency/magnitude relationship revealed a b-value of 1.43 higher than those previously determined, but more representative of volcanic media. Seismic energy release was gradual after the 2000 eruption started.  相似文献   

8.
Merapi volcano, in Central Java, is one of the most active volcanoes in the world. At least 23 of the 61 reported eruptions since the mid-1500s have produced source deposits for lahars. The combined lahar deposits cover about 286 km2 on the flanks and the surrounding piedmonts of the volcano. At Merapi, lahars are commonly rain-triggered by rainfalls having an average intensity of about 40 mm in 2 h. Most occur during the rainy season from November to April, and have average velocities of 5–7 m/s at 1000 m in elevation. A wide range of facies may be generated from a single flow, which may transform downvalley from debris flow to hyperconcentrated streamflow.Because of the high frequency and magnitude of the lahar events, lahar-related hazards are high below about 450–600 m elevation in each of the 13 rivers which drain the volcano. Hazard-zone maps for lahar were produced by Pardyanto et al. (Volcanic hazard map, Merapi volcano, Central Java (1/100,000). Geol. Surv. of Indonesia, Bandung, II, 4, 1978) and the Japanese–Indonesian Cooperation Agency (Master plan for land conservation and volcanic debris control in the area of Mt Merapi, Jakarta, 1980), but these maps are of a very small scale to meet modern zoning requirements. More recently, a few large-scale maps (1/10,000- and 1/2000-scale) and risk assessments have been completed for a few critical river systems.  相似文献   

9.
This paper presents an automatic system for the elaboration of volcanic hazard maps and scenarios. The methodology used for the generation of both maps is based on the use of numerical simulation of eruptive processes. The system has been developed in a Geographical Information System (GIS) framework, where models for the numerical simulation of different volcanic hazards have been integrated. The user can select in a toolbar one hazard and then decide whether to generate a scenario map (usually with a unique vent) or a hazard map (generally with a broader source area). Once the input parameters are selected, the system automatically generates the corresponding map. The system also incorporates a module to determine the spatial probability of vent opening, as this could be an important parameter for the computation of hazard maps. The tool has been designed in such a way that the inclusion of new numerical models and functionalities is rather easy. Each numerical model is programmed and implemented as an independent program that is launched from the system and, when it finishes the computation, returns the control to the GIS, where the results are shown. This structure allows that further analyses (specifically, risk analyses, that use as an input a hazard or a scenario map), could be also automated inside the system. Additional information, including tutorial and downloadable files can be found in www.gvb-csic.es.  相似文献   

10.
Preceded by four days of intense seismicity and marked ground deformation, a new eruption of Mt. Etna started on 17 July and lasted until 9 August 2001. It produced lava emission and strombolian and phreatomagmatic activity from four different main vents located on a complex fracture system extending from the southeast summit cone for about 4.5 km southwards, from 3000 to 2100 m elevation (a.s.l.). The lava emitted from the lowest vent cut up an important road on the volcano and destroyed other rural roads and a few isolated country houses. Its front descended southwards to about 4 km distance from the villages of Nicolosi and Belpasso. A plan of intervention, including diversion and retaining barriers and possibly lava flow interruption, was prepared but not activated because the flow front stopped as a consequence of a decrease in the effusion rate. Extensive interventions were carried out in order to protect some important tourist facilities of the Sapienza and Mts. Silvestri zones (1900 m elevation) from being destroyed by the lava emitted from vents located at 2700 m and 2550 m elevation. Thirteen earthen barriers (with a maximum length of 370 m, height of 10–12 m, base width of 15 m and volume of 25 000 m3) were built to divert the lava flow away from the facilities towards a path implying considerably less damage. Most of the barriers were oriented diagonally (110–135°) to the direction of the flow. They were made of loose material excavated nearby and worked very nicely, resisting the thrust of the lava without any difficulty. After the interventions carried out on Mt. Etna in 1983 and in 1991–1992, those of 2001 confirm that earthen barriers can be very effective in controlling lava flows.  相似文献   

11.
Spatial vent opening probability map of Etna volcano (Sicily, Italy)   总被引：1，自引：0，他引：1  
We produce a spatial probability map of vent opening (susceptibility map) at Etna, using a statistical analysis of structural features of flank eruptions of the last 2?ky. We exploit a detailed knowledge of the volcano structures, including the modalities of shallow magma transfer deriving from dike and dike-fed fissure eruptions analysis on historical eruptions. Assuming the location of future vents will have the same causal factors as the past eruptions, we converted the geological and structural data in distinct and weighted probability density functions, which were included in a non-homogeneous Poisson process to obtain the susceptibility map. The highest probability of new eruptive vents opening falls within a N-S aligned area passing through the Summit Craters down to about 2,000?m?a.s.l. on the southern flank. Other zones of high probability follow the North-East, East-North-East, West, and South Rifts, the latter reaching low altitudes (～400?m). Less susceptible areas are found around the faults cutting the upper portions of Etna, including the western portion of the Pernicana fault and the northern extent of the Ragalna fault. This structural-based susceptibility map is a crucial step in forecasting lava flow hazards at Etna, providing a support tool for decision makers.  相似文献   

12.
The Mt Cameroon volcano is the highest and most active volcano of the Cameroon Volcanic Line. Little geological information is available for improving the understanding of the structure of this large volcanic system and its relationship to regional tectonics. After reviewing the tectonic evolution of the region, the analysis of a Digital Elevation Model and results from a field campaign dedicated to mapping geological structures in the summit area and at the SE base of Mt Cameroon are presented. Mt Cameroon is a lava-dominated volcano with long steep (over 30°) flanks. It is elongate parallel to its well defined rift zone. The summit plateau is bordered by 10 m high cliffs formed by summit subsidence along normal faults. Geological profiles were measured along rivers cutting through a topographic step at the SE base of Mt Cameroon. This step is associated with deformed Miocene sediments from the Douala basin that are overlain by volcanic products. Weak sediments of this area are deformed by 050°–060° and 020°–030° trending asymmetrical folds verging toward the SE, and thrusts faults related to the spreading of the volcano over its mechanically weak substratum. Combined remote sensing and field observations suggest that spreading is accommodated by summit subsidence and flanks sliding. Both slow spreading movements and catastrophic collapses of the steep flanks are interpreted to result from complex interactions between the growing edifice, repeated dyke intrusions, the weak sedimentary substratum and tectonic structures.  相似文献   

13.
In order to zone the territory of Campania Region (southern Italy) with regard to the hazard related to future explosive activity of Somma-Vesuvio, Campi Flegrei, and Ischia Island, we drew a multi-source hazard map for tephra and pyroclastic flows. This map, which merges the areas possibly endangered by the three volcanic sources, takes into account a large set of tephra fall and pyroclastic flow events that have occurred in the last 10 ka. In detail, for fall products at Campi Flegrei and Somma-Vesuvio we used the dispersal of past eruption products as deduced by field surveys and their recurrence over the whole area. For pyroclastic flows, the field data were integrated with VEI = 4 simulated events; about 100 simulations sourcing from different points of the area were performed, considering the different probability of vent opening. The spatial recurrence of products of both past eruptions and simulated events was used to assign a weight to the area endangered by the single volcanic sources. The sum of these weights in the areas exposed to the activity of two sources and/or to different kinds of products was used to draw a hazard map, which highlights the spatial trend and the extent of the single equivalent classes at a regional scale. A multi-source risk map was developed for the same areas as the graphic result of the product of volcanic hazard and exposure, assessed in detail from a dasymetric map. The resulting multi-source hazard and risk maps are essential tools for communication among scientists, local authorities, and the public, and may prove highly practical for long-term regional-scale mitigation planning.  相似文献   

14.
在回顾总结了国外火山碎屑流灾害分析模型研究历史的基础上,本文选取了Flow3D模型对我国东北地区长白山天池火山未来大喷发可能产生的火山碎屑流进行了灾害区域划分。以长白山天池火山现代地形为依据,设定了11条未来爆炸式火山喷发时产生的火山碎屑流的可能流动线路。模拟结果表明,在喷发柱高度为10km的情况下,灾害区划最大半径为13.7km;在喷发柱高度为20km的情况下,灾害区划最大半径为35.4km;在喷发柱高度为30km的情况下,灾害区划最大半径为57.8km。在此基础上,得出了长白山天池火山未来发生中规模、大规模和超大规模火山喷发时火山碎屑流的覆盖范围,完成了我国第一幅长白山天池火山碎屑流灾害区划图。  相似文献   

15.
Mt. Yaké or Yaké-daké is a dissected dome-shaped volcano mainly composed of the biotite bearing augite-hypersthene-hornblende andesite lavas extruded on the high mountain ridge consisting of the granite and hard Palaeozoic rocks between two prefectures Nagano and Gifu in the central part of Japan. It had been almost in dormant state only with weak fumarole activity on and around its summit dome since the former active period from 1907 to 1932. Incandescent lava emission has never been recorded in the historic age. On 17th June 1962 at about 21 h 55 m, a sudden explosion took place on the northern side of the dome. After successive explosions a fissure, about 700 m in length, was formed. On 19th from the northeast end of the fissure, milky hot water suspending muddy material flowed out. The mud flow ran down on the slope along the dry gully and poured into the Lake Taisyo-iké, about 2.5 km east of the vent. The lake was formed in 1915-eruption when a tremendous mud flow dammed up Azusagawa, the river running through the valley east of the volcano. Ejected blocks were deposited on the area within 1 km from the vent. Ash was deposited about 1 cm in thickness on the area about 4 km east of the volcano. Several mud flows poured into the Lake Taisyo-iké and the River Azusagawa. But no red-hot ejecta was observed during the present eruption, and temperature near the vent was lower than 100°C. Thus the present eruption is said to be low temperature phreatic explosions. In suspensoids of the hot water and in clayey matter deposited around the new vent are contained the montmorillonites, which hove never been found in the rocks exposed on the volcano in spite of the detailed investigation of the writers over 10 years. On the other hand, the mineral is not expected to be formed in the altered rocks under oxydized state on the surface. It was fine, at least no rain, before and during the explosions and the mud flow ran down along the dry gully. So the hot water was purely derived from the inner part of the volcano and the mud flow was not brought about by rain fall after deposition of ejecta on the volcano. The mud flow must have been formed endogenously under the volcano where the katamorphism of the rocks forming the volcano had advanced owing to chemical action of volcanic gas in the long period before the eruption.  相似文献   

16.
In a companion paper, a methodology for ranking volcanic hazards and events in terms of risk was presented, and the likelihood and extent of potential hazards in the Auckland Region, New Zealand investigated. In this paper, the effects of each hazard are considered and the risk ranking completed. Values for effect are proportions of total loss and, as with likelihood and extent, are based on order of magnitude.Two outcomes were considered – building damage and loss of human life. In terms of building damage, tephra produces the highest risk by an order of magnitude, followed by lava flows and base surge. For loss of human life, risk from base surge is highest. The risks from pyroclastic flows and tsunami are an order of magnitude smaller. When combined, tephra fall followed by base surge produces the highest risk. The risks from lava flows and pyroclastic flows are an order of magnitude smaller. For building damage, the risk from Mt. Taranaki volcano, 280 km from the Auckland CBD, is largest, followed by Okataina volcanic centre, an Auckland volcanic field eruption centred on land, then Tongariro volcanic centre. In terms of human loss, the greatest risk is from an Auckland eruption centred on land. The risks from an Auckland eruption centred in the ocean, Okataina volcanic centre, and Taupo volcano are more than an order of magnitude smaller. When combined, the risk from Mt. Taranaki remains highest, followed by an Auckland eruption centred on land. The next largest risks are from the Okataina and Tongariro volcanic centres, followed by Taupo volcano.Three alternative situations were investigated. As multiple eruptions may occur from the Auckland volcanic field, it was assumed that a local event would involve two eruptions. This increased risk of a local eruption occurring on land so that it was equal to that of an eruption from Mt. Taranaki. It is possible that a future eruption may be of a similar, or larger size, to the previous Rangitoto eruption. Risk was re-calculated for local eruptions based on the extent of hazards from Rangitoto. This increased the risk of lava flow to greater than that of base surge, and the risk from an Auckland land eruption became greatest. The relative probabilities used for Mt. Taranaki volcano and the Auckland volcanic field may only be minimum values. When the probability of these occurring was increased by 50%, there was no change in either ranking.Editorial responsibility: J. S. Gilbert  相似文献   

17.
天池火山东北侧造盾玄武岩可划分出8个流动单元,熔岩流的流动距离主要集中在30~50km,熔岩流宽度以5km左右为主。通过由野外调查获得的天池火山东北侧不同熔岩流单元的地表坡度、熔岩流厚度等,结合温度、密度与黏度等物理参数,按照熔岩流速度公式恢复的头道组和早白山组0.5m厚晶体含量5%的玄武岩熔岩流流速集中在0~1m/s之间。晶体含量为30%、厚度为0.5m的晚白山组和老房子小山组玄武岩熔岩流的流动速度集中在0~0.12m/s之间。厚度增大至2m左右,晶体含量不变的头道组和早白山组的玄武岩熔岩流流动速度可加快至11m/s。天池火山2m厚的碱性熔岩流在12h内达到或接近了它的最远距离,而各组内2m厚拉斑玄武岩熔岩流在20h内接近了最远距离。0.5m厚的熔岩流在10d内接近最大距离。50km是预计的熔岩流长度,在未来制定减灾措施时,可将此长度作为重要依据之一。天池火山熔岩流灾害主要表现为熔岩流动时对房屋建筑、农田、道路、林地、电站的毁坏,火灾及大量的人口伤亡  相似文献   

18.
The 1224 Mt. Etna eruption is a significant event both in terms of the mass of erupted materials and because it involved the lower eastern slope of the volcano, reaching down to the sea. Nevertheless, it is unknown to current historical catalogues. According to the historical sources, only two other lava flows actually reached as far as the sea: in 396 BC, just north of the present-day inhabited area of Acireale, according to the geological data alone, and in 1669, when the lava covered the south-eastern flank of Mt. Etna and damaged Catania. We present and discuss the two medieval sources that attest to the eruption of 1224 and make available the original texts. Furthermore, through the close analysis of the historical and topographic context of the Etna area, taking account of the roads and ports in the early 13th century, we have tried to single out the possible area of the lava's outlet into the sea in 1224 on historical grounds. A repeat of an eruption similar to that of 1224 would have a serious impact today as the coast is densely populated.  相似文献   

19.
During long-lived basaltic eruptions, overflows from lava channels and breaching of channel levées are important processes in the development of extensive 'a'ā lava flow-fields. Short-lived breaches result in inundation of areas adjacent to the main channel. However, if a breach remains open, lava supply to the original flow front is significantly reduced, and flow-field widening is favoured over lengthening. The development of channel breaches and overflows can therefore exert strong control over the overall flow-field development, but the processes that determine their location and frequency are currently poorly understood. During the final month of the 2008–2009 eruption of Mt. Etna, Sicily, a remote time-lapse camera was deployed to monitor events in a proximal region of a small ephemeral lava flow. For over a period of ~10 h, the flow underwent changes in surface elevation and velocity, repeated overflows of varying vigour and the construction of a channel roof (a required prelude to lava tube formation). Quantitative interpretation of the image sequence was facilitated by a 3D model of the scene constructed using structure-from-motion computer vision techniques. As surface activity waned during the roofing process, overflow sites retreated up the flow towards the vent, and eventually, a new flow was initiated. Our observations and measurements indicate that flow surface stagnation and flow inflation propagated up-flow at an effective rate of ~6 m h−1, and that these processes, rather than effusion rate variations, were ultimately responsible for the most vigorous overflow events. We discuss evidence for similar controls during levée breaching and channel switching events on much larger flows on Etna, such as during the 2001 eruption.  相似文献   

20.
The Campi Flegrei caldera is a restless structure affected by general subsidence and ongoing resurgence of its central part. The persistent activity of the system and the explosive character of the volcanism lead to a very high volcanic hazard that, combined with intense urbanization, corresponds to a very high volcanic risk. One of the largest sources of uncertainty in volcanic hazard/risk assessment for Campi Flegrei is the spatial location of the future volcanic activity. This paper presents and discusses a long-term probability hazard map for vent opening in case of renewal of volcanism at the Campi Flegrei caldera, which shows the spatial conditional probability for the next vent opening, given that an eruption occurs. The map has been constructed by building a Bayesian inference scheme merging prior information and past data. The method allows both aleatory and epistemic uncertainties to be evaluated. The probability map of vent opening shows that two areas of relatively high probability are present within the active portion of the caldera, with a probability approximately doubled with respect to the rest of the caldera. The map has an immediate use in evaluating the areas of the caldera prone to the highest volcanic hazard. Furthermore, it represents an important ingredient in addressing the more general problem of quantitative volcanic hazards assessment at the Campi Flegrei caldera.  相似文献   

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