共查询到20条相似文献，搜索用时 31 毫秒
1.
Mauro Rosi 《Bulletin of Volcanology》1992,54(5):429-434
Observations on phreatomagmatic ash deposits of Phlegraean Fields and Vesuvius supply evidence for the origin of vesiculated tuff in a cool environment. Early deposition by fallout of a matrix-free bed of damp accretionary lapilli is followed by deposition of cohesive mud or a mud rain. The lapilli bed becomes partly or completely transformed into a vesiculated tuff by mud percolation and eventual coalescence of accretionary lapilli with consequent trapping of air originally contained in the interstices. The proposed mechanism accounts for vesiculated tuff formation in distal deposits beyond limits commonly attained by pyroclastic surges. This same mechanism may, nevertheless, also operate in proximal tuff-ring and cone deposits during fallout of phreatomagmatic ash separating bed sets in surge-dominated successions. The sequence of events in the proposed model fits well with the evolution of a cooling phreatomagmatic ash cloud in which early ash aggregation (accretionary lapilli fallout) is followed closely by steam condensation (mud or muddy rainfall). This new model invoking a cool-temperature origin is intended to be complementary to previously proposed theories. Although difficult to assess because of the often complete obliteration of original lapilli, the process is believed to be relatively common in the generasion of vesiculated tuffs within phreatomagmatic deposits. 相似文献
2.
Volcán Fuego erupted ash and ash flows during September 1971 and February–March 1973. The ash flows were restricted to existing drainage channels. Most damage was due to subsequent mud flows and floods. A catastrophe can be expected if the ash flows or mud flows increase in volume and overflow their channels in future eruptions. The only practical remedial measure is temporary evacuation, a formidable social and economic undertaking for an underdeveloped nation. Conscious of this, the geologist at the scene is unsure at what point to recommend evacuation. Probably the volcanologist can make his most useful direct contribution to society by cooperating in studies on the effect of volcanism on agriculture. The lives and wealth saved by even a slight increase in agricultural productivity would vastly outweigh losses due to volcanic disasters. 相似文献
3.
Red mud is a waste product in the reduction of bauxite in the production of aluminium. The exact composition of red mud depends on the source of the bauxite and its treatment during production. This variation has been responsible for conflicting reports about the damage caused by dumping red mud at sea. 相似文献
4.
B. M. Shen’kman 《Water Resources》2017,44(3):485-496
The article presents the results of a hydrogeological survey aimed to substantiate the engineering recultivation of accumulation ponds of lignin mud by inwashing it with coal ash. The ash bed causes compression consolidation of lignin bed, leading to an increase in the pond seal margin. The mass exchange between the ash and the lignin mud is accompanied by changes in the hydrogeochemical conditions: the mineralization of the liquid phase of technogenic soils increases by a factor of up to 8, and the concentration of microcomplex increases to very high values. The analysis of the qualitative state of groundwater showed it to be tolerant to the effect of accumulation ponds. The moderate deviation from the local natural background is due to other pollution sources. The applied recultivation technology is effective and environmentally safe, though it needs modernization. The alternative technology, proposed by OOO VEB-Inzhiniiring, i.e., grouting the pond content, is extremely hazardous, and the implementation of the project involves considerable environmental risk because of the possible loss of pond containment. 相似文献
5.
A moderately violent phreatomagmatic explosive eruption of Taal Volcano, Philippines, occurred from 28 to 30 September, 1965. The main phreatic explosions, which were preceded by ejection of basaltic spatter, opened a new crater 1.5 km long and 0.3 km wide on the southwest side of Volcano Island in Lake Taal. The eruption covered an area of about 60 square kilometers with a blanket of ash more than 25 cm thick and killed approximately 200 persons. The clouds that formed during the explosive eruption rose to heights of 15 to 20 km and deposited fine ash as far as 80 km west of the vent. At the base of the main explosion column, flat, turbulent clouds spread radially, with hurricane velocity, transporting ash, mud, lapilli and blocks. The horizontally moving, debris-laden clouds, sandblasted trees, coated the blast side of trees and houses with mud, and deposited coarse ejecta with dune-type bedding in a zone roughly 4 km in all directions from the explosion crater. 相似文献
6.
The present study elucidates the remediation of mine waters by means of geochemical barriers („active barriers“). Active barrier systems (ABS) are developed, which can prevent heavy metal dispersion by introducing the barrier into the mine. Therefore, low‐cost materials are investigated which can remove contaminants by chemical, and/or physical mechanisms from water. The materials investigated are industrial by‐products (e.g. fly ash, red mud, scale arrears), natural wastes (e.g. tree bark), and relatively cheap natural products (bentonite, zeolites). Red mud and fly ash show the best results for the removal of Zn, Cd, Ni, and Mn from model water. Cd seems to have the strongest binding of the investigated metals on the sorption sites. The main mechanisms of metal removal from solution in this case are sorption and precipitation. Both materials have very good sorption and acid neutralization capacities (ANC), but ANC seems to be the determining factor. 相似文献
7.
C. Lacasse H. Sigurdsson H. Jóhannesson M. Paterne S. Carey 《Bulletin of Volcanology》1995,57(1):18-32
Geochemical evidence shows that the silicic component of the widespread Ash Zone 1 in the North Atlantic is derived from a major ignimbrite-forming eruption which occurred at the Katla caldera in southern Iceland during the transition from glacial to interglacial conditions in Younger Dryas time. Both trace and major element evidence of the rhyolitic products excludes the Öræfajökull volcano as a source. The high-Ti basaltic component in the marine ash zone can also be attributed to contemporaneous eruption in the Katla volcanic complex. Dispersal of tephra from this event is primarily attributed to the generation of co-ignimbrite ash columns in the atmosphere, with ash fallout on both sea ice and on the ocean floor north and east of Iceland. Owing to the changing ocean circulation characteristics of the glacial regime, including suppression of the Irminger Current and a stronger North Atlantic Current, tephra was rafted on sea ice south into the central North Atlantic and deposited as dispersed Ash Zone 1. Sediments south of Iceland also show evidence of the formation of ash turbidites, generated either by the entrance of pyroclastic flows into the sea, or during discharge of jökulhlaups or glacier bursts from this subglacial eruption. 相似文献
8.
A prediction of sea level rising amplitude in 2030 and defensive countermeasures in the Zhujiang delta 总被引：1，自引：0，他引：1
HUANG Zhenguo ZHANG Weiqiang WU Houshui CHEN Tegu FAN Jinchun JIANG Peilin Li Zihao Huang Bensheng 《中国科学D辑(英文版)》2001,44(5):446-454
By analysing comprehensively the factors such as theoretical sea level, abnormal fluctuation of sea level, rising amplitude
of floodtide water level and land deformation, a rising amplitude of 22-33 cm of relative sea level by the year of 2030 is
forecasted in the Zhujiang Delta. From the forecasted amplitude of 30 cm, using hydraulic and hydrometric models the scope
influenced by sea level rise is delimited and the reappearing periods of floodtide water level, protecting ability of embankments,
design parameters of water conservancy project, drain waterlogging, saline intrusion, resource of mud beach and comprehensive
prevention measures are discussed. 相似文献
9.
10.
V. I. Kaevitser I. B. Slovtsov A. P. Krivtsov V. M. Razmanov I. V. Smol’yaninov A. V. Elbakidze 《Journal of Volcanology and Seismology》2016,10(4):242-247
Studies of the sea bottom around the Taman Peninsula were used as an example to demonstrate the abilities of sonar systems using signals subjected to linear frequency modulation (LFM) for the detection and study of underwater mud volcanoes. 相似文献
11.
12.
Jean-Claude Dauvin 《Marine pollution bulletin》2010,60(2):197-206
Since 1967, the alumina plants in the Marseilles area (Barasse and Gardanne) have been discharging the mineral residue (i.e., red mud) resulting from the alkaline processing of bauxite into the submarine Cassidaigne canyon (north-western Mediterranean Sea) through pipes situated at 320-330 m in depth. The Barasse pipe stopped being used in 1988. From 1987 to 1996, many decrees and regulations were promulgated by the French State to rule the conditions under which the Gardanne alumina refinery was authorized to dispose of the bauxite residue in the sea. The refinery was required: (i) to study the hydrodynamic circulation in the Cassidaigne canyon to evaluate the potential dispersion and transport of fine elements discharged into the water mass and their impact on the pelagic ecosystem; (ii) to survey the marine environment every five years to control the expansion and thickness of the red mud deposit and compare the evolution of the benthic macrofauna at representative sampling sites in the environment affected by the red mud discharge with that of reference sites outside of the red mud plume; (iii) to study the effect of the discharge on fishing activities; and (iv) to investigate the toxicity of the red mud, particularly its persistence, accumulation, interaction and effect on the marine ecosystem, paying special attention to the bio-accumulation of chromium and vanadium. A Scientific Committee was created to insure an independent evaluation of the studies promised by the manufacturer in response to the State’s regulations. Since the beginning of the 1960s, data have been accumulating on the structure and long-term functioning of the Cassidaigne bathyal ecosystem. This paper presents the collaborative efforts of the State-Manufacturer-Committee triplet and summarizes the main results obtained during the last period’s sea campaigns (1991-2007). This paper also illustrates how national regulations concerning manufacturers, such as Gardanne alumina refinery, have provided new knowledge about the structure and functioning of a bathyal ecosystem in the Cassidaigne canyon in the north-western Mediterranean Sea. 相似文献
13.
Mathijs van Ledden Geoffrey Vaughn Joost Lansen Frank Wiersma Mewburn Amsterdam 《Continental Shelf Research》2009
The objective of the research is to analyze in detail the causes and consequences of the unusual event at the coast of Guyana (South America) during October 16–19, 2005. Several sea defense structures were damaged and flooding of low-lying areas occurred. A data analysis of offshore wave and water level characteristics shows an abrupt change in wave direction from east to almost north on October 16, 2005 and a sudden increase in the offshore peak period up to extreme values. The offshore significant wave height was also relatively high, and these wave characteristics coincided with springtide conditions. The long-wave periods and the sharp transition in wave direction indicate that this event is associated with swell waves generated by a depression far away. An analysis of hurricanes and depressions reveals that a severe depression in the Northern Atlantic Ocean during October 11–15 was the origin of this swell event. Numerical computations with SWAN have been carried out to investigate the propagation of the offshore wave characteristics towards the shoreline. The SWAN model includes wave damping due to the presence of soft mud deposits. A calibration of the parameters has been carried out using joint offshore and onshore wave data from November 2006. The numerical simulations of the event in October 2005 clearly demonstrate that the mud banks damp the wave heights, but have almost no effect on the peak period. The resulting waves at the steep sea walls can be classified as surging waves causing severe runup and overtopping. The obtained insights are translated into practical recommendations for the Guyana Sea and River Defence Division in Guyana to build a sustainable management and maintenance of the sea defenses in the future. 相似文献
14.
Late Pleistocene sequences around Dundalk Bay, eastern Ireland, record glaciomarine sedimentation near the margin of a grounded ice lobe around 15 ka BP. A coastal exposure at Cooley Point consists of four major facies deposited outside this ice limit. (1) A basal mud facies deposited from sediment plumes accumulated following the initial ice marginal retreat inland. It contains a well-preserved Arctic microfauna dominated by the foram Elphidium clavatum and the ostracod Roundstonia globulifera. (2) A flat to undulating boulder facies (pavement), mostly one clast thick, is found pressed into the mud and is characterized by bevelled and striated upper clast surfaces. Pavement attributes are a result of intertidal activity in a cold climate. The boulder source is due to rafting by ice floes from glacigenic debris deposited during an ice advance. (3) Laminated sand facies drape the pavement and are a result of variable current activity. (4) The overlying gravel facies is separated from the sand facies by a marine erosion surface. The gravel facies is subaqueous, channelized and is overlain by late glacial raised beach ridges. Locally the gravels have been deformed by ice pressure from partially floating ice floes. Facies changes record terrestrial submergence and provide evidence for changes in relative sea level during part of the last deglacial cycle. The boulder pavement and deformed gravel facies suggest that ice floes and sea ice effects may be more common within stratigraphies along emergent coasts than previously thought, though they have a low preservation potential. Extreme conditions during the deglacial favoured opportunistic microfaunas during mud deposition. This event may be related to a major meltwater event within the Irish Sea Basin. 相似文献
15.
The June 15, 1991 climactic eruption of Mt. Pinatubo produced an extensive, largely co-ignimbrite-derived airfall ash layer on Luzon Island and across the central South China Sea. The layer covers an area of ~4×105 km2 with a volume of 5.5 km3. Near the coast of Luzon, the deposit consists of two units: a normally graded basal ash bed, unimodal in grain size, and a finer-grained, internally structureless upper ash bed showing grain size bimodality. With increasing distance from the source, the coarse particle populations of the two units merge and migrate towards a near-constant fine population (~11 m); the distal region is covered by a fine-mode dominated, virtually ungraded single ash layer. The reversal of the winds from easterly directions at upper-tropospheric and stratospheric levels to westerly directions in the middle and lower troposphere indicates that both the coarse- and fine-mode components fell out from high-altitude eruption clouds. The high-velocity upper-level winds, however, would have transported fine-grained ash particles far beyond the South China Sea, which suggests that their settling was accelerated by aggregation. The boundary between the units thus marks a change from fallout of predominantly discrete pyroclasts to simultaneous fallout of aggregated fines and freely falling, coarse-grained particles. The particle populations composing the upper ash bed were almost completely removed from the proximal areas by the upper-level winds. At lower elevations, the counterclockwise circulation of a typhoon over the coastal area advected the ash south and eastward, producing a thickness maximum in the medial region (at about 160 km from source). The strong displacement of fines, possibly aided by wind turbulence, led to a break in bulk tephra thinning rates close to the coastline. In the distal region, outside the influence of the typhoon, southwest monsoonal winds caused a distinct lobe axis inflection and thickness asymmetry. Within this region, at about 420 km from source, fallout of particle aggregates created a second thickness maximum. Comparison of the field data with previous experimental observations and tephra flux records in the deep sea (Wiesner et al. 1995; Carey 1997; McCool 2002) implies that the transport of ash in the water column was largely determined by vertical density currents. Differences in the reaction of coarse and fine particles to turbulence in the descending plumes probably suppressed the segregation of fines but allowed the coarser pyroclasts to maintain their initial order of arrival at the sea surface. Considering typical fall rates of convective plumes, modifications of the initial fallout position of the particles by the South China Sea current system are on the order of only a few kilometers. The results suggest that convective sedimentation processes ensure the preservation of atmospheric particle transport directions, distances, and fallout modes in the deep sea.Editorial responsibility: R. CioniAn erratum to this article can be found at 相似文献
16.
D. Macdougall 《Earth and Planetary Science Letters》1971,10(4):403-406
The fission track dating method is applied to glass shards from volcanic ash layers in deep sea sediments which have also been dated by other methods. Measured ages for three samples are in excellent agreement with previously determined K-Ar, paleomagnetic and paleontologic ages. The fission track method of dating of glass shards seems to offer itself as a valuable tool for dating marine sediments. 相似文献
17.
The majority of tephra generated during the paroxysmal 1883 eruption of Krakatau volcano, Indonesia, was deposited in the sea within a 15-km radius of the caldera. Two syneruptive pyroclastic facies have been recovered in SCUBA cores which sampled the 1883 subaqueous pyroclastic deposit. The most commonly recovered facies is a massive textured, poorly sorted mixture of pumice and lithic lapilli-to-block-sized fragments set in a silty to sandy ash matrix. This facies is indistinguishable from the 1883 subaerial pyroclastic flow deposits preserved on the Krakatau islands on the basis of grain size and component abundances. A less common facies consists of well-sorted, planarlaminated to low-angle cross-bedded, vitric-enriched silty ash. Entrance of subaerial pyroclastic flows into the sea resulted in subaqueous deposition of the massive facies primarily by deceleration and sinking of highly concentrated, deflated components of pyroclastic flows as they traveled over water. The basal component of the deposit suggests no mixing with seawater as inferred from retention of the fine ash fraction, high temperature of emplacement, and lack of traction structures, and no significant hydraulic sorting of components. The laminated facies was most likely deposited from low-concentration pyroclastic density currents generated by shear along the boundary between the submarine pyroclastic flows and seawater. The Krakatau deposits are the first well-documented example of true submarine pyroclastic flow deposition from a modern eruption, and thus constitute an important analog for the interpretation of ancient sequences where subaqueous deposition has been inferred based on the facies characteristics of encapsulating sedimentary sequences. 相似文献
18.
The semi-diurnal tides are amplified and distorted as they propagate into the Pertuis Breton, a semi-enclosed shallow basin in the north-eastern part of Bay of Biscay, in France. This paper investigates the influence of bottom friction on amplification and phase lag of the tidal constituent M2 and its overtide M4 in the Pertuis Breton. A fine resolution two-dimensional (2D) numerical model is implemented to simulate tidal propagation. The model solves the depth-averaged shallow-water equations on a finite element grid using the TELEMAC 2D software. A two-zone parameterisation of friction coefficient is introduced to evaluate the impact of smooth mud flats on the tidal asymmetry and amplification in the Pertuis. Fitting the model to observed amplitudes and phases of M2 and M4 evaluates the decrease of Chezy friction coefficient from the mud flats to the rest of the Pertuis as 100:60. This conclusion is supported by the direct estimation based on morphology and composition of sea bed in the Pertuis Breton. 相似文献
19.
J. G. Moore 《Bulletin of Volcanology》1967,30(1):337-363
A base surge, first identified at the Bikini thermonuclear undersea explosion, is a ring-shaped basal cloud that sweeps outward as a density flow from the base of a vertical explosion column. Base surges are also common in shallow underground test explosions and are formed by expanding gases which first vent vertically and then with continued expansion rush over the crater lip (represented by a large solitary wave in an underwater explosion), tear ejecta from it, and feed a gas-charged density flow, which is the surge cloud. This horizontally moving cloud commonly has an initial velocity of more than 50 meters per second and can carry clastic material many kilometers. Base surges are a common feature of many recent shallow, submarine and phreatic volcanic eruptions. They transport ash, mud, lapilli, and blocks with great velocity and commonly sandblast and knock down trees and houses, coat the blast side with mud, and deposit ejecta at distances beyond the limits of throw-out trajectories. Close to the eruption center, the base surge can erode radial channels and deposit material with dune-type bedding. 相似文献
20.
The Cenozoic sedimentary succession in Okinawa‐jima, including the upper Miocene to Pleistocene siliciclastic deposits (Shimajiri Group) and the Pleistocene reef to shelf deposits (Ryukyu Group), suggests a drastic paleoceanographic change from a ‘mud sea’ to a ‘coral sea.’ To delineate the paleoceanographic evolution of the mud sea, we quantified the stratigraphic distribution of the calcareous nannofossil assemblages from the Shimajiri Group in a 2119.49 m‐deep well (Nanjo R1 Exploratory Well) drilled in southern Okinawa‐jima (Ryukyu Islands, southwestern Japan). Four late Miocene and Pliocene datum planes were found in the studied interval: the first occurrence of Amaurolithus spp. (7.42 Ma), the last occurrence of Discoaster quinqueramus (5.59 Ma), the first occurrence of Ceratolithus rugosus (5.12 Ma), and the last occurrence of Reticulofenestra pseudoumbilicus (3.70 Ma). The calcareous nannofossil assemblages from the Tomigusuku Formation and the lower part of the Yonabaru Formation are characterized by a lower total number of coccoliths and abundant Sphenolithus abies that is associated, at times, with common Discoaster spp. Overall, these suggest the existence of oligotrophic conditions between 5.3 and >8.3 Ma. The total number of coccoliths increased and small Reticulofenestra spp. became more common in the middle part of the Yonabaru Formation, suggesting that eutrophic conditions were present between 3.5 and 5.3 Ma. The rare occurrence of calcareous nannofossils in the upper part of the Yonabaru Formation indicates a return to oligotrophic conditions at 3.5 Ma. Micropaleontological evidence suggests that these oceanographic changes were likely caused by local tectonic movement (shallowing of the sedimentary basin in which the Shimajiri Group was deposited). 相似文献