Vent Position Research Articles

Evaluation of Vent Position from Lizard Skeletons for Estimation of Snout: Vent Length and Body Mass

The body size of an organism significantly influences nearly every aspect of its biology; thus, accurate and reliable measures of body size are crucial components of many studies. One of the primary descriptors of body size is body mass. Although important to many types of research, body mass is used especially frequently in functional studies, which often compare body mass to skeletal dimensions. This is particularly true of examinations of the biomechanics of limb

The Bishop Tuff: New Insights From Eruptive Stratigraphy

The 0.76 Ma Bishop Tuff, from Long Valley caldera in eastern California, consists of a widespread fall deposit and voluminous partly welded ignimbrite. The fall deposit (F), exposed over an easterly sector below and adjacent to the ignimbrite, is divided into nine units (F1‐F9), with no significant time breaks, except possibly between F8 and F9. Maximum clast sizes are compared with other deposits where accumulation rates are known or inferred to estimate an accumulation time for F1‐F8 as ca. 90 hrs. The ignimbrite (Ig) is divided into chronologically and/or geographically distinct packages of material. Earlier packages (Ig1) were emplaced mostly eastward, are wholly intraplinian (coeval with fall units F2‐F8), Lack phenocrystic pyroxenes, and contain few or no Glass Mountain‐derived rhyolite lithic fragments. Earlier packages (Ig2) were erupted mostly to the north and east, are at least partly intraplinian (interbedded with fall unit F9 to the east), contain pyroxenes, and have lithic fractions rich in Glass Mountain‐derived rhyolite or other lithologies exposed on the northern caldera rim. Recognition of the intraplinian nature of Ig1 east of the caldera and use of the fall deposit chronometry yields accumulation estimates of ca. 25 hrs for an earlier, less‐welded subpackage and ca. 36 hrs for a later, mostly welded subpackage. Average accumulation rates range up to ≥1 mm/s of dense‐welded massive ignimbrite, equivalent to ≥2.5 mm/s of non‐welded material. Comparisons of internal stratification in Ig1 and northern Ig2 lobes suggest the thickest northern ignimbrite accumulated in ≥35 hrs. Identifiable vent positions migrated from an initial site previously proposed in the south‐central part of the caldera (F1‐8, Ig1) in complex fashion; one vent set (for eastern Ig2) migrated east and north toward Glass Mountain, while another set (for northern Ig2) opened from west to east across the northern caldera margin. Vent locations for Ig1 and Ig2 southwest of the caldera have not been identified. The new stratigraphic framework shows that much of the Bishop ignimbrite is intraplinian in nature, and that fall deposits and ignimbrite units previously inferred to be sequential are largely or wholly coeval. Fundamental reassessment is therefore required of all existing models for the eruption dynamics and the nature and causes of pre‐eruptive zonations in trace elements, volatiles, and isotopes in the parental magma chamber.

Side-vented gas explosions in a long vessel: the effect of vent position

Abstract Currently, the experimental data on the influence of vent position on the overpressure development during gas explosions in large length to diameter ratio (L/D) vessels are very sparse. Design guides such as NFPA 68 recommend the use of side-venting, but this is based on few experimental data and it was the objective of the present work to provide further information on vented explosions in tube configurations with side vents. Methane-air explosions (10 gas by volume) were undertaken in large L/D vessels and the influence of the side-venting position relative to the spark was investigated and compared with end-venting. The pressure development during side-venting was investigated and five stages of the explosion development were identified. The five pressure peaks were identified as follows: P1 due to the initial elongated flame acceleration, P2 due to the turbulence flame acceleration in the downstream gases ahead of the flame set in motion by the initial explosion gas expansion, P3 due to the flame acceleration around the 90° bend of the side vent, P4 due to the external gas cloud explosion downstream of the vent, and P5 due to the oscillatory combustion of trapped unburnt mixture in the vessel between the side vent and the far end of the tube. All these pressure peaks were not present for each vent position and the effect depended on the distance of the side vent from the ignition source. Very high flame speeds and overpressures were measured as the distance between the side vent position and the spark was increased. In the end-venting explosions the maximum overpressure was higher than the side-vented tests, except for the case where the side vent was placed at the middle of the vessel, which had a similar overpressure to end-venting. Induced gas velocities were also measured and associated turbulent parameters were calculated and were found to increase with an increase in the distance of the vent position from the spark.

Volcanic and structural evolution of Taupo Volcanic Zone, New Zealand: a review

The Taupo Volcanic Zone (TVZ) in the central North Island is the main focus of young volcanism in New Zealand. Andesitic activity started at c. 2 Ma, joined by voluminous rhyolitic (plus minor basaltic and dacitic) activity from c. 1.6 Ma. The TVZ is c. 300 km long (200 km on land) and up to 60 km wide, as defined by vent positions and caldera structural boundaries. The total volume of TVZ volcanic deposits is uncertain because a sub-volcanic basement has not been identified, but present data suggest bulk volumes of 15–20,000 km3, and that faulted metasediments form most of the immediate subvolcanic basement. Rhyolite (≥15,000 km3 bulk volume, typically 70–77% SiO2) is the dominant magma erupted in the TVZ (mostly as calderaforming ignimbrite eruptions), andesite is an order of magnitude less abundant, and basalt and dacite are minor in volume (< 100 km3 each). The history of the TVZ is here divided into ‘old TVZ’ from 2.0 Ma to 0.34 Ma, and ‘young TVZ’ from 0.34 Ma onwards, separated by the Whakamaru eruptions, which obscured much of the evidence for older activity within the zone. The TVZ shows a pronounced segmentation into northeastern and southwestern andesite-dominated extremities with composite cones and no calderas, and a central 125-km-long rhyolite-dominated segment. Eight rhyolitic caldera centres have so far been identified in the central segment, of which two (Mangakino and Kapenga) are composite features, and more centres will probably be delineated as further data accumulate. These centres account for 34 inferred caldera-forming ignimbrite eruptions, in the c. 1.6-Ma lifetime of the central TVZ. The modern central TVZ is the most frequently active and productive silicic volcanic system on Earth, erupting rhyolite at c. 0.28 m3 s−1, and available information suggests this has been so for at least the past 0.34 Ma. The rhyolites show no major compositional changes with time, though the extent of magma chamber zonation may have changed with the incoming of rifting and crustal extension in the past c. 0.9 Ma. Within the central TVZ, non-rhyolitic compositions have been erupted apparently irregularly in time and space; in particular there is no evidence for a geographic separation of basalts from andesites. Between 0.9 and 0.34 Ma, a major episode of uplift affected areas around the TVZ, while at the same time the main focus of activity may have migrated eastwards within the TVZ accompanying rifting along the axis of the zone. The modern TVZ is rifting at rates between 7 and 18 mm a−1 and restoration of the thin (15km) ‘crust’ (Vp ≤ 6.1 km s−1) beneath the central TVZ to its pre-rifting thickness (25 km) implies that rifting at such rates may have begun only at c. 0.9 Ma. The TVZ is a rifted arc, but its longitudinally segmented nature, high thermal flux and voluminous rhyolitic volcanism make it unique on Earth.

Mapping lava flow hazards using computer simulation

Computer simulations of the paths of flowing lava are achieved using a program, FLOWFRONT, that describes the behavior of flow and digital models of the terrain. Two methods of application of simulations to the hazards posed by lava flows are described. The first, deterministic, method requires that program parameters such as vent position, minimum flow thickness, and thickness/slope relationship be based on the ambient eruptive conditions so that the future course of a specific lava flow can be simulated. This is illustrated using retrospective modeling of the first 21 days of the eruption of an andesitic lava flow at Lonquimay volcano, Chile, in 1988–1989. The usefulness of this method for real‐time predictive modeling is likely to be limited by the lack of accurate field data on flow characteristics, the simple nature of the model, and the sensitivity to parameter choice of the final planimetric form of the model flow. The second application is probabilistic in nature and creates a map of the likelihood of inundation by lava flows that is useful for long‐term land use planning. This method uses the historical record of past eruptions to constrain a series of Monte Carlo simulations and is illustrated using data from Etna volcano in Sicily. A multivariate statistical analysis of nine parameters for the 1763–1989 eruption catalog using simulated annealing permitted a classification of Etna's flank eruptions into two types: A and B. Type A eruptions are short‐lived and produce linear lava flows; type B eruptions are long‐lived, and produce lava flows that are much broader in shape, and their vents are restricted to the eastern flank of the volcano. The simulation method consists of creating a probability surface of the location of future eruption vents and segmenting the region according to the most likely historical eruption on which to base the simulation. Analysis of the autocorrelation of the historical eruptions shows that type A eruptions are strongly autocorrelated but type B eruptions are only weakly autocorrelated. A library is created of simulation parameters that give reasonable retrospective fits to each of the historical lava flows. Monte Carlo sampling of the simulation space using this library and the above spatial constraints produces a map of probability of lava inundation.

A54 新富士火山 2000 年前以降噴出物の全岩・鉱物化学組成と火口位置との関係について

A54 新富士火山 2000 年前以降噴出物の全岩・鉱物化学組成と火口位置との関係について

Sedimentation in Volcanic Settings

The craters associated with the 1886 AD phreatomagmatic Rotomahana eruption, Okataina Volcanic Centre, New Zealand, and the near-vent geology are now hidden beneath Lake Rotomahana and its post-eruptive sediment fill. Lithic clasts from the near-vent lithic lapilli ash deposits of the Rotomahana Pyroclastics are used in this study to trace geological and geothermal conditions before the eruption, as well as vent excavation dynamics. Near-vent deposit characteristics were described in the field, representative lithic clasts were documented petrographically, and unaltered clasts were analysed for major and trace element compositions. The majority of the lithic clasts were rhyolites with subordinate ignimbrites and hydrothermally altered clasts, and trace siltstone and silicified clasts. The rhyolites were classified into four petrographic groups according to phenocryst content and assemblage and were more diverse with respect to geochemical compositions. Most of the rhyolite lithics in the Rotomahana Pyroclastics did not match the rhyolite domes exposed subaerially around the lake, but did have affinities with the pre-Matahina caldera Wairua Rhyolite, and potentially other older non-exposed domes. Ignimbrites most likely correlated either to the Matahina ignimbrite or older non-exposed units. Hydrothermally altered rhyolite and ignimbrite lithic clasts are common and suggest that there has been a long-lived hydrothermal system in this sector, possibly dating back to early activity of the Okataina Volcanic Centre. The diversity in lithic types indicate a spatial variation in country rock lithology and strength, which probably contributed to the vent position and morphology along the Rotomahana fissure.

The 1976?1982 Strombolian and phreatomagmatic eruptions of White Island, New Zealand: eruptive and depositional mechanisms at a ?wet? volcano

White Island is an active andesitic-dacitic composite volcano surrounded by sea, yet isolated from sea water by chemically sealed zones that confine a long-lived acidic hydrothermal system, within a thick sequence of fine-grained volcaniclastic sediment and ash. The rise of at least 106 m3 of basic andesite magma to shallow levels and its interaction with the hydrothermal system resulted in the longest historical eruption sequence at White Island in 1976–1982. About 107 m3 of mixed lithic and juvenile ejecta was erupted, accompanied by collapse to form two coalescing maar-like craters. Vent position within the craters changed 5 times during the eruption, but the vents were repeatedly re-established along a line linking pre-1976 vents. The eruption sequence consisted of seven alternating phases of phreatomagmatic and Strombolian volcanism. Strombolian eruptions were preceded and followed by mildly explosive degassing and production of incandescent, blocky juvenile ash from the margins of the magma body. Phreatomagmatic phases contained two styles of activity: (a) near-continuous emission of gas and ash and (b) discrete explosions followed by prolonged quiescence. The near-continuous activity reculted from streaming of magmatic volatiles and phreatic steam through open conduits, frittering juvennile shards from the margins of the magma and eroding loose lithic particles from the unconsolidated wall rock. The larger discrete explosions produced ballistic block aprons, downwind lobes of fall tephra, and cohesive ‘wet’ surge deposits confined to the main crater. The key features of the larger explosions were their shallow focus, random occurrence and lack of precursors, and the thermal heterogeneity of the ejecta. This White Island eruption was unusual because of the low discharge rate of magma over an extended time period and because of the influence of a unique physical and hydrological setting. The low rate of magma rise led to very effective separation of magmatic volatiles and high fluxes of magmatic gas even during phreatic phases of the eruption. While true Strombolian phases did occur, more frequently the decoupled magmatic gas rose to interact with the conduit walls and hydrothermal system, producing phreatomagmatic eruptions. The form of these ‘wet’ explosions was governed by a delicate balance between erosion and collapse of the weak conduit walls. If the walls were relatively stable, fine ash was slowly eroded and erupted in weak, near-continous phreatomagmatic events. When the walls were unstable, wall collapse triggered larger discrete phreatomagmatic explosions.

Influence of vent positions on smoke clearance from a room

Results of solutions to the equations governing the clearance of smoke in laminar and in turbulent flow from a single rectilinear room are presented fof five different vent arrangements. These results show that the average smoke concentration in the room decreases in an approximately exponential manner with time at a rate that depdends much more on room geometry (vent positions in the present case) than on whether the flow is laminar or turbulent. The benefit of this observation is that, provided the clearance air jet is disrupted by impingement on a solid surface within the room, the analysis of smoke movement can for many practical purposes be limited to consideration of laminar flow only. An exceptional case is when the jet is allowed to take a straight line path between the inlet and outlet vents. Here in the absence of the large scale eddies caused by jet impingement, the smaller scale eddies of turbulent flow become relatively important as a mixing mechanism and give higher clearance rates than in laminar flow. Even so, this type of geometry is best avoided. The appearance of the jet is shown in a graphic presentation of the numerical results for laminar flow.

Modeling and image processing for visualization of volcanic mapping

In countries such as Italy, Japan, and Mexico, where active volcanoes are located in highly populated areas, the problem of risk reduction is very important. Actual knowledge about volcanic behavior does not allow deterministic event prediction or the forecasting of eruptions. However, areas exposed to eruptions can be analyzed if eruption characteristics can be inferred or assumed. Models to simulate volcanic eruptions and identify hazardous areas have been developed by collaboration between the IBM Italy Pisa Scientific Center and the Earth Science Department of Pisa University (supported by the Italian National Group of Volcanology of the Italian National Research Council). The input to the models is the set of assumed eruption characteristics: the typology of the phenomenon (ash fall, pyroclastic flow, etc.), vent position, total eruptible mass, wind profile, etc. The output of the models shows volcanic product distribution at ground level. These models are reviewed and their use in hazard estimation (compared with the more traditional techniques currently in use) is outlined. Effective use of these models, by public administrators and planners in preparing plans for the evacuation of hazardous zones, requires the clear and effective display of model results. Techniques to display and visualize such data have been developed by the authors. In particular, a computer program has been implemented on the IBM 7350 Image Processing System to display model outputs, representing both volume (in two dimensions) and distribution of ejected material, and to superimpose the displays upon satellite images that show 3D oblique views of terrain. This form of presentation, realized for various sets of initial conditions and eruption times, represents a very effective visual tool for volcanic hazard zoning and evacuation planning.

霧島火山群高千穂複合火山の噴火活動史

Takachiho composite volcano, located in south Ky ?? sh ??, Japan, is one of major members of the Kirishima volcano group. The composite volcano consists of four volcanic edifices which are partly overlapping and aligned in E-W direction. On the basis of field geology and tephrochronology, its growth-history can be divided into four stages. During the first stage, a conical stratovolcano, Futagoishi, was formed in the eastern end of the composite volcano. It is com-posed of an alternation of pyroclastic beds and lava flows. The activity of Futagoishi ended before the eruption of Ito pyroclastic flow deposit (22, 000 yBP) from the Aira caldera. The second stage activity started about 10, 000 years ago, after a repose of more than 12, 000 years. It was characterized by vulcanian eruption which continued semi-persistently through a long period of time, probably more than a thousand years. During this period a stratovolcano, Old-Takachiho, was built up on the western flank of Futagoishi, and a large amount of volcanic ash accumulated concentrically around the volcano. The third stage activity was characterized by the eruption of several thin lava flows and scoria from the vent close to Old-Takachiho Volcano. This activity resulted in formation of a small conical stratovolcano, Takachiho-no-mine, on the western slope of Old-Takachiho. At the end of this stage, enormous lava flows were successively effused from the top crater and flowed downward widely. Later lava flows, however, did not reached the foot of the slope due to decrease in effusion rate and piled up around the crater, resulting in the construction of an exogeneous lava dome on the summit. After several hundred years of quiescence, the present stage activity began about 2, 500 years ago. This activity was characterized by sub-plinian eruptions which occurred intermittently and produced thick scoria and ash beds on the eastern foot of the composite vlocano. By repeated eruptions of a great volume of scoria and lava flows, a new vlocano, Ohachi, was born on the western flank of Takachiho-no-mine volcano, and has been active since then. The growth-history of Takachiho composite volcano revealed the following two features: 1) the volcanic activity may have been controlled by the underlying E-W fracture, as suggested by the shifting of the vent position from east to west, and 2) the styles of explosive activity of the composite volcano have gradually changed with time from vulcanian eruption to sub-plinian one.

Vented combustion of hydrogen-air mixtures in large volumes

Vented combustion experiments with hydrogen-air mixtures were conducted in a 2.3-m-diameter sphere connected to a cylinder (volume, 10.3 m 3). The experiments were carried out over a concentration range of 6 to 42% hydrogen by volume and at near atmospheric temperatures and pressures. Vent sizes of 15 and 25 cm have been used. It was found that venting was effective in reducing the peak pressures at low hydrogen concentrations; at high hydrogen concentrations, because of short combustion times, venting was less effective. In many cases instantaneous peak pressures exceeding the adiabatic pressures were observed. Experiments carried out with the igniter located at the near end, centre, and far end relative to the vent position showed that the igniter location had only a slight effect on combustion pressures. Increase in the vent area by a factor of 1.8 caused only marginal reductions in peak pressures for high hydrogen concentrations. Vent size did not have much effect on the peak pressures at low hydrogen concentrations.

Orientation of logs in the Taupo Ignimbrite as an indicator of flow direction and vent position

Research Article| March 01, 1981 Orientation of logs in the Taupo Ignimbrite as an indicator of flow direction and vent position P. C. Froggatt; P. C. Froggatt 1Geology Department, Victoria University, Wellington, New Zealand Search for other works by this author on: GSW Google Scholar C.J.N. Wilson; C.J.N. Wilson 2Geology Department, Imperial College, London SW7, England Search for other works by this author on: GSW Google Scholar G.P.L. Walker G.P.L. Walker 2Geology Department, Imperial College, London SW7, England Search for other works by this author on: GSW Google Scholar Author and Article Information P. C. Froggatt 1Geology Department, Victoria University, Wellington, New Zealand C.J.N. Wilson 2Geology Department, Imperial College, London SW7, England G.P.L. Walker 2Geology Department, Imperial College, London SW7, England Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1981) 9 (3): 109–111. https://doi.org/10.1130/0091-7613(1981)9<109:OOLITT>2.0.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation P. C. Froggatt, C.J.N. Wilson, G.P.L. Walker; Orientation of logs in the Taupo Ignimbrite as an indicator of flow direction and vent position. Geology 1981;; 9 (3): 109–111. doi: https://doi.org/10.1130/0091-7613(1981)9<109:OOLITT>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract The Taupo Ignimbrite is an unwelded rhyolitic ignimbrite that originated about 1,820 yr ago from an eruptive vent within Lake Taupo in the Taupo Volcanic Zone, New Zealand. This ignimbrite is rich in carbonized plant matter, including many logs. The logs lie subhorizontally throughout all levels of the ignimbrite but are especially common in the lower half. Regionally the logs show a strong radial orientation, indicating flow directions and position of the source vent. Log orientation is thus a reliable indicator of vent position. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

The Taupo pumice: Product of the most powerful known (ultraplinian) eruption?

The Taupo pumice is probably the most widely dispersed fall deposit currently known, representative of a proposed new class of ultraplinian deposits. Although the maximum thickness is only 1.8 m, the volume is 24 km 3 (calculated by a new method based on the eolian concentration of crystals), and about 80% of this has fallen at sea farther than 220 km from source. The grain size distribution in the initial population has been determined, and the fraction finer than 1 8 mm constitutes 80% of the total mass which is unexpectedly high in view of the coarseness of the exposed deposit. It is important when studying the products of explosive eruptions to distinguish between the various kinds of “bigness” they reveal, namely magnitude - the total volume; intensity - the emission rate; dispersive power - the extent of dispersal; violence - the importance of momentum; and destructive potential - the extent of destruction of life or property (real or potential). In magnitude the Taupo plinian eruption was not exceptional, but on all available criteria the dispersive power was beyond the known limit for plinian events; probably the best measures of this power are the dispersal index of the deposit and the areas enclosed by isopleths of maximum lithic size, median grain diameter, and median fall velocity. The eruptive column must have exceeded 50 km in height. The great height is attributed partly to the high intensity (estimated at about 10 6 m 3/s of dense rock equivalent volume) and partly to the high content of fine particles since heat is released rapidly from the smaller magma particles to stoke up the convective plume. One consequence of the great column height is that the deposit is thickest 20 km down-wind from vent: the isopach map of a widely dispersed fall deposit must therefore be used with caution as a vent position indicator. Another consequence is the most spectacular mobility of the immediately succeeding pyroclastic flow, attributed to the catastrophic collapse of the plinian column.

Acoustic Losses of a Resonator with Steady Gas Flow

Measurements have been made of the acoustic losses of a resonator with a small vent and of their dependence both on the speed of steady flow through the system and on the position of the vent. The resonator is physically modeled on the “T burner” used to test solid propellants for combustion instability, but measurements are made at room temperature and pressure. It is a closed circular cylinder, resonant in the fundamental plane-wave mode, with a vent through the wall near the center. Steady gas flow is introduced at one end through a slightly porous piston whose vibration also generates sound. Losses are determined from the rate of decay of pressure. Significant flow-dependent loss attributable to the vent is found for flow speeds in the vent exceeding about 0.02 times the sound speed. The loss depends on vent position. Good quantitative prediction of this loss at flow velocities above a critical value is achieved by a theory based on the characteristics of quasisteady fluid efflux from an orifice (total pressure quadratic in total flow).