Topic

# Plume

About: Plume is a(n) research topic. Over the lifetime, 10333 publication(s) have been published within this topic receiving 275216 citation(s).

##### Papers

More filters

••

Abstract: Theories of convection from maintained and instantaneous sources of buoyancy are developed, using methods which are applicable to stratified body fluids with any variation of density with height; detailed solutions have been presented for the case of a stably stratified fluid with a linear density gradient. The three main assumptions involved are (i) that the profiles of vertical velocity and buoyancy are similar at all heights, (ii) that the rate of entrainment of fluid at any height is proportional to a characteristic velocity at that height, and (iii) that the fluids are incompressible and do not change volume on mixing, and that local variations in density throughout the motion are small compared to some reference density. The governing equations are derived in non-dimensional form from the conditions of conservation of volume, momentum and buoyancy, and a numerical solution is obtained for the case of the maintained source, This leads to a prediction of the final height to which a plume of light fluid will rise in a stably stratified fluid. Estimates of the constant governing the rate of entrainment are made by comparing the theory with some previous results in uniform fluids, and with the results of new experiments carried out in a stratified salt solution. For the case of an instantaneous source of buoyancy there is an exact solution; the entrainment constant is again estimated from laboratory results for a stratified fluid Finally, the analysis is applied to the (compressible) atmosphere, by making the customary substitution of potential temperature for temperature. Predictions are made of the height to which smoke plumes from typical sources of heat should rise in a still, stably stratified atmosphere under various conditions.

2,259 citations

••

TL;DR: Continental flood basalt eruptions have resulted in sudden and massive accumulations of basaltic lavas in excess of any contemporary volcanic processes, thought to result from deep mantle plumes.

Abstract: Continental flood basalt eruptions have resulted in sudden and massive accumulations of basaltic lavas in excess of any contemporary volcanic processes. The largest flood basalt events mark the earliest volcanic activity of many major hot spots, which are thought to result from deep mantle plumes. The relative volumes of melt and eruption rates of flood basalts and hot spots as well as their temporal and spatial relations can be explained by a model of mantle plume initiation: Flood basalts represent plume "heads" and hot spots represent continuing magmatism associated with the remaining plume conduit or "tail." Continental rifting is not required, although it commonly follows flood basalt volcanism, and flood basalt provinces may occur as a natural consequence of the initiation of hot-spot activity in ocean basins as well as on continents.

1,110 citations

••

Abstract: Morgan [1,2] suggested that continental flood basalts appear as the first volcanic expression of new mantle plumes. Experimental studies in viscous liquids have shown that new, or "starting", plumes should consist of a large bulbous head followed by a narrow feeder conduit. Analysis of the plume flow [3] indicates that, if the plume ascent is driven by thermal buoyancy, the head will entrain the surrounding mantle as it rises. The head cools and enlarges, and develops a compositional zonation of source and entrained mantle. Uncontaminated, relatively hot material from the plume source continues to flow up the trailing conduit making the temperature of the plume axis greater than that of the remainder of the head. We explore the implications of this plume structure by comparing the physical and chemical characteristics of two flood basalt provinces (the Deccan and Karoo) with predictions of the dynamical model. The chronology, tectonics and geochemistry of the two provinces all fit well with the starting plume hypothesis. We attribute the sudden onset and short duration of continental flood volcanism, over an equant area 2000-2500 km across, to melting the plume head and its subsequent decline to a narrow chain of volcanic activity, - 200 km wide, to melting in the plume tail. A surface uplift of 500-1000 m is predicted but this gives way to subsidence due to lateral spreading of the plume head before the onset of the main period of volcanism. A period of enhanced subsidence is then predicted to occur as magma escapes from the mantle and loads the earth's surface, followed by slow subsidence over 109 years as the plume's thermal anomaly gradually decays. The timing and duration of volcanism has not been predicted with certainty, but activity is expected to begin as a burst and to die away rapidly over a total time of order 20 Ma, in agreement with dating which indicates that the bulk of the magmas in each province were ejected within 2-3 Ma and followed by smaller volumes over a further 5-10 Ma. The model predicts that the high-temperature picritic melts associated with continental flood basalts are derived from hot, relatively uncontaminated plume-source mantle at the plume axis and that the more voluminous tholeiitic basalts are produced by melting of cooler hybrid mantle in the plume head. This explains for why the picrites of the Karoo and Deccan are strongly enriched in highly incompatible elements, consistent with melting of an OIB-type source, whereas the associated basalts are weakly enriched in incompatible elements, consistent with derivation from a mixed OIB-lower-mantle source.

1,042 citations

••

Abstract: The available data, mainly topography, geoid, and heat flow, describing hotspots worldwide are examined to constrain the mechanisms for swell uplift and to obtain fluxes and excess temperatures of mantle plumes. Swell uplift is caused mainly by excess temperatures that move with the lithosphere plate and to a lesser extent hot asthenosphere near the hotspot. The volume, heat, and buoyancy fluxes of hotspots are computed from the cross-sectional areas of swells, the shapes of noses of swells, and, for on ridge hotspots, the amount of ascending material needed to supply the length of ridge axis which has abnormally high elevation and thick crust. The buoyancy fluxes range over a factor of 20 with Hawaii, 8.7 Mg s -1, the largest. The buoyancy flux for Iceland is 1.4 Mg s -1 which is similar to the flux of Cape Verde. The excess temperature of both on-ridge and off-ridge hotspots is around the 200oC value inferred from petrology but is not tightly constrained by geophysical considerations. This observation, the similarity of the fluxes of on-ridge and offridge plumes, and the tendency for hotspots to cross the ridge indicate that similar plumes are likely to cause both types of hotspots. The buoyancy fluxes of 37 hotspots are estimated; the global buoyancy flux is 50 Mg s -1, which is equivalent to a globally averaged surface heat flow of 4 mWm -2 from core sources and would cool the core at a rate of 50 o C b.y. -1. Based on a thermal model and the assumption that the likelihood of subduction is independent of age, most of the heat from hotspots is implaced in the lower lithosphere and later subducted. I.NTRODUCWION ridge plumes using Iceland as an example. The geometry of flow implied by the assumed existence of a low viscosity Linear seamount chains, such as the Hawaiian Islands, are asthenospheric channel is illustrated by this exercise. Then the frequently attributed to mantle plumes which ascend from deep methods for obtaining the flux of plumes on a rapidly moving in the Earth, perhaps the core-mantle boundary. The excessive plate are discussed with Hawaii as an example. These methods volcanism of on-ridge hotspots, such as Iceland, is also often involve determining the flux from the plume from the crossattributed to plumes. If on-ridge and midplate hotspots are sectional area of the swell and taking advantage of the kinematreally manifestations of the same phenomenon, one would ics of the interaction of asthenospheric flow away from the expect that the temperature and flux of the upwelling material plume and asthenospheric flow induced by the drag of the would be similar under both features. In particular, the core- lithospheric plate. The methods for extending this approach to mantle boundary is expected to be nearly isothermal so that the hotspots on slowly moving plates are then discussed which Cape temperature of plumes ascending from the basal boundary layer Verde as an example. An estimate of the global mass and heat should be the same globally provided that cooling by entrain- transfer by plumes is then obtained by applying the methods to ment of nearby material and thermal conduction are minor. 34 additional hotspots. The magnitude of this total estimated Finally, the global heat loss from plumes should imply a reason- flux is compatible with the heat flux expected from cooling the

1,033 citations

•

28 Feb 1973Abstract: I Molecular Diffusion- 11 Introduction- 12 Concentration- 13 Flux- 14 Fick's Law- 15 Conservation of Mass- 16 Instantaneous Plane Source- 17 Some Simple Examples- 18 Diffusion of Finite Size Cloud- 19 'Reflection' at Boundary- 110 Two- and Three-Dimensional Problems- 111 Continuous Sources- 112 Source in Uniform Wind- Appendix to Chapter I- Exercises- References- II Statistical Theory of Diffusion and Brownian Motion- 21 Introduction- 22 Dispersion Through Random Movements- 23 Diffusion with Stationary Velocities- 24 Brownian Motion- 25 Dispersion of Brownian Particles- 26 Simple Random Walk Model- 27 Reflecting Barrier- 28 Absorbing Barrier- 29 Connection of Random Walk to Diffusion Equation- 210 Deposition on Vertical Surfaces- 211 Deposition on Horizontal Surfaces- Exercises- References- III Turbulent Diffusion: Elementary Statistical Theory and Atmospheric Applications- 31 Fundamental Concepts of Turbulence- 32 Field Measurements of Concentration and Dosage- 33 The Statistical Approach to Environmental Diffusion- 34 'Lagrangian' Properties of Turbulence- 35 Consequences of Taylor's Theorem- 36 The Form of the Particle-Displacement Probability Distribution- 37 Mean Concentration Field of Continuous Sources- 38 Apparent Eddy Diffusivity- 39 Application to Laboratory Experiments- 310 Application to Atmospheric Diffusion- 311 Initial Phase of Continuous Plumes- 312 Atmospheric Cloud Growth far from Concentrated Sources- 313 The Non-Stationary Character of Atmospheric Turbulence- 314 The Hay-Pasquill Method of Cloud-Spread Prediction- Exercise- References- IV 'Relative' Diffusion and Oceanic Applications- 41 Experimental Basis- 42 Mean Concentration Field in a Frame of Reference Attached to the Center of Gravity- 43 Probability Distributions of Particle Displacements- 44 Kinematics of Particle Movements in a Moving Frame- 45 Phases of Cloud Growth- 46 History of a Concentrated Puff- 47 Initially Finite Size Cloud- 48 Use of the Diffusion Equation- 49 Horizontal Diffusion in the Ocean and Large Lakes- 410 Application to Diffusion of Sewage Plumes- 411 Vertical Diffusion in Lakes and Oceans- Exercise- References- V Dispersion in Shear Flow- 51 Introduction- 52 Properties of the Planetary Boundary Layer- 53 Particle Displacements in a Wall Layer- 54 Continuous Ground-Level Line Source- 55 Flux and Eddy Diffusivity- 56 Comparison with Experiment- 57 Continuous Point Source at Ground Level- 58 Use of the Diffusion Equation- 59 Elevated Sources- 510 Longitudinal Dispersion in Shear Flow- 511 Shear-Augmented Diffusion in a Channel- 512 Dispersion in Natural Streams- 513 Shear-Augmented Dispersion in Unlimited Parallel Flow- 514 Diffusion in Skewed Shear Flow- References- VI Effects of Density Differences on Environmental Diffusion- 61 Introduction- 62 Fundamental Equations- 63 Approximate Forms of the Equations- 64 Equations for Turbulent Flow- 65 Turbulent Energy Equation- 66 Diffusion Floors and Ceilings- 67 Diffusion in a Continuously Stratified Fluid- 68 Velocity Autocorrelation and Particle Spread in Stratified Fluid Model- 69 Bodily Motion of Buoyant and Heavy Plumes- 610 Dynamics of a Line Thermal- 611 Similarity Theory- 612 Bent-Over Chimney Plumes- 613 Theory of Buoyancy Dominated Plumes in a Neutral Atmosphere- 614 Comparison with Observation- 615 Flow Pattern within a Plume- 616 Effect of Atmospheric Stratification- 617 Approximate Arguments for Plumes in Stratified Surroundings- 618 Engineering Assessment of Ground Level Pollution from Buoyancy Dominated Plumes- 619 Effects of Plume Rise on Ground-Level Concentration- Appendix to Chapter VI- A61 Momentum Plumes- Exercise- References- VII The Fluctuation Problem in Turbulent Diffusion- 71 Introduction- 72 Probability Distribution of Concentration- 73 The Functional Form of the Probability Distribution- 74 Hazard Assessment on the Basis of Concentration Probabilities- 75 The Variance of Concentration Fluctuations- 76 Self-Similar Fluctuation Intensity Distribution- 77 Fluctuating Plume Model- References

844 citations