On Sedimentation

Hazen, Allen

doi:10.1061/taceat.0001655

Cited by 96 publications

(16 citation statements)

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“…where c(r, t) is the volume concentration of particles, r is the horizontal distance from the plume center, h(r, t) is the thickness of the umbrella layer, u(r, t) is the thickness-averaged horizontal velocity of the flow, and w s is the settling speed of the particle species being considered. The right-hand side represents the rate of particle fallout, which is modeled as proportional to the concentration and the settling speed 42,43,67,68 . Numerical analysis of the fully time-dependent gravitycurrent equations 66 shows that the current extends along a near-steady envelope.…”

Section: Methodsmentioning

confidence: 99%

Rapid heat discharge during deep-sea eruptions generates megaplumes and disperses tephra

Pegler¹,

Ferguson²

2020

Preprint

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Deep-marine volcanism drives Earth’s most energetic transfers of heat and mass between the crust and the oceans. Seafloor magmatic activity has been correlated in time with the appearance of massive enigmatic plumes of hydrothermal fluid, known as megaplumes, yet little is known of the primary source and intensity of the hydrothermal energy release that occurs during seafloor volcanic events. Consequently the origin of megaplumes remains ambiguous. By developing a model for the dispersal of submarine tephras, we show that the transport of pyroclasts requires an extremely rapid energy discharge, forming a hydrothermal plume with characteristics matching those of megaplumes. Our results show that megaplume formation, which we predict can occur in a matter of hours, is concurrent with lava extrusion. However, the predicted release rate of heat energy considerably exceeds that available from lava alone, giving evidence that syn-eruptive discharges of heated crustal fluids provide the dominant source of megaplume energy. The ubiquity of submarine tephra deposits suggests that powerful (∼1 TW) intervals of hydrothermal dis-charge must be commonplace during eruptions in the deep-ocean.

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Section: Methodsmentioning

confidence: 99%

Rapid heat discharge during deep-sea eruptions generates megaplumes and disperses tephra

Pegler¹,

Ferguson²

2020

Preprint

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“…A step-like concentration gradient develops at the base of the upper layer, as some particles settle from the layer, while others are swept back into it by turbulence rather than settling through the boundary. The solution is well-known in volcanology and sedimentation research generally [21,60,61]:…”

Section: Eulerian Analytical Formulationmentioning

confidence: 99%

The Development of Volcanic Ash Cloud Layers over Hours to Days Due to Atmospheric Turbulence Layering

et al. 2021

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Volcanic ash clouds often become multilayered and thin with distance from the vent. We explore one mechanism for the development of this layered structure. We review data on the characteristics of turbulence layering in the free atmosphere, as well as examples of observations of layered clouds both near-vent and distally. We then explore dispersion models that explicitly use the observed layered structure of atmospheric turbulence. The results suggest that the alternation of turbulent and quiescent atmospheric layers provides one mechanism for the development of multilayered ash clouds by modulating vertical particle motion. The largest particles, generally >100μm, are little affected by turbulence. For particles in which both settling and turbulent diffusion are important to vertical motion, mostly in the range of 10–100 μμm, the greater turbulence intensity and more rapid turbulent diffusion in some layers causes these particles to spend greater time in the more turbulent layers, leading to a layering of concentration. The results may have important implications for ash cloud forecasting and aviation safety.

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“…where 1 ¡ n is the solid mass fraction and v s represents the mean settling speed of particles in the current, which, for simplicity, we take as being constant (Bursik & Woods 1996). The sedimentation law (3.3) is a generalization of the settling law that has been introduced by various authors following Hazen (1904). Essentially, the law implies that particles that are swept to the base of the ®ow settle from the dilute suspension and into the basal deposit or some dense under®ow.…”

Section: The Gravity-driven°owmentioning

confidence: 99%

Dynamics of hazardous volcanic flows

Woods

2000

Philosophical Transactions of the Royal Society of London. Seri

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In this paper, some of the processes involved in the generation and propagation of hazardous volcanic ®ows are described. The paper focuses on the high-speed dilute suspension ®ows that develop following (i) the explosive collapse and decompression of a lava dome; and(ii) the collapse of an ash-laden fountain erupting from a volcanic vent.Using the model, we calculate the approximate vertical distribution of pressure in the ®ow, and show how this and the ®ow force evolve as the ®ow advances from the vent. The e¬ects of topography and sedimentation on the intensity and run-out of such ®ows are described. Where possible, we draw on eld examples of the di¬erent phenomena, and we review some analogue laboratory experiments that provide support for the modelling approach.

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On Sedimentation

Cited by 96 publications

References 0 publications

Rapid heat discharge during deep-sea eruptions generates megaplumes and disperses tephra

Rapid heat discharge during deep-sea eruptions generates megaplumes and disperses tephra

The Development of Volcanic Ash Cloud Layers over Hours to Days Due to Atmospheric Turbulence Layering

Dynamics of hazardous volcanic flows

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