Pyroclastic Density Currents

Dufek, Josef; Ongaro, T. Esposti; Roche, Olivier

doi:10.1016/b978-0-12-385938-9.00035-3

Cited by 57 publications

(40 citation statements)

References 20 publications

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“…Remobilized ash plumes consistently display characteristics similar to density flows (see supporting information). Wind speeds, and corresponding particle lofting, tend to respond to changes in slope angle, downslope obstacles, and changes in surface type, similar to the dispersion dynamics of pyroclastic density currents (Dufek et al, ). Ash remobilization is primarily driven by meteorological forcing (i.e., high near‐surface wind speed, low relative humidity) and therefore is relatively independent of eruptive activity at the volcano of origin.…”

Section: Distinguishing Plume Typesmentioning

confidence: 99%

Distinguishing Remobilized Ash From Erupted Volcanic Plumes Using Space‐Borne Multiangle Imaging

Flower

Kahn

2017

Geophysical Research Letters

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Volcanic systems are composed of a complex combination of ongoing eruptive activity and secondary hazards, such as remobilized ash plumes. Similarities in the visual characteristics of remobilized and erupted plumes, as imaged by satellite‐based remote sensing, complicate the accurate classification of these events. The stereo imaging capabilities of the Multiangle Imaging Spectroradiometer (MISR) were used to determine the altitude and distribution of suspended particles. Remobilized ash shows distinct dispersion, with particles distributed within ~1.5 km of the surface. Particle transport is consistently constrained by local topography, limiting dispersion pathways downwind. The MISR Research Aerosol retrieval algorithm was used to assess plume particle microphysical properties. Remobilized ash plumes displayed a dominance of large particles with consistent absorption and angularity properties, distinct from emitted plumes. The combination of vertical distribution, topographic control, and particle microphysical properties makes it possible to distinguish remobilized ash flows from eruptive plumes, globally.

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Section: Distinguishing Plume Typesmentioning

confidence: 99%

Distinguishing Remobilized Ash From Erupted Volcanic Plumes Using Space‐Borne Multiangle Imaging

Flower

Kahn

2017

Geophysical Research Letters

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“…Thus, understanding the generation, distribution, and persistence of positive pore pressure is an important prerequisite to accurately forecast flow behavior and the consequent hazards posed by these flows. However, there are several uncertainties in characterizing the effective permeability of polydisperse volcanic particle-fluid mixtures (Cashman & Sparks, 2013;Dufek et al, 2015). The current approaches to model dense pyroclastic currents may be grouped into three different types: (1) kinetic models, which represent block models with constant friction coefficients (Malin & Sheridan, 1982); (2) depth-averaged models, where the height-variant flow properties are vertically averaged and were modified granular flow (coulomb-like) theory accounts for gas pore pressure (Gueugneau et al, 2017;Kelfoun, 2011); (3) multiphase models, that simulate gas and particles as two different phases that interact and use the kinetic theory and frictional models such as the Srivastava-Sundaresan model for describing solid stresses (Dufek & Manga, 2008;Srivastava & Sundaresan, 2003).…”

Section: Introductionmentioning

confidence: 99%

The Permeability of Volcanic Mixtures—Implications for Pyroclastic Currents

et al. 2019

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Geophysical fluid‐granular flows, such as pyroclastic currents and debris flows, owe much of their runout and hazard behavior to the occurrence and time‐variant decay of a flow‐internal fluid pore pressure. However, modeling the effects of fluid pore pressure to forecast hazards is challenging because a unified method in Earth Sciences to quantitatively determine the permeability of these natural mixtures is currently missing. Here we combine experiments on fluidization and defluidization of pyroclastic materials, eolian sediments, and glass beads mixtures with numerical multiphase simulations to compare previous attempts to compute the permeability of complex natural particle‐fluid mixtures. In analogy to particle‐engineering studies on simple gas‐particle mixtures, we demonstrate that the effective length‐scale in the characterization of the fluid‐particle interaction of complex natural mixtures is the product of the Sauter mean diameter and the particle sphericity. Its use in the Kozeny‐Carman equation allows accurate prediction of mixture permeability, and we suggest the routine calculation of the Sauter mean from grain size distributions of the deposits of geophysical mass flows in Earth Sciences. We also show, through defluidization experiments, that the duration of gas retention in natural mixtures is well described when using the Sauter mean as the effective particle size. Further, we show through multiphase simulations that initial bed expansion extends the pore pressure diffusion timescale up to nine times. These results can be applied to small‐to‐large volume dense pyroclastic currents where the ranges of Sauter mean diameter predict gas retention for long duration and to debris flows and snow avalanches.

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“…Equally important, splash‐driven entrainment can be incorporated into 3‐D multiphase and multiphysics PDC simulations [e.g., Todesco et al , ; Dufek and Bergantz , ; Doronzo et al , ; Esposti‐Ongaro et al , ; Benage et al , ] to test how entrainment affects not only runout but concentration and concentration gradients, stratification, air entrainment, and thermal evolution within the flows. Three‐dimensional multiphase models can also explore how particle splash modifies the momentum flux into the currents and examine how high bed load concentrations [e.g., Andrews and Manga , ; Dufek et al , ] affect the occurrence and efficiency of particle splash.…”

Section: Discussionmentioning

confidence: 99%

Effect of particle entrainment on the runout of pyroclastic density currents

2016

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Pyroclastic density currents (PDCs) can erode soil and bedrock, yet we currently lack a mechanistic understanding of particle entrainment that can be incorporated into models and used to understand how PDC bulking affects runout. Here we quantify how particle splash, the ejection of particles due to impact by a projectile, entrains particles into dilute PDCs. We use scaled laboratory experiments to measure the mass of sand ejected by impacts of pumice, wood, and nylon spheres. We then derive an expression for particle splash that we validate with our experimental results as well as results from seven other studies. We find that the number of ejected particles scales with the kinetic energy of the impactor and the depth of the crater generated by the impactor. Last, we use a one‐dimensional model of a dilute, compressible density current—where runout distance is controlled by air entrainment and particle exchange with the substrate—to examine how particle entrainment by splash affects PDC density and runout. Splash‐driven particle entrainment can increase the runout distance of dilute PDCs by an order of magnitude. Furthermore, the temperature of entrained particles greatly affects runout and PDCs that entrain ambient temperature particles runout farther than those that entrain hot particles. Particle entrainment by splash therefore not only increases the runout of dilute PDCs but demonstrates that the temperature and composition of the lower boundary have consequences for PDC density, temperature, runout, hazards and depositional record.

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Pyroclastic Density Currents

Cited by 57 publications

References 20 publications

Distinguishing Remobilized Ash From Erupted Volcanic Plumes Using Space‐Borne Multiangle Imaging

Distinguishing Remobilized Ash From Erupted Volcanic Plumes Using Space‐Borne Multiangle Imaging

The Permeability of Volcanic Mixtures—Implications for Pyroclastic Currents

Effect of particle entrainment on the runout of pyroclastic density currents

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