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Bulletin of Volcanology

, 76:852 | Cite as

Dispersal and air entrainment in unconfined dilute pyroclastic density currents

  • Benjamin J. AndrewsEmail author
Research Article

Abstract

Unconfined scaled laboratory experiments show that 3D structures control the behavior of dilute pyroclastic density currents (PDCs) during and after liftoff. Experiments comprise heated and ambient temperature 20 μm talc powder turbulently suspended in air to form density currents within an unobstructed 8.5 × 6 × 2.6-m chamber. Comparisons of Richardson, thermal Richardson, Froude, Stokes, and settling numbers and buoyant thermal to kinetic energy densities show good agreement between experimental currents and dilute PDCs. The experimental Reynolds numbers are lower than those of PDCs, but the experiments are fully turbulent; thus, the large-scale dynamics are similar between the two systems. High-frequency, simultaneous observation in three orthogonal planes shows that the currents behave very differently than previous 2D (i.e., confined) currents. Specifically, whereas ambient temperature currents show radial dispersal patterns, buoyancy reversal, and liftoff of heated currents focuses dispersal along narrow axes beneath the rising plumes. The aspect ratios, defined as the current length divided by a characteristic width, are typically 2.5–3.5 in heated currents and 1.5–2.5 in ambient temperature currents, reflecting differences in dispersal between the two types of currents. Mechanisms of air entrainment differ greatly between the two currents: entrainment occurs primarily behind the heads and through the upper margins of ambient temperature currents, but heated currents entrain air through their lateral margins. That lateral entrainment is much more efficient than the vertical entrainment, >0.5 compared to ∼0.1, where entrainment is defined as the ratio of cross-stream to streamwise velocity. These experiments suggest that generation of coignimbrite plumes should focus PDCs along narrow transport axes, resulting in elongate rather than radial deposits.

Keywords

Pyroclastic density currents Experimental volcanology Entrainment Explosive volcanism 

Notes

Acknowledgments

R. Dennen was instrumental in the construction of the experimental facility used in this research. T. Gooding provided technical insights regarding instrumentation of the facility. R. Dennen and G. Ramirez helped run many of the experiments presented in this paper. M. Manga provided helpful feedback on an early draft of this manuscript. Thorough and thoughtful comments by O. Roche and B. Brand improved this paper. This research was supported by funding from the Smithsonian Institution Grand Challenges program, the National Museum of Natural History Small Grants program, and the SI Competitive Grants Program for Science.

Supplementary material

445_2014_852_MOESM1_ESM.pdf (270 kb)
Supplementary Material 1 Cartoon of density current structure. The current density, ρcurr, is greater than atmospheric density, ρatm. Current thickness is denoted with h, characteristic velocity is U. Particle fall velocity is uT. Turbulent length scale and turbulent component of velocity are noted with Λ and u’. (PDF 269 kb)
Supplementary Material 2

Oblique movies of ambient-temperature (20130625-1) and warm (20130716-4) currents. Currents have similar mass discharge (0.4 g/s) and durations (100 s), but different thermal energy to kinetic energy densities (0 and 2.2). Movies are sped up by a factor of 5. (AVI 80.6 MB)

Supplementary Material 3

Map projections of ambient-temperature (20130627-3) and warm (20130716-4) currents. Currents have similar mass discharge (∼0.1 g/s), durations >300 s, but different buoyant thermal to kinetic energy densities (0 and 2.5). Movies are sped up by a factor of 5. Streaking in the upper right corner of the movies is the result of imperfect background removal. (AVI 94.5 MB)

445_2014_852_MOESM4_ESM.avi (36.5 mb)
ESM 4 (AVI 36.4 MB)
445_2014_852_MOESM5_ESM.avi (34.9 mb)
ESM 5 (AVI 34.9 MB)

References

  1. Abdurachman EK, Bourdier JL, Voight B (2000) Nuees ardentes of 22 November 1994 at Merapi volcano, Java, Indonesia; Merapi volcano. J Volcanol Geotherm Res 100:345–361CrossRefGoogle Scholar
  2. Andrews BJ, Manga M (2011) Effects of topography on pyroclastic density current runout and formation of coignimbrites. Geology 39:1099–1102CrossRefGoogle Scholar
  3. Andrews BJ, Manga M (2012) Experimental study of turbulence, sedimentation and coignimbrite mass partitioning in dilute pyroclastic density currents. J Volcanol Geotherm Res 225–226:30–44CrossRefGoogle Scholar
  4. Branney MJ, Kokelaar P (1992) A reappraisal of ignimbrite emplacement; progressive aggradation and changes from particulate to non-particulate flow during emplacement of high-grade ignimbrite. Bull Volcanol 54:504–520CrossRefGoogle Scholar
  5. Branney MJ, Kokelaar BP (2002) Pyroclastic density currents and the sedimentation of ignimbrites. Memoirs of the Geological Society of London, London, 27. 143 ppGoogle Scholar
  6. Burgisser A, Bergantz GW, Breidenthal RE (2005) Addressing the complexity in laboratory experiments: the scaling of dilute multiphase flows in magmatic systems. J Volcanol Geotherm Res 141:245–265. doi: 10.1016/j.jvolgeores.2004.11.001 CrossRefGoogle Scholar
  7. Bursik MI, Woods AW (1996) The dynamics and thermodynamics of large ash flows. Bull Volcanol 58:175–193CrossRefGoogle Scholar
  8. Bursik MI, Woods AW (2000) The effects of topography on sedimentation from particle-laden turbulent density currents. J Sediment Res 70:53–63CrossRefGoogle Scholar
  9. Cantero M, Cantelli A, Pirmez C, Balachandar S, Mohrig D, Hickson T, Yeh T-H, Naruse N, Parker G (2012) Emplacement of massive turbidites linked to extinction of turbulence in turbidity currents. Nat Geosci 5:42–45CrossRefGoogle Scholar
  10. Cronin SJ, Lube G, Dayudi DS, Sumarti S, Subrandinyo S, Surono (2013) Insights into the October-November 2010 Gunung Merapi eruption (central Java, Indonesia) from the stratigraphy, volume and characteristics of its pyroclastic deposits. J Volcanol Geotherm Res 261:244–259CrossRefGoogle Scholar
  11. Dade BW, Huppert HE (1995a) A box model for non-entraining suspension-driven gravity surges on horizontal surfaces. Sedimentology 42:645–648CrossRefGoogle Scholar
  12. Dade BW, Huppert HE (1995b) Runout and fine-sediment deposits of axisymmetric turbidity currents. J Geophys Res 100:18597–18609CrossRefGoogle Scholar
  13. Dade WB, Huppert HE (1996) Emplacement of the Taupo ignimbrite by a dilute turbulent flow. Nature 381:509–512CrossRefGoogle Scholar
  14. Dellino P, La Volpe L (2000) Structures and grain size distributions in surge deposits as a tool for modeling the dynamics of dilute pyroclastic density currents at La Fossa di Vulcano (Aeolian Islands, Italy). J Volcanol Geotherm Res 96:57–78CrossRefGoogle Scholar
  15. Dellino P, Buttner R, Dioguardi F, Doronzo DM, La Volpe L, Mele D, Sonder I, Sulpizio R, Zimanowski B (2010) Experimental evidence links volcanic particle characteristics to pyroclastic flow hazard. Earth Planet Sci Lett 295:314–320CrossRefGoogle Scholar
  16. Druitt TH, Calder ES, Cole D, Hoblitt RP, Loughlin SC, Norton GE, Ritchie LJ, Sparks RSJ, Voight B (2002) Small-volume, highly mobile pyroclastic flows formed by rapid sedimentation from pyroclastic surges at Soufriere Hills Volcano, Montserrat: an important volcanic hazard. In: Druitt TH, Kokelaar BP (eds) The eruption of Soufriere Hills Volcano, Montserrat, from 1995 to 1999, vol 21. Geol. Soc. Lond. Mem, London, pp 263–279Google Scholar
  17. Dufek J, Bergantz GW (2007) Suspended load and bed-load transport of particle laden gravity currents: the role of particle-bed interaction. Theor Comput Fluid Dyn 21:119–145. doi: 10.1007/s00162-007-0041-6 CrossRefGoogle Scholar
  18. Dufek J, Manga M (2008) The in-situ production of ash in pyroclastic flows. J Geophys Res 113, B09207. doi: 10.1029/2007JB005555 Google Scholar
  19. Esposti Ongaro T, Neri A, Todesco M, Macedonio G (2002) Pyroclastic flow hazard assessment at Vesuvius (Italy) by using numerical modeling. II. Analysis of flow variables. Bull Volcanol 64:178–191. doi: 10.1007/s00445-001-0190-1 CrossRefGoogle Scholar
  20. Esposti Ongaro T, Neri A, Menconi G, de’Michieli Vitturi M, Marianelli P, Cavazzoni C, Erbacci G, Baxter PJ (2008) Transient 3D numerical simulations of column collapse and pyroclastic density current scenarios at Vesuvius. J Volcanol Geotherm Res 178:378–396. doi: 10.1016/j.jvolgeores.2008.06.036 CrossRefGoogle Scholar
  21. Fisher RV, Orsi G, Ort MH, Heiken G (1993) Mobility of a large-volume pyroclastic flow—emplacement of the Campanian ignimbrite, Italy. J Volcanol Geotherm Res 56:205–220CrossRefGoogle Scholar
  22. Fujii T, Nakada S (1999) The 15 September 1991 pyroclastic flows at Unzen Volcano (Japan): a flow model for associated ash-cloud surges. J Volcanol Geotherm Res 89:159–172CrossRefGoogle Scholar
  23. Gardner JE, Burgisser A, Stelling P (2007) Eruption and deposition of the Fisher Tuff (Alaska): evidence for the evolution of pyroclastic flows. J Geol 115:417–435CrossRefGoogle Scholar
  24. Palladino DM, Taddeucci J (1998) The basal ash deposit of the Sovana Eruption (Vulsini Volcanoes, central Italy): the product of a dilute pyroclastic density current. J Volcanol Geotherm Res 87:233–254CrossRefGoogle Scholar
  25. Roche O (2012) Depositional processes and gas pore pressure in pyroclastic flows: an experimental perspective. Bull Volcanol 74:1807–1820. doi: 10.1007/s00445-012-0639-4 CrossRefGoogle Scholar
  26. Scolamacchia T, Macías JL (2005) Distribution and stratigraphy of deposits produced by diluted pyroclastic density currents of the 1982 eruption of El Chichón volcano, Chiapas, Mexico. Rev Mex Cienc Geol 22:159–180Google Scholar
  27. Sigurdsson H, Carey S (1989) Plinian and co-ignimbrite tephra fall from the 1815 eruption of Tambora volcano. Bull Volcanol 51:243–270CrossRefGoogle Scholar
  28. Simpson JE (1997) Gravity currents in the environment and laboratory. Cambridge University Press, CambridgeGoogle Scholar
  29. Stagnaro M, Bolla Pittalyga M (2013) Velocity and concentration profiles of saline and turbidity currents flowing in a straight channel under quasi-uniform conditions. Earth Surf Dyn Discuss 1:817–853. doi: 10.5194/esurfd-1-817-2013 CrossRefGoogle Scholar
  30. Todesco M, Neri A, Esposti Ongaro T, Papale P, Macedonio G, Santacroce R, Longo A (2002) Pyroclastic flow hazard assessment at Vesuvius (Italy) by using numerical modeling. I. Large-scale dynamics. Bull Volcanol 64:155–177. doi: 10.1007/s00445-001-0189-7 CrossRefGoogle Scholar
  31. Turner JS (1986) Turbulent entrainment: the development of the entrainment assumption, and its application to geophysical flows. J Fluid Mech 173:431–471CrossRefGoogle Scholar
  32. Wells M, Cenedese C, Caulfield CP (2010) The relationship between flux coefficient and entrainment ratio in density currents. J Phys Oceanogr 40:2713–2727. doi: 10.1175/2010JPO4225.1 CrossRefGoogle Scholar
  33. Wilson CJN (1985) The Taupo eruption, New Zeland II. The Taupo Ignimbrite. Phil Trans R Soc Lond Ser A Math Phys Sci 314:229–310CrossRefGoogle Scholar
  34. Wilson CJN (2008) Supereruptions and supervolcanoes: processes and products. Elements 4:29–34. doi: 10.2113/GSELEMENTS.4.1.29 CrossRefGoogle Scholar
  35. Woods AW, Kienle J (1994) The dynamics and thermodynamics of volcanic clouds: theory and observations from the April 15 and April 21, 1990 eruptions of Redoubt Volcano, Alaska. J Volcanol Geotherm Res 62:273–299CrossRefGoogle Scholar

Copyright information

© Springer-Verlag Berlin Heidelberg (outside the USA) 2014

Authors and Affiliations

  1. 1.Global Volcanism Program, Smithsonian InstitutionWashingtonUSA

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