Bulletin of Volcanology

, 81:5 | Cite as

Recognizing unsteadiness in the transport systems of dilute pyroclastic density currents

  • Benjamin J. AndrewsEmail author
Research Article


Laboratory density currents generated with unsteady source conditions provide insight into the distances and timescales over which unsteadiness at the vent should persist in natural dilute pyroclastic density currents (PDCs). The laboratory experiments comprise heated 20-μm talc particles turbulently suspended in air and introduced as density currents into an 8.5 × 6 × 2.6 m air-filled chamber. The densimetric and thermal Richardson, Froude, Stokes, and settling numbers are all similar to those of natural dilute PDCs. Although the experiments’ Reynolds numbers are several orders of magnitude less than natural PDCs, the experiments are fully turbulent and are thus dynamically similar to some dilute natural PDCs. “Unsteadiness” in the experiments is generated by adding two pauses of duration t to the eruption (e.g., a 100 s experiment comprising three ~ 33 s pulses separated by two pauses of t = 10 s). Propagation distance of the leading head is proportional to the square root of time; positions of the trailing pulses have similar time dependence, but they generally travel slightly faster than, and thus catch and merge with the leading current. Trailing pulses are more easily distinguished from the body of the preceding current when t is large. Analysis of turbulent structures through space and time shows that unsteadiness at the eruption source can be distinguished from turbulent fluctuations in the currents when t is greater than the integral turbulent timescale of the current body τbody, a statistical measure of the characteristic timescale of unsteadiness within a turbulent flow. The distances over which unsteadiness in the transport system persist scale with t/τbody and the ratio of the thermal Richardson numbers of the trailing and leading pulses. As t/τbody increases from ~ 2 to ~ 4, trailing pulses remain distinct over an increasing fraction of the lead runout distance. When subsequent pulses have higher RiT than the leading current, they coalesce with the leading pulse at more proximal distances, but when RiT is much lower, they remain distinct over distances similar to that of the leading head even when t is similar to τbody. For currents that have depositional timescales comparable to or shorter than τbody, deposits should be expected to preserve a record of unsteadiness over the distances that unsteady pulses persist.


Pyroclastic density current Pyroclastic flow Pyroclastic surge Turbulence Experimental volcanology 



The author wishes to acknowledge T. Gooding for assistance with many aspects of the experimental volcanology laboratory. K. Befus provided very helpful discussions regarding the interpretation of the experimental results. Thoughtful and helpful comments by O. Roche, R.J. Brown, and an anonymous reviewer improved and clarified this manuscript.

Funding information

The Smithsonian National Museum of Natural History supported this research through its Small Grants Program. This research was also supported by a grant from the National Science Foundation (EAR-1447480) to the author.

Supplementary material

445_2018_1266_MOESM1_ESM.pdf (244 kb)
ESM 1 Schematic of the experimental apparatus located at the Smithsonian Museum Support Center in Suitland, Maryland, USA. Experimental currents are generated by loading (heated) 20-μm talc powder onto a conveyor belt that feeds the powder down a chute and into the “tank.” The inside of the tank measures 8.5 × 6 × 2.6 m. Experiments are illuminated with red, green, and blue laser sheets. Temperature was monitored by an array of 0.001″ K-type thermocouples mounted at heights of 5 and 30 cm. (PDF 243 kb)
445_2018_1266_MOESM2_ESM.avi (26.1 mb)
ESM 2 Movies of experimental density currents showing the streamwise vertical plane of the currents along the centerline of the tank. The color has been adjusted to the Matlab “hot” color scheme. 20150428-07, steady current; 20150428-03, 3.1 s pauses; 20150428-05, 6.2 s pauses. All movies have been sped up by a factor of 3 (i.e., 10 s in the movie corresponds to 30 s of observation). (AVI 26735 kb)
445_2018_1266_MOESM3_ESM.avi (20.3 mb)
ESM 3 (AVI 20802 kb)
445_2018_1266_MOESM4_ESM.avi (25.3 mb)
ESM 4 (AVI 25939 kb)


  1. Andrews BJ (2014) Dispersal and air entrainment in unconfined dilute pyroclastic density currents. Bull Volcanol 76(9):852–852. CrossRefGoogle 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) Turbulence, sedimentation, and coignimbrite partitioning in dilute pyroclastic density currents. J Volcanol Geotherm Res 225:30–44. CrossRefGoogle Scholar
  4. Andrews BJ, Gardner JE, Tait S, Ponomareva VV, Melekestsev IV (2007) Dynamics of the 1800 14C yr BP caldera-forming eruption of Ksudach Volcano, Kamchatka, Russia. In: Eichelberger J, Gordeev E, Kasahara M, Izbekov P, Lees J (eds) Geophysical monographVolcanism and subduction: the Kamchatka region, vol 172, pp 325–342CrossRefGoogle Scholar
  5. Andrews BJ, Dufek J, Ponomareva VV (2018) Eruption dynamics and explosive-effusive transitions during the 1400 cal BP eruption of Opala volcano, Kamchatka, Russia. J Volcanol Geotherm Res 356:316–330CrossRefGoogle Scholar
  6. Benage MC, Dufek J, Mothes PA (2016) Quantifying entrainment in pyroclastic density currents from the Tungurahua eruption, Ecuador: integrating field proxies with numerical simulations. Geophys Res Lett 43:6932–6941. CrossRefGoogle Scholar
  7. Branney MJ, Kokelaar BP (2002) Pyroclastic density currents and the sedimentation of ignimbrites. Memoirs of the Geological Society of London 27. 143 pp.Google Scholar
  8. Breard ECP, Lube G (2017) Inside pyroclastic density currents—uncovering the enigmatic flow structure and transport behavior in large-scale experiments. Earth Planet Sci Lett 458:22–36. CrossRefGoogle Scholar
  9. Browne BL, Gardner JE (2005) Transport and deposition of pyroclastic. Bull Volcanol 67:469–489CrossRefGoogle Scholar
  10. Burgisser A, Bergantz GW (2002) Reconciling pyroclastic flow and surge: the multiphase physics of pyroclastic density currents. Ear Planet Sci Lett 202:405–418Google Scholar
  11. 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. CrossRefGoogle Scholar
  12. Bursik MI, Woods AW (2000) The effects of topography on sedimentation from particle-laden turbulent density currents. J Sediment Res 70:53–63CrossRefGoogle Scholar
  13. Clarke AB, Voight B (2000) Pyroclastic current dynamic pressure from aerodynamics of tree or pole blow-down. J Volcanol Geotherm Res 100:395–412CrossRefGoogle Scholar
  14. Dade BW, Huppert HW (1995) Runout and fine-sediment deposits of axisymmetric turbidity currents. J Geophys Res 100:18597–18609CrossRefGoogle Scholar
  15. Dade BW, Huppert HW (1996) Emplacement of the Taupo ignimbrite by a dilute turbulent flow. Nature 381:509–512CrossRefGoogle Scholar
  16. 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
  17. Druitt TH (1992) Emplacement of the 18 May 1980 lateral blast deposit ENE of Mount St. Helens, Washington. Bull Volcanol 54:554–572CrossRefGoogle Scholar
  18. 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. CrossRefGoogle Scholar
  19. Esposti-Ongaro T, Clarke AB, Voight B, Neri A, Widiwijayanti C (2012) Multiphase flow dynamics ofpyroclastic density currents during the May 18, 1980 lateral blast of Mount St. Helens. J Geophys Res 117:B06208. CrossRefGoogle Scholar
  20. 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
  21. Gardner JE, Andrews BJ, Dennen R (2017) Liftoff of the 18 May 1980 surge of Mount St. Helens (USA) and the deposits left behind. Bull Volcanol 79(1):8–8. CrossRefGoogle Scholar
  22. Houghton BF, Wilson CJN, Fierstein J, Hildreth W (2004) Complex proximal deposition during the Plinian eruptions of 1912 at Novarupta, Alaska. Bull Volcanol 66:95–133CrossRefGoogle Scholar
  23. Komorowski J-C, Jenkins S, Baxter PJ, Picquot A, Lavigne F, Charbonnier S, Gertisser R, Preece K, Cholik N, Budi-Santoso A (2013) Paroxysmal dome explosion during the Merapi 2010 eruption processes and facies relationships of associated high-energy pyroclastic density currents. J Volcanol Geotherm Res 261:260–294Google Scholar
  24. Roche O (2012) Depositional processes and gas pore pressure in pyroclastic flows: an experimental perspective. Bull Volcanol 74:1807–1820CrossRefGoogle Scholar
  25. Rowley PJ, Roche O, Druitt TH, Cas R (2014) Experimental study of dense pyroclastic density currents using sustained, gas-fluidized granular flows. Bull Volcanol 76:855. CrossRefGoogle Scholar
  26. Simpson JE (1997) Gravity currents in the environment and laboratory. Cambridge University Press, CambridgeGoogle Scholar
  27. Smith NJ, Kokelaar BP (2013) Proximal record of the 273 ka Poris caldera-forming eruption, Las Cañadas, Tenerife. Bull Volcanol 75:768. CrossRefGoogle Scholar
  28. Streck MJ, Grunder A (1995) Crystallization and welding variations in a widespread ignimbrite sheet; the Rattlesnake Tuff, eastern Oregon, USA. Bull Volcanol 57:151–169CrossRefGoogle Scholar
  29. Sulpizio R, Dellino P (2008) Sedimentology, depositional mechanisms and pulsating behavior of pyroclastic density currents. Dev Volcano 10:57–96. CrossRefGoogle Scholar
  30. Sulpizio R, Mele D, Dellino P, La Volpe L (2007) Deposits and physical properties of pyroclastic density currents during complex subplinian eruptions; the AD 475 (Pollena) eruption of Somma-Vesuvius, Italy. Sedimentology 54:607–635CrossRefGoogle Scholar
  31. Valentine GA, Wohletz KH, Kieffer SW (1991) Sources of unsteady column dynamics in pyroclastic flow eruptions. J Geophys Res 96:21887–21892CrossRefGoogle Scholar
  32. Wilson CJN (1985) The Taupo eruption, New Zealand II. The Taupo ignimbrite. Philos T R Soc A 314:229–310CrossRefGoogle Scholar
  33. Woods AW (1998) Observations and models of volcanic eruption columns. Geol Soc Lond, Spec Publ 145:91–114. CrossRefGoogle Scholar
  34. Yamamoto T, Takarada S, Suto S (1993) Pyroclastic flows from the 1991 eruption of Unzen Volcano, Japan. Bull Volcanol 55:166–175CrossRefGoogle Scholar

Copyright information

© This is a U.S. government work and not under copyright protection in the U.S.; foreign copyright protection may apply 2019

Authors and Affiliations

  1. 1.Global Volcanism ProgramNational Museum of Natural History, Smithsonian InstitutionWashingtonUSA

Personalised recommendations