STRATI 2013 pp 1263-1267 | Cite as

Another Look at the Mechanisms of Formation of Ash Aggregates in Pyroclastic Deposits

  • Teresa ScolamacchiaEmail author
Conference paper
Part of the Springer Geology book series (SPRINGERGEOL)


Ash aggregation has been a subject of great interest in volcanology, due to its importance in removing the finer-grained fraction of the fragmented material generated during explosive eruptions. In such events, the amount of ash (<2 mm) represents a large fraction of the total erupted mass, and is dispersed into the surrounding atmosphere by vertical plumes and/or pyroclastic density currents (PDCs). Aggregation enhances sedimentation, reducing the residence time of solid particles in the atmosphere; therefore, understanding the processes that govern particle accretion is of critical importance for hazard assessment. Observations and experimental studies to date indicate that water, either in liquid or solid states, is able, in certain proportions, to provide the strongest bonds between particles, which are necessary to form spherical to oblate aggregates able to survive impact with the ground and to be preserved in pyroclastic deposits. In contrast, electrostatic attraction between particles forms only dry, loosely bound aggregates, several hundreds of microns in size, which rapidly disintegrate. In general, aggregates are sub-mm to a few mm in size, even if maximum sizes of several centimetres are sometimes reported. Nevertheless, the individual accreted particles rarely exceed 1 mm. Several types of aggregates were described in the PDCs produced during the 1982 eruption of El Chichón volcano (Mexico), characterized by the injection of 8 million tons of SO2 into the atmosphere, and responsible for a 5–6 °C warming in the tropical lower stratosphere. In such aggregates, individual components are strongly cemented by an S-rich film, in which particles between 1 and a few mm in diameter are common. Even if not visible at the outcrop scale, they represent a consistent proportion of the deposits and are extremely resistant to disaggregation, as shown by their capacity to survive not only the impact with the ground after falling, but also collisions with other clasts. Their similarities with aggregates found in sulphur cones at Poás volcano suggest that liquid sulphur is the cementing material. The explosive ejection of sulphur may occur in volcanoes with active hydrothermal systems. The ability of liquid sulphur to cement particles larger than 1 mm in diameter indicates that size fractions of lapilli can be efficiently removed from eruptive clouds at distances of a few km from the vent, which has important implications for hazard assessment.


Aggregation Liquid sulphur Eruptive clouds Hazard assessment 


  1. Bonadonna, C., Mayberry, G. C., Calder, E. S., Sparks, R. S. J., Choux, C., Jackson Lejeune, A. M., et al. (2002). Tephra fallout in the eruption of Soufriére Hills Volcano, Montserrat. In T. H. Druitt & P. Kokelaar (Eds.), The Eruption of Soufriére Hills Volcano, Montserrat from 1995 to 1999 (pp. 483–516). London: Geological Society of London Memoirs.Google Scholar
  2. Brazier, S., Davis, A. N., Sigurdsson, H., & Sparks, R. S. J. (1982). Fall-out and deposition of volcanic ash during the 1979 explosive eruption of the soufriére of St. Vincent. Journal of Volcanology and Geothermal Research,14, 335.CrossRefGoogle Scholar
  3. Brown, R. J., Branney, M. J., Maher, C., & Dávila-Harris, P. (2010). Origin of accretionary lapilli within ground-hugging density currents, Evidence from pyroclastic couplets on Tenerife. Geological Society of America Bulletin,122(1–2), 305–320.CrossRefGoogle Scholar
  4. Brown, R. J., & BonadonnaC, Durant A. J. (2012). A review of volcanic ash aggregation. Physics and Chemistry of the Earth, Part A/B/C,45–46, 65–78.CrossRefGoogle Scholar
  5. Christenson, B. W., & Woods, C. P. (1993). Evolution of a vent-hosted hydrothermal system beneath ruapehu crater lake, New Zealand. Bulletin of volcanology,55, 547–565.CrossRefGoogle Scholar
  6. Gilbert, J. S., Lane, S. J., Sparks, R. S. J., & Koyaguchi, T. (1991). Charge measurement on particle fallout from a volcanic plume. Nature,349, 589–600.Google Scholar
  7. Gilbert, J. S., & Lane, S. J. (1994). The origin of accretionary lapilli. Bulletin of volcanology,56, 398–411.CrossRefGoogle Scholar
  8. James, M. R., Gilbert, J. S., & Lane, S. J. (2002). Experimental investigation of volcanic particles aggregation in the absence of a liquid phase. Journal of Geophysical Research,107, 2191.CrossRefGoogle Scholar
  9. Lane, S. J., Gilbert, J. S., & Hilton, M. (1993). The aerodynamic behaviour of volcanic aggregates. Bulletin of Volcanology,55, 481–488.CrossRefGoogle Scholar
  10. Lorenz, V. (1974). Vesiculated tuffs and associated features. Sedimentology,21, 273–291.CrossRefGoogle Scholar
  11. Oppenheimer, C. (1992). Sulphur eruptions at volcán Poás, Costa Rica. Journal of Volcanology and Geothermal Research,49, 1–21.CrossRefGoogle Scholar
  12. Reimer, T. O. (1983). Accretionary lapilli in volcanic ash falls. Physical factors governing their formation. In T. M. Peryt (Ed.), Coated Grains (pp. 56–68). Heidelberg: Springer Verlag.CrossRefGoogle Scholar
  13. Scolamacchia, T., Macías, J. L., Sheridan, M. F., & Hughes, S. R. (2005). Morphology of ash aggregates from wet pyroclastic surges of the 1982 eruption of El Chichón volcano, Mexico. Bulletin of Volcanology,68, 171–200.CrossRefGoogle Scholar
  14. Schumacher, R., & Schmincke, H. U. (1995). Models for the origin of accretionary lapilli. Bulletin of Volcanology,56, 626–639.CrossRefGoogle Scholar
  15. Sheridan, M. F., & Wohletz, K. H. (1983). Origin of accretionary lapilli from the Pompeii and Avellino deposits of Vesuvius. In R. Gooley (ed), Microbeam Analysis. Conference Proceedings August 612 (336 p.). Phoenix, Arizona: San Francisco Press.Google Scholar
  16. Taddeucci, J., Scarlato, P., Montanaro, C., Cimarelli, C., Del Bello, E., Freda, C., et al. (2011). Aggregation-dominated ash settling from the Eyjafjallajökull volcanic cloud illuminated by field and laboratory high-speed imaging. Geology,39(9), 891–894.CrossRefGoogle Scholar
  17. Varekamp, J. C., Luhr, J. F., & Prestegaard, K. L. (1984). The 1982 eruption of El Chichón volcano (Chiapas, Mexico), character of the eruptions, ash fall deposits and gas phase. Journal of Volcanology and Geothermal Research,23, 36–68.CrossRefGoogle Scholar
  18. Waters, A. C., & Fisher, R. V. (1971). Base surges and their deposits, Capelinhos and taal volcanoes. Journal of Geophysical Research,76, 5596–5614.CrossRefGoogle Scholar

Copyright information

© Springer-Verlag Berlin Heidelberg 2014

Authors and Affiliations

  1. 1.Ludwig Maximilians UniversitätMüenchenGermany

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