Bulletin of Volcanology

, Volume 74, Issue 7, pp 1621–1643 | Cite as

Eruption of kimberlite magmas: physical volcanology, geomorphology and age of the youngest kimberlitic volcanoes known on earth (the Upper Pleistocene/Holocene Igwisi Hills volcanoes, Tanzania)

  • Richard J. Brown
  • S. Manya
  • I. Buisman
  • G. Fontana
  • M. Field
  • C. Mac Niocaill
  • R. S. J. Sparks
  • F. M. Stuart
Research Article


The Igwisi Hills volcanoes (IHV), Tanzania, are unique and important in preserving extra-crater lavas and pyroclastic edifices. They provide critical insights into the eruptive behaviour of kimberlite magmas that are not available at other known kimberlite volcanoes. Cosmogenic 3He dating of olivine crystals from IHV lavas and palaeomagnetic analyses indicates that they are Upper Pleistocene to Holocene in age. This makes them the youngest known kimberlite bodies on Earth by >30 Ma and may indicate a new phase of kimberlite volcanism on the Tanzania craton. Geological mapping, Global Positioning System surveying and field investigations reveal that each volcano comprises partially eroded pyroclastic edifices, craters and lavas. The volcanoes stand <40 m above the surrounding ground and are comparable in size to small monogenetic basaltic volcanoes. Pyroclastic cones consist of diffusely layered pyroclastic fall deposits comprising scoriaceous, pelletal and dense juvenile pyroclasts. Pyroclasts are similar to those documented in many ancient kimberlite pipes, indicating overlap in magma fragmentation dynamics between the Igwisi eruptions and other kimberlite eruptions. Characteristics of the pyroclastic cone deposits, including an absence of ballistic clasts and dominantly poorly vesicular scoria lapillistones and lapilli tuffs, indicate relatively weak explosive activity. Lava flow features indicate unexpectedly high viscosities (estimated at >102 to 106 Pa s) for kimberlite, attributed to degassing and in-vent cooling. Each volcano is inferred to be the result of a small-volume, short-lived (days to weeks) monogenetic eruption. The eruptive processes of each Igwisi volcano were broadly similar and developed through three phases: (1) fallout of lithic-bearing pyroclastic rocks during explosive excavation of craters and conduits; (2) fallout of juvenile lapilli from unsteady eruption columns and the construction of pyroclastic edifices around the vent; and (3) effusion of degassed viscous magma as lava flows. These processes are similar to those observed for other small-volume monogenetic eruptions (e.g. of basaltic magma).


Kimberlite Igwisi Hills Explosive eruption Lava Monogenetic volcano 



We dedicate this paper to Barry Dawson—the last geologist to visit the volcanoes in 1966—as thanks for his great encouragement, advice and help and for many fruitful discussions throughout this study. Field and laboratory studies were supported a National Geographic Committee on Research and Exploration grant (no. 8562_08) awarded to RJB, the Natural Environment Research Council Geophysical Equipment Facility (grant no. 894) and the Royal Society International Travel Grant scheme. RSJS acknowledges support from a European Research Council Advanced grant. Alan Hobbs and Colin Kay at GEF are thanked for training and support. We thank Craig Storey and Dan Condon for advice on radiometric dating. We are indebted to Rod Smith of Cranbrook School, Kent, Mama Kisinga and the Friends of Urambo and Mwanhala charity for logistical support, lodgings, help and advice. We thank Urambo district council and the villagers at Igwisi for permission to work at the volcanoes. Bruce Kjarsgaard, Pierre-Simon Ross and Greg Valentine are thanked for expert reviews that greatly improved the manuscript. James White is thanked for editorial input and discussion.


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Copyright information

© Springer-Verlag 2012

Authors and Affiliations

  • Richard J. Brown
    • 1
    • 8
  • S. Manya
    • 2
  • I. Buisman
    • 3
  • G. Fontana
    • 4
  • M. Field
    • 5
  • C. Mac Niocaill
    • 4
  • R. S. J. Sparks
    • 6
  • F. M. Stuart
    • 7
  1. 1.Department of Earth and Environmental SciencesOpen UniversityMilton KeynesUK
  2. 2.Department of GeologyUniversity of Dar es SalaamDar es SalaamTanzania
  3. 3.Department of Earth SciencesUniversity of CambridgeCambridgeUK
  4. 4.Department of Earth SciencesUniversity of OxfordOxfordUK
  5. 5.AMEC plc, Environment & Infrastructure—Growth Regions (Mining Services Group)AshfordUK
  6. 6.Department of Earth Sciences, Wills Memorial BuildingUniversity of BristolBristolUK
  7. 7.Isotope Geosciences Unit, SUERCEast KilbrideUK
  8. 8.Department of Earth SciencesDurham University, Science LabsDurhamUK

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