Bulletin of Volcanology

, Volume 72, Issue 7, pp 859–870 | Cite as

Clinker formation in basaltic and trachybasaltic lava flows

  • Sébastien Loock
  • Benjamin van Wyk de VriesEmail author
  • Jean-Marc Hénot
Research Article


Clinker is a term used to describe massive or scoriaceous fragments commonly associated with ‘a‘ā lava flows. Clinker is generally considered to form by fragmentation of an upper vesiculated crust, due to an increase in apparent viscosity and/or to an increase in shear strain rate. Surface clinker is considered to be transported to the flow front and incorporated at the base by caterpillar motion. Clinker that we have observed on a variety of lava flows has very variable textures, which suggests several different mechanisms of formation. In order to study clinker formation, we examined several lava flows from the Chaîne des Puys Central France, where good sections, surface morphology and surface textures are widespread and clearly visible. We observed basal and surface ‘a‘ā clinker that has fragmentation textures similar to those observed in ash formed in eruptions under dry conditions. In two pāhoehoe flows we have observed basal clinker that formed in-situ. Two other flows display clinker features identical to those commonly observed in phreatomagmatic ash, such as adhering particles, blocky shapes, spherical glass and attached microphenocrysts. Another pāhoehoe flow has a flakey, angular basal breccia, with microfaulted and abraded clasts. These were probably formed at a cooled lava base by large amounts of simple shear and consequent intra-lava brittle faulting. Using these observations we propose three different ways of fragmentation. (1) Clinker can form at the surface and eventually produce roll-over basal breccia. (2) Water/lava interactions can form basal clinker by phreatomagmatic fragmentation. Water/lava ratio variations may produce different clinker structures, in a manner similar to observed textural changes in phreatomagmatic eruptions. (3) Clinker can be formed by brittle brecciation during basal simple shear. The different clinker can provide information about the mechanisms and environmental conditions during lava flow emplacement.


Lavas ‘a‘ā pāhoehoe Clinker Fragmentation Phreatomagmatism Shearing SEM 



We would like to thank especially Edgado Cañon-Tapia, Thordar Thordarson, Steve Self, Harry Pinkerton and Chris Kilburn, who all have provided inspiration at the outcrops during their visits to Clermont-Ferrand. Frances Garland provided a thorough review of the English. We thank also the anonymous reviewers.


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Copyright information

© Springer-Verlag 2010

Authors and Affiliations

  • Sébastien Loock
    • 1
  • Benjamin van Wyk de Vries
    • 1
    Email author
  • Jean-Marc Hénot
    • 1
  1. 1.Laboratoire Magmas et Volcans (CNRS UMR 6524), Observatoire du Physique du Globe de ClermontUniversité Blaise Pascal Clermont IIClermont-Ferrand CedexFrance

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