A frictional law for volcanic ash gouge

Y. Lavallée*, T. Hirose, J. E. Kendrick, S. De Angelis, L. Petrakova, A. J. Hornby, D. B. Dingwell

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Volcanic provinces are structurally active regions - undergoing continual deformation along faults. Within such fault structures, volcanic ash gouge, containing both crystalline and glassy material, may act as a potential fault plane lubricant. Here, we investigate the frictional properties of volcanic ash gouges with varying glass fractions using a rotary shear apparatus at a range of slip rates (1.3-1300 mm/s) and axial stresses (0.5-2.5 MPa). We show that the frictional behaviour of volcanic ash is in agreement with Byerlee's friction law at low slip velocities, irrespective of glass content. The results reveal a common non-linear reduction of the friction coefficient with slip velocity and yield a frictional law for fault zones containing volcanic ash gouge. Textural analysis reveals that strain localisation and the development of shear bands are more prominent at higher slip velocities (>10 mm/s). The textures observed here are similar to those recorded in ash gouge at the surface of extrusive spines at Mount St. Helens (USA). We use the rate-weakening component of the frictional law to estimate shear-stress-resistance reductions associated with episodic seismogenic slip events that accompany magma ascent pulses. We conclude that the internal structure of volcanic ash gouge may act as a kinematic marker of exogenic dome growth.

Original languageEnglish
Pages (from-to)177-183
Number of pages7
JournalEarth and Planetary Science Letters
Publication statusPublished - 15 Aug 2014


  • Cyclic extrusion
  • Dome eruptions
  • Earthquake slip
  • Stick-slip
  • Strain localisation
  • Stress drop


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