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Frictional properties of the Mount St. Helens gouge: Chapter 20 in A volcano rekindled: the renewed eruption of Mount St. Helens, 2004-2006

Professional Paper 1750-20

This report is Chapter 20 in A volcano rekindled: the renewed eruption of Mount St. Helens, 2004-2006. For more information, see: Professional Paper 1750
By:
, , and ORCID iD
Edited by:
David R. Sherrod ORCID iD , William E. Scott ORCID iD , and Peter H. Stauffer

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Abstract

Frictional properties of gouge bounding the solid dacite plug that extruded at Mount St. Helens during 2004 and 2005 may have caused stick-slip upward motion of the plug and associated seismicity. Laboratory experiments were performed with a ring-shear device to test the dependence of the peak and steady-state frictional strength of the gouge on shearing rate and hold time. A remolded gouge specimen (~0.012 m3 ) was sheared under constant normal stresses ranging from 5 to 200 kPa and at rates ranging from 10-6 to 10-3 m/s. The gouge exhibited rate-weakening behavior at rates lower than 1×10-4 m/s and rate-strengthening at rates above 5×10-4 m/s. Peak strengths occurred during the onset of shearing, when displacements were generally less than 0.5 mm. In slide-holdslide tests, the peak strength of the gouge increased logarithmically as hold times increased from 3 s to almost 105 s. Rate-weakening friction is a requirement for stick-slip behavior that is satisfied by the Mount St. Helens gouge. Indeed, regular stick-slip oscillations were observed in two experiments performed at the highest normal stress and lowest rates of shear. The conditions under which this stick-slip motion occurred indicate that the gouge also satisfies a second criterion for stick-slip behavior of materials exhibiting rateand-state dependent friction-gouge stiffness exceeds that of the ascending magma that drives upward motion of the plug. The presence of highly compliant magma as a driving element may be crucial for generating stick-slip instabilities at the shallow earthquake focal depths observed during the eruption.

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Additional publication details

Publication type:
Report
Publication Subtype:
USGS Numbered Series
Title:
Frictional properties of the Mount St. Helens gouge: Chapter 20 in A volcano rekindled: the renewed eruption of Mount St. Helens, 2004-2006
Series title:
Professional Paper
Series number:
1750-20
Year Published:
2008
Language:
English
Publisher:
U.S. Geological Survey
Publisher location:
Reston, VA
Contributing office(s):
Volcano Hazards Program
Description:
10 p.
Larger Work Type:
Report
Larger Work Subtype:
USGS Numbered Series
Larger Work Title:
A volcano rekindled: the renewed eruption of Mount St. Helens, 2004-2006 (Professional Paper 1750)
First page:
415
Last page:
424
Country:
United States
State:
Washington
Other Geospatial:
Mount St. Helens