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
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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.
Study Area
| Publication type | Report |
|---|---|
| Publication Subtype | USGS Numbered Series |
| Title | Frictional properties of the Mount St. Helens gouge |
| Series title | Professional Paper |
| Series number | 1750-20 |
| DOI | 10.3133/pp175020 |
| 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 |
| Google Analytic Metrics | Metrics page |