USGS/Cascades Volcano Observatory, Vancouver, Washington

REPORT:
Explosive Tephra Emissions at Mount St. Helens, 1989-1991: The Violent Escape of Magmatic Gas Following Storms?

-- Larry G. Mastin, 1994,
Explosive Tephra Emissions at Mount St. Helens, 1989-1991: The Violent Escape of Magmatic Gas Following Storms?: Geological Society of America Bulletin, February 1994, v.106, p.175-185

From 24 August 1989 until 18 June 1991, Mount St. Helens produced at least 28 shallow, explosion-like seismic events with signatures similar to those produced by gas explosions on the dome during the mid 1980s. At least six were accompanied by violent emission of non-juvenile tephra, ejection of blocks of rock nearly 1 km from the vent, and avalanching of debris off the north side of the dome. Four produced no emission of tephra, and the remainder occurred when the crater could not be observed (although later crater visits found no new tephra deposits). All six confirmed emissions and most (although not all) other seismic events took place hours to days after storms. -- Mastin, 1994

In HTML Format
- Report -- 48K, with some graphics and tables
In PDF Format
- Report -- 900K, non-tagged PDF courtesy GSA Bulletin, 1994
Select Graphics and Tables
- Graphic [19K,GIF]: -- Map of the Mount St. Helens area.
- Graphic [26K,GIF]: -- Map of the Mount St. Helens crater (from 1988) showing the locations of vents, seismic stations, geodetic stations, and the Rampart fault scarp. NV, north vent; EV, east vent; A, geodetic station Ansel; Am, Amos 3; H, Hoser; Ha, Harold; L, Luther; S, Squab; T, Tiki; Tk, Tinker. Contour elevations in meters.
- Table [14K,GIF]: -- Summary of shallow, explosion-like seismic events and gas-and-tephra emissions, August 1989-June 1991.
- Table [13K,GIF]: -- Probability values for the fortuitous occurrence of shallow, explosion-like seismicity following a given amount of precipitation in a given time period.
Related Menus of Interest
- Volcano-Groundwater Interaction Project - Menu
- Mastin Online Publications - Menu

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05/28/04, Lyn Topinka

REPORT: Explosive Tephra Emissions at Mount St. Helens, 1989-1991: The Violent Escape of Magmatic Gas Following Storms?

REPORT:
Explosive Tephra Emissions at Mount St. Helens, 1989-1991: The Violent Escape of Magmatic Gas Following Storms?