Volcano Update from Archive

Wednesday, August 21, 2013 3:20 PM AKDT (Wednesday, August 21, 2013 23:20 UTC)

56°11'52" N 159°23'35" W, Summit Elevation 8225 ft (2507 m)
Current Volcano Alert Level: WATCH
Current Aviation Color Code: ORANGE

The unrest and eruptive activity at the intracaldera cone of Veniaminof Volcano that began June 8-13 is continuing. After an increase in seismicity on August 13-20, the level of seismic activity over the past few days has diminished somewhat, and the intensity of the eruption appears to have fallen slightly.

Over the past two months, eruptive activity has been characterized by minor, mainly low-level ash emissions, small explosions from the cone, lava fountaining, and effusion of short lava flows that have descended the cone onto the surrounding ice field. At this level of activity, quite similar to that observed during the last two lava producing eruptions in 1983-84 and 1993-94, the primary hazards are limited to the area immediately within the caldera.

The eruption clouds to date have been relatively diffuse plumes of ash, gas, and steam that are mostly low-level (<12,000 feet), but have occasionally risen as high as 15,000 feet above sea level, and typically extend less than 1-2 miles downwind from the cone. Fallout from these clouds has produced trace to minor ash fall within the intracaldera ice field and on the upper slopes of the volcano. Possible trace amounts of ash fall were reported in Perryville on August 20. Samples of mostly fine ash were collected about ΒΌ mile from the vent on August 18 and consist of angular, black, glassy, scoriaceous particles up to 0.08 inches in diameter.

The lava flows consist of short, rubbly to viscous flows approximately 1000 - 3000 feet in length and up to 150 feet in width, that extend from the cone a short distance over ice and snow in the caldera. These hot lava flows have melted some snow and ice and subsided into the ice surrounding the intracaldera cone. The melt rates of ice beneath the lava are relatively slow and have not resulted in the production of significant volumes of water. The melt water that has been generated is either seeping back into the edifice, gradually flowing away from the eruption site toward Cone Glacier to the northwest, or ponding somewhere below the glacier surface in the vicinity of the intracaldera cone. There is no evidence for significant outflow of water from the terminus of Cone Glacier and no sign of any disruption to the glacier itself, except in the vicinity of the lava flows. We do not anticipate any significant melt-water flooding associated with this eruption unless conditions at the volcano change significantly.

AVO has been monitoring the eruption, primarily using seismic data from six of the eight working seismic stations on the volcano, pilot reports, web camera images, and daily satellite image analysis. The seismicity has been characterized by nearly continuous to gradually fluctuating tremor with occasional explosions, some of which have been detected by instruments at Pavlof Volcano (110 miles west of Veniaminof) and at an infrasound array in Dillingham (200 miles northeast). Residents of nearby communities (Chignik Lake, Perryville) have reported hearing rumbling noises and explosions and feeling tremors accompanying the explosions. Such sounds can be expected to continue during times of elevated explosive activity. Satellite observations of the volcano have revealed a strong, persistent thermal signal at and near the intracaldera cone, consistent with the observed lava effusion. So far the ash emissions have generated only a few plumes large enough to be observed in satellite data, and are typically confined to periods of more energetic eruptive activity.

At this point in the eruption, it is uncertain how long activity will continue. Similar historical eruptions have lasted for several months to nearly two years, so the current low-level eruptive activity may continue for several months or more. Analysis of the monitoring data to date does not indicate that the eruptive style is changing, and AVO anticipates that if the volcano continues erupting, it will produce occasional low-level ash plumes and additional small lava flows confined to the area near the intracaldera cone. The ash plumes are unlikely to pose major hazards to overflying aircraft, although local air travel may be temporarily affected, and communities downwind could experience very small amounts of ash from time to time. It remains possible for explosive activity of greater intensity than observed thus far to occur, and higher rising and more voluminous ash clouds could be generated. However, this is less likely than continued activity similar to that characterizing the eruption to date. The lava flows emplaced at the foot of the cone will slowly melt into the glacier and are not expected to generate significant volumes of meltwater such that hazardous outflows of water from Cone Glacier will result.

More information about the ongoing eruption of Veniaminof Volcano including photographs of the activity can be found on the AVO web site (www.avo.alaska.edu). Citizens of the Alaska Peninsula who experience any ash fall can submit a report to the new "Is Ash Falling?" online reporting system at this address: https://www.avo.alaska.edu/ashfall/ashreport.php. Specific questions about potential hazards, or observations can be handled by calling 907-786-7497.

VOLCANO INFORMATION ON THE INTERNET: http://www.avo.alaska.edu

John Power, Scientist-in-Charge, USGS
jpower@usgs.gov (907) 786-7497

David Fee, Acting Coordinating Scientist, UAFGI
dfee@gi.alaska.edu (907) 474-7564

The Alaska Volcano Observatory is a cooperative program of the U.S. Geological Survey, the University of Alaska Fairbanks Geophysical Institute, and the Alaska Division of Geological and Geophysical Surveys.