Printer friendly versionALASKA VOLCANO OBSERVATORY
Friday, February 10, 2006 1:55 PM AKST (2255 UTC)
59.3633°N 153.4333°W, Summit Elevation 4134 ft (1260 m)
Current Level of Concern Color Code: ORANGE
Thirteen explosions of Augustine Volcano occurred between January 11-28, each sending volcanic ash to more than 30,000 feet (9,000 m) above sea level. Since January 28 the eruption has been characterized by short-duration explosive events and the extrusion of lava which is forming a new lava dome on the volcano's summit. Current information indicates that the rate of lava extrusion has been decreasing slowly over the past few days. Based on all available data AVO believes that dome building eruptive activity will continue over the next few days or weeks and may continue intermittently over the next several months. Dome building activity may be accompanied by pyroclastic flows that can generate low-level ash clouds and possibly some explosive activity. AVO continues 24-7 monitoring of the volcano.
Observations and Background
Each of the thirteen explosive eruptions between January 11 and 28 produced a significant ash plume and small mud flows and pyroclastic flows on the volcano's flanks. The most recent explosion occurred on January 28, 2006 at 7:42 AM (AST). Since January 28 the eruption has been characterized by the extrusion of lava that has formed a new lava dome at the summit. Analysis of past photographs and satellite data indicate that the lava dome may have begun to form as early as January 14. All available data indicate that as the dome grows it periodically becomes unstable and small portions of it avalanche down the north flank producing pyroclastic flows. The number of these flows has been slowly decreasing over the past few days suggesting that the rate of lava extrusion also has been slowly declining. Data from continuous GPS receivers on the island indicate that the flanks of the volcano began to subside (or deflate) on approximately January 28. This trend marks the reversal of the swelling trend that had been observed beginning in roughly June of 2005, that was likely caused by the movement of magma beneath the volcano.
Eruptive activity at Augustine in 2005-06 can thus far be divided into four phases:
1) Early Precursory Phase:
This phase of the eruption began in late May 2005 and is characterized by a slow increase in the rate of earthquake activity and a slight swelling of the volcano's flanks. The average earthquake rate was 1 to 2 per day in May, and 3 to 4 per day in October. The total amount of uplift or swelling of the volcanic edifice was about 2 inches during this period.
2) Later Precursory Phase:
In early to mid December the volcano began to steam vigorously, and increased earthquake activity and gas emission were observed. In response to this activity, AVO deployed additional seismometers, GPS receivers, and time-lapse cameras on the flanks of the volcano, and established a web-based camera system for remote observation.
3) Explosive Phase:
There were 13 individual explosions recorded between January 11 and 28. Most of the explosive activity was concentrated on January 13 and 14. A small lava dome was observed forming on the volcano's summit between January 14 and the explosion on January 17. Each of the 13 explosions produced ash plumes that rose in excess of 30,000 ft (9100 m)above sea level and generated pyroclastic flows and mudflows on the volcano's flanks.
4) Dome Building Phase:
Since January 28 the eruption has been characterized by the slow extrusion of lava that is forming a new lava dome on the mountain's summit. Visual observations and analysis of photographs taken on over flights indicate that the growth of this lava dome began prior to the cessation of explosive activity on January 28. Small portions of the dome have occasionally become over-steepened and have collapsed forming small pyroclastic flows that have moved principally down the volcano's north flank. Over the past several days the number of discrete pyroclastic flow events has decreased indicating that the rate of lava extrusion also has declined.
Interpretation and Hazards
Based on our understanding of Augustine's past eruptions and analysis of the current activity, AVO considers the following as possible future scenarios:
1) Eruption Ends:
Extrusion of the lava dome slowly ends and earthquake activity, ground deformation, gas output, and steaming slowly decrease over several weeks or months.
2) Dome Building Eruption Continues:
An extended period of dome building similar to the activity in 1976 and 1986 will ensue. The explosive phase of both the 1976 and 1986 eruptions was followed by several months of intermittent dome building and low-level eruptive activity. The dome building phases of these eruptions were characterized by the slow and intermittent extrusion of lava at the summit of the volcano. As in 1976 and 1986, portions of the lava dome may become over-steepened, break off, and form rock avalanches and pyroclastic flows that stream down the flanks of the volcano. These flows may produce small to moderate sized ash plumes. Depending on the prevailing winds, the ash plumes might be large enough to affect air traffic and communities in south-central Alaska.
3) Renewed Explosive Activity:
Explosive activity such as that observed between January 11 and 28 could resume. Thus far, the current eruption appears to be somewhat smaller than those that occurred in 1986, 1976 and 1963-64, and a return to explosive activity cannot be ruled out at this time. Historical reports of the 1963-64 eruption indicate that explosive activity continued for as long as 11 months, much longer than the duration of either the 1976 or 1986 eruptions.
4) Larger Explosive Eruption:
A significantly larger eruption could occur, perhaps similar to eruptions that are thought to have taken place prehistorically. Such an eruption could involve the production of larger, more voluminous ash plumes, significant modification of the volcano summit, and large pyroclastic flows and mudflows on the island.
5) Flank Collapse:
The intruding magma or other processes could destabilize a portion of the Augustine cone that could result in a large landslide. If such a landslide entered Cook Inlet, a localized tsunami could be generated. A landslide and tsunami occurred during the 1883 eruption of Augustine Volcano.
Based on all available monitoring data AVO, regards scenario two as the most probable at this time, and scenarios one, three, four and five are considered less likely. It is also possible that continued or renewed extrusion of the lava dome may be accompanied by additional explosive activity, which would involve a combination of scenarios 2 and 3.
AVO will continue to monitor the volcano closely. We plan to add additional instrumentation on the volcano to help us better understand the nature of the current eruption as conditions allow. New data and observations may lead us to change our assessment. Any changes would be announced in a subsequent Information Release.
Additional information on Augustine Volcano and related hazards can be found on the following web sites:
Information on Augustine Volcano:
Information on drifting ash clouds:
Ash cloud trajectories and aviation warnings:
Tsunami issues related to Augustine:
ABBREVIATED COLOR CODE KEY
(contact AVO for complete description):
GREEN volcano is dormant; normal seismicity and fumarolic activity occurring
YELLOW volcano is restless; eruption may occur
ORANGE volcano is in eruption or eruption may occur at any time
RED significant eruption is occurring or explosive eruption expected at any time
VOLCANO INFORMATION ON THE INTERNET: http://www.avo.alaska.edu
RECORDING ON THE STATUS OF ALASKA'S VOLCANOES (907) 786-7478
Tom Murray, Scientist-in-Charge, USGS
firstname.lastname@example.org (907) 786-7497
Steve McNutt, Acting Coordinating Scientist, UAF-GI
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.