Printer friendly versionALASKA VOLCANO OBSERVATORY
Tuesday, January 10, 2006 1:05 PM AKST (2205 UTC)
59.3633°N 153.4333°W, Summit Elevation 4134 ft (1260 m)
Current Level of Concern Color Code: YELLOW
Since last spring, the Alaska Volcano Observatory (AVO) has detected increasing volcanic unrest at Augustine Volcano in lower Cook Inlet. Based on all available monitoring data AVO regards that an eruption similar to those in 1976 and 1986 is the most probable outcome. We expect such an eruption to occur within the next few weeks or months. There is currently no indication that an eruption will occur within the next few days and Augustine remains at color code Yellow
Observations and Background:
Rates of earthquake occurrence increased slowly from an average rate of 1 to 2 per day in early May, to 3 to 4 per day in October and 15 per day in mid-December. These earthquakes are occurring directly beneath the mountain's summit at depths close to sea level. The largest event located to date is a magnitude 1.2. Concurrent with this increase, we have also detected a small uplift of the volcano using Global Positioning Systems (GPS) instruments permanently installed on the mountain. The total swelling to date is approximately 2 inches (5 cm). In early and mid December, a number of small steam explosions were recorded by seismic instruments on the volcano. Views of the summit following these explosions revealed new steaming cracks and localized deposits of debris. In addition, airborne gas measurements and thermal imaging measurements have shown an increase in the output of volcanic gas and heat at the summit of the volcano. The highest temperature recorded, on January 4, was 390 C (750 F). AVO interprets these changes as a sign that new magma is accumulating beneath the volcano's summit. Based on an analysis of past and current earthquake locations, GPS, gas, and heat data, this new magma may have risen to sea level or higher.
In response to this activity, AVO has deployed additional seismometers, GPS receivers, an infrasound sensor, and time lapse cameras on the flanks of the volcano, and established a web-based camera system. Further deployment of additional monitoring equipment is ongoing. We plan continued visual and infrared surveillance of the volcano's summit and frequent measurements of gas output.
The most recent eruptions of Augustine were characterized by an initial explosive phase lasting from 4 to 14 days. The explosive phase produces large ash plumes, that depending upon the prevailing winds and height of the eruptive column, can be carried hundreds to thousands of miles. Most communities in south-central Alaska experienced some ash fall with accumulations of several millimeters during both the 1976 and 1986 eruptions (Anchorage received 0.12 inches (3 mm) in 1976 and less than 0.04 inches (1 mm) in 1986; Homer received about 0.2 inches (5 mm) in 1976 and 1986). During the explosive phase of the eruption, many portions of Augustine Island are also overrun by pyroclastic flows (fast flowing mixtures of hot volcanic gasses, steam, rock and ash) and mud flows (fast moving mixtures of volcanic rock, ash and water). The explosive phase is generally followed by the extrusion of a lava dome which is generally accompanied by smaller explosions and pyroclastic flows. Communities in south-central Alaska may again experience minor ash fall during these later phases of the eruption.
Interpretation and Hazards:
Based on our current understanding of Augustine's past eruptions and our analysis of the current episode of unrest, AVO considers the following future scenarios as possible:
1) Failed Eruption:
No eruption occurs as magma does not reach the surface. Earthquake activity, ground deformation, gas output, and steaming slowly decrease over several weeks or months.
2) Eruption similar to those of 1976 and 1986:
Unrest continues to escalate culminating in an eruption that is similar to those that occurred in 1976 and 1986. An eruption such as this would likely spread volcanic ash throughout and perhaps beyond Cook Inlet depending upon the prevailing winds. Much of Augustine Island would be inundated by pyroclastic flows, mud flows, ash fall, and ballistic showers.
3) Larger Explosive Eruption:
A significantly larger eruption could occur, perhaps similar to eruptions that are thought to have taken place prehistorically. Such an eruption might involve the production of larger ash plumes, significant modification of the island's summit, and large pyroclastic flows and mud flows on the island.
4) Flank Collapse:
The intruding magma or other processes could destabilize a portion of the Augustine cone that could result in a large landslide. If this landslide entered Cook Inlet, a localized tsunami could be generated. Such a landslide and tsunami were associated with the 1883 eruption of Augustine Volcano. It is also likely that a landslide of this type would be accompanied by an eruption.
Based on all available monitoring data AVO, regards scenario number two, an eruption similar to those in 1976 and 1986, as the most probable outcome at this time. At this time scenarios one, three and four are considered less likely.
Comparing the time frame of pre-eruptive activity in 1976 and 1986 with the current unrest, we would expect such an eruption to occur within the next few weeks or months. There is currently no indication that an eruption will occur within the next few days. Both the 1986 and 1976 eruptions were preceded by short-term (hours to days) increases in seismic activity. Should earthquake activity or other monitoring data suggest that an eruption is expected within hours or days, AVO would move Augustine from its current level of concern color code Yellow to Orange or Red.
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 this unrest. New data and observations may lead us to change our assessment. Any changes would be announced in a subsequent Information Release.
Further information on Augustine Volcano and related hazards and response plans can be found at the following web sites:
Alaska Volcano Observatory: Most recent information on Augustine Volcano
U.S. Geological Survey: Hazards associated with volcanic ash fall
NOAA National Weather Service: Ash cloud trajectories and aviation warnings
NOAA West Coast and Alaska Tsunami Warning Center: Tsunami issues related to Augustine
Alaska Division of Homeland Security and Emergency Management: Community preparedness
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
email@example.com (907) 474-7131
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.