From the Editor
by Paul Britt
Not Your Father’s AVO
Tsunamis, hurricanes, and now volcanoes are in the news as potential geo-hazards. AVO to our readers usually means amplitude variation with offset. But in this case it is the Alaska Volcano Observatory (AVO), a joint program of the United States Geological Survey (USGS), the Geophysical Institute of the University of Alaska Fairbanks (UAFGI) and the State of Alaska Division of Geological and Geophysical Surveys (ADGGS). AVO, formed in 1988, uses federal, state and university resources to monitor and study Alaska’s hazardous volcanoes, to predict and record eruptive activity, and to mitigate volcanic hazards to life and property. Mt. Augustine in Cook Inlet, Alaska (Figure1), poses the potential of eruption and possible tsunami, based on increasing seismic activity around the mountain (Figure 2).
Mt. Augustine Volcano is a 1250-meter-high stratovolcano in southwestern Cook Inlet about 280 km southwest of Anchorage and within about 300 km of more than half of the population of Alaska. Explosive eruptions have occurred six times since the early 1800s (1812, 1883, 1935, 1964-65, 1976, and 1986). The 1976 and 1986 eruptions began with an initial series of vent-clearing explosions and high vertical plumes of volcanic ash followed by pyroclastic flows, surges, and lahars on the volcano flanks. Unlike some prehistoric eruptions, a summit edifice collapse and debris avalanche did not occur in 1812, 1935, 1964-65, 1976, or 1986. However, early in the 1883 eruption, a portion of the volcano summit broke loose forming a debris avalanche that flowed to the sea. The avalanche initiated a small tsunami reported on the Kenai Peninsula at English Bay, 90 km east of the volcano. Plumes of volcanic ash are a major hazard to jet aircraft using Anchorage International and other local airports. Ashfall from future eruptions could disrupt oil and gas operations and shipping activities in Cook Inlet. Eruptions similar to the historical and prehistoric eruptions are likely in Augustine’s future.
Mt. Augustine is one of the many volcanoes on the USGS’watch list. Like the Gulf Coast hurricanes late last year, it has the capacity to pose a threat to oil and gas operations in Alaska, as well as potential harm to human activities and wildlife. Like a hurricane, an eruption cannot be prevented through human intervention, and the only response possible is advance warning and preparation. The AVO maintains a website on volcanoes, at www.avo.alaska.edu, that includes detailed seismic activity, and also a webcam of Mt. Augustine Volcano based in Homer, Alaska, which updates every 5 minutes. The backbone of AVO’s volcano monitoring program consists of networks of continuously recording seismometers installed at selected volcanoes. Seismic data are relayed to AVO facilities in Fairbanks and Anchorage where they are analyzed both automatically and by analysts. Alaska has 129 major volcanic areas, 44 of which are historically active, and 45 that were active in the Holocene.
The West Coast/Alaska Tsunami Warning Center (WC/ATWC) in coordination with the USGS is watching the current activity at Mt. Augustine closely, because it has the potential for generating a tsunami that could threaten the US coastal populations. A tsunami resulting from an eruption of Mt. Augustine could cause dangerous flooding of low-lying coastal areas surrounding the Lower Cook Inlet between the Barren Islands to the south and Kalgin Island to the north. The shallow depths of the upper region of Cook Inlet would cause the tsunami to diminish considerably, making the risk to Anchorage extremely low.
“Large flank collapses have been observed on other volcanoes in modern times: Bezymianny 1956, Sheveluch 1964, and Mt. St. Helens 1980. The seismic energy release from each was approximately equivalent to a magnitude 5 earthquake. These events are our best indication of what may be observed on seismic networks due to a potentially tsunamigenic flank collapse at Mt. Augustine. During the last two Mt. Augustine eruptions, the largest recorded seismic energy release associated with the eruption was equivalent to a magnitude 3.2 earthquake.”2 So, if magnitude 5 equivalent seismic activity is recorded at Mt. Augustine, a tsunami generating flank-collapse could occur.
The Mt. Augustine Volcano is just one example of potential geo-threats that can be found around the world. Fortunately, in at least some areas, resources are devoted to the study and observation of these threats, an example of geology being used to protect the public welfare and safety.
Footnotes
1 From the Alaska Volcano Observatory Website
2 From the National Oceanic and Atmospheric Administration - National
Weather Service Website.
EDITOR’S NOTE: As the Bulletin was going to press, the AVO reported two eruptions of Mt. Augustine Volcano in the early morning hours of January 11, and again on January 13. Ash clouds were reported to 30,000 ft and 34,000 ft, respectively. The ash cloud from the January 13 eruption is expected to impact the shoreline of Kamishak Bay and could impact Kodiak Island as well. No tsunami threat was issued. The “Level of Concern Code” remains at red. More details are available at www.avo.alaska.edu