|Start:||August 7, 2008 ||Observed|
|Pyroclastic flow, surge, or nuee ardente: ||
|Tephra plume: ||
|ColHeight: ||15240 m |
|Duration: ||about 24 hours |
|MaxVEI: ||4 |
From Waythomas and others, 2008: "Kasatochi Volcano, a small, 3 km diameter, 300 m high, island volcano in the central Aleutian Islands of Alaska (52.1693 degrees N latitude, 175.5113 degrees W longitude) erupted violently on August 7, 2008 after an intense period of precursory seismic activity. Kasatochi has received little study by volcanologists and has had no confirmed historical eruptions; it is not monitored with seismic instruments on Kasatochi Island. The island is part of the Alaska Maritime National Wildlife Refuge and has been a long-term study site for the US Fish and Wildlife Service (USFWS), which has annually deployed scientists to the island to monitor seabirds for 13 years.
"The 2008 eruption occurred less than a week after USFWS personnel on the island began feeling small tremors. On August 4, the USFWS contacted the Alaska Volcano Observatory (AVO) to report these observations. At the time, the reports of earthquake activity were considered normal, as the area has frequent, and sometimes large, earthquakes and an early analysis suggested that the activity did not appear volcanic in origin. By early evening August 6, it became clear that a significant volcanic earthquake swarm was occurring in the vicinity of Kasatochi Island and that the scientists on the island could be endangered should they remain at their camp. At about 7 PM AKDT, AVO issued a formal Volcanic Activity Notice stating that Kasatochi volcano had become restless and raised the aviation color code and volcano alert level to yellow/advisory. AVO also recommended that the scientists on the island be evacuated as soon as possible.
"Strong seismicity continued throughout the evening and into the next day. At about 10:30 AM AKDT August 7, a magnitude 5.8 earthquake occurred within a few km of Kasatochi. Soon after this earthquake, seismic instruments on nearby Great Sitkin Volcano began recording periods of strong volcanic tremor usually indicative of fluid (magma, gas, or both) motion and often associated with eruptive activity. AVO responded by raising the volcano-alert notification to orange/watch at 1:57 PM AKDT, indicating that an eruption was possible. Just after 2 PM AKDT, satellite images confirmed an eruption of Kasatochi was in progress and AVO issued a Volcanic Activity Notice announcing an aviation color code and alert level of red/warning. Thankfully, a local fishing boat had safely evacuated the two scientists less than 30 minutes prior to the opening blast.
"The eruption was characterized by three distinct explosions that were detected by the seismic network on Great Sitkin Volcano, at approximately 2:01 PM, 5:50 PM, and 8:35 PM AKDT. The first two events produced relatively ash-poor, but gas-charged, eruption clouds that reached 45,000 - 50,000 feet above sea level and apparently no or very little local ash fall. The third event generated an ash- and gas-rich plume that also rose to 45,000 - 50,000 feet and produced several inches of ash and lapilli fall over the ocean and on islands southwest of Kasatochi, including minor amounts on Adak Island, the closest island with a year-round population, about 50 miles from the volcano. Boats in the vicinity of the volcano reported 4-5 inches of coarse grained ash fall, darkening skies, and lightning, likely caused by static electricity in the ash plume. The third event was followed by about 17 hours of continuous ash emission as determined from satellite data. The cumulative volcanic cloud from Kasatochi (Fig. 1
) contained a large amount of sulfur dioxide gas that was detected by the Ozone Monitoring Instrument on NASA's EOS-Aura satellite for more than a week after the eruption as the cloud circled the globe. The ash and gas cloud drifted east and interfered with air travel between Alaska and the conterminous US causing at least 40 flight cancellations and stranding many thousands of travelers. The cloud was visible for thousands of miles downwind and apparently was the cause of some brilliant sunsets over the Midwestern US.
"AVO and USFWS scientists visited Kasatochi Island on August 22 and 23. Photographs of what they found can be seen on the AVO web site (www.avo.alaska.edu). The visit confirmed that a major eruption had occurred, and thick deposits of gray volcaniclastic debris and ash now covered the formerly lush volcanic island that was home to over a hundred thousand seabirds (Fig. 2
, Fig. 3
). Pyroclastic-flow deposits exposed along the new coastline, now about 400 m further into the sea were noticeably warm when visited on August 22 and 23 (Fig. 4
). These deposits recorded significant collapse of the vertical eruption column to produce hot avalanches of rock debris, gas, and ash. The pyroclastic flows also initiated a small tsunami that was recorded by tide gages at Atka, Adak and Amchitka. Attempts to locate the USFWS camp were unsuccessful and the ca. 75-year-old cabin was either swept from the island or buried beneath the new deposits. A few thousand chicks of nesting seabirds had not yet left their nesting burrows or crevices and were most likely entombed under the ash. Few signs of life remained on the former major seabird colony. The summit crater had enlarged in diameter by about 100 m and the crater floor was steaming profusely from a number of circular vents and warm areas on the crater floor.
"The 2008 eruption of Kastochi was a significant test of AVO's ability to assess the reawakening of a seismically unmonitored and little-studied, remote volcano. Fortunately, the earthquake activity was strong enough to be recorded on existing seismic networks on nearby volcanoes and scientists on the island were able to communicate with local contacts to coordinate a rescue. These seismic networks were installed with funding from the Federal Aviation Administration to reduce the hazard to aviation from volcanic ash. In this case, the instrumentation was crucial in recognizing the signs of significant unrest and potential for major eruptive activity, saving the lives of two biologists and providing the aviation community with advance warning of a possible eruption. AVO and its partner agencies in DOI now have a unique opportunity to evaluate the response of Kasatochi's ecosystem to a major volcanic event and to address how the landscape evolves following significant physical, chemical, and biological changes. "
For a record of AVO's Information Statements and Weekly Updates during the eruption, please see http://www.avo.alaska.edu/activity/Kasatochi.php
For an account of the biologist's evaucation from Kasatochi, please see Rozell, 2010.
From Neal and others (2011): "Analyzed 2008 juvenile pumice clasts are crystal-rich andesite with plagioclase, orthopyroxene, clinopyroxene, hornblende, and Ti-magnetite phenocrysts in a clear glass matrix that also contains elongate plagioclase, pyroxene, and amphibole microlites. Preliminary petrology and melt inclusion work suggests pre-eruption storage at depths of about 6.5-12.5 km (4-8 mi) and rapid ascent to the surface (Izbekov, 2008; Izbekov and others, 2009). Gabbroic inclusions in Kasatochi pumice contained amphibole up to 11 cm (4 in.) in length (P. Izbekov, AVO/UAFGI and C. Nye, AVO/ADGGS written commun., 2010).
"Biological impacts of the eruption were significant in the short term; quantifying impacts to plant and animal inhabitants and the nearby ecosystem is the subject of an ongoing interdisciplinary research program (Buchheit and Ford, 2008). Aviation impacts also were severe. The ash and aerosol cloud drifted east during the week following the eruption interfering with air travel between Alaska and the conterminous U.S., causing at least 40 flight cancellations, and stranding many thousands of travelers. At least one commercial jet aircraft flew through what the flight crew reported as a thin volcanic cloud layer prompting an inspection and precautionary replacement of some equipment. A second aircraft over Canada also reported entering a sulfurous, yellowish-brown haze layer (Guffanti and others, 2010). In both cases, no in-flight malfunctions were noted and there was no discernible damage or verifiable volcanic ash contamination upon inspection.
"The eruption cloud was visible for thousands of miles downwind and was the cause of some brilliant sunsets over the Midwestern U.S. The SO2 cloud from this eruption was detected by the Ozone Monitoring Instrument on NASA’s EOS-Aura satellite as it circled the globe. A small tsunami [35 cm (14 in.) in amplitude] associated with the eruption was recorded by a tide gage at Adak, however, no damage was reported."