(1) VOLCANO OBSERVATORY NOTICE FOR AVIATION (VONA)
(2) Issued:(20081030/2341Z)
(3) Volcano:Kasatochi (CAVW# 1101-13-)
(4) Current Color Code:UNASSIGNED
(5) Previous Color Code:
(6) Source:Alaska Volcano Observatory
(7) Notice Number:2008/A31
(8) Volcano Location:N 52 deg 10 min W 175 deg 30 min
(9) Area:Aleutians Alaska
(10) Summit Elevation:1030 ft (314 m)
(11) Volcanic Activity Summary:Over the past 2 months, seismic activity detected on regional networks in the vicinity of Kasatochi Volcano has steadily declined in intensity. Overflights and satellite imagery show no indication of significant continuing unrest. The likelihood of resumed eruptive activity at Kasatochi has greatly diminished, therefore, we are reducing the Aviation Color Code to UNASSIGNED and Volcanic Alert Level to UNASSIGNED.
(12) Volcanic cloud height:Unknown
(13) Other volcanic cloud information:Unknown
(14) Remarks:The 2008 eruption occurred on August 7, 2008 after several days of felt earthquakes, observed rockfalls, and sulfur smell reported by USFWS biologists on the island. At least three violent explosions sent ash and gas clouds as high as 60,000 ft above sea level. Pyroclastic debris from the explosions blanketed the entire island and extended the shoreline seaward. The summit crater widened and the lake vanished during the explosions; water is now re-filling the summit crater producing a brownish-green, warm, and probably acidic lake.

Continuing earthquake activity measured on the Great Sitkin Island seismic network is dominated by regional tectonic events unrelated to Kasatochi. Occasional thermal anomalies visible in satellite images are produced by the still-warm, fresh, volcanic deposits and crater lake. It is important to note that AVO has no seismic instrumentation on Kasatochi Volcano. Our reliance on adjacent networks on Great Sitkin and Atka Islands means small earthquakes that may occur prior to an eruption could go undetected. Despite this, the steadily declining regional seismicity and no visual signs of accelerated unrest seen in satellite data or by flight crews or mariners suggests renewed eruption is unlikely.

Kasatochi Island is the summit of a predominantly submarine volcano composed of basaltic and andesitic lava flows and pyroclastic deposits. The volcanic cone has a circular central crater more than 1 km (3300 ft) across. Prior to the 2008 eruption, the high point of the crater rim was about 314 m (1030 ft) above sea level.

Historical eruptions at Kasatochi are poorly documented, although it is possible that eruptions attributed to nearby Konuiji volcano in 1760, 1827, and 1828 were actually eruptions of Kasatochi. Eruptive activity in 1899 may have destroyed the lake within the Kasatochi crater. Kasatochi is 83 km (52 mi) east of the community of Adak, and 90 km (55 mi) west of the community of Atka.
(15) Contacts:Tom Murray, Scientist-in-Charge, USGS
tlmurray@usgs.gov (907) 786-7497

Steve McNutt, Coordinating Scientist, UAF
steve@giseis.alaska.edu (907) 474-7131
(16) Next Notice:A new VONA will be issued if
conditions change significantly or alert levels are modified. While a VONA
is in effect, regularly scheduled updates are posted at
http://www.avo.alaska.edu