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AVO/USGS Volcanic Activity Notice

Volcano: Kasatochi (CAVW #1101-13-)

Current Volcano Alert Level: UNASSIGNED
Previous Volcano Alert Level: ADVISORY

Current Aviation Color Code: UNASSIGNED
Previous Aviation Color Code: YELLOW

Issued: Thursday, October 30, 2008, 3:41 PM AKDT (20081030/2341Z)
Source: Alaska Volcano Observatory
Notice Number: 2008/A31
Location: N 52 deg 10 min W 175 deg 30 min
Elevation: 1030 ft (314 m)
Area: Aleutians Alaska

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.

Hazard Analysis:
[General hazards] Despite declining seismicity and cessation of eruptive activity at Kasatochi, hazardous conditions persist. The thick mantle of loose pyroclastic debris on the steep slopes of the volcano may be unstable and prone to remobilization by rainfall to produce fast-moving debris flows that could reach the coast. Rockfalls from the precipitous inner walls of the summit crater are likely to occur for some time. Continuing heat and gas flux into the lake at Kasatochi could produce explosions with no warning. These events would not be expected to produce ash clouds of concern to aviation, however, they would be hazardous to anyone near the crater rim. AVO has received reports of intermittent sulfur smell in the vicinity of Kasatochi since the eruption. This is likely to continue, however, frequent high winds should minimize any gas exposure hazard except very near or inside the summit crater.

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.

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

Next Notice: A new VAN will be issued if
conditions change significantly or alert levels are modified. While a VAN
is in effect, regularly scheduled updates are posted at
http://www.avo.alaska.edu

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.


(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:yellow
(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
VOLCANO ALERT LEVELS
NORMAL
Volcano is in typical background, noneruptive state or, after a change from a higher level, volcanic activity has ceased and volcano has returned to noneruptive background state.
ADVISORY
Volcano is exhibiting signs of elevated unrest above known background level or, after a change from a higher level, volcanic activity has decreased significantly but continues to be closely monitored for possible renewed increase.
WATCH
Volcano is exhibiting heightened or escalating unrest with increased potential of eruption, timeframe uncertain, OR eruption is underway but poses limited hazards.
WARNING
Hazardous eruption is imminent, underway, or suspected.
AVIATION COLOR CODES
GREEN
Volcano is in typical background, noneruptive state or, after a change from a higher level, volcanic activity has ceased and volcano has returned to noneruptive background state.
YELLOW
Volcano is exhibiting signs of elevated unrest above known background level or, after a change from a higher level, volcanic activity has decreased significantly but continues to be closely monitored for possible renewed increase.
ORANGE
Volcano is exhibiting heightened or escalating unrest with increased potential of eruption, timeframe uncertain, OR eruption is underway with no or minor volcanic-ash emissions [ash-plume height specified, if possible].
RED
Eruption is imminent with significant emission of volcanic ash into the atmosphere likely OR eruption is underway or suspected with significant emission of volcanic ash into the atmosphere [ash-plume height specified, if possible].
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