(1) VOLCANO OBSERVATORY NOTICE FOR AVIATION (VONA)
(2) Issued:	(20140904/1858Z)
(3) Volcano:	Semisopochnoi (VNUM #311060)
(4) Current Color Code:	UNASSIGNED
(5) Previous Color Code:	YELLOW
(6) Source:	Alaska Volcano Observatory
(7) Notice Number:	2014/A13
(8) Volcano Location:	N 51 deg 55 min E 179 deg 35 min
(9) Area:	Aleutians
(10) Summit Elevation:	2625 ft (800 m)
(11) Volcanic Activity Summary:	The rate and intensity of earthquake activity at Semisopochnoi has been decreasing over the past two months and there are no indications from satellite observations of any changes on the surface of the volcano. Thus, the Aviation Color Code and Volcano Alert Level have been decreased to Unassigned. Although we are confident that earthquake activity has decreased significantly, the seismic data from Semisopochnoi has suffered from frequent data outages. We are unable to assign the Green/Normal alert levels until the data transmission proves to be more reliable. We will continue to monitor Semisopochnoi with seismic data when available, and with satellite data.
(12) Volcanic cloud height:	None
(13) Other volcanic cloud information:	None
(14) Remarks:	Remote Semisopochnoi volcano occupies the largest, young volcanic island in the western Aleutians. The volcano is dominated by an 8-km (5-mile) diameter caldera that contains a small lake and a number of post-caldera cones and craters. The age of the caldera is not known with certainty but is likely early Holocene. The last known eruption of Semisopochnoi occurred in 1987, probably from Sugarloaf Peak on the south coast of the island, but details are lacking. Another prominent, young post-caldera landform is Mount Cerberus, a three-peaked cone cluster in the southwest part of the caldera. The island is uninhabited and part of the Alaska Maritime National Wildlife Refuge. It is located 65 km (40 mi) northeast of Amchitka Island and 200 km (130 mi) west of Adak.
(15) Contacts:	John Power, Scientist-in-Charge, USGS jpower@usgs.gov (907) 786-7497 Jeff Freymueller, Coordinating Scientist, UAFGI jeff.freymueller@gi.alaska.edu (907) 322-4085
(16) 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

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AVO/USGS Volcanic Activity Notice

Volcano: Semisopochnoi (VNUM #311060)

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

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

Issued: Thursday, September 4, 2014, 10:58 AM AKDT
Source: Alaska Volcano Observatory
Notice Number: 2014/A13
Location: N 51 deg 55 min E 179 deg 35 min
Elevation: 2625 ft (800 m)
Area: Aleutians

Volcanic Activity Summary: The rate and intensity of earthquake activity at Semisopochnoi has been decreasing over the past two months and there are no indications from satellite observations of any changes on the surface of the volcano. Thus, the Aviation Color Code and Volcano Alert Level have been decreased to Unassigned. Although we are confident that earthquake activity has decreased significantly, the seismic data from Semisopochnoi has suffered from frequent data outages. We are unable to assign the Green/Normal alert levels until the data transmission proves to be more reliable. We will continue to monitor Semisopochnoi with seismic data when available, and with satellite data.

Recent Observations:
[Volcanic cloud height] None
[Other volcanic cloud information] None

Remarks: Remote Semisopochnoi volcano occupies the largest, young volcanic island in the western Aleutians. The volcano is dominated by an 8-km (5-mile) diameter caldera that contains a small lake and a number of post-caldera cones and craters. The age of the caldera is not known with certainty but is likely early Holocene. The last known eruption of Semisopochnoi occurred in 1987, probably from Sugarloaf Peak on the south coast of the island, but details are lacking. Another prominent, young post-caldera landform is Mount Cerberus, a three-peaked cone cluster in the southwest part of the caldera. The island is uninhabited and part of the Alaska Maritime National Wildlife Refuge. It is located 65 km (40 mi) northeast of Amchitka Island and 200 km (130 mi) west of Adak.

Contacts:
John Power, Scientist-in-Charge, USGS
jpower@usgs.gov (907) 786-7497

Jeff Freymueller, Coordinating Scientist, UAFGI
jeff.freymueller@gi.alaska.edu (907) 322-4085

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

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