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Iceland raised the alarm after its largest volcano was hit by the biggest tremors since 1977. Two quakes larger than 4 in magnitude early Monday rocked the crater of Katla, the country's Met Office said in a statement. That was followed by at least 10 more tremors at the volcano, which rises 1,450 meters (4,757 feet) into the air on the North Atlantic island's southern coast.
AVO/USGS Volcanic Activity Notice
Volcano: Bogoslof (VNUM #311300)
Current Volcano Alert Level: WARNING
Previous Volcano Alert Level: WATCH
Current Aviation Color Code: RED
Previous Aviation Color Code: ORANGE
Issued: Friday, December 23, 2016, 11:12 AM AKST
Source: Alaska Volcano Observatory
Location: N 53 deg 55 min W 168 deg 2 min
Elevation: 492 ft (150 m)
Volcanic Activity Summary: An explosive eruption occurred at Bogoslof this morning at about 09:30 AKST (18:30 UTC). A Coast Guard ship in the vicinity reported ash emission as well as ejection of lava and fragmental material. The eruption cloud did not penetrate the regional cloud tops at 30,000 ft and winds are to the north-northeast. According to the Coast Guard, ash emission subsided at about 10:37 AKST (19:37 UTC). On the basis of this information, the Aviation Color Code is raised to RED and the Alert Level to WARNING.
AVO has no ground-based volcano monitoring equipment on Bogoslof volcano. We will monitor satellite images and data from distant seismic and infrasound instruments for indications of significant explosive activity, although high winds in the are presently limit detection abilities.
[Volcanic cloud height] Below 30,000 ft
[Other volcanic cloud information] Unknown
Remarks: Status of the ash cloud can be found at the Alaska Aviation Weather Unit website at aawu.arh.noaa.gov...
Bogoslof is in an active eruption sequence. On December 20, a powerful, short-lived explosion occurred at about 15:35 AKST (00:35 UTC Dec 21) that sent ash to over 30,000 ft asl. After a day of relative quiescence, another explosion occurred December 21 at 16:10 AKST (01:10 UTC Dec 22) as seen in satellite images and seismic data from neighboring islands. This eruption lasted about 30 minutes and sent ash as high as 35,000 ft asl. These first two eruptions dramatically altered Bogoslof Island and a new vent appears to have developed at the northeast end of the island, immediately offshore. This morning, a third strong ash-producing explosive eruption occurred at about 09:30 AKST (18:30 UTC). During today's event, observers aboard a Coast Guard vessel reported ash emission, lightning, and the ejection of incandescent lava and fragmental material. Ash emission and lava ejection subsided after about an hour, at 10:37 AKST (19:37 UTC). The ash cloud was carried northward over the Bering Sea and did not penetrate above the regional cloud tops at 30,000 ft. Elevated seismicity continues; however, signals are affected by a strong storm that moved across the Aleutian Islands in the past 24 hours.
Retrospective analysis of seismic, air-wave, and satellite data reveal that Bogoslof showed signs of unrest as early as December 12. Ash emissions may have occurred on December 16 and 19 on the basis of recorded lightning strikes, seismic data, and sulfur dioxide clouds detected in satellite, though there were no direct visual observations from satellite or ground observers.
Bogoslof is not monitored by a local geophysical network, which limits our ability to forecast and closely track activity at this volcano. AVO is using seismic and infrasound (airwave sensors) on neighboring Umnak and Unalaska Islands to monitor activity. In addition, we are using satellite imagery and information from the Worldwide Lightning Location Network to identify volcanic lightning; lightning strikes have been detected during the current eruptive sequence.
Bogoslof Island is the largest of a cluster of small, low-lying islands making up the emergent summit of a large submarine stratovolcano. The highest point above sea level prior to this eruption was about 100 m (300 ft); however, the volcano is frequently altered by both eruptions and wave erosion and has undergone dramatic changes in historical time. The two main islands currently above sea level are Fire Island and Bogoslof Island, both located about 98 km (61 mi) northwest of Unalaska/Dutch Harbor, 123 km (76 mi) northeast of Nikolski, and 149 km (93 mi) northeast of Akutan. The volcano is situated slightly north (behind) the main Aleutian volcanic front. Bogoslof volcano is within the USFWS Maritime Wildlife Refuge and is habitat for sea lions birds.
At least 8 historical eruptions have been documented at Bogoslof. The most recent occurred from July 6-24, 1992, and produced episodic steam and ash emissions including an ash cloud up to 26,000 ft (8 km) asl on July 20, followed the next day by extrusion of a new 150-m-high (492 ft) lava dome on the north end of the island. Previous eruptions of the volcano have lasted weeks to months, and have on occasion produced ash fall on Unalaska. Eruptions of the volcano are often characterized by multiple explosive, ash-producing events such as we have seen in 2016, as well as the growth of lava domes.