Friday, January 31, 2014

Alaska's Shishaldin Volcano Alert Status Raised To Yellow

Another volcano in Alaska is being raised to Yellow Alert status by AVO after satellite images detected heightened thermal activity, and webcam observations showed steam emissions from the summit of Shishaldin Volcano. Shishaldin is one of many Alaskan stratovolcanoes lining the Aleutian Arc. It is one of the most symmetrical cone stratovolcanoes in the world, with only a cone vent to throw of fits perfect cone shape on the NW flank.

Image of Shishaldin Volcano from the Smithsonian GVP

The last activity of Shishaldin was reported in October of 2009, when AVO declared its last eruptive event to be over. The last event was a lava dome building event that did not turn into a full scale eruption. The current activity may be another such event, but as the previously emplaced dome could be unstable, collapse and subsequent explosions/ash emissions are possible. There are no significant human populations nearby Shishaldin, and thus very little risk to human life should an eruption occur, although if a significant eruption does take place, ash emission could divert flight patterns, as is common with Alaskan volcanoes. 

Image of last dome building event at Shishaldin Volcano from AVO

Avo has reported the current activity:

"The Alaska Volcano Observatory is raising the Aviation Color Code to YELLOW and the Alert Level to ADVISORY at Shishaldin Volcano based on satellite observations over the past day of increased surface temperatures in the summit crater, as well as increased emissions of steam observed yesterday in satellite and web camera images. These observations represent a departure from normal background activity at Shishaldin, but do not necessarily indicate that an eruption will occur. Similar levels of unrest were last noted during 2009, and did not result in an eruption. Shishaldin is monitored by a local seismic network, satellite data, web camera, telemetered geodetic network, and distant infrasound networks. Seismic monitoring of Shishaldin is significantly impaired due to equipment failures of seismic stations close to the volcano. We hope to be able to detect significant explosive activity (should it occur) using remaining functioning seismic stations in the region, satellite, and distant infrasound networks. AVO will continue to watch Shishaldin carefully for additional signs of increased unrest."

AVO is at this time hesitant to declare that an eruption is imminent. As always with Alaskan volcanoes (most of which are only monitored by seismographs, webcams, and satellites) it is difficult to adequately monitor them with the methods at hand, so typically AVO will wait for more direct evidence of an eruption before elevating the volcanoes alert status above Yellow (which is advisory, meaning aircraft are advised to use extra caution when approaching that airspace). But keep your eye on this volcano, as it has erupted over 20 times since record keeping began around 1824. Most eruptions have been quite minor or small (VEI 1-2), but it did have a couple of VEI 3 events in the late 1990's.

*****UPDATE 2/11/2014*****
AVO has released the following:

2014-02-11 11:02:42

"Unrest continues. Overnight, weakly elevated surface temperatures were seen satellite images. Partly clear web camera images from this morning show no activity. No anomalous seismicity observed in data from the one working station, though wind noise currently could be obscuring low levels of seismic activity."

2014-02-07 12:02:08 - Weekly Update

"Elevated unrest continues at Shishaldin. A possible volcanic cloud was observed this morning in satellite images beginning around 1545 UTC (6:45 AKST). This cloud may have resulted from a small explosive event at the volcano. The event was small enough that it was not detected by the one working seismic station near the volcano, but it appears to coincide with a signal recorded by a nearby tiltmeter. Satellite images suggest that the cloud may have reached as high as 25,000 ft asl, was ash poor, and short lived. There was no evidence of elevated surface temperatures observed in satellite data following this event, suggesting that it was primarily a gas event and very little to any hot material was produced and deposited on the flanks of the volcano. There have been no visible observations of the volcano since this event and AVO will continue to evaluate new data as it becomes available.Persistent elevated surface temperatures in the summit crater of Shishaldin have been observed during clear-weather intervals over the past week. Nothing unusual has been seen in seismicity from the nearest working station off the flanks of the volcano."

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