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Eruption of the Kasatochi volcano
on the Aleutian Islands
August 2008

Kasatochi volcano on 23 Aug. 2008
Kasatochi volcano from the southeast on 23 Aug. 2008.
[Image: Chris Waythomas; source: AVO/USGS website]

On 8 August 2008 an alert was issued shows a large SO2 concentration patch with a very high SO2 peak value. The cloud is no doubt related to the eruption of the Kasatochi volcano on the Aleutian Islands (52.17N, 175.51W; summit 314 m), a volcano that has not been active for more than 200 years. According to messages on the Alaska Volcanic Observatory:

A US Fish and Wildlife field crew reported feeling earthquakes on Kasatochi around August 2, 2008. On August 7, the level of earthquake activity increased and was also accompanied by volcanic tremor. The field crew has been evacuated off Kasatochi. By 22:30 UTC, satellite data showed an ash plume to an altitude of at least 35,000 ft.
Satellite imagery of e.g. AVHRR showed a big ash cloud moving away from the volcano in a wonderful spiral (see this image taken on 8 Aug.). The eruption has lead to cancellation of 44 flight from Alaska Airlines on 10-11 August.

The eruption blew large amounts of SO2 into the atmosphere, up into the lower stratosphere, which was subsequently transported across the Northern Hemisphere, as the details given below show. In addition to SO2 other gases were released during the eruption, including a large amount of BrO -- which was the first time volcanic BrO was seen from satellite.


SO2 detection from 7 August onwards

About 2 hours after the eruption OMI passes over the volcano and detected a small cloud of SO2 with a peak value of 238 DU!! (this value is probably not correct, as such high SO2 concentrations saturate the retrieval process) -- see the image on the right.

On this map, the SO2 is almost overhead of the volcano. GOME-2 measured over that area on 7 Aug. at about 21:45 UTC. and SCIAMACHY shortly after that, i.e. just before the eruption, and they saw nothing.

The next day, 8 August, SCIAMACHY measured very large concentrations, with a peak of 136 DU, close to the volcano and on account of this SACS issued an alert. By then the SO2 cloud has grown quite a bit, as the following images show.

      OMI SO2 from Kasatochi on 8 Aug. 2008
SO2 from Kasatochi as seen by OMI at 00:15 UTC on 8 August 2008; since the orbit during which this measurement was made started on 7 Aug., the map is dated 7 Aug.

GOME-2 SO2 from Kasatochi on 8 Aug. 2008 SCIAMACHY SO2 from Kasatochi on 8 Aug. 2008 OMI SO2 from Kasatochi on 8 Aug. 2008
SO2 cloud from Kasatochi as seen by (from left to right) by GOME-2, SCIAMACHY and OMI in the evening of 8 August 2008. (Click on the images to enlarge.)

During the days following the eruption, it appeared that a really massive amount of SO2 was released and a very large SO2 cloud moves to the East, drifted a bit to the South and then started going North-east with a beautiful curl. On 10 Aug. the cloud reached the Canadian coast. On 11 Aug. the cloud stretched out in a curl across Canada, all the way to the far north, with another curl reaching into the USA.

Image showing sulphur dioxide measured by OMI and volcanic ash measured by AVHRR on 10 August 2008, around 23:00 UTC. Note that the SO2 cloud covers a much larger area than the ash cloud; minor amounts of ash may be associated with the gas cloud, though. The red triangle to the left marks the location of the volcano.
Image courtesy of AVO/USGS
Source: Alaska Volcano Observatory
     Eruption of Kasatochi; Image courtesy of AVO/USGS


Movie of SO2 transport across the Northern Hemisphere

Kasatochi released SO2 in three or four phases over a period of several hours, and depending on the altitude reached by the SO2 and the winds at the time, the SO2 follows different tracks across the Northern Hemisphere in the days after the eruption. This can be seen nicely when combining the SO2 maps of GOME-2 and OMI into one animation.

Animation of the SO2 cloud from Kasatochi as seen by by GOME-2 and OMI from 7 to 23 August 2008.

GOME-2 measures a few hours before OMI, and therefore the movie shows a small jump going from a GOME-2 to an OMI image, followed by a larger jump going from the OMI image to the GOME-2 image of the next day. (Grey means no data.)

Click here for:

     GOME-2/OMI SO2 from Kasatochi on 7-23 Aug. 2008

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