Semisopochnoi from Space – http://www.avo.alaska.edu/images/image.php?id=3134
Earthquake activity has increased at Semisopochnoi in the Aleutian Islands. Heightened activity began in January and has progressed to the point where brief periods of seismic tremor have been observed. This may indicate movement of magma or volcanic gasses. While the current swarm has not yet surpassed the June – July 2014 swarm in amplitude or earthquake frequency, it is well on its way. Alaska Volcano Observatory activity page can be found here: http://www.avo.alaska.edu/activity/Semisopochnoi.php
Semisopochnoi Webicorder from Mar 26, 2015 – http://www.avo.alaska.edu/webicorders/Semisopochnoi/CERB.php
Ashfall prediction for March 26 can be found here: http://www.avo.alaska.edu/activity/ash3d/ashfall.php?vid=ak248
Basics
Semisopochnoi Detail – http://www.avo.alaska.edu/images/image.php?id=66661
Semisopochnoi Island is a basalt volcanic island some 2,100 km southwest from Anchorage. It sits approximately two thirds of the way along the Aleutian Island chain toward Kamchatka.
Map of Rat Islands – http://www.avo.alaska.edu/images/image.php?id=10003
The island itself is some 20 km in diameter. It is topped with a caldera some 8 km in diameter. There are three stratovolcano cones and multiple parasitic cones currently building in the caldera. These include Sugarloaf, Anvil and Cerebus
Maximum height of the island above the Pacific is 1,221 m.
Anvil Peak on Semisopochnoi – http://www.avo.alaska.edu/images/image.php?id=3317
The island is uninhabited and there are no permanent settlements within 100 km. The closest town is Adak, some 204 km southeast.
Like most of the Aleutians, it is a home for birds.
Tectonics
Eruptive melt is supplied via the subduction of the Pacific Plate under the North American Plate. The Aleutian Trench is south of the island. It is part of the Rat Islands. The island sits on the end of a small submarine ridge in the Bering Sea called Bower’s Ridge. AVO does not know if the location of the ridge drives the production or composition of eruptive materials. http://www.avo.alaska.edu/volcanoes/volcinfo.php?volcname=Semisopochnoi
Location of Semisopochnoi Island near Aleutians Trench. Island is marked. Google Earth
Eruptions
Ravine showing multiple tephra layers – http://www.avo.alaska.edu/images/image.php?id=65911
The island is a typical basaltic andesitic structure with multiple layers of lava and pyroclastic materials. The caldera forming eruption is thought to have taken place some 7950 BC. Total materials produced were on the order of 150 km3 leading to the creation of the caldera. It was mainly dacitic pumice and pyroclastic flows. The island appeared to be topped with glaciers at the time of the eruption. This eruption would have been a VEI7. http://www.bgs.ac.uk/vogripa/searchVOGRIPA.cfc?method=detail&id=1036
Cerberus Volcanic Complex – http://www.avo.alaska.edu/images/image.php?id=4640
The most recent eruption was an explosive eruption out of Sugarloaf Peak, one of the stratovolcanoes growing inside the caldera. The eruption was a VEI2; took place in 1987 and lasted about six weeks starting in April 1987.
Multiple vents on top of Cerberus – http://www.avo.alaska.edu/images/image.php?id=48071
The most recent eruption before that was 1873. There are at least four earlier eruptions reported, though due to the remoteness of the island, actual details are few and far between.
Conclusions
Like all the Aleutians, Semisopochnoi has the ability to produce massive eruptions. It’s location under the air route across the North Pacific make any eruption an immediate concern for air traffic and resident wildlife, but little immediate concern for people. There is no prediction as yet about impending eruptions, though any earthquake swarm that shows occasional tremor is something to pay attention to.
Ragged Top, view from east flank of Cerberus – http://www.avo.alaska.edu/images/image.php?id=4642
Additional Reading
http://pubs.usgs.gov/bul/1028o/report.pdf
http://www.volcano.si.edu/volcano.cfm?vn=311060
http://www.bgs.ac.uk/vogripa/searchVOGRIPA.cfc?method=detail&id=1036
agimarc
Spica
Granyia
volcanohotspot.wordpress.com 
multiple parasitic cones currently building in the caldera. These include Sugarloaf, Anvil and Cerebus
Not Cerebus The Aardvark, surely? 🙂 Great post as always; this is yet another of those basaltic shields which has ‘gone caldera’ with a massive silicic eruption in the Holocene (Okmok, Ambrym, etc)
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This morning’s webicorder. Think it is the one on Cerberus. Looks like it has been a busy weekend. Cheers –
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Is that a couple more tremor episodes there?
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Wish I knew. I don’t read these things very well other than look at the frequency and amplitude of the smaller quakes. It reminds me a lot of what the webicorders looked like during the leadup to Redoubt. Not saying that anything like that is underway. But the smaller quakes started coming early and often along with other stuff I didn’t understand at the time. Cheers –
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Thank you Agimarc. A new volcano to keep an eye on….
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Hi agimarc, thanks for the heads up! That’s one of those I have never heard of before!
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To the NtV riddlers – are the remaining ones too tough to find out, do you want me to add hints? Come on now, you should at least make out #034 without a hint:
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Villarrica is doing its Strombolian dance again!
Animated gif from the Llafenco webcam:
GIF http://i.imgur.com/rewLwaa.gif
http://volcams.malinpebbles.com/pubweb/CHILE.htm
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Yes please for hints…
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Hurricane “Niklas” is raging outside and I am sitting in my loft apartement, waiting for the roof to take off…
All afternoon messages have come in of fallen trees, collapsed walls, flying roofs etc., some people died. In many areas train traffic has been stopped completely for danger of trees on the rails, and some large buildings, as for exemple Munich Main Railway Station, have been evacuated and closed until winds would calm down – something unheard of before.
To me the most impressive picture was this one: a train had hit a tree fallen onto the rails – luckily, nobody was killed in this accident:
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Stay safe! Night storms are scary! Hope your night passes without incident and you can get some rest as it dies down! Check in tmrw so we know u r OK!
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We had some very strong winds too, but not that strong. Stay safe Granyia
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Thank you maggiemom and dfm! Me and my family have suffered no damage, just my potted tree on the balcony which I had tied securely to the iron railings – or so I thought – was torn loose and lost a few branches. The house I live in was built in 1910. I always think firstly that they built sturdier at that time, and secondly, if it had withstood all storms for 105 years there is no reason that this should change just now. 😀
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So true! Don’t build them like they used to! Glad all is well and your town can recover soon.
Gosh,the train does look like it devoured that tree. . .
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That must have been one hungry train…. 😉
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LOL, very true! I also keep seeing those big jaws scrunching that tree trunk! 😀
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Okay, I’ve added clues to the remaining NtV riddles! Good luck!
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Clues have been appended to my riddles as well!
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Hi
Bardarbunga is nearly quiet these days so it’s time to make a retrospective.
I did not supply plots for some time, so I try to amend and change that a bit.
Here is the first of a new series. Unfortunately I lost some of my data (the file was corrupted) and this plot uses data from august to end of december 2014. The good news is that I can rebuilt the data file but it will take some time.
I tried a new approach, filtering by magnitude range (ie 0-2, 3-4 and 4-6, instead of simply > or > to…) and showing only a maximum number of quakes (here 750) so that the time window of the display varies (see title bar for mag adn time span)
So this is an hour by hour earthquake plot for bardarbunga area.
Earthquake magnitude is selected from 0 to Mag 2.
Only 750 events are shown at all time to avoid overcrowding.
Dot color is date dependant (see left colorbar). Blue is older and red is younger.
There is also some terrain altitude information (see right side of colorbar)
First view is from the east, then from the top and finally all events are shown with rotation and some tilt.
There seems to have been some dyke like activity under Herdubreid (see at 0:17 to 1:00 and 3:44-4:15, the aligment is remarquable).
On the top view the dyke progression is well seen including it’s change of direction @ 3:37)
Data from IMO (>99% quality) , NOAA, Made on Gnu Octave for Volcanohotspot.wordpress.com
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Here is another plot.
Earthquake magnitude is selected from 2 to Mag 3.
Only 500 events are shown at all time to avoid overcrowding.
Dot color is date dependant (see left colorbar)
First view is from the east, then from the top and finally all events are shown with rotation and some tilt.
There seems to be some dyke like activity under Herdubreid (see at 0:17 to 1:00 and 3:44-4:15, the aligment is remarquable)
You can also “see” the building of the fissure eruption chamber (twin chambers it seems) from 20 s (not an expert). Then from 1:00 and onward the activity goes back nearly solely under the Caldera.
On the top view there may have been another intrusion between the caldera and the dyke’s progression around 1:40.
@2:15 have a look at the linear structure near Heirdubreid on the upper right fo the plot.
After 3:40 the images of the previous plot appear (my bad).
Data from IMO, NOAA, Made on Gnu Octave for Volcanohotspot.wordpress.com
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And the last one – Mag 4-6
Interestingly the first part of the dyke intrusion does not show with these magnitudes. Look @0:50
An hour by hour earthquake plot for bardarbunga area.
Earthquake magnitude is selected from 3 to Mag 6.
Only 250 events are shown at all time to avoid overcrowding.
Dot color is date dependant (see left colorbar)
First view is from the east, then from the top and finally all events are shown with rotation and some tilt.
Interestingly the first part of the dyke intrusion does not show with these magnitude. Look @0:50
After 1:50 the plot is not relevant (old pictures)
Data from IMO, NOAA, Made on Gnu Octave for Volcanohotspot.wordpress.com
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Spectacular work, dfm. Many thanks. Amazed with all the activity under Bardarbunga and never a peep of an eruption. Fascinating that the dike appears to have extended to Herdubreid without it participating. Perhaps sometime soon…. Cheers –
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Second question is where do you obtain the datasets to input into Octave? Cheers –
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Thanks Agimarc
Partly from the listi directory
Otherwise from the IMO page (cut and paste, yeah I know, it’s not optimized….)
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Thanks dfm, that must be a labour of love, and a revealing experience for the trained eye. Special thanks for your explanations and conclusions, as for the not so trained eye (as mine) it is difficult to make sense of the dancing dots. With the help of some hints, I look more focussed on events and even replay them until I see what you see, and then I go on with own thoughts or conclusions.
As to Herdubreid, it would be interesting to see what the rest of the MAR towards north is doing at the same time. There must be many similar spots where the magma is coming up in dike like intrusions, as the MAR itself is a constantly active line shaped feature. I expect that at every weaker spot magma comes up, but how far up depends on the conditions of the overlying rocks.
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Well to be totally honest, the way the data is displayed can sometimes be misleading. In that case I keep a “window” of 250 to 750 quakes after the first events there is always the same number of events (but the date span changes). If you look at the title bar, you’ll see that the “time window” gets larger as we move forward in time.
in my opinion, the more interesting video is the mag 2 to 3 one. maybe I’ll try to display successively the different magnitude “slices” for a different view. Everyone suggestions or comment are of course welcome.
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The lunar eclipse was visible here in ANC last night. Beautiful clear night. Stunning full moon that went very dark. Started around 2 AM. Totality around 3:30. Ended around 5 AM. Haven’t seen one of these in a long time. Very nice. Cheers –
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