Tag Archives: fire fountaining

The count of Etna paroxysms in February 2013 now stands at 4 (and NTV Riddle)

This screenshot shows the first sight i got when i woke up this morning. Bruce Stout had been watching the event from the time it started and had left comments on VC which made me aware of what is going on. Etna changed its behavior the last days and displayed a 4th paroxysm today early in the morning after being active twice yesterday.

INGV analysed the paroxysms of the 20 in this articles in Italian and English. You can most likely expect a new report on todays events at http://www.ct.ingv.it/ a little later. Dr. Boris Behncke made some comments over at Eruptions where Erik had been writing a post on Etnas behavior too yesterday:

http://www.wired.com/wiredscience/2013/02/etnas-explosive-last-three-days/#comment-806546971

Yesterday someone zoomed in one Radiostudio7 cam and so i could take nice screenshots…

This picture was created out of the best screenshots i got of the Radiostudio7 cam yesterday.

http://www.radiostudio7.it/webcam.asp?web=7&id=7

Claude Grandpey reported live on his blog yesterday.

Check the lower right side of this image. I have not seen that spot before!

I´d like to paste some of the comments into this post to start a discussion:

Bruce noticed that same lava break-out feature has reappeared:
http://i40.photobucket.com/albums/e211/NoEnz/Bildschirmfoto2013-02-21um061250_zpsa0fbc1d1.png but Newby could be assured that no people are in danger because the ava flows down into an uninhabitet valley called Valle del Bove.

Bruce Stout says: February 21, 2013: Good morning, everyone, (yawn), oh look, Etna is at it again (no. 4) instant wake-up call.

Initial thoughts on Etna. A while ago I postulated that the periodicity in Etna’s paroxysms was caused by a steady magma feed into a piston like chamber with a narrow opening to the surface (this piston might be nothing more than the conduit itself). In this case the mechanism would be that magma enters the piston, starts to degass due to drop in pressure and slowly fills the piston until the pressure and volume was high enough to clear out the flimsy plug left by the last event. The built-up pressure in the piston coupled with rising levels of exsolution of gases leads to the fountaining as the piston empties itself. Rinse and repeat.

Now, if this is correct, why the sudden increase in the frequency of these paroxysms? Two possibilities come to mind: Faster rate of magma feed from below or a smaller piston.
Working in favor of the latter, is that the volumes of these paroxysms seem to be smaller than the previous series (though I am flying on the seat of my pants on this one, just guessing from the videos/webcams). It is most likely a combination of both faster feed and a smaller piston volume in the upper conduit. If higher feed, we might see a flank eruption at some stage which Boris once said often follows such series of paroxysms.
Just some random thoughts put here for discussion…
February 21, 2013 at 05:04

Well, bang goes that theory… this paroxysm is back to the old levels:
http://i40.photobucket.com/albums/e211/NoEnz/Bildschirmfoto2013-02-21um055948_zps359e23dd.png

Webcams are offering some very atmospheric shots as the wind is blowing the cloud towards the cam, obscuring the vent:
http://i40.photobucket.com/albums/e211/NoEnz/Bildschirmfoto2013-02-21um052759_zpsa67f8318.png

Spica: Ok the tremor is down again. The event seems to be over.
Bruce took a screenshot of the tremor being at 121 i saw it at 123 and when you check the graph now it shows that is was never as high as with the first paroxysm on the 19th. Can anyone explain this to me, this is not the first time i saw this behavior of the tremor graphs and i never understood it.

Boris mentioned on eruptions that it is not the first time Etna shows many paroxysm. In 2000 it started paroxysms in January and till late August the count ran up to 66 ! of those explosive events. I am bringing the webcam list over again so you have a chance to watch the show on your own.
Etna webcams:

One more screenshot for all who missed the show!

taken from the Lave cam: http://www.lave-volcans.eu/webcams_etna.php?numero=2

Name those Volcanoes Riddle

4 volcanoes 4 points

No 1 – Does it serve as a warning beacon for ocean going ships? Its nickname includes the name of an ocean. SOLVED
No 2 – This volcanic island’s artifacts/treasures, specifically A & A,  can be found in both the B M and the L. A & A are the names of ancient statues. SOLVED
No 3 – Here the salty craters hold a current ‘known’ subaerial world record. SOLVED
No 4 – During a warm, summer month in 2012 its summit displayed an historic ‘first’. Icelandic volcano. SOLVED

Spica

Urban volcanism!

The ironically named Mount Eden, near downtown Auckland.

Most people in the world agree on one thing: it is safer to live far from a volcano then it is living right on top of it. Living next too, or on top of a volcano is like sleeping in a cave with a friendly bear. Sure, it has it’s advantages, you stay nice and warm, you don’t have to worry about other predators, a good part of the year it is nice and quiet, but still….. you know that some day he will grab you and eat you. The inhabitants (some more permanent than others) of Herculanum, Pompeï, Heimaey and the Hawaiian Royal Gardens have found out the hard way.

New Zealand is, apart from being stunningly beautiful, one of the least populated countries in the World. When Western settlers arrived they could have chosen any location to go and build large cities. For some reason however, the inhabitants found it neccesary to build their largest city directly on top of a volcanic field with about 50 scoria cones, maars and tuff rings dotting the landscape. I suppose the knowledge of volcanism was not as developed back then as it is today, but nevertheless it is quite unfortunate.

Photograph by Mollivan Jon. Mount Taranaki.

New Zealand is dominated by subduction volcanism, with famous Mount Taranaki (or Egmont) as one of the most visually stunning stratovolcanoes in the world from both the ground and above, and with the infamous Taupo Volcanic Zone, best known for being one of the worlds “super” volcanoes. At 250 km from Auckland this is already quite a hazard on itself.

The Auckland Volcanic Field is a monogenetic volcanic field, meaning that an eruptive episode only happens once through a vent. Each eruptive episode generates a new vent somewhere within the volcanic field as opposed to “normal” volcanism where a volcanic vent has succesive eruptive episodes causing a volcano to build up and blow up occasionaly. The Auckland Volcanic Field produces basaltic scoria cones, maars and tuff rings (with the exception of the island of Rangitoto which erupted several times). All three are caused by the same type of magma, basaltic magma in this case, but the location the surface penetration, the eruptive flowrate and the total volume of the basalt determine the type of surface expression. The volcanic field has been active for about 150.000 (0.15M) years now. Older volcanic fields are found towards the south; South Auckland (1.5-0.5M), Ngatutura (1.8-1.5M) and Okete (1.8-2.7M).

The source of the basalt is not quite clear however. Basalt is normally not associated with subduction volcanism. Petrology and earthquake data have practically ruled out the possibility of the lava having an origin in melt generated by the subducting Pacific Plate. The Auckland volcanic field also sits some 200 km behind the active volcanic front of the Taupo Volcanic Zone. Furthermore, there is no evidence that the subducted Pacific plate reaches all the way to the Auckland volcanic Field.

Basalt is usually associated with mid-oceanic ridges/spreading centers or hotspot volcanism. Again, petrology has not been able to find much evidence for hotspot volcanism either. Additionaly, the propagation of the volcanic fields is directy opposite to the relative motion of the plate; the oldest volcanic field should have been in the north and the youngest in the south if a hotspot or mantle plume was involved. It is possible that the complex geology with major plates subducting, twisting and turning in the area is causing localised decompressional melting , leading to magma migration upwards right below the city of Auckland. There is some extention ongoing in the area, so this seems like a plausible explanation.

The Pacific plate and the Australian plate in a complicated geological setup

This image shows the subdution margin, the strike-slip faults to the southwest and extention(volcanic back-arc) to the northwest of the subduction margin.

Monogenetic volcanic fields are very interesting and highly unpredictable. The eruptions are not very large or extremely violent, but they can occur pretty much anywhere within the field at any time. With a large city with hundreds of thousands of inhabitants spanning the field, this is exactly what you don’t want. Paricutin in Mexico is the most famous example of this type of volcanism. One day you are happily working your crops, the next day you have to flee from your land because a volcano decided to take over your land. Bad luck, deal with it. Any new eruption within the Auckland Volcanic field will have as much compassion with buildings, streets, highways, parks and emergency shelters as Paricutin had with the crops that were growing there. This is what makes Auckland a relatively dangerous place to live in because it is not clear how much warning time there will be and how accurately the location of an eruption can be predicted with modern equipment.

The reason why new volcanoes pop up at random has to do with the generation of the magma. It is important that the generation occurs very slow. Slow enough to be unable to build a plumbing system that would efficiently conduct the magma to surface. Every new, hot, fresh slug of magma finds it’s own path to the surface, erupts and that’s it. The conduit cools and is no longer usable for the next slug of magma that arrives several decades or hundreds of years later below a slightly different part of the volcanic field. There is not enough magma flowing into one area to create a magma chamber in which the magma can evolve and produce more silicic types of magma.

Ridiculous in Los Angeles, not so ridiculous in Auckland. Bring out Tommy Lee Jones!

We have all seen the Hollywood movie “Volcano” and no doubt that many Los Angeles citizens have had a very good laugh at it (the La Brea tar pits are the surface expression of a leaking oilfield through a fault, it has nothing to do with volcanism whatsoever), but for the citizens of Auckland, those images are not even very far from the truth. The past gives an excellent example of what can happen. The next eruption in the field will most likely follow this scenario:

1 – Magma is forced upward through weak points in the crust.

2 – Either the magma contacts ground-water, or reduced pressure near the surface causes gases to bubble out of solution. The result is a phraetic or steam-blast eruption. The heaviest material is thrown out horizontally to form a tuff ring. Lighter material is blasted vertically to form an eruptive column. After a few days, weeks or months, the volcano falls quiet. Several of Auckland’s volcanos became extinct at this point.

3 – Additional magma may rise in the conduit. If enough magma is supplied, fire fountaining starts through one or more vents. Small lava flows may be produced, which do not escape the tuff ring. Sometimes the eruptions build scoria cones.

4- If fire fountaining continues beyond this point, the scoria cones can coalesce to rise and bury the tuff ring. Lava flows can also fill the surrounding valleys.

5 – Sometimes the outflow of lava is so great that it undermines the cone, which collapses into the flow and is carried away, leaving a horseshoe-shaped breached crater. If lava flows for long enough, nearby valleys are totally filled in and the lava floods the entire area with a large sheet.

Isn’t that just wonderful right in your own neighbourhood?

Map showing the city of Auckland and the eruptive centers.Pick your favourite spot to build your house.

The big question that remains is then: When is the next eruption going to be? Well, you will have to chop off one of the arms of a geologist to get a clear answer on that, but there are usually several hundred to several thousand years between eruptions in this field. The last one was about 600 years ago, so it might be a while before it is “overdue”, but it might be soon as well.

El Nathan