Monday, November 7, 2011

Interesting and Disturbing Happenings In The Canary Islands

Caption The north side of El Hierro Island in the Canary chain, about a year ago.

Image credit: Mataparda/Flickr


Unbeknown to me, it would seem there's been a very interesting volcanic eruption going on in the Canary Islands, as the U.K. Guardian reports:
Homes have been evacuated and roads closed on the southern-most Canary Island following a government-issued warning about a possible volcanic eruption.

The southern tip of El Hierro was shaken by a 4.3-magnitude quake late on Saturday as an underwater volcano just off the coast started spewing matter some 60ft into the air.

The island, which has 500 volcanic cones, has experienced more than 10,000 tremors in the past four months.

Renewed fears of an eruption came as vast quantities of magma - the molten rock from just under the earth's crust - began bubbling into the sea off the port of La Restinga.

Ready to blow? Homes evacuated on Canary Island as underwater volcano spews molten rock 60ft into the air
The Associated Press reports that some of the debris has been accompanied by a foul smell. There are some folks in the area live blogging for Earthquake Report, and this is how they describe it:
Update 06/11 – 21:34 UTC :

Raymond is still at his (safe) viewpoint position and says that he is smelling a faint sulfurous odor. He isn’t seeing the Jacuzzi in the dark, but he hopes to see the red glow of the magma later at night as he sees that the harmonic tremor is still saturated and as the earthquake activity has increased again.

El Hierro Volcano (Canary Islands)
That's not the worst news when it comes to gases, though:
Update 06/11 – 21:57 UTC :

PEVOLCA confirms a further increase in carbon dioxide emissions in El Hierro (see also Patrick Allard comment just below). The emission of CO2 is one of the parameters of a volcanic eruption precursors but has to be assessed jointly with others, such as deformation and seismicity depth


El Hierro Volcano (Canary Islands)
The news on the seismicity depth front isn't looking terribly good. There was this a little later:
Update 07/11 – 09:28 UTC :

- Reader Marco Schaapherder just told us that we might not have seen a shift in earthquake depth since midnight. He was right! Magma may have found his way up a few more km, as the focal depths are getting up to 14 km now.

El Hierro Volcano (Canary Islands)
Which I take to mean that magma is getting closer to the surface. That's probably why people are being evacuated.

Let me just stress that even the experts seem to be unsure what all this means, and I'm not even close to being an expert. This is why everyone is jumpy in that part of the world right now, though.

Dana Hunter passed on via e-mail that this might end up being what's called a Surtseyan eruption, which is the name used to describe an eruption that happens in shallow water. Since the activity noted so far has been occurring out at sea, that seems like a reasonable expectation. That probably would be better than having some eruption on land. As the quote from the Guardian mentioned, El Hierro is riddled with volcanic cones, so you'd have to think that an eruption on dry land is at least a possibility.

For those of us who aren't in harm's way, there are some other interesting tidbits, in the form of rocks like this one:


Image credit: NHArq

According to the caption at the Image credit link, it floats. It's probably pumice, with some rhyolite embedded in it (the silvery crystals). I've never seen anything quite like it before.

Geoscience Professor Erik Klemetti, a columnist at Wired, comments:
There are also some new images of the floating pyroclastic chunks that have been coughed up during this eruption – and they continue to look as strange as they sound (see below) with a mixture of light rhyolite/phonolite that is highly vesicular (filled with bubbles) and dark basalt/basanite (that is also full of bubbles). There is an unsubstantiated report of a “big rock” being ejected from the eruption, but no image (or size) so far.

El Hierro Volcano (Canary Islands)
At the moment, the harmonic tremors are subsiding a bit, but that isn't necessarily a good sign. Hopefully, this will turn out to be something other than a full-blown eruption, and everyone who has had to evacuate can go back to their homes soon.

(h/t to Expat, who e-mailed me a link to the Earthquake Report live blog.)

UPDATE: It looks like maybe the harmonic tremors haven't subsided after all. The problem may be that the seismic chart the Earthquake Report bloggers were using isn't quite as reliable as it could be:
Update 08/11 – 08:32 UTC :

IGN and Graphics rescaling
Caption: (by Cujo359) This is the chart this quote refers to. Note that about midway the blue strip chart seems to change. To the left its peak values are clearly off the scale, and past the center line to the right they are visible. That's what they mean by rescaling.

- When discussing the activity with Raymond during the night, he hard a hard time believing that the harmonic tremor decreased seriously (see update 07/11 – 23:59).
- He did not detect any serious change while i reported this (of course it was dark and he was reflecting the explosion vibrations he felt)
- I was unable to confirm him that it was a real decrease because the graphics we use are coming from the IGN website and IGN NEVER REPORTS RESCALING the graph. Most of the time it can be seen by white spaces or blue lines in the seismograms and harmonic tremor graphs, but at the time of reporting no visible change was detected. Since midnight it is obvious that the scale was adapted a number of times. We request @ IGN that they will indicate the rescaling actions in a separate log.

El Hierro Volcano (Canary Islands)
I use the word "reliable" advisedly here. When a graph is suddenly rescaled like this with no notation to indicate this has been done, it's easy to misinterpret. If you can't be sure what you're looking at, that makes the interpretation of that data unreliable.

To make a long story short, it appears there has been no real change in harmonic tremors in the last day or so. So maybe they don't need to be quite so jittery as they were a couple of hours ago.





2 comments:

Dusty,Hells most vocal Bitch said...

Christ, it's amazing how little the Corporate Media tells us ain't it?

Thank you for this information Cujo! Its so alarming to me, I can't begin to describe the feeling of dread I have right now and I live in Cali, where earthquakes are a daily occurance.

Cujo359 said...

I stopped paying attention to most corporate news a long time ago. They could be blabbing about this 24/7 and I still wouldn't have been aware of it.

Of course, one of the reasons I don't bother paying attention to them is that they had a habit of ignoring stuff like this. So, yes, there probably isn't much talk of this on the news, which is kinda crazy given how important it might be that an eruption happens near a popular resort location...