Bob – Why bother to stop erupting?

Photograph by Santiago Ferrero. Southern part of El Hierro.

The volcanic vent affectionately known as Bob, a part of the Tanganasoga Volcano, south of El Hierro has resumed its eruption. Many people have declared it dead, Pevolca, IGN and Nemesio Perez has together declared the volcano dead more than 20 times. Declaring an active volcano to be dead seems like a rather futile endeavor. Something the learned gentle-persons should have learned by now.

Yesterday reports started to come in that there was a visible disturbance in the waters south of La Restinga (El Hierro). About the same time there was a marked uptick in earthquake strength and number. The Earthquakes are deep, mainly between 15 and 25 kilometers in depth. The distribution of the earthquakes is well spread, this points towards it being a non-localized event, probably a shock-result as new magma arriving from the depth hits the underside of the crust.

Image by IGN. Earthquakes during the last 48 hours.

This is probably confirmed by the return of the 0.59Hz harmonic tremor visible at the CCAN and EOSO (Gran Canaria) SIL-station.

Image by IGN. Clear and visible harmonic tremor at 0.59Hz.

Today there have been reports at various sites (AVCAN among them) that there is now a visible stain, something that requires an ongoing eruptive process. Also, there is a photograph published at Earthquake Report showing a side scan SONAR image of the ongoing eruption.

Photograph of a sidescan SONAR image, source IGN (via Earthquake Report).

The image is very well defined, a sign of a large amount of coarser ashes and solids being suspended, and ejected upwards in the water. Light ashes and gases are less well defined than shown on the image. To the right one can see a spot where material is falling back onto the sea-floor. This is where the heavier aggregate looses buoyancy and gets separated from the lighter material.

Effects

I have written many times that as long as the eruption continues at Bob there is not any great risk for the island and its inhabitants. This is due to Bob functioning as a pressure release valve stopping pressure to build up enough for a catastrophic failure in the volcano proper’s overburden (the volcanic edifice of Tanganasoga).

The current spot of eruption is the original cone that started the eruption, not the later vent up on the ridge (a bit further to the right than the image shows). Last figure set the vent at 120 meters depth. The reason for it being lower now is that it is constructed mainly out of loose material (pillow-lava and tephra) that has both compacted due to its own weight, and been reduced in volume by the local currents in the water.

There is currently no indication that this new eruptive phase will stop any time soon since the earthquake activity is continuing to increase in frequency and strength.

Sadly due to the supression of GPS data by Involcan and its managing director Nemesio Perez there is no GPS data whatsoever that can be published. Due to this censorship we can not say anything about how and if the volcano is inflating. I find this behaviour despicable and dangerous for the residents of El Hierro. I would also state that it is sad that the webcams are now gone as a result of Alpidio Armas machinations.

CARL

The Kerguelen Hypervolcano™

Below the Clouds Stair-case by Swedish architects at Stockholm-based TAF Architect Office.

OK, so what in Gódabunga’s name do Swedish stairs and volcanoes have in common! Apart from the fact they can do you a real mischief if you fall down, a staircase in Swedish is trappa and this gives the name to the extensive flood basalt flows of the Traps volcanic provinces from the stair-like appearance of the flows!

Deccan Traps from: www.volcano.oregonstate.edu/vwdocs/volc_images/europe_west_asia/india/deccan.html

Kerguelen

A little known, but very extensive trap province exists in the southern Indian Ocean, some 4000km west of Australia and 1500km north of Antarctica – the Kerguelen Plateau that has developed over the Kerguelen mantle plume.

The Kerguelen Plateau – the second largest submarine plateau -  lies at approximately 1-2000 metres depth, in an abyssal depth of 3-4000 metres, and has three small island groups, Kerguelen, Heard Island and Mcdonald Island as surface expressions. The plateau extends north-westwards for c2200km covering an area of about 2.2m sq km.

Geologically, the plateau has had a colourful history, being classed as a ‘micro-continent’, it is a remnant of the break-up of the Gondwanaland super-continent and is located over the Kerguelen hot-spot. Deep water geological information is from the JOIDES ODP (ocean drilling programme) and seismic interpretation of oil prospecting data; the plateau is shown to be constructed on a general base of Cretaceous terrestrial and/or shallow water sediments – including coal horizons for at about 40m years. Volcanism began during the middle/late Cretaceous (c120m years ago) with emplacement of trachytes and basalts and continued on a large scale into the Miocene/Oligocene and continues up to the present on Mcdonald Island. Recovered ODP samples of felsic and metamorphic rock indicate the possible presence of a crystalline basement at least in part below the Cretaceous deposits. The total volume of the Kerguelen volcanic province is estimated to be in the order of 25million cu km giving an average of 0.2cu km/year. Submergence of the whole plateau was around 20m years ago.

The references below are superb!

http://www.ga.gov.au/energy/province-sedimentary-basin-geology/petroleum/offshore-southern-australia/kerguelen-plateau.html

http://petrology.oxfordjournals.org/content/43/7/1121.full.pdf

Kerguelen plateau, from Wikipedia: Kerguelen plateau topography.

The island groups involved here, are the tiny yellow dots near the north-west end on the elongate NW-SE pale blue area, Antarctica is the orange-red area at the bottom.

Kerguelen Island is the largest of the island groups surfacing above the Kerguelen Plateau; administered under the French Southern and Antarctic Terretories; covers an area of about 3400sq km and rises to 1850m at Mt Ross, the youngest volcanic expression of Plio/Pleistocene lavas – brown on the map below.

Simplified geological map of the Kerguelen Islands from Wikipedia.

The majority of the island is composed of flood basalts, in grey above, along with minor amounts of trachyte, pinkish, and the plutonic complexes (buff-grey) of Foch -north centre – and Rallier du Baty – sw bottom and the small Mt Crozier intrusion – northern of the two eastern promontories. Volcanism, related to the Kerguelen hotspot, began c40m years ago and continued until about 100,000 BP.

Heard & McDonald Islands

Heard Island and the stratovolcano Big Ben
(photo by A. J. Graff, Australian Antarctic Division)

The Heard and McDonald Islands (colloquially the HIMI) are administered by Australia and as such are home to Australia’s only active volcanoes.

Heard Island, apart from having the highest point on Australian territory at 2745m on Big Ben (9006 ft), has two main volcanoes in Big Ben, in part a 5-6km diameter, glacier covered caldera and the smaller Mt Dixon, plus small scoria cones. Big Ben, approximately 18km in diameter, is mainly of basalt/trachytic composition.

Heard Island shows 3 distinct stages of development, the oldest being the deposition of Miocene limestones 40-50my ago being found over much of the Kerguelen Plateau. These carbonates were followed around 9my ago, by 300-350m of volcaniclastic sediments and pillow lavas of the Drygalski Formation. A period of peneplanation of the Drygalski deposits preceeded the present volcanism, starting about 1my ago.

Satellite image from July 2000, showing an active two kilometre long (and 50-90 metre wide) lava flow trending south-west from the summit of Big Ben.
Photo: Thermal Alert Team, University of Hawai'i

The McDonald Island group lies about 27 miles west of Heard Island and is home to the second of Australia’s most recently active volcanoes and the whole total about 1sq mile in area, rising to 212m at Maxwell Hill. McDonald Island burst into action in 1992 after a 75,000year sleep and has been sporadically active since in late 1995-early1996, 2000-2001 and lastly in 2005 from Samarang Hill. The effect these eruptions had on the island was to almost double the size and increase the height by about100m!

The island is composed mainly of interbedded ,viscous phonolitic tuffs and lavas; phonolite being named after the resounding ‘ring’ when struck, is tough, pale coloured with a high felsic content of predominant feldspathoids over feldspar and is characteristic where a mantle plume is overlain by a thick continental crust.

2004 satellite image of McDonald Island showing island's extent in 1980 (striped).

ALAN C

El Hierro and the art of Bad Science

The first of the phreatomagmatic explotions that was caught on a picture back when the eruption was going at a much higher rate than today. It was most likely not a real phreatomagmatic explosion, it was more likely to have been a combination together with a massive gas release. But this is what will be in store most likely for the residents of La Restinga.

After releasing the sixth missive that volcanic vent affectionately known as Bob is dead, the authorities have now finished the monitoring of the volcano.

This declaration of cessation of activity is contrary to all known data. All released data point towards that the volcanic edifice is still growing at a rate of 10 to 15 meters per 2 weeks. There is still harmonic tremor associated with new magma arriving into the volcanic system from the deep. There was a steady and visible disturbance over the volcanic vent, and the gas-measurements are still above normal readings.

Instead of happily following what is happening the authorities have decided to shut down the web cameras, discontinue active monitoring, abandoning bathymetric scans of the volcanic edifice, and generally trying to hide that there is a volcano on the island of El Hierro.

This is most likely done due to political pressure to achieve a former state of touristic bliss, since it does not have any good scientific foundation.  The responsible organizations have instead chosen to only rely on data that supports cessation, disregarding contrary factual information. This is the Popperian “Art of Bad Science”.

Only problem here is that soon Bob will be hitting the threshold of where hydro magmatic activity will be clearly visible on the surface. Something that was caught on video a couple of days ago by our commentators in here. This activity will only grow during the upcoming weeks.

In 2 to 4 weeks the authorities will most likely have a set of rather distraught residents at La Restinga as they start to see ‘rooster-tail’ explosions surfacing on top of Bob. If activities then continue we are somewhere around 14 to 20 weeks before the volcano surfaces.

Now somebody with a bit of math skill will say, “What? It grows with more than five meters per week! It should be up faster”. Not really, this is due to a cone needing more material to grow, the higher it get. So, the speed of growing in height will decrease over time.

The authorities are probably betting/hoping that the eruption will finish within the next few weeks and save their collective behinds. Sadly they will just then issue a proclamation that the volcano have “re-awakened” to save them.

I am sadly reminded of George Orwell’s 1984, where the author describes “newspeak”, where the meaning of words changes as the powers that be see fit. I never thought I would see scientists involved in the Newspeak of Volcanoes.

I feel very much for the poor residents of La Restinga that in a short time will be scared uselessly and without cause out of scientists running the errands of political buffoons.

CARL

El Hierro – Survival of a stubborn Volcano

Image by IEO. Here we can clearly see the vents of Bob.

Life normally is filled with patterns. El Hierro has a pattern of its own, IGN declares the volcanic vent affectionately named Bob as dead, and a couple of days later the scientific crew of the ship Ramon Margalef publishes a report proving them wrong.

This time in addition to the bathymetric data we also got acidity values and electrical conductivity curves. The interesting thing with these is that they prove that during the measurement period there was a point source feeding acidic compounds into the water. The most likely culprits for the acidity are sulphuric acid and CO2. The values are still roughly the same as during the last measurements was taken, and this leads to the obvious conclusion that the vent is open and active. Also the electrical conductivity is pointing to an active source changing the conductivity.

The bathymetry gives at hand that the cone has now reached 88 meters from the surface. This gives that the growth rate during the last month has been 36 meters. At the going rate we should start to see surface disturbances in about two to four week as hydro magmatic explosions start.

Also noteworthy is that the shape of the volcanic main vent has changed from the stratovolcanic type with steep angle of slopes, to a shallower angled shield volcano type (26 to 33 degrees). One should though remember that a sub-aquatic volcano always has steeper angles compared to a sub-aerial one. This due to the water cooling the lava faster than the air does.

Image by IEO. Here we can see how shallow the angles of Bob have become during the last couple of months. The true angle is now between 26 and 33 degrees, normal angle for a sub-aquatic shield volcano constructed from unevolved basalts.

Another tidbit given is that the lava now is more fluid then before. This goes well with the less steep angles that we see now.  It all points towards that the first phase of eruption was containing large parts of reactivated rhyolitic material. This gave a high discoloring of the stain due to the high amount of ash content suspended in the water. Now the old rhyolitic mush is cleared out from the system, and the volcano is emitting predominantly unevolved basalt of deep origin.

This last part explains the low harmonic tremor since basalts travel easily in the conduits compared to the semi-solid rhyolitic mush, especially in a well worn feeder tube like the one leading to Bob. Another thing is that rhyolites are famously explosive and creates a lot of noise when erupting.

As I have now said time and again. Bob is not a volcano. The volcano is Tanganasoga, with the feeder system leading to Bob functioning as a pressure relief valve at the far end of the fissure swarm leading south from Tanganasoga. During the eruption there have been long periods of very low tremor associated with possible deep magmatic movement. This low frequency tremor is most easy to spot at the stations named EOSO and EGOM, and are found as clear red lines at the 0.59Hz and the 0.3Hz bands.

This gives that as the pressure has gotten into equilibrium the noisiness falls even more. Bob is now ejecting magma at the same rate as it is introduced into the system by the hotspot. With this in mind we can rule out any large changes in the eruption as long as the vents are open. And the eruption can be a very long one.

Thanks to the regular commentators Judith and CarlosB for digging out the newly released reports in a very quick fashion.

http://www.ieo.es/apartar/ieoprensa/hierro/hierro_leg11.pdf

http://www.ieo.es/apartar/ieoprensa/hierro/hierro_leg12.pdf

CARL

Update: El Hierro & Iceland

Photograph showing Malpaso, El Hierro.

El Hierro

IGN and Pevolca have given us the final good bye of the volcanic vent affectionately known as Bob. It is the fifth time that they declare that the activity is dead. I also note that they claim that they “have put an end to the eruption”. I for one did not know that humanity could put an end to any eruption.

In the same missive they say that there is still tremoring and inflation going on, and that the earthquakes are ongoing. And I who thought this was signs that you should not state that an eruption had ceased.

On the contrary the volcano seems to have been rather active, and has by now reached a distance of only 88 meters from the surface. This with the above given signs make the Pevolca statement rather iffy in my opinion.

Another thing is that the low level harmonic tremor has steadily increased for a week; it is best seen on the EOSO and EGOM stations. This tremor at 0.59 and 0.3 respectively is a sign that most likely is associated with deep magmatic movement. Due to the wave-length a wave of such a low frequency cannot build in a narrow tube or small magmatic chamber. The increase probably means that new magma is moving upwards.

Either we should see new activity at the old vents around Bob, or a new vent formation will take place in the coming week or so.

Iceland

Photograph by Ragnar Palmason. Showing red Brimstone in a volcanic cave of Brennisteinsfjöll.

After the medium sized earthquake swarm that took place at the MAR 20 km to the SSW of Reykjavik there have been reports of HS2 gas smell in the vicinity. The first one to report that was our own commenter Irpsit, who went trekking in the area of Lake Thingvellir. He reported strong smell on both sides of the lake, and that it numbed his nose within minutes. This tells us that the concentration was higher than is technically good for you. The danger with HS2 is that numbs the nose and then you can get into an area with poisonous levels of gas.

It is interesting that the gas emission rate in that area has increased after the 4.2M earthquake swarm. It probably means that in some way one of the volcanic systems in the area was affected since the area is rather large and requires more than a little gas puffing up to affect the nose in such away on both sides of the lake.

In reality there could only have been two volcanoes responsible for this emission, one of them is of course Hengill. Hengill is the largest of the volcanoes in that part of Iceland. But, I would like to make the culprit into Brennisteinsfjöll.

Photograph by Freysteinn Sigurðsson. The photograph shows weathered brimstone (sulphuric oxides) at Brennisteinsfjöll.

 

It erupted at 1000AD, 1200AD and at 1341AD. What makes into a likely culprit is that it is known to stink. The actual meaning of the name of the volcano says it all. Etymology is sometimes a useful science for volcanological purposes. Brennisteinsfjöll quite simply means Burnstone Mountain, or even more precisely, the Mountain of Brimstone.

Brennisteinsfjöll normally erupts in an effusive fissure style yielding between 0.2 to 3 cubic kilometers of lava. Two of the eruptions have VEI-2 numbers, the latest during 950AD. So if it erupts it should not be an ashy affair. At least at long as the lake does not get involved.

CARL