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.


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.


69 thoughts on “Bob – Why bother to stop erupting?

  1. And I still can’t change my name for some odd reason. I am not that much a fan of being semi-permanently stuck with this name.

    • Good to see those GPS data back. Both the large Hierro eq swarms were simultaneous with GPS signals indicating shifts NE-wards. Which have not reversed to date.

  2. I’m a bit conflicted.

    I could make an allusion to Laurel and Hardy (Armas & Perez) getting what they deserve, but that would infer that the residents are party to the idiocy, which they are not. Hell, I don’t even know if there method of suffrage put Armas in his position or not. Perez is just a government hack, a dime a dozen. Armas is worried about tourism and green energy investments, so he will make light of anything that he perceives as jeopardizing that. I wonder if he has noticed that financially, there is a lot more threatening that from the financial sector than from Bob. Perez has an even trickier problem. He has to acknowledge that there is something worth doing research on so that Universities and organizations will spend money in his realm doing so.

    Yeah, I said it. It’s all about the money. It’s pretty obvious that the science is not his goal.

    So, once again… best-o-luck El Hierro. With those two entrenched in your bureaucracy, you need all the luck you can get. Just be happy that Bob is being well behaved… venting pressure just like a safety valve should.

    • more of good luck then management and what a difference a day makes, some of the population reported all was well, they have seen wales etc. around the island, the wales must have left a stain and now it shakes again…..

  3. Is Bob really erupting? In Avcan the people who took that sonar images posted a comment saying the plume consists mostly of gases, ant that the ash they saw could be suspended mainly due to the currents, not necessarily eruptive activity, and that they couldn’t see any significant temperature variations above that vent. So, Im a bit skeptical about Bob really continuing its eruption, but todays increase in activity (quakes, return of this 0,5 Hz tremor in other stations) could mean that Bob is still alive.

    • Take a look at the fall-back area.
      Also, gases do not show up that clearly on a side scan sonar.

    • Dunno ….. the fall back plume may be more degassing than ash or a second point of emission. But what we can see of the cone is asymetric which may mean that there has been tephra fall since the previous images which were more symetric (from memory). Bob may have been erupting quietly without stopping as she managed to cone-build earlier on the ridge with few EQs and a low HT.

      The plume is fairly weak; it is not reaching the surface – the currents are affecting it. This could be why no significant temperature changes were detected.

      • No, the fall back can not be gases, at least as long as the gas is not heavier than the water it is suspended in. And that is not the case. Even light ashes will remain suspended for quite some time, and be dispersed over a large area.
        The back fall plume is by laws of physics heavier material that cannot remain suspended at a certain fallback point. Actually what you are seeing is a current affected projectile trajectory. Physics, one gotta love it.

  4. There’s some weird tremor at Askja, weird for Askja that is. At least seven days of almost sinoidal tremor in the 2 – 4 Hz band (blue), peaking at aroun 9 pm and at its lowest around 9am. Since it’s so regular and coincides with what you’d expect from melting, my guess is that this is what it is. Spring has arrived at Askja.

  5. Former National Science Council deputy-minister Chen Cheng-hong (陳正宏) yesterday said the Atomic Energy Council (AEC) should evaluate the impact that a volcanic eruption would have on nuclear power plants in northern Taiwan.

    Chen, a geologist, was invited to give a speech on volcanic activity in northern Taiwan at the AEC’s 57th anniversary event.

    The potential scenarios of a nuclear power plant being affected by an earthquake or tsunami disaster have been discussed recently, given the meltdown of the reactors at Japan’s disaster-hit Fukushima Dai-ichi plant in March last year.

    However, while tsunamis are clearly an important threat, volcanic activity and earthquakes are also closely related and thus should also be addressed, Chen said.

    Considering the lava composition of the Datun Mountain range and referencing the 1991 eruption of Mt Pinatubo in the Philippines, if the volcano at Datun erupts, up to three meters of ashes could be generated, Chen said. Clark Air Base in the Philippines was paralyzed by the ashes from Mt Pinatubo, Chen added.

    Considering the impact volcanic activity could have on the greater Taipei area, the Datun Mountains volcano group in northern Taiwan are of critical importance, Chen said….

    • I’m not entirely sure this guy is on the up and up. GVP lists no known or inferred Holocene activity in that country, and Wikipedia notes that the last eruptive period was about 200,000 years ago. Hydrothermal activity is still there, but other than that, and that it sits next to a subduction zone, I’m not sure what the issue might be, other than the normal hazards of being in a volcanic region.

      Awareness an monitoring are of course, wise, but phearmongering is not.

      • I would have understood it if it had been aimed at Typhoons and Tsunamis… Something that now and then hits Taiwan.

  6. Govs should pay more atention to Geologists and other tecnics studies when they want to construct structures like a Nuke Plant or other’s…

  7. Sigh, Just prepared a monster of a post which will go in tomorrow morning but not where you are used to but in OT Regulars table, because it is mostly OT. It is about the transit of Venus happening 5th/6th of June depending where you are at. There are some facts on Venus ( very few) and some stuff about the volcanoes there too, and tons of links, and when i say tons, i mean tons.

    • Hi Spica, I was looking forward to watching the transit of Venus but from what I understand, in my timezone (Tenerife) this will occur at 5am..& the sun does not rise that early here,so I think I will not be able to see it…I had my husband´s soldering mask at the ready…. can anyone here confirm if I have got this wrong…..thanks

    • Cool, a post on monsters!

      My fav was the Père Malfait from the old Night Stalker series. That one gave me nightmares. And the reptilian lizard critter from “The Sentry” episode could have been an inspiration for the “Tremors” movies. In that one, workers in a subterranean storage facility (for stuff like microfiche records etc) inadvertently find eggs for an ancient bipedal dinosaur like creatures (about human sized, more like a guy walking around in a crocodile suit.. which it probably was) that then starts whacking people in order to protect it’s eggs.

      Of course nowadays, we have the real Zombies of Miami City to occupy our minds.



      June 04 11: 40 (Jun 04, 16: 40 GMT)For the last 24 hours, the system of monitoring Popocatepetl registered 91 exhalaciones of low and moderate intensity accompanied by water vapor, gas and ash. The most representative occurred yesterday at 3: 13 p.m. (see image 1), and 15: 40 h (see image 2), same that were accompanied by moderate amounts of ash, and which reached one height less than 1 km above the crater, dissipated towards the West-Northwest.In addition, at 15: 11 hrs local time were spasmodic tremor of low-amplitude 5 min.At the time of this report there is no visibility due to dense clouds. However, hours before it was possible to distinguish a column of steam, gas, along with a broadcast of ash, at 06: 33 am (see image 3).Volcanic alert level remains yellow phase 3. This level of alert means the probability of observing the following scenarios:Explosive activity of intermediate scale to high, growth of domes and possible expulsion of lava; increasing intensity and rain of ash explosions notorious on nearby towns and in smaller quantities in towns more far, depending on the direction of the winds.Special emphasis is placed on the following recommendations:1 Continue with the security of 12 km radius, so stay in that area is not allowed.2. Maintain the transit controlled between Santiago Xalitzintla and San Pedro Nexapa, via Paso de Cortés.3. To the authorities of Civil protection, maintain its preventive procedures, according to its operational plans.4. To the population, be attentive to the official information that is disseminated.Monitoring of the volcano Popocatépetl is performed continuously 24 hours.Links to documents of the national system of Civil protection with information about fall of ash and volcanic activity

      • Hi Judith, how was the holiday? Hope you had a fab time. Have you had the results of your test yet—hope all is OK

  8. Hi Debbie had an accident on holiday ended up in a wheelchair (fault of hotel they have offered us another 2 weeks holiday ).

    I go in hospital tomorrow for my test so still a waiting game hope I will know something soon.

    • oh dear Judith, what on earth happened to make you end up in a wheelchair? If it had been your husband I could understand (BTW how is he?) ..Fingers and toes crossed that you will get a good “negative” result from the tests. My friend has just had the same test and although she had about 3-4 weeks to wait for the result, it was a good result! Hope the same will happen for you. Best wishes xx

      • Thanks Debbie will just be glad when its all over up early starting to get ready .
        I fell down at the bottom of a ramp that had two paving stones missing my flip flop got caught in the hole and I fell heavily on my right side and knee. Good job my husband was fit enough to push me around in the wheelchair. The sun and swimming did his toe good.

  9. Hi I just wanted to say thanks to Schteve, for his excellent post….and to Spica and her telepathic timing of when to post it here…I have been trying to understand the questions that Schteve raised, and have to admit I am really struggling with understanding the science here…but I will learn…just not as quickly as I would like…with all you brilliant natural teachers here, it is only a matter of time before I will grasp things, but I am begining to realise, I am not as clever as I once thought I was! This has just got to be the most brilliant place for an old dog to learn new tricks..not that I am admitting to being old!

    • oops, and also need to send thanks to Carl for his post today which was extremely interesting to me,,,,btw Carl are you now moved to Barcelona?…my daughter has just booked a holiday to go there this month, and she has got sooo much to see & do in just 5 days.

      • Hello DebbieZ!
        No, I have not moved yet, and currently it is a bit iffy if I will move at all. Loooong story…
        And do not worry, no problems at home 🙂

  10. no Eclipse or Venus transit here, cold, rain bucketing at times and windy ( my abode shook last night, rr) blizzard in the hills, warning for ships to go to sea a bit further north, winter is here with a vengeance in sunny Australia

    • yeah was ahead of myself, forgot I am ahead of UTC, mostly cloudy, windy, cold, the rains have gone for now, I am not sure I can go to town, water over causeway? will find out when I get there

  11. Morning people!
    I am running a test now,new post will go in, i am not sure it will appear in the normal place too,It should not.

  12. Ok it did not completely work but, oh well. It does apear as first post when you normally log on too.

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