Eruptions

A review of ash cloud classification

Jonathan Castro has reminded me that I need a refresher on the proper terminology for ash columns related to volcanic eruptions. It is very easy to start mincing words and using them inappropriately – and that is the sort of sloppy reporting and discussion I am trying to avoid.

So, to refresh my (and our) memory on ash clouds and how to classify them, we can go back to one of the indispensable textbooks on volcanology, Cas and Wright’s Volcanic Successions. The classification scheme they provide is summarized in the figure above. It shows the heights of various eruption columns and the relationship between types of eruptions and their “explosiveness”. Jonathan is likely correct in classifying this eruption in the vulcanian range (<20 km ash column), especially if it was driven by explosions in the dome. If anything, Chaiten’s activity today could be sub-plinian, but a true plinian eruption requires a taller ash column height and higher levels of explosivity.

UPDATE 2/20/2009: Here is a link to an article that talks about the processes that go along with each eruptive style. Remember, the ash column nomenclature is not solely dependent on height, but also process and composition. {Thanks to Boris for reminding me to emphasize this.}

Comments

  1. #1 gg
    February 19, 2009

    Video of TV showing Chaiten:

    http://vinnyswebsite.com/blog1/video-chaiten-erupts-volcano-eruption-021909-youtube/

    I don’t speak Spanish. Is this real?

  2. #2 Ron de Haan
    February 20, 2009

    What I have seen today Chaitén Volcano qualified for a “Strombolian” category column just after the increase of the eruption, returning to “Hawaiian” for the remainder of the day.

  3. #3 Boris Behncke
    February 20, 2009

    now, now … the term Strombolian is applied to strictly to a type of mildly explosive activity that produces discrete ejections of fragments of molten lava, and in the Hawaiian case we’re dealing with still more fluid lava producing fountains, lava lakes, and very mobile lava flows. Such terms do not at all apply to silicic volcanoes such as Chaitén where you will never see any liquid lava to be thrown out. In fact, the use of Strombolian and Hawaiian in a scheme denoting the size of tephra plumes can lead to misinterpretations.
    The case of the Chaitén activity yesterday is one of partly explosive, partly gravitational disruption of a gas-rich lava dome. Normally the explosive part is called Vulcanian, while there is no generally accepted term for plumes rising from dome collapse, although their generation from pyroclastic flows makes them most similar to “co-ignimbrite” clouds. In such complex cases rather than trying to forcefully apply a technical term from the existing terminology (with its obvious advantages but also limits), it would be appropriate to remain largely descriptive, and speak of – as said above – partly explosive, partly gravitational disruption of an active lava dome. How much gravitational versus explosive, will remain to be seen from analysis by the volcanologists on site.
    Greetings from a volcano that indeed is often producing Strombolian activity, Mount Etna

  4. #4 Vinny
    February 20, 2009

    Hi I found some live video from Chaiten, I was watching it last night and it seemed to be erupting still. Here’s the link it’s still streaming:

    http://teletrece.canal13.cl/t13/html/Chaiten/index.html

  5. #5 Bruce
    February 20, 2009

    That classic photo of Redoubt from April 21, 1990 (the atomic like mushroom cloud one) for instance was apparently also produced more by dome collapse rather than eruptive (i.e. explosive) activity, which in my book would exclude it from being termed Plinian.. pity nobody has come up with a name for dome-collapse- ash-columns that sticks… Unzenian..Redoubtful..Montserratian.. hmm.

  6. #6 Erik Klemetti
    February 20, 2009

    Boris – Thanks for pointing out the fact that I didn’t emphasize the connection between the ash columns and the eruptive style. The ash column nomenclature isn’t solely dependent on the height of the column, but also the physical processes going on during the eruption and, to an extent, the composition and volatile content of the magma involved. I’ve posted a link (yes, to Wikipedia, but its a good summary) as an update to this post that details the types of eruption styles that go with the ash column nomenclature. Hope that clears things up a bit.

  7. #7 Steven
    April 2, 2009

    What is the composition of the gas carrying the ash? Water vapour?

  8. #8 buy phenazepam
    November 18, 2010

    Was your site not working last night ? anyways it seem fine now ta

  9. #9 Donella Champaco
    November 21, 2010

    My my my, I can feel the nostalgia. Those Golden days are still worth remembering. You presented a true picture of Alfred Rugby and i hope they will keep our heads high

  10. #10 Interest Rates on Home Loans
    November 23, 2010

    How are you ?, is it possible that may be on your way topic however nonetheless, searching for checking in existance your web blog also it for you to be totally in truth professional. I have been building a newly purchased wordpress blog then experiencing struggles repair their fortunes look good, everytime our place a specific thing we all screw it up. The ways not easy had they to produce your web blog? Perhaps an employee as i am without using routine do it now, and even integrate cherished ones improve results while not destroying this kind of everytime?

  11. #11 Interest Rates on Home Loans
    November 23, 2010

    Good day, may be this will be above theme yet , either way, we looking through in your internet-site therefore it would seem extremely totally uncluttered. We are constructing a the latest write while attempting to get it back look good, each i will crunch a little my family and i spoil it. Tips on how extremely seemed to be to it’s to construct a web site? May possibly well one more just like me without using a endure do the work, in addition incorporate members of the family post web pages owning endangering the software training routine?

  12. #12 Hello Kitty Bedroom
    November 24, 2010

    Things you brought up a lot of sense. But, picture this, imagine if you integrated a little more? I am talking about, I don’t want to tell you how you can run your blog, but if you actually added extra content that can certainly get people’s notice? Just simply like a video clip or perhaps a graphic or few to obtain viewers psyched concerning what you mentioned.

  13. #13 Erica Pribbeno
    November 25, 2010

    “You possess a truly fascinating weblog. Too many blogs that I see now don’t actually provide something that I am interested in, but I’m definitely interested in this one. Just thought that I would pass that message on. “

  14. #14 Kelly Collica
    November 27, 2010

    I am a huge fan of this website and I check it regularly. Keep up the good work! – Don’t count the days, make the days count. Muhammad Ali

  15. #15 Rob Newstead
    December 12, 2010

    You are a very clever individual!

The site is undergoing maintenance presently. Commenting has been disabled. Please check back later!