Eruptions

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The Halema’uma’u Crater at Kilauea on June 29, 2009, prior to a rockfall on June 30th that has blocked the vent. Image courtesy of HVO.

There is a bit of a buzz today about significant rockfalls that occurred in Halema’uma’u Crater at Kilauea on June 30th. Some articles have suggested that the rockfall has “snuffed out” glowing vent in the Crater. Well, this is partially true. HVO is reporting that the glow that has been seen at Halema`uma`uma has been, in fact, gone since the rockfall. Here is the report of the event:


A sequence of rockfalls, some quite large, within the Halema’uma’u vent at the summit of Kīlauea Volcano began at 1:38 p.m. H.s.t on June 30, 2009.
The initial rockfall produced a seismic signal equivalent to a magnitude-2.4 earthquake and was felt at the Hawaiian Volcano Observatory (HVO) and the adjacent Jaggar Museum. A nearby scientist heard the beginning of this rockfall followed by a loud
explosion. The normally white gas plume turned a thick brown for several minutes; later collection confirmed an increase in tephra entrained in the plume with at least one later dusting.

So, it seems that the vent has become clogged with debris from this rockfall, some of which may have interacted with the magma in the vent (thick brown ash plume). The rockfall itself may have been triggered by draining of the magma in the vent, but it was big enough to generate a M2.4 earthquake. Later observations since the rockfall seem to confirm the idea that the vent is blocked with debris:


Aerial observations yesterday morning, and views from the ground with a thermal camera last night, confirmed that the throat of the vent in Halema`uma`u crater had been choked with debris from Tuesday’s collapses. By late yesterday afternoon, sporadic gas jetting sounds from the vent were heard by geologists on the rim of Halema`uma`u Crater. Overnight, the Webcam on the rim of Halema`uma`u Crater recorded a few points of incandescence, waxing and waning in brightness, deep within the vent.

Now, before everyone gets all excited that the “vent is blocked” and waits for an explosion, remember that Kilauea has a long history of lava from the crater region draining to vents on the flanks, so magma in the vent that is being blocked could very well merely drain from the summit to the flanks of the volcano. Also, the event might have been triggered by the fact that magma is draining from the summit in the first place. There is still magma under the collapsed region as the gas jetting sounds and points of glowing might suggest, but how the magma will react to its newly closed vent is hard to tell. It wasn’t erupting from the Halema’uma’u Crater before the rockfall and gases are still able to escape, so [SPECULATION] any fears of pressure from behind the blockage are likely unnecessary [/SPECTULATION]. However, saying the vent is “snuffed out” in any way is premature (it might have been the product of the HVO Press Release titled “Glow From The Halema`uma`u Overlook Vent Snuffed Out by Collapse”), but rather there is enough material in the vent to block any light from the hot magma.

{Hat tip to Eruptions readers Anne Carrington Cotton and David for links for this post.}

Comments

  1. #1 David Lee
    July 2, 2009

    I figure if the magma keeps dropping more of the surface will fall in and the hole will get even bigger. Last I saw the molten stuff was 300 feet down. I predict a bigger hole and a pond of fire by Christmas ;-)

  2. #2 Barb
    July 2, 2009

    There was a little incandescence seen in the Webcam last night, per the HVO; there is still a plume, though a small one, too. It’s not totally blocked, apparently. They also say that geologists heard some gas jetting sounds late yesterday afternoon, but apparently there haven’t been any sulfur dioxide measurements since the collapse.

    That’s the question: how much gas is getting through? If not a lot, where is the rest going to vent from…Pu’u O’o? If not…pressure is going to build. Is that the reason for the threefold increase in RB2S2BL quakes, or is it magma movement, or a combination of the two?

    It’s all very, very interesting, and my (nongeology) office isn’t even located nearby, as the HVO’s are.

    PS: Thank you for this blog!

  3. #3 Zora
    July 2, 2009

    I’ve always seen the name of the main crater as Halema’uma’u. No extra ma on the end. It’s spelled Halema’uma’u in my copy of Place Names of Hawai’i, by Pukui, Elbert, and Mookini, the canonical reference.

    Is there some significance to the extra syllable? Or could it be a mistake?

  4. #4 Erik Klemetti
    July 2, 2009

    Zora – Oops! I have been cursed by “copy and paste”. I spelled Halema’uma’u incorrectly the first time and just pasted it in from there. Thanks for catching my error.

  5. #5 MadScientist
    July 3, 2009

    It obviously wasn’t the rock slide – it was the human sacrifices which appeased the fire god.

    I wonder what will happen – will the rocks slowly melt and the glow return, will it plug, is magma receeding for some other reason, or what not.

  6. #6 Boris Behncke
    July 3, 2009

    Looking at the Halema’uma’u overlook vent webcam (http://hvo.wr.usgs.gov/cams/HMcam/) you will see, in this moment (that is, about 10 a.m. GMT), some glow from a variety of spots within the vent, one in the lower center-right portino of the image is particularly persistent and intense.

    It is quite usual for basaltic volcanoes to quietly resume mild intracrater eruptive activity, even after the clogging of a vent, without any spectacular explosive phenomena. On Etna it has been repeatedly observed that a small pit opens on the blocked crater floor and soon this will be the site of incandescence and possibly mild eruptive activity. At this volcano this is usually Strombolian activity, which will gradually build a cone over the vent. At Halema’uma’u I would expect the surface of actively convecing lava to reappear in such a pit. However, to see some slightly different scenario, take the 1961 eruptions in Halema’uma’u, which are very well described in USGS Professional Paper 474-D (this can be downloaded in djvu format at http://pubs.er.usgs.gov/usgspubs/pp/pp474D)

  7. #7 Ross
    July 3, 2009

    Checked the webcam view this morning and there was a couple points of bright glow.

  8. #8 theroachman
    July 3, 2009

    MadScientist

    More specifically that be Hawaiian Goddess Pele her home is the Halema’uma’u crater.

  9. #9 Thomas Donlon
    July 8, 2009

    Boris Behncke put up a link with an extra “)” on the end.

    This link gets you to where Boris Behncke intended.
    http://pubs.er.usgs.gov/usgspubs/pp/pp474D

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    December 6, 2010

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    December 15, 2010

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    December 23, 2010

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