Posted on by Jón Frímann

Friday update on Bárðarbunga volcano 26-September-2014

This is the Friday 26-September-2014 update on Bárðarbunga volcano. This information is going to get outdated quickly.

Current status in Bárðarbunga volcano at 20:31 UTC

  • Largest earthquake today had the magnitude 5,2, it happened at 16:49 UTC. Second largest earthquake today took place at 18:54 UTC and had the magnitude of 4,3. There have so far been fewer larger earthquakes today than in last days.
  • The caldera dropped 30cm in the magnitude 5,2 earthquake. The caldera continues to drop around 50cm/day according to GPS measurements. Total caldera drop is now around 29 meters.
  • Smaller earthquakes have been taking place in Bárðarbunga volcano. This means the drop is continuing during those earthquakes.
  • Magma continues to flow into Bárðarbunga volcano around the same rate as before. This can be seen on GPS data on nearby GPS monitoring stations. For GPS information please check University of Iceland GPS information page here.
  • Bad sandstorm was in Holuhraun today. It was so bad that it was only possible to see 50 – 100 meters in front of people according to Rúv news earlier today.
  • The eruption in Holuhraun continues in the same manner today as yesterday. The lava field is now larger than 40 square kilometres. What the exact size is I don’t know since it is not known today due to weather.
  • Earthquake activity continues under the dyke and that suggests the pressure is increasing in it.
  • Currently there is no eruption under the glacier. If it was it would be visible on SIL stations around Vatnajökull glacier.
  • Nothing more has happened in Bárðarbunga volcano today far as I know. That might change without warning.
  • Storms are expected to take place in Iceland all weekend. There is going to be around three or four storms taking place this weekend with strong winds up to 20m/s and it can go up to 40m/s in wind gusts. This is going to effect SIL stations and my geophones as the storms pass over parts of Iceland.

Current status Saturday 27-September-2014 at 20:30 UTC

  • No major change has taken place today in the eruption in Holuhraun. There is also no sign that is ending. Most of the eruption takes place in one crater at the moment. New fissures might open up without warning in the area where the dyke is located.
  • Bárðarbunga caldera continues to drop around 50cm/day.
  • Largest earthquake today so far is a magnitude 5,2 that took place at 19:31 UTC. Second largest earthquake today was at 02:00 and had the magnitude of 5,0.
  • Due to snowstorm there is almost no visibility to the eruption area in Holuhraun. For the people in the field the visibility today was reported to be 50 to 100 meters.
  • There has been a lot of smaller earthquakes taking place in Bárðarbunga volcano. Some of those earthquakes are taking place due to caldera subsiding. Some of those earthquakes are taking place because the magma inside Bárðarbunga volcano is looking for a new pathway up the surface. It either has not found it or does not have the pressure yet to go up the crust yet.
  • There is less activity today in the dyke. There is however worrying earthquake activity in the dyke at the start of Dyngjujökull glacier. It might mean that magma is trying to get up to the surface. There already have been eruptions under the glacier in this area without any earthquake activity before they started. All of those eruptions lasted for a short period of time.
  • Nothing else is to report so far today (27-September-2014).

Update Sunday 28-September-2014 at 17:17 UTC

  • Largest earthquake today took place at 12:34 UTC. Other earthquakes have been smaller today.
  • Bárðarbunga caldera has dropped 7,4 meter since 12-September-2014 according to GPS measurements in the centre of the caldera. That GPS data can be found here.
  • The lava field is now 44,5 square kilometres wide. It is now larger than Mývatn (around 40 square kilometres wide) for comparison.
  • Harmonic tremor suggest that pressure is increasing in the Bárðarbungu volcano magma chamber. It drops once the magma finds way out, then it starts building up again.
  • No other information have been released today. Other activity is the same as for the past few days.

Storm notice!

Three bad storms are expected in Iceland in next few days. In parts of Iceland wind is expected to go up to 50m/s in wind gusts. This is going to effect all earthquake recording and monitoring of Bárðarbunga volcano.

Next update

Next update is going to be on Monday 28-September-2014. I wish everyone a good weekend.

Article updated at 20:31 UTC on 27-September-2014
Article updated at 17:17 UTC on 28-September-2014

447 Replies to “Friday update on Bárðarbunga volcano 26-September-2014”

  1. Regarding the VEI expected from a Bardarbunga caldera eruption.

    A minor eruption would probably rank VEI3 or VEI4, because less wouldn’t break through the ice and be visible.

    A caldera event would be VEI5 to low VEI6, because that’s what happened when other Icelandic volcanoes have caldera events. For example Askja in 1875 was a VEI5. Bardarbunga has a similar size caldera.

    There is no geological evidence in Iceland for anything larger than a mid VEI6. So probably a VEI7 has never happened in Iceland, because the chambers of the Icelandic volcanoes are not big enough for that.

    Bardarbunga chamber is at best around 235km3 (cilinder 10x10x3km). Usually only 10% of a chamber erupts. As best as I know, never 100%. If it would, then we would have a VEI7 similar to Tambora. But it will not. So, we would never reach a VEI7, as best as we know.

    A probable limit would be anything between 4km3 and 23km3. Which is already big. But a VEI6. At its largest, it would be an eruption 30times stronger than Grimsvotn 2011, but most likely an eruption 10 times larger than it (around 8-10km3).

    This has happened in Hekla 3 eruption, 1104 Hekla eruption, 1362 Oraefajokull eruption, or Katla Vedde ash eruption some 10.000 years ago. Veidivotn was 10km3 but spread over time.

    1. And it is my opinion that such a caldera will NOT happen.

      I think subsidience will slow and then stop. Subsidience probably occurred already during Veidivotn and Vatnaoldur eruptions. If it stops, then a caldera event could only occur sometime in the future, either near future or far future.

      But IF subsidience continues non-stop for the next weeks, then a caldera event is more likely, and this will be a few months from now. Not days, not years. Still, a caldera can sunk hundred of meters without eruption (example of Katmai)

  2. As mentioned in my post number 148 on the 24th September update, things are changing. It started changing slowly on the 20th/21st. Prior to that you could set your watch as to when the next drop would be. If you studied the GPS you noticed that the fall or slips were between every 6-9 hrs then it changed to about thirty hours. But for the last few days there has been another change. Still slipping or dropping but with the chart as said before going sideways. It has now moved above the top range line and is how moving in a different range with a new trend.
    It will be interesting to see if this will be maintained, but I personally think in the near future we will see some big drops related to the time frame, but there again this could be a general slowing down of the subsidence I think in a few days we will find out.
    The big question is what has caused this change ? I have been reading everyone ideas and trying to find a link . Anyway time will tell, and remember that we can all see history but we are all trying to predict the future, this is what is so interesting about this event.

    1. With the mess with the GPS instruments yesterday, I want to see a radar pass before making any judgments.

    1. “The observed crustal thickness of up to 46 km implies
      active fluxing
      of source material through the melt zone
      by the mantle plume
      at up to three times the passive rate.”

      It also talks about “vast plumbing systems”.

  5. Last 12 hours, only few 1’s have been above 5km, all the rest have been clustered around 8-12 km.

  7. Seems like the cluster of quakes directly around the caldera has increased in the last couple of days.

    1. What is interesting to me is the quakes shallower than 1.5km. We just had a M3.4 5 hours ago at 100 meters depth.

  8. Now that the weather has turned colder, we are no longer seeing the steady drop in the level of the ice. We do see some settling when we have a large quake but the steady drop is now greatly reduced.

      1. Thought I did before the light changed, in the distance on webcam 1 looking straight ahead

    2. I think it could just be the early morning light and the new snow covering playing tricks! I often get excited and think there is something happening. But to know avail.

  10. I agree, there’s definitely SOMETHING odd happening in the distance, dead centre on Mila 1, peeking through the main plume….

    1. Yes, I’m convinced and maybe something nearer too – will have to wait for confirmation – or not!

    2. The steam goes sometimes a little bit down…if you look at the Kverkfjöll cam you see the the scenery from the other side. If something goes in front of the glacier it must be seen from here…
      Really…if something is happening I wish i could see it in the cam, but for now… 😉 nothing new.

  11. Looks like more snow overnight. R2D2 is getting cold, it’s is a shame he can’t wrap up and keep warm. I am still trying to workout if it is water of just snow to the bottom right
    next to the lave flow. Lets see what today brings us regarding EQ’s !

    2. I’ts snow on the ground, where the lavaflow stopped. The ground is even and not as hot as the lava, so the snow could cover it.

    1. Acca Dacca.

      Unfortunately one of the founding members (Malcolm Young) this week has had to retire to a nursing home. Has acute dementia. He’s only 61.

      2. Ye gods. Early onset. I wish Malcolm well, for all the joy he has given me over the years. Very sad news.

      3. IngeB.
        The Music on the video is by the band AC/DC (Acca Dacca)
        In case you weren’t aware.

  14. RUV has a great video with great information for newbies to volcanoes – like me!
    I am sort of both a newbie and an oldbie I guess.
    http://www.ruv.is/frett/what-is-going-on-at-bardarbunga-video

    Bardycam 1 had white SNOW! this morning. Quite a site with my coffee today.

    Vedur warnings posted
    Sunday gas pollution from the volcanic eruption is expected towards the east and southeast of the eruption site.
    Tomorrow (Monday) the pollution will affect areas to the north and northwest.
    A strong gale (more than 20 m/s) is expected widely tomorrow and heavy rain in the southeast

    Some blogs post Iceland is splitting along the Mid-Atlantic Ridge.
    I websearched because the quake pattern on vedur looked like Earth was splitting along the ridge. I have observed earthquakes all down that ridge. The South Atlantic has had some huge quakes the past year or so. I dont believe this should be discounted.

    1. Thank you Shepherd – very clear and consice video with good animation. Helps consolidate what I have learned so far.

  15. The 16 day plot shows that something happened around the 19th. The plot is remarkably linear but at two rates. You can draw a straight line through the centre of the variations up to the 19th and another one from the 19th onwards – the rate of fall since the 19th is slightly less than the rate of fall before that date but is still constant. In other words, the rate of fall is not lessening day by day – it just decreased around the 19th. There are still small plateaus and drops on a day by day basis but I can’t see an overall slowing yet.

    It needs some regression analysis to properly plot but you can do a fairly convincing assessment using a straight edge on the plot.

      1. I noticed that too a few days ago and mentioned it here, but was too lazy even to apply the straight edge. Thanks for doing that and confirming my suspicions. As you say though, it would be better to apply some real statistical methods. Who knows what the range of best fits really is. I’m still also interested in seeing a graph of the change in fractal dimension, at least after smoothing. How much is that ice heaving up and down and is that changing over time beyond the noise? It looks rougher more recently.

        Others have wondered whether the change in air temperature could be playing a role — but then you’d expect the appearance of accelerating subsidence. Do glaciers shrink as they get colder on any short time scale?

      2. On the contrary ice should be expanding when it gets colder. Water is the only material that expands in this condictions.

      4. Thought about this more and started to wonder again. A quick search comes to

        “No, ice does not expand as it gets colder.

        When water freezes, it increases in volume about 9%. The ice then shrinks as the temperature decreases. The shrinkage is tiny, about 0.4% going from 30F to -50F.

        As a side note, liquid water is densest at a temperature of 39.2F. The density differences at higher and lower temperatures are very tiny. Cooling 39.2F water to 0F expands it only 0.01%.

        Another note, there are at least 12 forms of ice. Most can be obtained only in the laboratory under high pressure. “

  16. Around the start of the current Holuhraun eruption SO2 emissions were ‘measured’ at around 20000 tonnes per day, does anyone know roughly what it is now?

  17. Great views from Mila Cam 1. Anyone know why Cam 2 has such poor quality and visibility. It looks like smoke but the wind is blowing from the same direction on both Cams, and should be just as clear, don’t quite get it.

    1. I think it is because yesterday Cam 2 had much ice/snow on the lens and now it is out of focus because they could not adjust it yesterday. Hopefully it is not broken and someone can do the adjustments today (sometimes in the afternoons someone does zoom out and pan the camera left and right). Anyway, I think this is right.

  19. The earthquake acc. to IMO:
    “At 12:34, a magnitude 5.2 earthquake occurred at the northeastern rim of Bárðarbunga caldera.
    Written by a specialist at 28 Sep 13:08 GMT”

    Sunday
    28.09.2014 12:34:15 64.669 -17.469 1.7 km 5.2 99.0 4.3 km NE of Bárðarbung

      1. Now it seams a cloud but some frames ago they were 100% distinct and with diferent origins… it’s possible…

  21. The method for manually calculating the magnitude of these EQs and/or the numerous people involved in making these calculations almost certainly has something to do with the seemingly erratic results.

    Although there seems to be a rather regular pattern of EQs in the magnitude 5.0 range… the drumplots tell a very different story. Perhaps the measurements aren’t intentionally spurious… but I no longer have any faith in them. The drumplots seem to be a much better indicator of the magnitude and duration of these EQs.

    1. Better than IMO’s manually confirmed figures? How so? How can you tell the magnitude, position & depth of an earthquake from the drumplot? Do tell…

      I think you’ll find the IMO numbers are accurate, the automated results from EMSC, USGS etc are not.

      1. I did not dispute “position & depth”, nor did I suggest the drumplot provided such information.

        Perhaps researching the information in Jón’s reply will give me a better understanding of EQ measurements in general, and specifically the difference between low-high freq. EQs.

    2. This are low frequency earthquakes. It means that they are releasing more energy on the lower bands (0.5 – 1Hz) than on higher bands (2 – 4Hz). The SIL network is not built to properly detect this type of activity, since it is the first time this happens since modern recording began in Iceland.

      3. @Tyler Mannsion. Maybe. It is difficult to know at this moment. It does mean that magma or gas is pushing into the cracks in the crust.

        @Kolla. Yes, this is a similar process taking place in Bárðarbunga volcano.

      5. On page 38 (won’t allow me to copy/paste) it says their dispersive quality allows properties of the surrounding liquid volume to be determined. Hopefully 3d models of the magma chamber are being developed as we speak.

      6. I would say to be careful trying to compare Montserrat magma with that in Iceland. Montserrat is a subduction zone volcano with magma that has a high silicon content, much like that in the US Cascade range. The magma in Iceland is more mafic, runnier, less likely to have the sort of stress and breakage described in that paper. Not to say it can’t do it, but it would not be a pronounced as with a magma having a higher silicon content such as that at Montserrat.

      7. The paper’s literature review covers several cases of low frequency eqs and voices a similar caution, in the next paragraph on pp 38-39. Low frequency eqs have been found to be predictive in the one case of Montserrat, but not in several others. However the general principle remains: they occur due to changing viscosity in the magma and specifics about their occurrence, so the article claims, happening unlike most quakes in a liquid medium, can give valuable information about the dimensions of a magma chamber or dike.

      8. Big Icelandic central volcanoes – and Bárdarbunga is one – tend to have at least pockets of rhyolite or rhyolitic domes, as is eg. the case with Askja and Katla.

        The Gjálp eruption, which is in this paper said to be petrologically between Grímsvötn and Bárdarbunga produced a mixture between Andesite and Icelandite, a magma seemingly produced by magma mixing of an sicilic component with a basaltic component from the mantle.
        http://www.sciencedirect.com/science/article/pii/S0377027399001869

        BTW in Iceland – contrary to other regions of the MAR -, there are big regions dominated by rhyolite, like Torfajökull and regions of extinct volcanism like Lón (near Höfn) and Borgarfjördur Eystri.

  25. Regardless of anything else going one, the Mila webcams have shown some stunningly beautiful cloud formations, both day and night.

    1. I collect some of the webcampictures just for fun because of the cloud and steam formations… 🙂 perhaps I make a poster with some of them…
      I made this with some nice webcam-pictures from Klyuchevskoy, it’s hanging in my office.

      1. Just take off “&quot” and it’s fine.

        Shows a change in subsidence behaviour from Sept. 19 on. Interesting.

    2. I have been tracking this chart from the start. If you add in some additional trend lines and a FSW you can see it much more clearly, you could then practically tell when the next fall was due. You should now be tracking it from the 19/20th, you will need another days data before you can get a new trend. it is just like tracking FX. don.t worry about the up’s and downs the TL’s remove these and gives you something you can work with.I always use TL’s not MA’s to read a chart.

    1. Ah, thank you for the update 🙂 I was just going to ask about a dark cloud that is visible on the horizon just above where the eruption is taking place. It has been there for a few hours and the sky is clear elsewhere. Now I think maybe it is the bad weather that is coming in?

  28. Is there summary earthquake data available, say day by day of total # earthquakes (above some xx minimal value) with the verified magnitude? what would be best
    source. I am interested in looking at percentage of earthquakes that are above 3.0,
    say day by day. and/or pct. above 5.0, week by week. mainly just to check out
    for potential to use as an example in my new method of analyzing percentage data
    that I am working on. thanks.

    2. If you are writing a science article and need data, best to address IMO about it. They also have the copyright of their data.

      1. thanks. actually my article is about new way to analyze percentage data when the denominator varies considerably,
        to correct for a bias problem when ranking the percentages.
        I was merely thinking some earthquake ratios would be potential application.

  29. Either the low frequencies are due to breaking glass as magma makes micro fractures in rock or water has come into contact with magma. What is the double couple moment of the EQs beachball(dire tional fracture) or isotropic(explosion) ?

    1. a while back (Sep 3) I saw an image at VC showing white centers indicating subsidence. Not sure what they’re doing now.

    2. This is just real reminder of the dangers associated with volcanoes. In the case of Iceland’s eruption, people trying to enter this area that’s closed to the public could very well find themselves in the same boat. DEAD!

    1. Thank you so much for this link! Incredible information from the field, including how various measurements are taken with great illustrative photos. One of the best links yet!

  32. John Seach @johnseach · 9 min
    #Bardarbunga volcano, #Iceland. Sulphur dioxide plume extending 1100 km ENE towards #Norway. #Bárðarbunga.

    1. Also high SO2 levels, but nothing larger than just city smog detected in Paris and Austria. I couldn’t believe but SO2 satellite data confirms it. Up to 200ug/m3 in parts of Austria, that’s a considerable smog level, but nothing that irritates you.

      1. Yes, the compact area of very high SO2 gets to those parts of Europe untouched or undiluted (still marked in red). Of course, it’s a pretty small area, but in Austria it hit precisely where measurements were revealed to be abnormally high. Perhaps just for a few hours.

        We only got one day of thick haze here in south Iceland, and that was the Saturday one week ago. This weekend there was some haze here but it was little. I think so far we are pretty lucky in south Iceland. The wind has been nearly constantly from west or south. Never was a strong northeast.

  33. The cluster of quakes around the caldera is definitely the most I’ve seen so far. It’s getting closer and closer to an eruption there.

  35. As the sunset has progressed on Mila Bard1 this evening, the lava streams over the southern track seem to be very visible, behind R2D2. Are the PTBs sure that there have been no break-outs on the southern side of the old lava?

    1. It also seems to me that I can see a small steam/smoke column rising from this side of the first lava lake to the left of the main vent. Light shines off it as it rises in front of the lava flowing behind. There may also be more than one…

  36. GPS going into steep decline this past 90 minutes or so. No major quakes to speak about, but could of course be error readings that will be smoothed out by the 180 minute average.

    1. I was going to ask if there had been any quakes……don’t think think the plot is spikey enough to have much effect on the 180 average…

  37. Seem like this is the place open,dicussion,unlike “volcano cafe”.Thanks for the ban,Carl!

    1. If you register then you don’t have to type in the anti-spam protection. Just be nice to other, on topic (little off-topic is fine) and don’t expect everyone to know everything about volcanoes, because in reality nobody knows everything about volcanoes.

      Also, welcome. 🙂

  39. Jon,
    There has been much debate about the glacier covering Bunga, and the fact it is an “Ice plug” in the volcano.
    Surely the plug is connected to the whole of the glacier? so that means the ice plug is being held up and supported by the vast surrounding glacier?
    I understand that cauldrons may form above Bunga, but wouldn’t there be cracks around the rim of Bunga if it was starting to slowly collapse?
    (ps, its taken a week or two to attempt to ask a half sensible question)

    1. The glacier just covers the caldera. Nothing more. The plug is inside the volcano, at least that is the idea. If it is in accordance with what we are seeing is a different matter and something for later studies to figure out.

      1. Jon, do you have updates regarding the point of no-return? Would that be related to the geometry of the floor of the caldera?

        I am curious about that. Although I think most of the scientists do not have a model to predict when such subsidience would trigger an explosive caldera event.

        I am fascinated to see calderas that subsided but never erupted violently in doing so, like Krafla in the seventies, Mt Katmai in 1912, and possibly many other cases in Iceland, that we have no geological evidence for. I estimate for instance that Bardarbunga caldera already subsided during the Veidivotn episode and did not erupted during that time.

        And then Askja went caldera in 1875, and it was a relatively minor fissure eruption that occurred weeks before that.

        Another episode that interests me is a ring-shaped rhyolite large eruption at Torfajokull 70000 years ago, as the caldera subsided. That eruption was estimated to be quite large. And it was also under thick ice.

        Perhaps water leaking in and reaching high steam pressure is what triggers such event. Or perhaps the mix of basaltic and rhyolite magma. Well, sincerely I have no idea.

      2. It has not updated from 55 – 75 meter mark. My models are still conflicting each other at this point and I am not sure why. It has however come to my attention that if an eruption starts in any part of the caldera rim or in Bárðarbunga volcano slopes (that are all under glacier) it might trigger an collapse in the caldera regardless of what the subsidence is. Since it might open up a way for the magma to leave easier then current paths it is now using.

        New eruption along the dyke is still an high probability since current eruption crater is ending slowly.

      3. You are using pressure. Hence gravity flow … If the caldera floor starts rising due to a net influx of magma, would it make things more unstable? An ascending cap has diffent stresses upon it.

  41. There seems to be centralised subsidence ,with perhaps some uplift on the North rim.Is there crytodome development distorting the caldera floor?

    1. There might be old magma in there. I find it however unlikely to be the case since last eruption in Bárðarbunga volcano was long time ago. What is the problem here is that nobody has clear picture of what is going on in Bárðarbunga volcano at the moment.

      1. For that matter, there is no agreement (or really, knowledge) on what Bárðarbunga looks like below ground. It never made the lists of particularly dangerous or particularly likely to erupt Iceland volcanoes and there is very scant evidence of its eruptive history in the last 1000 years. What we do know of that eruptive history is that it is very light in material compared to many other Iceland volcanoes and particularly its neighbor Grimsvotn.

        There is not a lot to like here.

  42. Could the almost rythmic +5 mw quakes in Bardarbunga be caused by a constant outflow of magma from the chamber to the Holuhraun eruption? And would this not be a healthy sign that the inegrity in the caldera is unchanged and solid despite the deflation we’re seeing?

  43. Gotta say, i think the feeder to the fissure eruptions has it’s own feed now.

    Since we don’t see much of a spike in pressure quakes, or plume heights with these big quakes, i think they are on their own now.

    Now if the MAR moves, it may close off the supply.
    That would prob take a 5 up where the MAR turns, above and west of Askja,
    Or more likely down below, beyond the SW edge of the glacier. It hasn’t moved much since the start, and if it releases, it may allow the MAR to slip, and close off the feeder dyke, thou maybe not the sheet to Bard.

    I am firmly behind the dome building tho, don’t know if it will blow the side of the caldera out – or up, before the MAR moves.
    Time will tell…

    My own obs, NASS (not a serious scientist)

  44. Are there any updated photos or Infra Red images of the extent of the lava flows? . . . particularly crossing the river?

    Have searched extensively and found none. Maybe Monday will come up with some.

  45. I know a lahar and a joküllaup are synonyms. Is there a difference between them I am missing?

    OBC hen

    1. A lahar is a mud flow, while a jokulhlaup is a flood that comes from underneath a glacier because of a subglacial eruption. The jokulhlaup can carry along boulders but it is principally a water flood. Lahars can happen anywhere, not just from glaciers, and they have more solids in them. IANAG and am happy to be corrected by the more knowledgeable.

      1. That is what I thought – lahar= volcanic material mixed with other material and water. Joküllaup= volcanic material mixed with other material (rocks, huge chunks of ice, etc.) and lots of water. Then I read that they are synonyms and became confused. Are there never huge chunks of ice in lahars and are the latter never as fluid as a joküllaup?

      1. A lahar doesn’t have to be associated with volcanism either. Mt. Rainier has had several in the last few decades (none serious), none of which had associative eruptive acidity at the time. Of course the hydrothermal alteration on Rainier plays a big part in generation of them, which is of course due to underlying past and current volcanism. I think all jökulhaups are lahars, but not all lahars are jökulhaups.

  46. Interesting note: the past 48 hours has averages 25cm/day subsidence. Bit slow the past couple days. Though this doesn’t seem to have effected the periodic m5+ quakes.

  47. This is a reply to hen (the reply link under the comment is not showing):

    About lahars, from Wikipedia:
    Lahar” is a Javanese word that describes volcanic mudflows or debris flows.[2] Lahars have the consistency, viscosity and approximate density of wet concrete: fluid when moving, solid at rest.[3] Lahars can be huge. The Osceola lahar produced by Mount Rainier (Washington) some 5,600 years ago resulted in a wall of mud 140 metres (460 ft) deep in the White River canyon, which covered an area of over 330 square kilometres (130 sq mi), for a total volume of 2.3 cubic kilometres (0.55 cu mi).[4] A lahar of sufficient size and intensity can erase virtually any structure in its path, and is capable of carving its own pathway, making the prediction of its course difficult. Conversely, a Lahar quickly loses force when it leaves the channel of its flow: even frail huts may remain standing, while at the same time being buried to the roof line in mud. A lahar’s viscosity decreases with time, and can be further thinned by rain, but it nevertheless solidifies quickly when coming to a stop.

    By contrast, a jokulhlaup can only come from a subglacial eruption – lahars can happen anywhere that the right kind of volcano is erupting.

    1. Thank you Wee Mama and GeoRaving. That is how I understood it from the beginning – just got confused when someone called them synonyms. (I saw the damage at Mt St Helens, others in the news, and never thought of them in terms of a glacial flood.) Just wanted to make very sure it wasn’t my head that was wrong. 🙂

  49. Using pi=3, density of basalt=3, radius of plug=5000m, depth=10000m, gravitational constant=10ms-2 and a movement of .25m we have 5000x5000x3x10000x3x10x.25=5.6×10**12 Joules = energy in an M5.2 earquake (2.8×10**12J for M5.0). So im missing another factor of about 2 for the transfer to vibration coefficient.

    1. I think you’re seeing the same earthquake from two different reporters (GFZ and EMSC). We’ll have to wait and see the magnitude IMO reports!

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