The great eruption of Krakatau continued

Part 2 of a guest post by Albert:

The big explosions

Up to Aug 25, the eruption of Krakatau was not a major one. The largest event had been the initial explosion, May 20th 1883. The long continuation, and the presence of multiple eruption sites, was similar to the 1680 event. Magma had traveled from a deep chamber (estimated at 30 kilometers deep) to a shallow reservoir around 9 km below the surface. This magma migration could have caused the earthquakes which began three years earlier. The pathway from the reservoir to the surface used a rift or dyke, with multiple exit sites. But now the eruption changed, and became unique.

Reports on the events of Aug 26 and 27 are patchy, and the full story was only pieced together over the next few years. People on the coast were too busy surviving, and ships in the Sunda Strait were in complete darkness. The main events are clear, though. This post is based heavily on the description in a report from the Royal Society, dated 1888 (see reading list below).

The eruption rapidly intensified during August 25 and 26. By 1pm on Sunday, Aug 26th, the explosions were heard in Batavia, 150km away. By 2pm, a ship 100km away reported a black mass rising to to a height of 25 kilometer. By this time explosions occured every 10 minutes. By 3pm the explosions were heard 250 km away and by 5pm, all over Java. The explosions were not accompanied by earthquakes. The nearest ship, 10 miles from Krakatau, reported that the explosions came from the northeast of the island. Between 5pm and 6pm, a rain of large pieces of warm pumice began to fall on the ship. On the shore, waves from the eruption began to arrive from 5:30pm. They were at first just feet high, but continued through the night.

Sleep became impossible that night in the main cities of Batavia and Buitenzorg. The explosions were loud and frequent, rattled windows and cracked buildings, in spite of the great distance from Krakatau. During the night, ships in the Sunda Strait battled a hot stormy wind, carrying a sulphurous smell. Cinders fell, and the sea was warm to the bottom, 50 meters down. From midnight to 4am, explosions were continuous and one second, the sky was intensely black, the next a blaze of light. The roar grew less only towards morning. By that time many places on the Sunda Strait coast had already been devastated, but even worse was to come. Around 5am, the first of the large explosions must have happened. But in the blackness and deafening roar, this did not seem to have been noticed.

In the morning, the ash column was seen to have reached a height of 30 km. As it spread, blackness followed and ships had to take anchor. The clouds reached Java and Sumatra around 10:30am. Batavia was in complete darkness from 11am to 3pm, while a rain of dust fell. The dust contained some 10% water. In the Strait, falling pumice the size of pumpkins was reported. This continued during the morning; later the dust became falling mud.

The darkness precluded observations of Krakatau during the 27th and the exact sequence of events there is not known. The explosions reached their peak during the morning, ending after 11am. After a quieter afternoon, there was another set of smaller explosions during the following night. Activity finally ceased at 2:30am on the 28th. The next day, the Sunda Strait was almost impassable due to the mass of floating pumice and other debris. And although Krakatau’s peak was still there, the rest of the island had gone.

Together, the confused reports indicate four distinct major eruptions. Air pressure measurements of the shock waves at Batavia provide their times. Large explosions occured at 5:07pm on the 26th, 5:30am, 6:44am, and 10:02am on the 27th, and a smaller one at 10:52 (all local time). The fourth was by far the largest and loudest. There may have further strong explosions at 4:30am and 9am. The 10:02 explosion has an estimated energy equivalent to 150 megatons TNT – comparable to a M8.6 earthquake, and three times larger than all the other explosions combined.

The dust and ash reached very high altitudes. The ash columns were reported at 30 km high, but that was before the 10am explosion. Estimates for that explosion give values up to 50 km.

Sound

The sound of the 10:02 explosion was reported as far away as Diego Garcia, 3600 km distant, and possibly Rodriguez at 5000 km(!), four hours later. They sounded like distant cannons and in many places were thought to come from ships in distress. The map below shows where the sound was heard.

sound areaIt seems strange that the later explosions were not heard closer to Krakatau (such as Batavia), but were heard at very distant locations. Many people would have been stone deaf by now. But the ash in the atmosphere also dampened the sound, in the same way that falling snow brings silence. But sound could still travel over the top of the ash layers, at high altitude. Far away these waves curved back to the ground, causing the sound to be heard there. Over short distances sound weakens with the square of the distance, quickly rendering distant noise inaudible. But over much larger distances, the sound travels horizontally (the lack of atmosphere above 10km altitude stops it carrying much energy further up), and now the sound only decays linearly with distance. It weakens much slower, and this is why sound could be carried over such large distances.

The pressure wave from the explosion traveled much further, and circled the world several times. This was detected by barometers everywhere and lasted for five days. But this wave should not confused with the sound: it is not audible. The sound ‘only’ traveled 5000 km.

Pyroclastic flows

Pyroclastic flows were not known at the time. But some of the descriptions show that they happened. They may have come directly from the explosions, driving material laterally outwards, or from the collapse of the columns of ash. People received burn wounds on various ships in the Sunda Strait. At Ketimbang, Sumatra, 40km away, as many as 1000 people were killed by a ‘rain of hot ash’. One family survived inside a hut, and describe how the hot ash was pushed through the cracks and floorboards, and the air was sucked out. This was clearly a pyroclastic flow coming over the sea. Ships 80 km away experienced hot winds but escaped burning. Thus, the pyroclastic flows became survivable only between 40km and 80km from their origin.

How can pyroclastic flows travel such large distance over water, and still remain so hot? Pyroclastic flows have temperatures up to 600oC, are denser than air, but have density comparable to sea water. This allows them to travel along the sea surface and reach large distances. Much of the sub-sea deposits around Krakatau have been shown to come from pyroclastic flows. The pressure of the flows can also push up the sea – causing tsunamis. In this way, Tambora, exploding well in-land, caused a tsunami.

Tsunamis

Waves from the eruption began to reach the town of Anjer, to the east of Krakatau, from 5:30pm on the 26th,at first only a few feet high. Around 7pm, houses on the coast were damaged both on Java and Sumatra, and a camp of labourers was washed away. The waves continued irregularly through the night, at first not at damaging heights. But at 1:30pm two towns were submerged, and Anjer was destroyed at 6:30am and again submerged at 7:30am. After 10am, a much larger wave completed the destruction and affected the entire coast along the Sunda Strait. However, there are few eye witness reports on this wave. By this time the Sunda Strait was in darkness. At Anjer, noone was left on shore to see the large wave. Few had survived the two earlier waves, and those survivors had fled to the hills. This must have been the case at many locations along the coast.

The 6:30 wave at Anjer was 10 meters high. The height of the later wave is not known. Damage to buildings along the coast was seen up to 15 meters above sea level, but at one location at the head of a bay, to 38 meters. A men-of-war ship was carried 2.5 km inland, left 10 meters above sea level.

tsunami area

The earlier waves were local, causing destruction in one place but not in another not far away. The big wave traveled in all directions and caused devastation everywhere along Sunda Strait. But little damage was done outside of the Strait. At Batavia, the earlier waves were recorded by a tide gauge at 5-10 cm, but the big wave was a wall of water, and the height was 2.5 meters. This shows how much larger this event was. The large wave started as a rise. This indicates that the tsunami was not caused by a sub-sea collapse, but by water being pushed up.

Tidal gauge at Batavia
Tidal gauge measurement at Batavia (analyzed by Pelinovsky et al.)

The height of the wave rapidly diminished beyond the Sunda Strait. Still, the waves reached all over the Indian ocean, with a measurable wave even at Honolulu. Reported waves at Cardiff and New Zealand, attributed to Krakatau, probably were not related and had a local origin.

The cause of the tsunamis is still debated. Four explanations have been proposed: the collapse of the caldera, atmospheric shock waves from the explosions pushing up the water, pyroclastic flows from the explosions pushing the water out, and the fall-back of a cubic kilometre of ejecta into the sea. The second and third one seem most likely. They explain why the times of the tsunamis agree with the explosions (especially for the big explosion at 10am), and why the wave started with a rise. However, for the other waves the other explanations may also have contributed.

After the end

There was no volcanic activity seen after Aug. 28th. Reports of steam can be explained by the hot deposits, and an explosion on Oct. 10 may have been due to rock fall from the unstable slopes.

After the eruptions had ended, only the southern third of Krakatau, including half of Rakata, remained. Rataka now showed a vertical cliff to the north, from the peak of the mountain. The peak had increased in height by 40 meters, probably due to the blanket of ejecta. The rest of Krakatau had disappeared. Verlaten Island and Long island had grown considerably. At a distance of 15 kilometers, in all directions, the sea had become less deep by 3 to 15 meters. The channel to the north had become completely blocked, and some new islands had formed (which were quickly destroyed by the sea). But around the centre of the eruption, over several kilometers, the depth of the sea had increased. This is the 1883 caldera.

Rataka_cliff

The floating pumice traveled across the Indian ocean, eventuallt reaching Australia and South Africa. There is an unconfirmed report that in Zanzibar, human skeletons were found on the pumice rafts. The dust at great height in the atmosphere spread across the world. Along the equator, the dust encircled the earth twice, each circumference taking 13 days. It caused strangely coloured Sun and Moon, and suppressed the rains over India. Deeply red sunsets were seen for many months. A small drop in temperature occured. Many descriptions claim that temperatures dropped by 1.2 degrees the next year, but published temperature data do not confirm this. The global effect was minus 0.1-0.3 degrees, lasting 2 years. This was similar to, or a bit less, than Pinatubo which caused a drop of 0.5oC

Over time, the sea claimed back the new islands leaving only the Rataka remnant. But eventually, in 1927, new volcanic activity was seen, from a location midway between Danan and Perwoebatan, at the edge of the 1883 caldera. This volcano, Anak Krakatau, has been above sea level since 1930 and is still growing with frequent eruptions. Krakatau is not finished with us yet.

Anak_krakatau
(From Deplus et al. 1994, Journal of Volcanology and Geothermal research)

Cause and effect

The Krakatau eruption was not extraordinary, and behaved very much like the the 1680 eruption, up to mid-August. But the enormous explosions set the event apart. Was this caused by interaction with sea water? If so, why not in 1680? Or did something else occur? The ejecta did contain some water, but the volcanic deposits do not show alteration by magma-water interaction. Sea water rushing into the magma chamber cannot have been the direct cause of the explosions.

A strong hint comes from seismological maps of the shallow magma chamber, 9km deep. They show a double chamber, separated along an east-west line, a few kilometers apart. The two chambers are on either side of the 1883 caldera. Shouldn’t there have been a chamber underneath Danan, the centre of the 1883 caldera? Perhaps there was. The best explanation for the events of August 1883 is that the roof over the centre of the 1500-meter deep magma chamber collapsed. The collapse pushed the remaining magma into the two magma pockets on either side, and upward. The collapse caused chaos near the surface.

The different explosions can have been caused by the collapse of different parts of the island. The 5:30am explosion may have been related to Perwoebatan collapsing, the later ones to Danan. The fact that mud falls were not reported until after 10am suggests that the explosions happened above sea level: submarine explosions did not happen until the end.

Krakatau: volcanic danger

The death toll was officially 36417. It included the entire population of nearby Sebesi island where there were no survivors, hit by pyroclastic flows and tsunamis. The death toll is the second largest reported from an eruption in historical time, after Tambora. The majority of the casualties came from the tsunamis.

Still, Krakatau was a large but not exceptional eruption. The total ejecta are estimated at between 15 and 25 cubic kilometer. Tambora ejected in excess of 50 km3, Pinatubo around 10km3, and the Novarupta eruption (1912) and Laki (1783) both around 15 km3. The Taupo eruption in New Zealand, AD 180, erupted some 120 km3. So Krakatau was large, but there have been comparable and larger eruptions in historical times. The island was not recognized as a dangerous volcano, even when erupting in May to August 1883. If the cause of the calamity that followed is the collapse of a deep magma chamber, this could happen at any volcano, whether in the sea and on land.

The conclusion is that what makes a volcano dangerous is not primarily the eruptive history. Its location, including how many people live within 100 km, and the size and stability of the magma chamber are important. Krakatau is much more than gripping history. It is a warning from the past.

ALBERT

Further reading

The eruption of Krakatoa, and subsequent phenomena (1888): report by the Royal Society. https://archive.org/details/eruptionkrakato00whipgoog
http://blogs.scientificamerican.com/history-of-geology/2011/08/27/august-27-1883-krakatoa/ Reports from ships in the Strait.
http://www.geology.sdsu.edu/how_volcanoes_work/Krakatau.html
http://www.drgeorgepc.com/Tsunami1883Krakatau.html

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86 thoughts on “The great eruption of Krakatau continued

  1. Again, many thanks to Albert for bringing this beast back to our attention. A very fine article!

    I also think that it puts the explosive force question to rest. My estimates, though within the ballpark, were a bit short of what the experts came up with. (and I was thinking that I would be over the published estimates)


    Pinatubo’s mass ejection rate at the height of it’s eruption was 102,483 m³/s for it’s 32.25 km plume above the edifice. Krakatoa, with a 29.1 km plume above the edifice was ejecting at 67,021 m³/s. (DRE) So, in reference to a comment from the first half of this post, Pinatubo was in fact likely to have been a bit larger. And yes, that goes against my assumptions as well.

    Using: “A multidisciplinary effort to assign realistic source parameters to models of volcanic ash-cloud transport and dispersion during eruptions” Mastin et al (2009)

    • This seems correct for the earlier explosions. The height of the column of the 10am explosion is not known though, but may have been as high as 50 km. This estimate comes from the trajectory of rocks being blown out, and from the dust layer over the following months and may not be particularly accurate (I have ignored one estimate of 100km which seemed mainly a guess).

      • 50 km would be 49.1 km above the edifice with an ejection rate of 586,776 m³/s.

        100 km → 10,806,505 m³/s

        So, the jury is still out on which one was actually larger. Again, Thank You!

  2. Great article, Albert.

    My uneducated guess is that all four possible causes for the tsunamis are correct and also collapse of the edifices, especially as there were many tsunamis.

    • Regarding the magma chambers, seismic studies would be comparatively recent. The two shallow magma chambers could have accumulated since the 1883 eruption.

      Which magma chamber feeds Anak Krakatoa?

      • Excellent question. Its lava shows a mix, with crystalization at different depths from 5 to 25 km. It seems quite dynamic. The paper I read suggests a diffuse magma storage (meaning many small pockets rather than one big chamber) at 3-7km depth. It needs to be diffuse because it didn;t show up in the seismological surveys.

  3. A chilling collection of data and accounts. Thank you Albert. Certainly a time to pause for thought and although we all like looking at eruptions and discussing all the aspects, other volcanoes come to mind and the people who live close to them. Thankfully the article also highlights the huge steps that have been taken in monitoring and best guessing probable scenarios so that evacuation of settlements can be organised to save lives. Completely accurate prediction is still many years away, if ever.

    • You are completely accurate in stating that there will be an eruption. The tricky part is narrowing that down to “when?”

      I am almost certain that the rift lines passing down through Laki will rift and open up again. When? is the real question. Could be this afternoon, could be in a thousand years.

  4. Resurrecting a plot from the past, here is my AVERAGE tropopause elevation plot. The actual elevation for it will depend on prevailing weather conditions. Pushing the SO2 load past this elevation and into the stratosphere is how volcanoes can affect the climate. About 2 months after an SO2 injection, the sulfate levels will peak. After about 50 months that sulfate screen will have dissipated.

    As you can see, higher latitude volcanoes don’t have as much work to do to reach the stratosphere.

    • Great stuff this post I always blame the Bad Boyz of Kamchatka for my “Green Tomato summers” . Lurk is right-there is less work to do to get the SO2 up into the stratosphere..

  5. And what appears to be a BBC docu thingie about it. In English with Indonesian subtitles… except when the people on screen are speaking Indonesian… then they have English subtitles. {I guess someone was thinking} There may be some issue with the events as depicted… in one scene, the water can be seen receding from the beach, and as Albert noted, the tsunami wasn’t preceded by a noticeable pull-back.

    The tsunami arrival scenes remind me of the flooding simulator at shipboard damage control school. They stick you in a compartment and open up the valves. You and your group have to make and install several different shoring set-ups to slow the flooding and then secure the piping. Fantastic training scenario. It makes it easier to think and work in a chaotic setting.

    • … heh. Love the dialog.

      A shy young lady enters the room where two guys are frantically discussing the geology of the system.

      “What’s this?” The older one asks. The other responds “A girl.” The older guy states ” I can see that, what does she want?” Meekly, the girl then states that “the mountain has done this before.”

    • Regarding sea water receding before a tsunami, in one of the contemporary report (from a Dutch family?), the sea was noted as receding.

      • I don’t doubt that there was some. That’s only natural from the way that waves stack up the water as they approach shallower depths. But unlike the more recent tsunami examples, it was probably not as pronounced of an effect.

      • The report above is based on measurements in Batavia, outside of the Sunda Strait, and only the big explosion was big enough to show this. However, it seems likely that the same happened in the Strait. The earlier waves may have been different. The reports I read started with with a big wave coming in, and do not mention the sea receding first. To start with a receding sea, you need to create empty volume for the sea to sink into. A subsea collapse.

  6. “It seems strange that the later explosions were not heard closer to Krakatau (such as Batavia),”

    This is a well-known phenomenon which was also noted at St. Helens; close to the volcano, the cataclysmic blast was not heard at all. Further away, it was heard across multiple states.

    A point of note is the simultaneous eruption of craters at different parts of the island. My gut feeling (and it is just that, I’ve done no formal analysis) is that this is a Very Bad Sign. The same was seen in the runup to Pinatubo, at least in the seismicity and phreatic blasts; they were so widely dispersed that the scientists were initially sceptical that this was all related to one event, magmatic in nature; the scale deceived them. What was happening of course was that advance ‘tendrils’ of magma were approaching the surface at varying points – but all sourced from the same large magma body at depth, which then became fully involved when the preliminaries were over and the main event started.

    Rabaul is another example; when Vulcan and Tavurvur start going simultaneously and strongly, worry!

    I would be nervous when any volcano starts that kind of multiple-vent behaviour, especially if has a history of large eruptions.

    • For them that don’t know. Vulcan and Tavurvur are both “independent” cones situated on the ring fault of Rabaul’s caldera. That bay that separates them is about the extent of the caldera. (actually, it is the caldera)

      That island has a collection of ancient Rabaul sized calderas stretching off to the south-west on New Britain.

      • Actually, GL the caldera is even bigger than the bay. The town of Rabaul is inside the caldera rim – the Rabaul Volcano Observatory behind the town is built on the rim.itself

    • At http://en.wikipedia.org/wiki/1980_eruption_of_Mount_St._Helens I read the following about the sound of the Mt. St. Helen’s eruption:

      “Superheated flow material flashed water in Spirit Lake and North Fork Toutle River to steam, creating a larger, secondary explosion that was heard as far away as British Columbia, Montana, Idaho, and Northern California. Yet many areas closer to the eruption (Portland, Oregon, for example) did not hear the blast. This so-called “quiet zone” extended radially a few tens of miles from the volcano and was created by the complex response of the eruption’s sound waves to differences in temperature and air motion of the atmospheric layers and, to a lesser extent, local topography.”

      If Laacher See Volcano in the VulkanEifel in southwest Germany erupts with a VEI6-force, the sound of that eruption will be heard across the whole of Central and Western-Europe.

    • Hi Mike. You may be right., I would expect multiple eruption sites in two cases. One is where the flow rate exceeds the carrying capacity of the conduit. Pressure will rise until something gives. The second is when the magma reservoir is very close to the surface. If the depth is much less than the width of the reservoir, different parts will act and erupt independently. Both have their inherent dangers.

  7. Thank you cdaley55. It’s not over until the ….. emissions stop and quakes return to pre eruption MAR rifting data for that area of Iceland. I am impressed though by the accuracy of attempts to forecast the progress of the event by our commentors and regular plot creators. (Albert, ianF and Lurking et al ).
    They may not be professional volcanologists but they are professionals in other disciplines and they apply what they know to a wide range of situations. They “think outside their own boxes” .
    The result is not wild speculation and sensationalism, but quietly honest and plain evaluation of data which is available, or uses of already existing scientific laws and models.
    The comments in here mirror the findings from the IMO and all who work with them. This record has given this blog an acceptance and respect from many professionals.
    Thank you to all people who help to make VC what it is…….. and that is actually everyone reading this :).

    Now I have done my Oscar acceptance impersonation 😀 Lurking’s latest comment on SO4 emissions above demonstrates my point followed by tgmccoy’s comment about “green Tomato” summers…..

    I have been criticised for talking OT about such things as gardening…….

    Many people will understand “Green tomato” summers. without going into full blown scientific detail of average temperature and Lux levels. Scientific jargon deters many people from reading on……
    This short essay says it all very concisely…. Thank you to Sumit Ranjan for this extract from his ebook “Jargon as a barrier to Communication”

    “Jargons are terminologies used by professionals to simplify a particular concept. Jargons are meant to enhance communication but at times it can act as the biggest barrier to communication. Jargons can also be used to hide certain facts so that the listener does not realize the shortfalls or aberrations. One cannot comment if he/she cannot apprehend the language.Jargons are used to maintain secrecy. Hence we find that different institutions have different jargons so that the trade secrets are not revealed to a third party.New employees are not aware of corporate terms and hence require certain amount of timeto imbibe this knowledge. Using jargons with them at the inaugural stage may leave them disconcert. Unless the employee understands his/her task, it’s difficult for them to work on it. Some time if donated to explain these jargons, the question of barrier does not arise. Employees face hesitation while accepting that they are unaware of certain terms. They chose to keep quiet and not ask questions as the seniors might feel that they don’t have the basic knowledge. Juniors are apprehensive about asking questions thus it is the seniors’ responsibility to maintain a complacent environment and enhance communication.”

    Now time for coffee #2 whilst I remember the days of Staff development training where I counted how many times the latest “in words and phrases” were used to stop myself falling asleep in the after lunch, warmth and darkness of the conference room . Often those making the presentations could have passed on their knowledge in a quarter of the time allowing the rest of us to go back to productive use of our working time. Sometimes The jargon spouting presenter actually didn’t have a clue when it came to question time at the end……. and answered with more jargon and cliché’s……
    Hands up who has had this experience? 😀

    • One word that I absolutely hate, is “proactive.” It’s a fluffy made-up adjective/adverb (depending on use). ‘conduct a proactive search’ → ‘do your job’ (since that is what my job was). Find it, report it, log it. Not that difficult of a task if you ask me. What they were getting at was to not sit around conversing with each other while your supposed to be doing what I mentioned. And for this a special made up statement with a fluffy verbiage? ‘proactive?’ Seriously? I asked the author of that statement what he was getting at and all I got was more fluff about the fact that HE had personally written the document that it was seen in. I gained no more insight than that. And this #@%%% had ridden a Helo over to our ship specifically to tell us this. When we detached to go off and play with the StaNavForLant guys I was quite happy at not being in his group of ships. We didn’t have to deal with his group until we formed back up for the transit home. By the time that happened, most of our original group was ticked of at us because the group we were operating with tended to hit port more often than 6th Flt units. In part this is because the units tend to be slightly smaller and the ports are pretty near… and they use them all the time so it’s not a big deal to go to a specific port.

      • Yes, Diana, I work for a government department and we get jargon all the time. I particularly like our Chief Executive’s weekly newsletter where he attempts to communicate with his staff. One of these was so full of dense verbiage that I had to read it twice before I understood what he was trying to say: that cuts had to be made and the ‘best’ way was to get rid of staff. Often his letters make no sense at all but are just fluffy bits of puff. 🙂

      • I agree that “proactive” is hugely overused. That is the point though. I find that in the text and Twitter dominated world the same few words become trendy and then get used to death. I recon that we would all forgive documents containing the odd naff word (& perhaps I have used one in this sentence). It is the endless repitition without regard to whether the chosen word is appropriate or even the best choice. After all we have some one million words available to us in the English language (admittedly this includes all the old ones that have gone out of use) so a writer should be spoilt for choice.

    • One example of unintentional jargon use with fatal consequences: the hazard report by geologists before the Nevado Del Ruiz disaster, when they said that “there was a 100% probability” that a lahar would reach Armero. Many non professionals didn’t cotton on that they meant “absolute certainty”

  8. Nice series of articles, thanks. Frustrating (yet understandable) that there is so little in the way of actual observations and such from the main events!

  9. Thanks again, Albert, for re-telling this story: like many others here, it was the accounts of Krakatoa and Vesuvius that fascinated me as a child and I can never tire of them. I’ve never thought about the noise aspect of the eruption before, but the relentless bombardment of noise over the period of the eruption must have caused temporary deafness to anyone within range. We must have all weathered noisy storms during the night and not heard the breaking branch or falling tile that would have woken us on quiet nights. I think peoples hearing would have been compromised after the shock waves from the first explosions.

    • I don’t know about that… I was awake all the way through Hurricane Ivan’s landfall. I had the wife and dogs hunkered down in the hallway with blankets and pillows just in case the house let go. (we had ridden out a tornado using the same method a few years before) The center part of a house where the most walls are at is usually the strongest part of the house and will be the last part to suffer complete failure in the event it gets that bad. At no time did I hear the oak tree out front eating my truck…. but the whole ordeal was quite noisy… for about 4 hours non-stop. The eye passed west of here so it was mostly just eyewall winds the whole time. (and the wrong side of it to be in if you have a choice)

      … oh, and yes I had installed shoring on the garage door to provide it some extra strength. Having worked as part of a damage control party came in handy for that. I even went as far as installing anchor bolts on the concrete floor a few day prior to arrival so that I would have a place to put the footing of the braces.

      • Hard to keep the dogs settled? We waited up like that for a hurricane landfall in Jamaica. It did a 90 degree veer and missed the island completely. Not a nice thing to wait for.

      • I have been through several hurricanes too, including Katrina. I was never so scared in my life! I have always taped up the windows and bring out the kerosene lamps (the power ALWAYS goes out sometimes days or sometimes weeks) so we shored up the house and put blankets and pillows near the bathroom (the safest place to be during a storm)….anyway, We were going to ride out Katrina as we did all others….bad move! I will NEVER forget the sound of the wind….A combination of a wolf howling and a fighter jet overhead.w The whole house was SHAKING. Our house was torn to pieces….NO ROOF. You may You may ask “Why did you stay when officials were saying how dangerous that storm was? “The answer to that is, nine times out of ten, past storms were never as bad as the media made it out to be. ALL DRAMA lol! But I soon realized that Katrina was different, and it was too late to leave. I am amazed that we didn’t get killed! I will never stay during a hurricane again!

        • Sorry to be a naysayer, but window taping is quite ineffective. At most, you will lessen the amount of shrapnel when the window does go, but that won’t stop most of the debris. I typically clip plywood into the exterior frames with purpose designed clips.

          I’m 146 feet above sea level and have 15 miles of terrain to knock down the surface wind. The downside is that can promote the fast spin-up tornadoes in the land-falling feeder bands due to the turbulance.

  10. Thank you Albert. I enjoyed your Krakatau two-parter very much. My son had to endure me reading the whole post out to him! I have to admit – he looked interested in it, for a teenager.

  11. One interesting thing here is I had always assumed water entering the magmatic system was the primary culprit behind the main explosion. IT still may be, but as albert said, most of the tephra didn’t show signs of water mixing.

    Knowing this, I still think water played at least some role. Even if water didnt cause the penultimate caldera eruption, it *could* trigger a large initial phreatic blast, which would in turn, result in a great enough depressurization of the lower magma, allowing the gas to be released leading to the very large explosions.

    • This surprised me too. I had assumed (as had may others) that the magma reservoir rifted below the water line and let the sea in. That would mean a Krakatau could only happen near the sea. But this does not seem to have happened. Only at the very end did under-water explosions occur. Did water play any role? I now think not. Large explosions do come from volatiles. Perhaps the collapse at depth reduced the pressure in the surface magma chamber above. Lower pressure means volatiles in the magma suddenly turning to gas. Boom. One paper commented that Anak Krakatau shows mixing between old (crystallized) magma and fresh magma, and that this is particularly unstable. Did the old Krakatau also showed this? Any model should explain, however, why the 1680 eruption did not lead to large explosions. Something extra happened.

      • I’m currently stuck at the auto dealer for regular PM. But I think the the bend In the subducting line promotes a pleat in the plate there. If so, Krakatau could have a deep 670 km source as well as the 110 to 125 km source.

      • Hi Albert! Another “Krakatau” did happen on dry land: Huaynaputina, Peru, in 1600 AD. It does have two magma sources, one at the lower mantle boundary and one below the tip of the subduction wedge. The result of the eruption was that the whole edifice was blown to dust, leaving just a hole in the ground. I have done an article on it (Peru 3, will be published next week over at VH), and the story reads quite similar to Krakatau. So I can readily agree with the idea that such type of eruption does not need a lot of water in the equation.

      • In fairness, we could use the simple argument that the wad of magma in the current eruption was larger than in the 1680 eruption. This would be completely fitting given how normal volcanoes erupt – most eruptions don’t trigger caldera eruptions, but after a long enough time and enough build up, you may get a larger release of magma from depth resulting in too-great disruption to the instable magmatic system.

        One of the most interesting cases I know of similar to this (on a much larger scale) is the ancient eruption of Crater Lake (aka Mt. Mazama).

        Most people who know volcanoes are familiar with Crater Lake’s caldera eruption as the largest known eruption in the cascades, and one of the largest eruptions in the last 10,000 years (it was a VEI-7, roughly the size of Tambora).

        The interesting thing about this eruption is that not even 300 years before the VEI-7, there was a VEI-6 eruption, roughly the size of Pinatubo from the same volcano. This clearly throws a wrench in any prevailing thought that volcanoes always need to “recharge” after a large eruption. Remember, it’s all relative to how large the magmatic system is below the volcano, and how much erupts in a given eruption.

        My pet theory on Crater lake is that there were stacked magma chambers as is so common in large stratovolcanoes. The VEI-6 erupted, and the subsequent depressurization from the VEI-6 event sent in motion the eventual VEI-7 eruption from the much larger chamber.

        But the precedent that this happened makes you think twice about large eruption that have happened recently, and other “patterns” in a volcano, which are always subject to change.

        • I agree with that possibility. Mazama ash is ubiquitous in NE Oregon. Years ago I was on a dig at a spear point manufacturing site that has had usage for oh 10,000 years. High quality basalt. very good evidence of the earlier eruption btw at first they thought it was from one of the other cascade volcanoes. No it was Mazama. here in NE Oregon there is .5 to 1 meter of
          Mazama ash…

  12. Is it a common thing for sound near the volcano to be quieter than sound traveling away. I feel like I have this wrong. Some clarification would be appreciated.

    With Bardarbunga calming down activity around the rest of Iceland is picking back up. Askja and the volcano that is next to Bardarbunga on the left are what I’m looking at.

  13. Grimsvotn is having some tremorish signals. And quite isolated to its region. Could be water moving. We will see when IMO updates the quakes, to see if there are any at Grimsfjall.

    • The eruption is fading, though. Earthquake activity under Bardarbunga has further declined, and dramatically so, even in the past week. The sheet reports still some slow outflow from Bardarbunga. The fact that Holohraun mirrors this so well shows that even now, the Holohraun magma comes from underneath Bardarbunga. How deep underneath is another question. Congratulations to the people who predicted a February end! They were not far off.

      IIt seem the pressure pushing the magma along the rift is declining. Perhaps this is why Askja is stirring: adjusting to changing strain along the MAR?

      • I notice the IMO is verifying nearly every one of those small quakes. Meaning? 1) The EQs are important to keep track of, and/or 2) They’d hired more seismographers and need to keep them busy.

        There is clearly still a lot of heat along the path of the lava tunnel, as there is still a lot of steam rising.

        Looks like I’ve got to decide how important it is to me to get out to see (walk near?) the no-longer-active vent. (SO much harder to justify a helicopter, but maybe I’ll reserve a date just in case there is something else to see on that day 🙂 )

        • IMO are probably monitoring closely to see what is going on. If Holuhraun is shutting down rather than just taking a break, will the eruption have finished or will it emerge somewhere else?

          Interesting times.

    • An influential role model to an entire generation of kids who saw that it’s okay to be so intently focused on science for the sake of science, and that it’s okay to not really fit in.

      • Star trek was a pioneer in creating superb multicultural role models. Uhura was one of the first Black women to take a leading part as an equal to the male characters. The cold war was just ending and there was a Russian on the bridge….it was all very new and exciting. I loved the 60’s 🙂 Though I didn’t like the Vietnam War, and the rising use of drugs. Generally it was an optimistic time or maybe I felt it was because I was young then 🙂

        • Don’t forget that a lot of what we take for granted were presaged by gadgets in Star Trek. Hello Cell Phones. The actual technology was enabled by communications research to support Apollo, but the hand held communicators, even to the idea of them being “flip phones” at first, appeared in that show. I guess at the root of it, you can thank the cosmetics industry since the first Star Trek communicators were based off of compacts.

          As for the Vietnam war, I don’t think anyone actually “liked” it. I missed the draft by about 3 years. I was sitting in the living room when my date of birth was called. Fortunately, I was 3 years short of the age bracket.

          I switched the vid link from Country Joe McDonald since I like Alice’s Restaurant better. It still tends to get air-play around Thanksgiving here in the US.

          Alice’s Restaurant” recounts Guthrie’s true, but comically exaggerated, Thanksgiving Day adventure as a satirical, deadpan protest against the Vietnam War draft

          The song itself was far too long (8 minutes and 34 seconds) to be released (or even fit) on a 45 rpm single, and so never made the Billboard Hot 100

          One key aspect of the song (towards the end) are his experiences at the induction center. These can be quite intimidating places. When I enlisted (several years later), during processing at the AFEEs station, one of the members of my group was pulled aside for further examination because he urinated what amounted to pure water according to the specific gravity test.

  14. Good morning all.
    Having done my morning world tour and had a peek at Erebus, Iceland, Italy and Sakurijima belching ash and gas, I popped over to the Aleutian Islands and for some reason I was attracted to Westdahl Volcano.
    This is the largest Volcano on the Aleutian Islands but yet I have never really looked at it.
    Here’s the info page with thanks to the Alaska Volcano Observatory (AVO). Looking at the data, dates and general seismic activity I think this is one volcano to keep an eye on.. It is close to Shishaldin which is a “regular” and is at the moment showing a low level plume. The AVO site is a mine of information , not just for Alaskan activity but also Kurile Islands and the Kamchatka Peninsula.
    I gave our Alaskan Friend Motsfo a wave as I flew past. Motsfo, I have forgotten which Volcano you are closest to …..my memory isn’t wonderful. I know that for Lent you will not be available during the week so I hope you get to read this message. I also hope the arthritis is not too bad and that you are seeing some signs that Spring is round the corner for you.
    http://www.avo.alaska.edu/volcanoes/volcinfo.php?volcname=Westdahl

    • …..and a follow up to the above comments. A nice animation of deformation and quakes of both Shishaldin and Westdahl.

      On Land Unimak Island appears to be a wild and inhospitable place. I couldn’t find many really good clips . There seems to be a thriving tourist industry based around trophy hunting. Brown bears. The local wolf population seems to be beleaguered too. I wont go into this topic as I feel so very anti hunting of any wild species. Culls may be necessary but should be carried out humanely. In a place like Unimak nature has her own way of keeping a balance.

      This clip gives some idea of the majesty of the Volcanos and the beauty of the brief summer (I advise turn off the music!)

  15. I don’t know which Redoubt you are discussing but the pictures I found on either one are stunning and breathtaking, thank godness for photographers and people willing to share 😀

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