Merapi 2010: pyroclastic surges wreck villages in front of the world's press

 

WARNING: THE PHOTOS THAT ILLUSTRATE THIS TOPIC INCLUDE IMAGES OF BOTH SEVERELY INJURED AND DEAD PEOPLE AND CATTLE. AS INDONESIA HAS LARGE POPULATIONS OF BOTH MUSLIMS AND HINDUS, PLEASE TRY TO UNDERSTAND THAT SOME OF THESE IMAGES WILL APPEAR EXTREMELY OFFENSIVE TO EITHER OR BOTH. THEY ARE ONLY SHOWN TO ALERT OTHERS IN THE VICINITIES OF DANGEROUS VOLCANOES OF WHAT MAY BEFALL THEM, IF THEY FAIL TO EVACUATE IN TIME.

 

PART 1. The eruption

 

When the lethal eruption of Soufriére Hills Volcano on Montserrat (SHV) occurred in 1997, digital photography was in its infancy and the press only heard of the disaster after about a day. When Mt Merapi in Indonesia erupted on 26 October 2010, the world’s press and their photographers were nearby, reporting on a tsunami that had killed hundreds. Therefore such famous agencies as Reuters, AP and Getty Images all collected sets of top-quality images. Shortly afterwards a website related to the Boston Globe newspaper published a superb set of images from both events. I’ve used some of these photos to illustrate points made below. The “attributions” of each image can be found on the Boston website. Further excellent photos appeared on the websites of other newspapers etc worldwide and I have also used some of these.

Merapi resembles SHV, in that its eruptions are associated with a long-lived summit lava dome that sometimes collapses and sometimes is the site of vulcanian explosions (see Topic 2). The big differences are that: (1) Merapi is much higher than SHV and towers over the surrounding densely populated area; (2) There is a deep notch/ravine/chasm cut into one side of the summit, so that it is possible for an explosion there to be directly laterally, as happened at Mt St Helens in 1980. This greatly increases the risk for people living below in this sector of the volcano. Therefore pyroclastic flows (PFs) and surges (Topic 2)can reach much further downhill than on Montserrat and frequently destroy villages and any residents who have not already evacuated. As of 5 November 2010, the surges have already caused fatalities up to 20km from the peak and lahars (volcanogenic mud flows; an Indonesian word, by the way) are beginning to add to the misery and hamper rescuers. On 26 October the volcanological observatory there recorded seismic signals indicating the first six PFs of the eruption in quick succession, associated with a dozen vulcanian eruptions. Preliminary accounts suggest that each PF was the product of a vulcanian explosion (photos of the summit show little or no dome at the eruption site at present). Most of the images below are of the results of the first day of activity. You can also see an excellent short YouTube video of one of the PFs, posted by Russia Today., and another posted by the BBC. By the end of 2010 about 350 people had died; the number slowly rose after the eruption ended, as severe burns and lung damage from ash inhalation took their toll.

Evacuation around Merapi is the same messy business as on Montserrat. All the same problems arise: After generations of living so close to the volcano, many people think that they can predict its behaviour better than the scientists employed to do so; Farmers are extremely reluctant to leave their land and livestock; Older people and families with young children refuse to leave their homes and move to noisy, squalid and overcrowded shelters. If the first few PFs are small ones but plainly visible, people get the message and move away fast. But the first Merapi explosion was violent and shortly before dusk. Therefore PFs reached villages that were not yet evacuated. The surprising distance reached by one of the surges, combined with one of the press photos of explosions a few days later, make me suspicious that maybe one or more of the lethal explosions were indeed partly laterally directed. The following photos illustrate the sad story and I’ll add further comments where necessary.

 

Could be a valley on Dominica? So like Montserrat at sunset on a fine evening.  Photo  Bernard Tey / CC BY-ND

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Intense precursor seismicity for several days before eruption begins.

Photo CLARA PRIME/AFP/Getty Images

 

This 6 November photo shows a vertical vulcanian explosion at dusk. It’s the best image of one I’ve ever seen.

 Photo  BAY ISMOYO/AFP/Getty Images

Typical daytime photo on 6 November. The eruption was clearly increasing in intensity at that time.

Photo  REUTERS/Beawiharta

 

More 9-11 November photos.

Montserratians laconically call life under the fallout from this mayhem "heavy ashing"!

 

The ravine down one side of the volcano channels most of the PFs.

The PF will add to the older PF debris visible in the gully below the new flow. The surge clouds are spreading out on both sides of the ravine.

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Note the obvious lateral (sideways) explosion just below the summit.

This NASA thermal image from space shows one of the early PFs.

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My only excuse for including this photo is that it’s such a superb image!   Photo  Ulet Ifansasti,Getty Images

The world’s press was full of photos of “fleeing villagers”, like these folk. One of them doesn’t seem to realise that he’s meant to be fleeing! This recalls the Montserrat situation in summer 1997. We all hope that the guy shown here didn’t go too close later that day (see Topic 10).

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Detail of summit by day.

A low-power vulcanian explosion is collapsing and feeding a small pyroclastic flow channelled down the ravine.  Photo  REUTERS/Dwi Oblo

At night the extruding viscous lava dome is spectacular but menacing. The “trickling lava” is clearly continuous rockfall  It’s obvious that the shape of the mountain will channel PFs and their surges much more than on Montserrat. It’s like looking along a giant gunsight. The deadly PF and surge from Mt Pelée in 1902 was channelled towards St Pierre by a similar summit notch on the volcano. Photo REUTERS/Beawiharta

 

More photos from 9-11 November. Probably heavy continuous rockfall, rather than a small PF.

 Photo REUTERS/Beawiharta.

Continuous incandescent rockfall (maybe verging on a PF but not lava, despite press accounts). Strangely beautiful -- from a safe distance; just like big explosions on Montserrat.

Photo SONNY TUMBELAKA/AFP/Getty Images

 

The "ashing" looks very unromantic from this angle.

 

 

The main volcanological interest here is the volcanogenic lightening. Really good photos of this phenomenon during an explosive eruption are quite rare because they need the right combination of a dustproof camera, daylight, excellent weather and an eruption far enough away to see everything clearly and not  be running for your life!

Photo REUTERS/Beawiharta

 

 The 8 Jan 2007 partial dome collapse of the Soufriere Hills Volcano on  Montserrat cut a smaller similar notch in the old crater wall, directly above residents several km below. It was the implications of this notch for future eruptions that forced the Volcano Observatory scientists there to recommend a very controversial evacuation -- just like Merapi in late October. The old saying "shoot the messenger" is true for all volcanology teams trying to persuade residents to save themselves from deadly volcanic danger (see end of Topic 10).

This photo was taken from the Montserrat Volcano Observatory on 28 January 2007. The summit lava dome is much higher in 2010.

© BGS

 

Lahars; the cause of so much subsequent destruction (and often further deaths, up to years later).

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At first this looks like nothing more impressive than a small muddy stream flowing down a valley. But look more closely at the foreground and you will see that the "muddy water" is, in reality, thick viscous mud. This is why it can carry huge boulders within larger flows.

 

Although  very dilute lahars grade into muddy floods, the bigger and more viscous lahars have awesome destructive capacity.

 

Photo by Marc Szeglat

 

The zone below Merapi where pyroclastic flow debris in a small canyon is converted to lahar by tropical rainfall. This now also happens quite frequently in the Belham Valley, Montserrat, within the forbidden zone. You can see it well with field glasses from high on Garibaldi Hill.

Typical dilute lahar further downstream. The fluid in the river varies in space and time from muddy water to thick mud carrying large boulders.

Lahars are slowly burying  Chaiten, below Merapi.

 

Seen in the context of the previous photos, the large distances (up to 20 km) of devastated villages  (yellow triangles) from the volcano make sense. Several representative fatality sites are marked. The more distant destroyed villages seems to be associated with partly lateral explosions, extremely violent and prolonged vulcanian eruptions (approaching sub-plinian) or both. The official hazard map for Merapi is at: http://mappery.com/map-of/Merapi-Volcano-Hazard-Map

 

NASA satellite image

 

 

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This view uphill from the nearest devastated village to the volcano (on the map) shows a close resemblance to the scenes of scythed forest around St Helens in 1980, after the huge lateral blast there. Of course, being a relatively dense flow of air and dust etc, the surge would have accelerated down the steep slope towards the village below.

 

 

Typical damage by a powerful but relatively-cool surge. The bark is striped from the snapped stumps of mature trees but the wood (especially note upper right) is not strongly charred. Only a few cm of fine ash deposited. Photo  SUSANTO/AFP/Getty Images

Close-up of smashed cinder blocks shows that the agents of demolition were not only the dense surge cloud but also flying tree trunks, house timbers etc.

Photo  AP Photo/Slamet Riyadi

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Same point -- looks like a hit by a flying bulldozer! See how far away the volcano is from this wrecked village.

Ditto elsewhere, far from the volcano. The house timbers in the foreground look charred, despite the lack of obvious PF debris. Probably the very hot core of a surge.

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In this village the damage is less intense. Some trees remain upright (no leaves but also no charring) and damage clearly much less on the ridge to the left.

Photo  Ulet Ifansasti/Getty Images

Same situation elsewhere: least damage on ridge and most along valley floor. Remember that a volcanic surge is a dense current of dust-laden air and flows much like water, concentrated along valley floors.  Photo  CLARA PRIMA/AFP/Getty Images

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On hard indoor surfaces, resistant to heat, the very thin surge-derived ash layer shows no sign of gas escaping while/after it was deposited. Clearly someone’s drink was ruined!

Photo  REUTERS/Beawiharta

Where the ash was deposited on porous or plastic-covered furniture, subsequent escaping gas has pitted the coating. Photo Slamet Riyadi/Associated Press

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If you fail to evacuate before a "relatively-cool" marginal zone of a pyroclastic surge arrives, this could be your face. Is your "personal freedom" worth such a price?. Photo AP Photo/Trisnadi

This could be you, if you rate your livestock, crops, homework etc higher than your life.

 

So much for the safety of your own home. There is something obscene about the way the fine scorching ash has invaded everything. In part 3 below, we shall discuss ways to make a corner of your house a safe place to hide from the surge, if you are caught too late to get to safety. Photo REUTERS/Dwi Oblo

The fine ash neither burned the tyres on the bicycle nor singed the feathers on the parrot. So what killed the poor bird? Probably the ash itself did the fatal damage, by blocking its lungs, so that it couldn't get enough oxygen to survive. Photo AP Photo/Trisnadi

 

Obviously the ash here was quite cool because the tyres of the scooter are undamaged. How could such a thin innocuous ash layer destroy all life in a big room like this one?

 Photo  Ulet Ifansasti,Getty Images

If you have any doubt that this happened, look at the YouTube video published on 5 November 2010 by Russia Today, showing a rescue team finding bodies in a similar house.

This scooter has its tyres burned to cinders by hotter air than most of these photos imply. The seat and paint have vanished and the hand grips are melted. Notice that the strong steel petrol (gasoline) tank has survived without exploding.

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