2018-12-22 - Volcano induced tsunami in Indonesia

[davenn]

I heard a news clip whilst lying in bed watching TV but there was no mention of an eruption
I rushed into look at my seismograph screen and there was no quake ... so was left shaking
my head wondering what happened ... till now ...

https://www.bbc.co.uk/news/amp/world-asia-46663158

The Anak Krakatoa (Krakatau) volcano is the small brother that has grown up since the major of Krakatoa
in 1883
Dave

 

[Klystron]

Thanks for this post. My US-based news readers have not picked up the story yet, even Reuters.

 

[Borg]

It's on CNN and they're stating that there hundreds of confirmed deaths already - including many people who were attending a concert.

 

[Ophiolite]

Some additional information from the Jakarta Post. The absence of any seismic signal is puzzling.

 

[OmCheeto]

Some additional information from the Jakarta Post. The absence of any seismic signal is puzzling.

According to the article you posted, there were seismic signals:

“At 21:03 [Saturday night] Krakatau erupted again and damaged nearby seismometers, but the Sertung Seismic Station recorded continuous tremors,” she said in a statement on Saturday.

She added that seismic sensors in Cigeulis, Banten also recorded seismic activity lasting around 24 seconds.​

Also, it appears that the volcano is continuing to erupt.

 

[OmCheeto]

If you've never subscribed to Facebook, now might be the time.

https://www.facebook.com/Oystein.Lund.Andersen

He's a photographer, and only 50 km from the volcano(Anyar, West Java). He took a great picture of it yesterday. (It has a © on the image, which is why I'm not sharing it directly.)

He also posted a video of a drone flight over the volcano on Aug 9th. It has a great shot of how steep the flank of the volcano is. I can imagine it sliding off into the sea.
(I watched it at double speed, as otherwise it looks like slow motion.)

Oh wait. What's this.

"This footage is available for purchase/licensing. For more information see my website: www.oysteinlundandersen.com or contact me directly on email: andersen_oystein(a)hotmail.com"​

Ugh.

Anyways, you can see it on his youtube channel: https://www.youtube.com/user/OysteinLundAndersen/videos

Look for "Drone vs lava-bombs - Krakatau volcano, Indonesia -"

It's the 12th one on the list

[Edit]
Doh! Be sure and watch and LISTEN to the video after that one:

"Rare - The Sound of Krakatau volcano erupting (AUDIO) (July 2018)"​

And be sure your sub-woofer volume is all the way up.

 

[davenn]

... The absence of any seismic signal is puzzling.

because it was volcanic eruption related, rather than a big earthquake which is the usual cause

 

[Ophiolite]

because it was volcanic eruption related, rather than a big earthquake which is the usual cause

True, but seismic signals are important measures of volcanic activity. Given its history I would expect Anak Krakatau to be well endowed with observation stations that I would have thought could pick up relatively low level signals. And Om Cheeto spotted reference to such signals that I totally missed in my initial quick scan of the Jakarta Post article. (However any small knowledge I have regarding vulcanicity is focused on magma genesis rather than eruption mechanics, so my expectations for seismic signals may be wildly out.)

 

[davenn]

True, but seismic signals are important measures of volcanic activity. Given its history I would expect Anak Krakatau to be well endowed with observation stations that I would have thought could pick up relatively low level signals.

Yes but the seismic signals for moving magma ( harmonic tremor) are usually relatively low in amplitude and are not going to
produce a tsunami. As I noted in the OP, there was no big tsunami generating quake, else I would have recorded it on my system

It's not the low level signals you are worried about for tsunami generation. Krakatoa is almost constantly erupting, on at least a monthly basis.
Just this morning I have watched YouTube videos of eruptions in Aug, Oct, Nov and Dec of 2018
Dave

 

[Ophiolite]

Yes but the seismic signals for moving magma ( harmonic tremor) are usually relatively low in amplitude and are not going to produce a tsunami. As I noted in the OP, there was no big tsunami generating quake, else I would have recorded it on my system

My apologies. I have been unclear. I was not suggesting that they would generate a tsunami, but that they could intiate a submarine slide capable of generating a tsunami. Surely that would be detectable by seismometers located only tens of kilometres away from the source? The apparent absence of such signals was what I was orginally commenting on, though - as noted earlier by OmCheeto- it seems such signals were detected.

 

[davenn]

My apologies. I have been unclear. I was not suggesting that they would generate a tsunami, but that they could intiate a submarine slide capable of generating a tsunami.

ahhh OK yes agreed quite possible

Surely that would be detectable by seismometers located only tens of kilometres away from the source?

Yes, should have been able to. I would have expected the even the undersea landslide would have produced a seismic signal.
But I suspect that it's signal/significance would have been lost within all the other harmonic tremor signals

Gosh, I cannot even remember/recall the last time a volcanic landslide caused a tsunami ... relatively rareDave

 

[Ophiolite]

Gosh, I cannot even remember/recall the last time a volcanic landslide caused a tsunami ... relatively rare

I've only been aware of the slides associated with the Azores and Hawaii, which predate historical records. But I located this more recent one: Stromboli, 2002.

 

[davenn]

But I located this more recent one: Stromboli, 2002.

wasn't even aware of that one !

Thanks for the linkD

 

[Tom.G]

but that they could intiate a submarine slide capable of generating a tsunami.

from: https://www.volcanodiscovery.com/kr...e-portion-of-Anak-Krakatau-appears-to-ha.html

Videos have surfaced that seem to show that at least part of the cone of Anak Krakatau has collapsed.



Cheers,
Tom

 

[davenn]

Thanks for the post Tom, good info

 

[OmCheeto]

The following image popped up in my Twitter feed this morning:

What most caught my eye, was the date: 6 years ago!
So I tracked down the original paper:

Tsunami hazard related to a flank collapse of Anak Krakatau Volcano, Sunda Strait, Indonesia
T. Giachetti, R. Paris, K. Kelfoun and B. Ontowirjo
Geological Society, London, Special Publications, 361, 79-90, 3 January 2012

Abstract
Numerical modelling of a rapid, partial destabilization of Anak Krakatau Volcano (Indonesia) was performed in order to investigate the tsunami triggered by this event.
...
...the maximum wave height recorded off Anyer and Merak is around 1.5 m in our simulation...​

According to one news account; “Actually, the tsunami was not really big, only 1 meter (3.3 feet),” said Prasetya, who has studied Krakatoa. [ref]

It looks as though that was a very good simulation.

This also, from the news article:

A devastating tsunami took Indonesians by surprise because an early warning system – designed to detect changes in wave height in coastal areas near an active volcano – hasn't worked since 2012, government officials said.

The system uses a series of 22 buoys, tidal gauges and seismographs to alert a network of sirens in coastal areas vulnerable to tsunamis. But Sutopo Purwo Nugroho, spokesman for Indonesia's National Board for Disaster Management, said the system has been crippled by vandalism, damage and neglect. ​

Very sad, to think that it was unnecessary for all those people to perish.

 

[Tom.G]

Here are some before/after RADAR images of Anak Krakatau from the Geospatial Information Authority of Japan (GSI).
http://www.gsi.go.jp/cais/topic181225-index-e.html

Quite a difference between the 1st and 3rd images!

Cheers,
Tom

 

[Ophiolite]

Since a substantial volume of the island has slipped and since the failure occurred to the portion identified as at risk, it seems unlikely that further significant tsunamis would be generated in the near future. This assessment does not take account of the consequences of a more powerful eruption on the scale of the 1883 event.

 

[eachus]

Lots more landslide caused tsunamis, including a man-made one at Vajont Dam in Italy in 1963, which killed almost 2000 people, one that many of us watched on TV: Spirit Lake was mostly filled by the (sideways) eruption of Mount St. Helens. The man-made one? . There have been small ice-slide (from glaciers) and landslide tsunamis in Alaska. The one which has caused the most concern was at Lituya Bay, Alaska in 1958. That has led to investigations of potential landslides on volcanic islands in Hawaii, Alaska and elsewhere. There is evidence for megatsunamis in geologic time, created by these--and also by meteor strikes. (The Chicxulub crater in Yucatán) The Wikipedia article for more detail: https://en.wikipedia.org/wiki/Megatsunami

One thing to be careful about though, there is a huge difference between a scientific debate, and a risk to large numbers of human lives. A case in point is Cumbre Vieja Volcano on La Palma in the Canary Islands. Could a major landslide there cause a megatsunami which would reach most of the US East Coast? Sure, but extremely unlikely anytime soon. Could a much smaller tsunami in the Canaries (or elsewhere for that matter) cause a major loss of life, including yours? Much, much higher probability. As long as the monitoring equipment stays in good condition, and you know what to do in a tsunami, the risk is small.

Since it can't be said often enough, if you are near the ocean, or any large body of water, and the water level starts to drop significantly, start walking up the beach, or uphill, whichever applies. (If you have young children? Teach them. Yell once to get their attention, but if they don't follow you, don't you follow them toward the ocean. They might be lucky, and figure out that you are not kidding, or they might have a floatation device.) If you are in a car, you will have to work out the right thing to do, minute by minute. Heading downhill, or sitting in traffic are very poor choices. After the tsunami, you can provide first aid, and do other good things. But while the disaster is unfolding the most you can hope to do is help yourself and/or get out of others way. (Am I a nasty person? No! Voting with your feet, and possibly with a gesture or one or two word yell, will save more lives than anything else you could be doing. If you can carry someone, or help support them? Go ahead. But you certainly don't want to be walking--or running--the wrong way on the beach and blocking others. Later there may be opportunities for heroics. Don't believe me? Look carefully at the footage of recent tsunamis on the web if you have a strong enough stomach.)

 

[Nik_2213]

D'you remember footage from a terrace of the Boxing Day Event, when the adults just stood around gaping at the receding ocean until their pre-teen yelled, "TSUNAMI !" ??

He'd seen a documentary in school, his quick wits may have saved many of the people within ear-shot at ground level...

 

[Borg]

CNN has a clearer set of before and after images in this article - Satellite images show extent of Indonesian volcano's collapse.

 

[Nik_2213]

Yikes.
Apart from some surviving 'twiddles' at upper left, you'd doubt it was the same island...

 

[davenn]

CNN has a clearer set of before and after images in this article - Satellite images show extent of Indonesian volcano's collapse.

View attachment 236722

thanks for that
I am pleased you posted the images because when I visit that link, those images are not there ... tho they are spoken of

 

[Astronuc]

CNN has a clearer set of before and after images in this article - Satellite images show extent of Indonesian volcano's collapse.

I think North is to the top of the images.

I was looking for maps of the damaged areas, and I'm not currently finding a lot of details, but there is this BBC article.
https://www.bbc.com/news/world-asia-46663158

Areas to the NW and SE got hit hard, from what I gather from limited reports. However, it appears in the images Borg posted, that the landslide and cone collapse or explosion was on the W side of the island. I would think that nearby Sertung Island would have provided some protection to the coastlines of Sumatra, and the larger Krakatau Island to the SE would have protected the Java coastline near Pandeglang, but that doesn't seem to be the case. This is puzzling.

I was looking at GoogleMaps to try to understand how the tsunami(s) were generated.
https://www.google.com/maps/place/A...e9ed2ab4cb9d00!8m2!3d-6.0992786!4d105.4214515

It seems to me that Anak Krakatau was not instrumented such that there was no definitive warning/alert that the volcano was erupting and part of the island collapsing.Edit/Update: Back in October, 2018