Anak Krakatau: Indonesian volcano's dramatic collapse

BBC News ^ | 29 DEC 2018 | Jonathan Amos

[E. Pluribus Unum]

The scale of the dramatic collapse of the Indonesian volcano that led to last Saturday's devastating tsunami in the Sunda Strait is becoming clear.

Researchers have examined satellite images of Anak Krakatau to calculate the amount of rock and ash that sheared off into the sea.

They say the volcano has lost more than two-thirds of its height and volume during the past week.

Much of this missing mass could have slid into the sea in one movement.

It would certainly explain the displacement of water and the generation of waves up to 5m high that then inundated the nearby coastlines of Java and Sumatra.

ndonesia's disaster agency says more than 400 people are confirmed dead with 20 or so still missing. In excess of 40,000 have been displaced.

[Bobibutu]

I went thru in ‘73 on a geo/exploration survey boat. The waters approaching were about 60 feet deep. Then plunge suddenly to over 300 feet as we steamed thru the old volcanao caldera area betwen the 3 outer surviving isles.
There was one small coconut tree that had sprouted on the solid black beach of Anak K. The new cone was only about 100” high then. Solid black from the beach to the lightly smoldering top.

[Zhang Fei]

[I went thru in ‘73 on a geo/exploration survey boat.]

---

Did you strike oil? If I recall correctly, that was the theme of the late 1970’s King Kong movie with Jeff Bridges and Jessica Lange.

[Bobibutu]

“Did you strike oil?”

Exploration searches for locations that have high potential for possible oil.

All the data collected during exploration went back to Houston. They analyse and if warranted, comission a “Discovery” well to be drilled.

If that turns out potentially profitable (determined by the well flow rate) 10,000 bbl/day was a good well and “Developmental” drilling additional production wells if warranted.

It’s a lenghtly process.

I was primarily “exploration” centered but positioned a number of on-shore & off-shore rigs for discovery drilling from Sumatra to Irian Jaya. Lots of time in the Flores Sea back then - a hot spot for oil production at the time.

Lots of WWII aircraft, vehicles and other (mostly Japaneese) equipment in the open and hidden in the jungle.

Fun.

[Crucial]

More than man has in a hundred years probably.

[Paul R.]

Interesting comparative table, here:

https://en.wikipedia.org/wiki/Mount_Tambora

(scroll down)

Krakatau’s VEI was 6, however, it’s ash column went up to an astonishing 80 km. Tambora was “only” 43 km. Also, it appears Krakatau was heard much further away.

https://en.wikipedia.org/wiki/1883_eruption_of_Krakatoa

Reading further, I found that duration of the explosion is a factor in determining VEI.

https://en.wikipedia.org/wiki/Volcanic_Explosivity_Index

My guess is that the peak intensity of the explosions at Krakatau was higher than at Tambora, but Tambora’s bursts were more sustained, ejecting more material in total.

[Paul R.]

My, my. I thought I was just about the only FReeper who recalled that Mighty Mouse episode.

Oh, golly, I remember that too!!! (Ok, it was already an "old" cartoon by the time I saw it.)

I was small for my age and would fantasize I was another sort of "Mighty Mouse". Here I come, to save the day! Heheh.

I seem to recall another, longer(?) cartoon about "Krakatoa" that included the tsunami, but I can't find it ...?

[Paul R.]

The Mighty Mouse cartoon:

https://www.youtube.com/watch?v=iVMQcPAKfGk

[crz]

Interesting. I just watched a lecture on the Cascadia fault. Did you know that every 500 years, on average, the Juan DeFuca plate does its thing and the last time it popped was in 1700? That leaves us with another couple hundred years before the next big one is due right? BUT, here is the ticker. The southern part-from southern Ore to its end at N CA has slipped every 2 to 3 hundred years. BTW. It slips and the coast will move over 150 feet to the west while dropping some 30 feet. Portland, will move over 6 feet to the west and drop some 4 to 5 feet. EAST of the Cascades, the land will shift 1 to 3 feet and drop a few inches. That fault effects everything to Idaho. They know for a fact that The northwest area of the northwest rotates counter clockwise to the north east for 14 months, then stop and actually slides back to the southeast for a fraction of an inch. Then it continues its 3/4 inch or so travel to the Northeast-and the whole N American plate is moving to the southwesterly direction. They think that the fault is slipping under the land mass and not in the ocean and the discussion is..when does it trigger the big one?
What does this have to do with volcanoes? Well, those volcanoes are connected to that fault and have not erupted in a long while-other than Mount St Helens. They have measured Mnt Hood for example, and it is moving, as are the rest.

My question to that Professor would have been. When the vent system lines up correctly, do they erupt? No doubt those volcanoes vent system might be out of line because of the land mass movements? When I say vent systems I mean weaker down areas from the Peaks where the rock is easily fractured to allow magma to come up. He might answer that if that were the case then there would be a new appearance of a vent someplace else, but, do they know that the rock aside from the original vent systems might be harder and all.

[crz]

BTW again..the 1883 eruption of Krakatowa-thats how they spelled it by some back then. Was the most studied of any by that time. The Brits really did a hell of a fine job with that.

Krakatau studies by the Brits is truly the father of modern volcanism studies.

The last big eruption of the Long Valley volcano erupted over 100 cubic miles. It is now listed at the USGS as a very high risk of exploding. But, since that eruption there have been many smaller eruptions there. Same with Yellowstone.

Point is..even if they do blow, it most likely will be a VEI 5 or 6 and not the massive blast from the past. Depends on how many vents are opened up.

[Paul R.]

Given that Anak Krakatau seems to be ratcheting up, I also am linking to a very sobering documentary:

https://www.youtube.com/watch?v=MrEIT66oPqU

[Paul R.]

Interesting and also terrifying stuff... And good questions of yours, BTW. :-)

I went and compared those slip values you cited to those of the 2004 Indian Ocean earthquake.

https://en.wikipedia.org/wiki/2004_Indian_Ocean_earthquake_and_tsunami

150 feet of slip with a 30 ft. drop is a LOT. Any guess as to the length of the rupture?

[fieldmarshaldj]

*ping*

[SunkenCiv]

Thanks f. "Krakatoa: East of Java" was (it sez here) nominated for Best Visual Effects (Oscar) -- which makes sense, but the title s/b "West of Java" or even "North by Northwest of Java".

krakatoa keyword (lots of recent topics)

Krakatoa - The Great Volcanic Eruption

[SunkenCiv]

https://www.google.com/maps/place/Krakatoa/@-6.1021171,105.4054777,7355m/data=!3m2!1e3!4b1!4m5!3m4!1s0x2e415e18b8f2e3ff:0x9e495f8e33b912dc!8m2!3d-6.1021175!4d105.4229873

[fieldmarshaldj]

I never realized it was that close to Jakarta. Not the place I’d have wanted to be when the old Krakatoa went boom.

[crz]

That was a comparable to the Japan earthquake. Along the entire length.

I guess some geologist did that to see what might happen along the entire area.

The most aggressive stress point of that fault, cascadian, is 50 miles inland from the coast.

They simply do not know yet what will happen because of the ground deformation up there. They can only guess and use computer models to get an idea. So..their prediction of anything east of the Cascades being toast I would imagine is pretty accurate?

There was a vid of volcanologists doing a study in S America on if far off earthquakes can effect volcanoes. They put sound recorders near active vents down there and recorded the normal sounds of the volcano and to see if there was any change from a earthquake. There was a massive BANG when an earthquake happened and the normal sounds of the volcanic system changed for quite a long time.

So as you know, there are quite a lot of volcanoes-heck the whole Cascade range is volcanoes.

I wish I would've went to school for geology.

[Zhang Fei]

[I was primarily “exploration” centered but positioned a number of on-shore & off-shore rigs for discovery drilling from Sumatra to Irian Jaya. Lots of time in the Flores Sea back then - a hot spot for oil production at the time.

Lots of WWII aircraft, vehicles and other (mostly Japaneese) equipment in the open and hidden in the jungle.

Fun.]

---

Good times. Did you stay local for R&R or did you rotate back stateside?

[Bobibutu]

I was sponsored by MACV when in-country. (civillian contractor).

When I left Nam I started picking up private contracts with Pertamina (Indonesian Oil Co.) & Shell mostly. Some with Satellite Positioning Corp. out of Houston and Western Geophysical.

R&R was defined by the Co. I worked for in Nam. Very different from what the troops options were. My peers and I got to see a lot of the world while winding down between stints in-country.