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Wow, Anak Krakatau is just gone..

Written By: - Date published: 11:17 am, December 31st, 2018 - 14 comments
Categories: auckland supercity, science - Tags: , , , ,

Just reading an article about what has happened in the volcanic eruption in Indonesia that caused the Dec 22nd tsunami that killed 400+ people and displacement of more than 40,000. From the BBC(my italics):-

Anak Krakatau: Indonesian volcano’s dramatic collapse

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.

I’m now way less surprised at the size of that tsunami. That is a colossal amount of material.

The current loss estimate is that 150-170 million cubic metres of material has just gone, including all of the dome. To give you an idea, there is one man made structure in the world that has a similar volume at 153 million cubic metres. That is (apparently) a earth core irrigation and power project in India called the Nagarjuna sagar project. Which I’d never heard off before looking up large man-made solid volume objects.

You can see the missing mountain in the satellite radar mapping:-

Satellite radar images

Anak Krakatau is a very young volcano within and around the old area of Anak Krakatoa which partially disintegrated in a major eruption in 1883 and caused a global average drop in temperature of about 1.2 C in the following year. Anak Krakatau is driven from the same plume of hot magma that formed the Krakatoa cone, but only broke above the water surface in 1930 and has been growing continuously since.

Because of the depth and enclosed nature of the surrounding waters, largish tsunamis are very likely from such fast growing volcanoes.

But I wouldn’t get too complacent in NZ. The large hole that is Lake Taupo is one of the world’s most dangerous volcanoes. The Oruanui eruption around 26,200 years ago is the largest known eruption in the last 70,000 years. The more recent Hatepe eruption about 1800 years ago ejected 30 km, about 150 times the current Anak Krakatau eruption, in minutes. It was the most violent eruption world wide in the last 5,000 years.

On that cheery note, I leave you to the New Years celebrations. I’m having mine in the kiwi city that contains at least the 53 recent basaltic volcanoes of (currently) dormant Auckland volcanic field. To someone trained in earth sciences, this is one of the safest places in New Zealand.

14 comments on “Wow, Anak Krakatau is just gone.. ”

  1. fender 1

    There is a God, it’s Mother Nature.

    Totally unrelated but this presentation on the Milky Way with accompanying graphic renderings is one fascinating watch.

  2. Andre 2

    I’ve got family roots in the Mt St Helens area and been there before and after, so that eruption and mountain collapse is kinda my benchmark.

    Just in case anyone else is familiar with that. for a sense of scale the Mt St Helens debris avalanche is estimated at 2900 million m^3, a bit less 20 times bigger volume, so about 2 1/2 times bigger in 3 linear dimensions.

    So yeah, I can see why Anak Krakatau made a helluva splash.

  3. Massive, and ominous just because it happens.

  4. indiana 4

    All previous climate change models targets may be meaningless.

    • lprent 4.1

      Ah we have a simpleton in the house. Someone who fails to understand some really basic statistics.

      Indiana: please contemplate that

      1: weather is not climate.
      2: that a single volcanic event is to the earth what a storm is to weather
      3: that volcanoes are just statistical noise compared to the continuous stream of greenhouse gases released from fossil sources by humans.

      Also be a simpleton on OpenMike. I don’t appreciate trolling for effect on my posts.

      Or if you prefer the less refined response.. Fuck off you arselicker of Trump ignorance or I will see how funny you find my responses to your trolling.

      • DJ Ward 4.1.1

        Your point 2.
        The vast majority of the time your comment is correct. Pinatubo is a good example of a measurable effect over a short duration. Similar in volume ejected to the volume of oil we use every year. We use gas a well on top of that so it puts in perspective how dangerous our use of fossil fuels is. Pinatubo effects were gone within a few years but mankinds fossil fuel effects pile on top of each other based on volumes and lifespans of the gases.


        Super-volcanos are a different story. Even your No 3 worst case scenarios can’t compete with Toba or Yellowstone events. At least a debate worth looking at in terms of what could happen with man made climate change. Volcanos causing cooling, while man made climate change causes heating which we have no references for, unless we go back to the Dinosaur era.


        • lprent

          Even your No 3 worst case scenarios can’t compete with Toba or Yellowstone events.

          Sure. That would be more than a statistical blip. But:-

          1. Very Rare

          Last Toba eruption was about 75,000ya. The last large Yellowstone one was about 630,000ya.

          The last decent world affecting volcano in the size range you are describing was the Oruanui eruption at Taupo about 26,500ya and that was a relative tiddler – but was the largest in the last 70,000 years.

          Since the total pulse effect of the current human production for the last few centuries is only destined to be measurable over the next 3 thousand years, the probability of a natural event of that order interrupting is slight. And I rather suspect we’d have a different issue if one of them blew off, like the direct loss of life and disruption to distribution systems.

          2. Your analogy with plate subduction volcanoes is somewhat flawed. All volcanoes are not alike in their greenhouse gas effects.

          Subduction volcanoes like Mt St Helens or Pinatubo or for that matter Tongariro have a relatively large amount of carbonates to expel from the melting of recent sediments. But they are localised and of short duration.

          Almost all super-volcanoes that have a rhyolitic magma pool largely formed by the proximity of high heat from the mantle. They get set off by a large intrusion of much higher temperature basaltic magma causing the eruption, and typically get most of their explosive effect from ground water. They don’t appear to have a much greater greenhouse gas emission than subduction volcanoes. They just blow a lot more material out but not that much greenhouse gas (they generally outgas steam).

          3. The real long term climate changers are long life basaltic flows like the Deccan Traps or the older Siberian Traps. But these are low probability for human timescales and require tens of thousands of years to get to the kind of effect that humans have had over the last few centuries.

          It always annoys me when I read sites that breathlessly proclaim the possible greenhouse gas effects of volcanoes while not also looking at the long years between significiant events. Quite simply punctuated events like volcanoes or even super-volcanoes don’t really affect climate over decades. The existing natural systems for sequestration make their effects go to a wisp over decade. Whereas they don’t handle the sustained increases in load that human fossil fuel gurning produces.

          And then they ignore the effects of actual climate change processes like the basaltic traps, which do mimic what humans are currently doing. However they do it a hundreds of times slower.

  5. I climbed Anak Krakatau about 20 years ago. It erupted shortly before we landed by chartered fishing boat. Reasoning that it wouldn’t erupt again straight away we climbed to the cone crater edge. I had the impression the volcano was an island about the size and shape of Rangitoto. It had some sparse forest cover near the shore line similar to Rangitoto.

  6. Jenny - How to get there? 6

    ‘To someone trained in earth sciences, this is one of the safest places in New Zealand.’

    I wouldn’t be anywhere else.

    Give me Auckland over Christchurch or Wellington any day.

    I read somewhere once, that you don’t get the sort of earthquakes that they get in Christchurch, or Wellington. In a volcanic zone, the tectonic energy is being released in a different manner. Sure you get the earth tremors associated with the movement of volcanic plasma underground, but this is usually as a fair warning that something is going to happen. So when it does happen you have had ample to time to pack up and immigrate to a new town or country.

    Happy new year to you Lynn

    • lprent 6.1

      It’s not just the earthquakes.

      Large chunks of Wellington, the Hutt valley, and for that matter Dunedin are just landslides waiting to happen.

      Our settlers also had an interesting propensity to site cities and towns on flood plains. I suppose because most of them came from relatively geologically stable continental areas.

      But in NZ almost all of the hilly areas are inherently unstable, and so are the floodplains that they spread their debris and catchment waters to.

      Auckland doesn’t suffer from catchment rivers and the hill are small. Plus it has two large harbours buffering most of the seashore.

      Pretty safe on top of its numerous basalt cones.. At least for NZ it is

      • Jenny - How to get there? 6.1.1

        And that’s not all, that recommends Auckland, disaster-wise.

        The Great Barrier Island, is well named.
        Both the Great Barrier Island, and the Coromandel Peninsula* form a wall between Auckland and some of the worst cyclonic storms, which usually strike upper New Zealand from the East.

        Tamaki Makaurau is well named.

        *(The Coromandel Peninsula on the North Island of New Zealand extends 85 kilometres north from the western end of the Bay of Plenty, forming a natural barrier to protect the Hauraki Gulf and the Firth of Thames in the west from the Pacific Ocean to the east. )

        Less fortunately, tornados seem to follow a corridor from the North into the heart of the city. (something you may know something of Lynn)

        And with climate change we are likely to see a lot more of both these sorts extreme weather events.

        • lprent

          …tornados seem to follow a corridor from the North into the heart of the city

          Yep. But I’m on the south side of the Ponsonby / K Rd ridge just over the ridge line and perched over the shallower part of Newton Gully. Tornados aren’t that happy climbing ridges and tend to go downhill. So it’d have to pretty much touch down on or just above my place (and these days that mostly means in 3 storey commercial buildings or apartment blocks) to cause my apartment any damage.

          Did I ever mention that I’m kind of hyper-aware about environmental threats.

  7. halfcrown 7

    Thank you Iprent and the other posters. This is one of the reasons I visit this site, I learn something new everyday.

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