Surprise Tsunami Hits Indonesia, Killing Hundreds

By Erik Klemetti | December 23, 2018 8:01 am
Destruction from the December 23, 2018 tsunami in the Sunda Strait, Indonesia. BNPB.

Destruction from the December 23, 2018 tsunami in the Sunda Strait, Indonesia. BNPB.

For the second time this year, an unexpected tsunami hit the coast of Indonesia resulting in hundreds of deaths. This tsunami may have been generated by an eruption of Anak Krakatau in the Sunda Strait, with Indonesian officials speculating that an eruption that occurred late last night may have triggered undersea landslides. So far, at least 220 people are known to have died , over 800 were injured and multitudes are missing. Many of the deaths were in Pandelang, located at the end of bays that could have amplified the height of the waves. The tsunami waves were as high as 3 meters. You can see some of the destruction from these waves in the video and images below. UPDATE: The death toll is now over 400 and local authorities are asking people to stay off the beaches until midweek.

Whatever happened at Anak Krakatau to cause the tsunami, it appears that the volcano has experienced a major eruption as well. The Darwin VAAC report for the volcano indicate ash reaching as high as 17 kilometers (55,000 feet). The Himawari-8 weather satellite caught the plume from the eruption — you can see it in the false color loop:

UPDATE: Here’s another GIF showing last night’s eruptive plume from Anak Krakatau:

There are unconfirmed reports that the tsunami was generated by more than half of the existing Anak Krakatau cone collapsing into the sea. No significant earthquakes were recorded in the area last night, so the eruption of Anak Krakatau may be the likeliest source of the tsunami. There are some video that claim to be from after the eruption showing that does look like a dissected cone for the volcano:

UPDATE: Here’s another video from today of Anak Krakatau showing the strong “rooster tail” plumes being produced by magma interacting with seawater. It really does look like the island has changed significantly:

UPDATE: These images from Sentinel-1 show evidence of a collapse of Anak Krakatau along with potential waves generated by the collapse:

UPDATE: Apparently, this exact scenario was hypothesized in a 2012 paper by Giachetti and others. Hat tip to Jonathan Amos for that find.

UPDATE: Apparently the current eruption of Anak Krakatau has produced more volcanic lightning than possibly any eruption observed. Over 30,000 strikes since the eruption 2 days ago:

Sector collapse is one of the major ways that volcanic eruptions can produce tsunamis. An eruption of Unzen in 1792 caused part of the volcano to collapse into the sea, killing over 15,000. Krakatau, the volcano that preceded Anak Krakatau, famously produced a massive eruption and tsunami in 1883. Unlike this event, the 1883 tsunami that killed 36,000 was produced by a caldera collapse, where the entire volcano collapsed into itself forming a bowl that was filled by the sea (below). Anak Krakatau has been built over the past 125 years within that 1883 caldera.

Sentinel-2 image of Anak Krakatau erupting in September 2018. The three outer islands outline the shape of Krakatau prior to the 1883 eruption. NASA Earth Observatory.

Sentinel-2 image of Anak Krakatau erupting in September 2018. The three outer islands outline the shape of Krakatau prior to the 1883 eruption. NASA Earth Observatory.

As Simon Carn speculates, part of the volcano has grown rapidly over this year and Anak Krakatau has had an active fall, with frequent strombolian eruptions and lava flows – see the images above taken in September. One scenario [SPECULATION] is that a collapse of part of the volcano would allow seawater to interact with the erupting magma, causing the explosive eruption seen last night [SPECULATION] UPDATE: Simon Carn sees characteristics in the eruption that suggest a lot of magma and seawater interaction. Whatever the case, it may be a while before the full reason how the tsunami was generated.

You can watch some of the eruptions going on at Anak Krakatau only a few hours before the tsunami hit, taken by Øystein L. Andersen.

Øystein and his family escaped the tsunami (just barely) and he’s been updating with images of the aftermath of the tsunami.

I’ll add more information about this tragedy when possible.

CATEGORIZED UNDER: Rocky Planet, Science, Science Blogs
  • Louis Turi

    “Tsunami kill hundreds in Indonesia” Dr. Turi’s unarguable UFO’s predictive Legacy Christmas days SOS to the world deadly window warning!

    The dates and more predictions were broadcasted on Dr. J national radio!

    Also on the Church of Babus radio show – Please share, help me save lives!

    • hikingmike

      I won’t click your links, but I will say that whatever UFO/volcano prediction you are talking about is not unarguable, lol.

      • Louis Turi

        May I suggest you to listen to the show and assume later?

        • 7eggert

          I assume that each youtuber randomly predicts three quakes in one year, we will see at least one true prophet.

  • Chris DeVries

    Yeah, you wouldn’t get Surtseyan activity like that without good reason – Anak Krakatau hasn’t seen activity like that for a long long time (since it became a subaerial volcano). Clearly enough of the mountain has fallen apart that the magma is now directly interacting with seawater again.

    I am saddened by the deaths here, but also really curious as to what happens next. Does the rest of the volcano collapse in a sort of total sector collapse achieved piecemeal? Or is the remnant of the island basically stable, and will the new land that builds around and on top of it be an unstable addition that causes tsunami decades hence? Sector collapse is a super rare thing to see at a volcano – before Mt. St. Helens in 1980, it was a very poorly-understood process, and honestly, ONE example of it being witnessed by scientists with pretty modern equipment (and a modern understanding of geology) could have led to people drawing conclusions that won’t bear out as strongly as the sample size is increased (while scientists have studied sector collapses in the geological record to gain an increased understanding of the process, there is no substitute for actually capturing realtime data on a geological phenonemon as it is happening if you are trying to understand that phenomenon). Two fatal tsunami caused by the same volcano within less than 150 years could be a fluke, or it could be the uniformitarian reality at Krakatau. Tsunami could just be pretty frequent events (geologically-speaking) at this volcano…and wouldn’t that be a scary situation for the tens of millions of people who live in Java and Sumatra these days!

    • 7eggert

      Krakatau and Anak Krakatau and Anak Anak Krakatau – the danger will not stop in foreseeable future. It’s like a “surprise” you get while playing Russian Roulette.

  • 7eggert

    I’m currently watching a report. If they had watched for water retreating from the shores, they could have warned the people.

    • Chris DeVries

      Reports from Indonesia have already come in saying that seawater did NOT recede in the way it does with seismogenic tsunami. And I think the reason it didn’t has to do with the shorter wavelength of the waves due to the way the tsunami was created. “Normal” tsunami waves contain massive amounts of energy, derived from the large-scale and rapid deformation of the seafloor. Hundreds (sometimes thousands) of square kilometers of seafloor rises up all at the same time (over a period of a minute maybe), sometimes by 10 or 20 metres. This generates waves whose wavelengths (twice the distance between peak and trough) can be measured in hundreds of kilometers, and whose speeds are at least 100 kph. The receding water, as the wave trough hits land, can give people several minutes warning. But in this case, shorter wavelength (from a large volume of rock sliding a short distance underwater) meant that if water did recede, it would recede a shorter distance, and come back much more quickly. Also, sea floor geometry significantly impacts how a tsunami wave manifests itself on land – if there is a steep dropoff as you go offshore, the trough of the wave hitting may not produce an anomalous retreat of water (to the human eye).

      • 7eggert

        The interview I watched was with a man who fled to high ground because the water did not stop retreating from the shore.

  • OWilson

    One recurring theme to these tsunamis and indeed to all floods, is just how vulnerable are low lying coastal lands, as illustrated in the two photos of devastation.

    Undersea earthquakes, volcanoes, even an occasional asteroid (not to mention hurricanes) can wreak havoc at any time om these areas, with little warning.

    It points up how precious a location is high ground, as they always say in real estate, location, location, location!

    (As long as the high ground is not on a dormant volcano!)


Rocky Planet

Rocky Planet covers all the geologic events that made and will continue to shape our planet. From volcanoes to earthquakes to gold to oceans to other solar systems, I discuss what is intriguing and illuminating about the rocks beneath our feet and above our heads. Ever wonder what volcanoes are erupting? How tsunamis form and where? What rocks can tell us about ancient environments? How the Earth might change in the future? You'll find these answers and more on Rocky Planet.

See More


Discover's Newsletter

Sign up to get the latest science news delivered weekly right to your inbox!

Collapse bottom bar