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.
Jumlah korban dan kerusakan akibat tsunami di Selat Sunda per 23/12/2018 pukul 16.00 WIB tercatat 222 orang meninggal dunia, 843 orang luka-luka & 28 orang hilang. Kerusakan fisik: 556 unit rumah rusak, 9 unit hotel rusak berat, 60 warung kuliner rusak, 350 kapal-perahu rusak. pic.twitter.com/7esz00fnD7
— Sutopo Purwo Nugroho (@Sutopo_PN) December 23, 2018
At least 222 dead people died and another 800 injured on Sumatra and Java islands after a tsunami struck them on Saturday night. It was caused by an undersea landslide resulting from eruption of Anak Krakatau | via https://t.co/rl0mcvAtL8 (Reuter photo) pic.twitter.com/MkNR1VVJbJ
— Palawan Daily News (@palawandaily) December 23, 2018
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:
— Luca Caricchi (@LucaCaricchi) December 23, 2018
UPDATE: Here’s another GIF showing last night’s eruptive plume from Anak Krakatau:
— Dan Lindsey (@DanLindsey77) December 23, 2018
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:
Mt. Krakatoa Eruption, one hour ago. Credit to Capt. Mykola from Susi Air#PrayForBanten#prayforanyer#PrayForLampung#PrayForSelatSunda#prayforindonesia#Krakatau#TsunamiSelatSunda#TsunamiAnyer#tsunamibanten#TsunamiLampungpic.twitter.com/xI2TU1ysBv
— Safiro (@hudasafiro) December 23, 2018
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:
— 🇲🇨MT🔝🆔🇵🇸 (@Maulana_Tigor) December 23, 2018
UPDATE: These images from Sentinel-1 show evidence of a collapse of Anak Krakatau along with potential waves generated by the collapse:
GIF comparison between 12/19 – 12/22 pic.twitter.com/nPOdKcZeh3
— R. Natsuaki (@flyingwktk) December 23, 2018
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:
— Chris Vagasky (@COweatherman) December 24, 2018
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.
Growth of Anak #Krakatau #volcano since May 2018 from @planetlabs imagery. Fairly rapid recent expansion to the south could possibly have caused some flank instability. Still awaiting post-#tsunami imagery to assess any changes. @Sutopo_PN @vulkanologi_mbg @id_magma pic.twitter.com/ETLqo68Awf
— Simon Carn (@simoncarn) December 23, 2018
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.
Just completed a hi-speed video of yesterdays (22th December) eruptive activity at #Krakatau volcano. A new lava-flow can be seen descending to left of the island. Filmed 47km away from it, only a few hours prior to the #tsunami hitting the coast of Java. @id_magma@infoBMKGpic.twitter.com/VQaFU7pVvQ
— Øystein L. Andersen (@OysteinLAnderse) December 23, 2018
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.