Spectacular aerial video of Anak Krakatoa now with crater lake
- The crater area has closed to become a lake which showed steaming (no explosions have been recorded since yesterday, as the activity has continued to calm down, perhaps only temporarily).
- The forest on the island is completely destroyed by ash fall and surges, but still visible.
Rakata Island (Krakatoa): beach destroyed by tsunami waves
The entire beach and the slightly higher, up to 50 m wide forested platform behind it, separating it from the cliff, have been washed away and/or collapsed in landslides following the receding wave.
Surviving fishermen who were in the caldera at the time of the event reported seeing massive waves sweeping over the entire, lower island of Sertung (west of Anak Krakatau), estimating them to be about 25 m in height.
Video was taken by a friend and local guide Black from Carita who also confirmed that the forest and beach of Anak Krakatau are gone as well...
Reconstruction of recent events: collapse, tsunami and regrowth of the Anak Krakatau island
Comparing the morphology of the island as seen on the pictures, a plausible reconstruction of events would be as follows:
22 Dec: part of the lava flow terrace that forms the western shores of Anak Krakatau collapse, probably involving a significant underwater volume. This caused the tsunami that hit the Java west coast around 21:30 local time.
23-24 Dec: additional collapses (but involving much less volume each) in combination with violent explosions remove more material from the island, eating away until the whole summit cone is gone (3rd picture).
25 Dec: heavy and very wet water-lava explosions deposit meters of fresh, wet ash and blocks all over the island, along with sea current that wash the muddy material to shores. This way, the crescent-shaped island seen on the 27 Dec (and later) pictures with the open crater bay is formed. Significant land addition has extended the island's eastern shores (compare the satellite overlay image posted earlier).
Radial erosion gullies formed quickly as result of torrents of water carving down the loose material now covering the island. This water is both from a) heavy rains as well as b) ejected liquid and b) condensation of steam from the water-rich explosions.
Source: Teka Teki Gunung Anak Krakatau (Dongeng Geologi)
Krakatoa volcano (Sunda Strait, Indonesia): extraordinary footage showing intense explosions of water with lava
Even though it is from 40 km away, it shows the activity in amazing detail. It takes place at the island of Anak Krakatau, hidden from view now behind Panjang island seen in the foreground. The active vent is now under water and lets sea water interact violently with the rising magma: the result is so-called Surtseyan activity, a type of volcanic eruption that takes place in shallow seas or lakes, named after the island of Surtsey which appeared off the southern coast of Iceland and had this activity in 1963.
In this video, very powerful explosions can be seen generating jets of ash, debris, steam and water to several hundred meters ("rooster tails") radially from the explosion point.
In addition, large surges (horizontally expanding hot clouds of steam mixed with ash) can be seen sometimes engulfing the whole island of Panjang, which is hiding the view of Anak Krakatau itself.
Be sure to watch to the end, at times, the explosions tend to be bigger and bigger throughout the video.
The video was generously granted for display here by local resident and videographer Doni Janskulo, who lost most of his equipment during the 22 Dec 2018 tsunami that devastated Java's west coast.
If you want to support him, subscribe to his youtube channel or embed this video.
ССЫЛКИ / ИСТОЧНИКИ:
Krakatoa volcano (Sunda Strait, Indonesia): ash plume reported to 35-40,000 ft altitude
Seismic activity is still relatively low, but has picked up again after a phase of near absence at the end of 2018.
Krakatoa volcano (Sunda Strait, Indonesia): fresh aerial image showing the island's dramatic change in shape
it shows in more detail what the 29 Dec satellite image already confirmed: the island of Anak Krakatau has now the shape of a 270 deg almost closed crescent, with a water-filled crater in the center where once the 330 m tall summit cone stood (which collapsed on 22 Dec causing the tsunami).
Although the image is not detailed enough, it seems (and it would be expected so after the violent phreatomagmatic activity following the collapse) that virtually all of the island has been covered and reshaped, smoothed out by fresh pyroclastic deposits. What if any of its flora and fauna has survived needs to be found out yet by visiting it.
Happy New Year to all!
This processed satellite image from 28 Dec below shows the change in morphology even clearer, but includes a significant land gain after the collapse as well, which seems to have build most of the southern "arm" of the crescent. Most of the new land is probably due to accumulated material (tephra) from the intense sursteyan activity in the days after the landslide, building a new large tuff ring around the crater:
Bukti tsunami akibat flank collapse yang tak terbantahkan (dalam gambar yg lebih jelas) pic.twitter.com/Cspa7mJa87— Daryono BMKG (@DaryonoBMKG) December 30, 2018
ССЫЛКИ / ИСТОЧНИКИ:
Krakatoa volcano (Sunda Strait, Indonesia): new satellite imagery reveal both rapid land loss and growth of Anak Krakatau in detail
It shows that actually not all, but most of the summit cone is now missing as well as significant parts of the western and southern shores previously formed by young lava deltas. On the other side, there has been a significant enlargement of the coast on the eastern shore.
This poses several big questions (we cannot answer at this point):
1) How much of the enlargement of the coast occurred by debris flows from the collapse(s) itself (if any traveled towards the east and not only SW down into the sea); and
2) how much of it might have been added by a) the violent explosive activity during the following days, and/or b) how much of it can be attributed to sea currents washing loose material deposited into the sea back to shore ?
The latter is likely to be significant, as the coasts in the eastern parts of Anak Krakatau are very shallow, and large amounts of mud can be seen floating around Anak Krakatau in the satellit image.
3) Another question is how large was the collapse that actually led to the generation of the tsunami? Was it only one? - did the summit cone collapse in one go, or did several collapses occur? The latter idea might explain that there were two tsunami waves observed, the first being relatively small, the second one following after a few minutes (but not immediately) and much higher.
At the moment, as mentioned, we can not give answers. But at least some of them could be given by doing more research and, first of all, by detailed ground observations. We hope our team on location around our expedition leader Andi will be soon able to visit the island from close and bring us more information.
Brief review of Dec. 28 Sentinel-1 data (@sentinel_hub) for #Anak #Krakatoa #eruption #landslide. Well visible areas of land loss and gain (prior Dec. 22nd eruption/landslide). Question remains how much of the dome loss contributed to #tsunami? pic.twitter.com/HVeQSASowc— CATnews | Andreas M. Schäfer (@CATnewsDE) December 30, 2018
Krakatoa volcano (Sunda Strait, Indonesia): first estimates on the effect of the tsunami-triggering landslide
This trend corresponds to the seismic signals showing a marked decrease since the surge of supply of magma that led to the paroxysm during 21-22 Dec, which accumulated lots of new lava. This in turn might have been "the last straw that breaks the camel's back", i.e. the additional sudden weight on the slopes and/or the shaking induced by the continuous explosions could might have been the final trigger for the landslide to occur.
The Indonesian Center for Volcanology and Geological Disaster Mitigation (PVMBG) published a first official estimate on the effects of the landslide:
- The summit of Anak Krakatau originally 338 meters high is now reduced to only 110 meters, i.e. most of the summit cone has indeed disappeared.
- As a consequence, Anak Krakatau island is no longer visible from the mainland, as the island of Panjang (Long Island) blocks the view from Java's west coast.
- The volume of the collapse is estimated to be between 150-180 million m3, while the remaining volume is currently estimated at between 40-70 million m3.
- For this reason, unless tectonic faults in the area of the Sunda Strait are activated, the risk of other massive landslides and tsunamis is currently deemed to be low.
However, it is likely that the current eruption continues and is only in a phase of low activity currently; if the cyclic pattern of increased supply every few weeks continues, another phase of stronger activity during January would not be surprising.
ССЫЛКИ / ИСТОЧНИКИ:
- Perkembangan Terkini Aktivitas Gunung Anak Krakatau, PVMBG: Tinggi Gunung Tinggal 110 Meter (PVMBG press center)
Krakatoa volcano (Sunda Strait, Indonesia) activity update: Major eruption ends
Krakatoa volcano (Sunda Strait, Indonesia): strong explosive activity continues as sea water meets lava
A video of an overflight earlier today shows powerful steam explosions of this so-called Surtseyan activity, generating dense steam and ash clouds, often ejected as "fingers" of larger ejected rock fragments with training steam behind, as well as billowing surges that shoot horizontally above the water.
Civil Protection (BNPB) raised the alert level of the volcano from Waspada (Level II) to Siaga (Level III) on the Indonesian 1-4 scale and the exclusion zone was extended from 2 to 5 kilometers around the volcano, where people are prohibited from carrying out activities.
Kondisi Gunung Anak Krakatau yang divideokan dari KRI Teluk Cirebon 543 pads 26/12/2018, 16.33 WIB. Erupsi masih berlangsung. Tipe erupsi Gunung Anak Krakatau strombolian yang mengeluarkan abu vulkanik dan lontaran batu pijar terus menerus. Status Waspada (level 2). pic.twitter.com/ESydS9UCTc— Sutopo Purwo Nugroho (@Sutopo_PN) December 26, 2018
Seismic activity from the volcano has been lower following the paroxysm on 21-22 Dec, following the pattern of phases of increased activity roughly every 3-4 weeks, suggesting that magma supply to the vent is currently reduced.
ССЫЛКИ / ИСТОЧНИКИ:
- STATUS GUNUNG ANAK KRAKATAU DINAIKKAN SIAGA (LEVEL III), RADIUS BERBAHAYA DIPERLUAS MENJADI 5 KM (BNPB)
Krakatoa volcano (Sunda Strait, Indonesia): scientists had explained and warned about the tsunami risk 6 years earlier - prediction came true
In January 2012, scientist around volcanologist Dr Thomas Giachetti from the University of Oregon published results of numerical modelling simulating a flank collapse and associated tsunami at Anak Krakatau island and warned about the devastating effects it would have on nearby coasts:
In their paper adequately called "Tsunami hazard related to a flank collapse of Anak Krakatau Volcano, Sunda Strait, Indonesia", they "numerically simulate a sudden southwestwards destabilization of a large part of the Anak Krakatau Volcano, and the subsequent tsunami formation and propagation."
Anak Krakatau island - the intra-caldera complex called "Child of Krakatau" - has been growing rapidly growing since it first breached the surface of the sea in 1928. Since then, in less than 100 years, it built an overlapping cone during several eruptions, the latest being the one that started May 2018 and still continues. What makes the island particularly prone to gravitational flank failure is that it has been constructed close and above a steep submarine slope, the NE margin of the caldera basin left by the massive 1883 eruption.
As a consequence of this underwater topography, combined with strong sea currents, the western slope of Anak Krakatau has developed to be much steeper than the eastern. Giachetti et al. observed that as the volcano continues to grow towards the SW (which it had done particularly well visible during the recent eruption, s. attached image comparing 2007 and 2018), "landslides along its southwestern ﬂank cannot be excluded. Such a landslide would be directed southwestwards into the 1883 caldera and would trigger waves that would propagate into the Sunda Strait, possibly affecting the Indonesian coasts".
The modeled waive heights in various location correspond amazingly well with what had been observed. At Anyer, for example, waves of up to 1.5 meters would arrive in 38 minutes. Inside the caldera, neighboring islands such as Rakata or Sertung would be hit by waves 15-30 meters in height in less than a minute after the event.
Since the local tsunami warning systems in place was built only with earthquakes as trigger in mind, no warning could be given to the people on the beaches. In addition, the flank collapse occurred at night and the resulting large ash plume (which eventually reached about 15 km altitude), and violent steam explosions as result of sudden interaction of water with magma and hot rocks could not be seen by people. When the tsunami waves arrived they caught everyone by surprise.
It should be noted that the report was written 6 years ago. Since then, the new eruption, everything described in there had even become more true: compared to the situation described in 2012, the cone of Anak Krakatau had significantly been enlarged to the SW and grown in height by estimated 30%.
Change in activity style
The eruption style changed drastically right after the landslide occurred, as it exposed the conduit and the rising magma to the water. As it no longer erupted from the now-gone summit crater, but at or below sea level in the new scar left by the landscape (which can be seen in the video below), violent steam explosions were the result. As seawater interacted with hot exposed rocks and the magma continuing to rise in the conduit, these so-called phreatomagmatic explosions ejected dense jets of steam, debris and ash, and produced a very large plume. Small surges of overheated steam can be seen traveling over the water as well, in the video by Adam Sidiq/Kumparan published on youtube:
As of now, it appears that the activity at the volcano itself has calmed down again, following the pattern since June of phases of increased magma supply occurring rhythmically about once every 4 weeks, followed by quieter phases.
ССЫЛКИ / ИСТОЧНИКИ:
- T. Giachetti, R. Paris, K. Kelfoun and B. Ontowirjo (2012) "Tsunami hazard related to a ﬂank collapse of Anak Krakatau Volcano, Sunda Strait, Indonesia"
Victim count continues to rise
At least 882 homes and 73 hotels were damaged or destroyed.
Example of a (small) lateral blast from Krakatoa:
Something like this might have occurred on Saturday, leading to the partial collapse of the cone.
What caused the tsunami?
- a slide simply caused by the weight of rapidly accumulated new lava material on the flanks, both above and below water
- a sudden lateral blast caused by an explosion as magma rising could not be released quickly enough from the established summit vent.
It is also unclear how much of the island disappeared by the initial event and how much crumbled away during the following erosion by eruption and adjustments by gravity.
A sketch published on twitter illustrated the version implying a larger lateral blast:
This picture explains how the Indonesia volcanic tsunami was generated. Many volcanic eruptions cannot generate tsunami. The Krakatoa volcanic mass should have been very large; probably a volume of a few kilometers cubed #IndonesiaTsunami #Krakatoa #Tsunami #Indonesia pic.twitter.com/lQCx3yrAgg— Dr Mohammad Heidarzadeh (@Mo_Heidarzadeh) December 23, 2018
A smaller version - without flank collapse, fortunately (or the video and people involved would not exist any more) - was filmed in Oct by Ronny, one of our participants on the Krakatau Volcano Special tour: (you have to watch carefully where the eruption starts):
Call for donations for victims
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Large part of Anak Krakatau has collapsed into the sea - reconstruction of the eruption
An overflight of was undertaken today by the Kumparan agency and revealed continuous, violent phreatomagmatic explosions, i.e. driven by lava and water interaction.
The combined information allows a rough reconstruction of the events:
#1 A new surge of magma arrives in the upper conduit of Anak Krakatau from around 20-21 Dec, causing increasing explosive and effusive activity - strombolian explosions or lava fountains, and lava flow emission - from the summit vent. It looked more or less like this:
(video from a similar paroxysm in Sep 2018)
A photo submitted by a visitor, taken on 22 Dec at 11:15 shows the advancing lava front close to the southern shore and strong strombolian explosions, which occurred at intervals of 15-30 seconds according to the report. This activity probably reached its peak on the evening of 22 Dec, when it was clearly visible by naked eye from more than 40 km away on the coast.
#2 In the evening of 22 Dec, lava fountains fed flows that reached the sea, probably on the south or southeast shores of Anak Krakatau, in similar locations as during previous episodes this year.
#3 Around 21:00 local time, the weight of rapidly accumulated lava on the subaerial and submerged cone of Anak Krakatau triggered an instability and a larger landslide removed a part of the southwestern cone - a flank collapse occurred. This rapid displacement caused the (small, but devastating) tsunami which reached the Java coast around 21:30 (local time).
#4 As a consequence, sea water gained access to large masses of hot rocks and possibly the conduit itself, triggering an ongoing series of steam explosions that produced the steam and ash plume first observed later this morning on satellite data and seen in this video:
Erosion of material from the ongoing explosive activity and along the new shoreline continues to eat away parts of the island.
What will come next?
This is difficult to say, but at least to a large extent it will depend on how much magma continues to rise, whether new collapses occur and so on. A possibility of even larger explosions, pyroclastic flows, tsunamis is clearly increased.
The alert level of the volcano was raised to red.
At least 222 people dead
Media worldwide was unaware of disaster for 8 hours
On a side note, it is quite strange to see that it took international media about 8-9 (!) hours before they became aware of this major disaster. The tsunami occurred around 21:30 local time (14:30 GMT), but it was only about 8 hours later, on the next morning (local time) or late evening GMT time that Øystein Lund Andersen posted his eyewitness report, which we picked up first and only then it spread quickly around the world to all channels.
Death toll continues to rise
Krakatoa volcano (Sunda Strait, Indonesia): possible major eruption with ash to 55,000 ft following deadly tsunami
Whether it is is from the eruption still needs to be confirmed, but seems rather likely. What role the yesterday's deadly tsunami plays here is also still unknown, but they are hardly unrelated.
In the meanwhile, more material is emerging on social channels about the tsunami, such as this dramatic video, showing the arrival of the first wave, destroying a band and its audience playing a concert (at the end of the video):
Krakatoa volcano (Sunda Strait, Indonesia): strong eruptive phase, tsunami hits West Coast of Java
According to the latest information, 43 people died, 584 were injured and two persons are still missing persons from last evening's tsunami on Java's west coast. In addition, 430 houses and 9 hotels were heavily damaged according to information from PNBG.
The current eruptive phase of the volcano seems to be in fact rather strong. A new lava flow is reaching the sea and strong explosive activity, likely pulsating lava fountains are occurring at the summit vent.
Our friend Øystein Lund Andersen reported that a small tsunami, possibly caused by stronger explosions from the volcano, hit the west coast of Java near Anyer, where we was on the evening of 22 Dec observing the volcano. A first wave traveled 15-20 m inland and was followed by another (stronger) one that invaded the street and buildings near the coast. According to his report, it drowned cars, injured and possibly killed an unknown number of people. However, not much other news have reported a major incident, so it might have been not as severe as reported, fortunately.
UPDATE: another possibility is that the waves were unusually strong spring tide waves; there is no official confirmation for a tsunami to have occurred (yet).
2nd UPDATE: more news is slowly emerging. Unfortunately, it seems that indeed the waves were a tsunami and caused at least 20 fatalities, according to BCC, referring to Indonesian governmental sources.
Indonesia's Civil Protection Agency (BNPG) has officially announced that a tsunami has occurred and hit several coastal areas in the Sunda Strait, including on the coast in Pandeglang, Serang, and South Lampung Regencies. The tsunami occurred on 12/22/2018 around 9:27 p.m. WIB.
According to them, the tsunami was not caused by earthquakes (as no tectonic activity was detected), but most likely by an underwater landslide of accumulated sediments giving way. Whether it was caused by the eruption of Krakatoa and where exactly is still unclear. Its size also may have been increased by the influence of the full moon spring tide.
The Geological Agency detected that the start of the current paroxysm of the volcano began at 21:03 WIB local time. It damaged the local seismic station (probably it was hit by lava bombs).
The full impact of the tsunami is still unclear, but preliminary data indicate 20 people died and 165 people were injured; 2 people were missing and dozens of buildings were damaged. Unfortunately, the number of victims is likely to continue to grow considering that it is still night in Indonesia and not all areas have been investigated.
People are encouraged to remain calm and avoid the coast of the Sunda Strait for a while. BMKG and the Geology Agency are still conducting further research.
Below is Øystein's original post:
ССЫЛКИ / ИСТОЧНИКИ:
- Øystein Lund Andersen on facebook
- Benar, Tsunami Menerjang Pantai di Selat Sunda (BNPG on facebook)
Krakatoa volcano (Sunda Strait, Indonesia): increased activity, likely new phase of lava fountains and lava flow
Seismicity at Anak Krakatau has sharply increased during the past days and now shows continuous explosive/effusive activity. The observatory informed us that a lava flow is occurring from the summit vent, likely accompanied by lava fountaining, similar to what we observed in Sep and Nov during our latest expeditions to Krakatau.
This is what it probably looks like now:
(eruption in Sep, daytime)
(Nov eruption, evening)