In Part 1 and Part II we went over the current state of Krakatau and its history over the 300 years before the Big One. Now it is time to find out what caused the Big Bang, whether it is a recurrent offence, and to try our hand at the big question: why is such an offensive volcano located in the middle of an otherwise volcanically inactive region? Let’s begin at the end.
The ending began on September 1, 1880, when there was a strong earthquake in the Sunda Strait. It was felt far and wide, damaged houses, and destroyed a light house. It happened to be the day after the birth of Wilhelmina, future queen of the Netherlands, and early the following morning after the earthquake the residents of Batavia were shaken -and frightened- again when woken up by cannons being fired in celebration. Over the next three years, there were reports of smaller earthquakes around the Sunda Strait. Whether these quakes were related to the coming eruption is difficult to know. They were almost certainly tectonic and the main one was not caused by Krakatau. But Krakatau lies on the fault where the Sunda earthquakes occur. Physical damage to its plumbing by a large earthquake is not impossible.
A few months before this earthquake, in July 1880 Verbeek had make a quick visit to Krakatau and to the small island of the ‘Polish Hat’, spending only a few hours here. On Long Island he found a light grey lava with small crystals, whilst on Polish Hat there were glassy, greenish-black rocks. The collected rocks were identified as pyroxenic andesite: the rocks on Polish Hat were a dark andesitic obsidian. Analysis showed 72 to 73% of silicic acid, very different from the volcanoes on Java or Sumatra.
After a quiet interlude, small earthquakes were noticed again around the Sunda Strait in May 1883. On May 20, again the people in Batavia were woken up by the booms of cannon fire. But this time, the booms were continuous – and volcanic. The explosions lasted two days. There was much speculation about which volcano was to blame, but no one knew. The towns around the Sunda Strait reported by telegraph that they had heard nothing. It was only when ships that had been in the Sunda Strait reached Batavia, that they reported the source: Krakatau, 150 km from Batavia. Why had the towns around the Sunda Strait, much closer to Krakatau, not heard any explosions? That sounds strange but in fact is normal: the sound waves bend away from the Earth surface, leaving a zone where there is silence. The ships reported black clouds and white ash, and floating pumice. There were no reports from Krakatau itself: the island was not inhabited at the time and was visited only by fishermen who stayed on the coast. No one had noticed any precursor activity.
Traders quickly saw an opportunity to make money. An excursion was organised from Batavia, for a picnic at Krakatau with a view of the spectacle. 86 people paid up and went for the trip of a life time. It could easily have been the last trip of their life time, but they were very lucky. The famous picture of the exploding Krakatau, subsequently coloured by the Royal Society, comes from this trip. The ship left on Saturday after work and arrived after an overnight trip, on Sunday May 27. (Sunday had been chosen deliberately, so people could go without having to miss work.) The ship stayed until Sunday evening, allowing people to explore the eruption site. The island had been stripped of vegetation, apart from the trees on the southern side of Rakata. The tourists found that the eruption came from a crater at Perboewatan. Again, any health-and-safety manager would have vetoed the entire event! But the eruption was seen as a harmless affair, and Krakatau was too far from the main land for anyone to be inconvenienced. It was much like Hawai’ians view Kilauea.
To see how dangerous it really was, I am including the report from Schuurman from this expedition:
“Toward midnight, when we reached Anjer, we saw on the horizon, in the direction of the island of Rakata, a red intermittent glow, from the activity of the volcano. The flare appeared every 5 at 10 minutes, for a few moments only, and from which fell a rain of fire.” […]
“Strange was the appearance of the island, which instead of the lush tropical vegetation, had only arid and bare soil, which raised a smoke like the smoke of a furnace. The peak [Rataka] alone still showed greenery, but the northern slope was buried under a thick layer of grey ash, from which came out here and there a few rare tree trunks stripped of branches and leaves, meagre remnants of the impenetrable forest which only recently had covered the island. Within this dark and desolate landscape, standing out on the sea as a picture of the most complete destruction, stood with a indescribable splendour a powerful column of smoke; several tens of meters wide at its base, this column was expelled with a roar of thunder, rising and swirling, up to a height of 1000 to 1200 meters, then 2 or 3000 meters higher, fading more and more and giving up in the easterly wind, the ash with which it was charged and which, falling in the form of a blackish fog, constituted the covering of the ground.”
“[…] Although rising without interruption, she was, every 5 to 10 minutes, considerably widened at the bottom by emitted smoke clouds, which were exceptionally powerful, and announced by a terrible noise; during these periodic eruptions, the dark-coloured smoke was expelled more quickly than usual, and dropped, at the height of about 200 meters, a shower of stones, which, viewed from the ship, seemed like black shadows moving in the air. Those dark clouds of smoke, even during the day, sometimes presented a reddish glow; at night they took the appearance of red flames, while the rain of stones, so hardly visible by day, changed into a rain of fire: phenomena that must be explained by the reflection, on the clouds of smoke, of ignition materials contained in the crater, and by the incandescent state of the ejected stones.”
“Along the north coast of the island, which in places is rocky and steep, we landed at a point where the coast came down to a wide beach. […] On the white sand, which constituted the proper beach, rested a bench of pumice stone a foot thick, and on these pumice had fallen the ashes, forming a 2-foot layer. […] The ash, which seemed soft, had actually packed enough to carry us; by putting the foot on it, we recognized that it only sank to the ankle, and therefore any objection to an excursion inside the island was overcome. Following the trail of the most courageous, perhaps also the most stunned, we climbed the bare mounds, which presented no obstacle other than the ash, yielding under our feet. The route followed went first to a hill, where one still saw, emerging from the ashes, some parts of trees, stripped, broken, a few meters high and showing undeniably that the branches had been violently torn. The wood was desiccated, but there was no indication for burning or charring; in addition, in the volcanic ash there were no leaves or barbs, so the deforestation must probably be attributed to a whirl of wind, such as occurs frequently during volcanic eruptions within atmospheric layers disturbed in their equilibrium by local and excessive heating.”
“Soon all traces of vegetation disappeared, and the ascent was continued among the dark mounds of ash that hid the sea from our eyes, without being able to hide the column of smoke, still growling and roaring. Finally, the last hill climbed, We stood on the steep edge of the eastern wall of the crater. Hollowed out from the ashes, a beautiful cavity was seen in a basin shape, with a diameter of about 1000 meters, whose circular bottom, located 40 meters lower and 150 to 250 meters wide, had sunk a few meters and was covered with a black crust, a little shiny. Through this crust, but only in a circle 50 meters across and touching the opposite edge of the crater, emerges, with a terrible crash, the powerful column of smoke.”
[.. .] Among the sublimated materials, sulfur was deposited in fine dust not only in two small solfatares, but also on the ash that covered certain hills, and to which it gave a yellowish-green colour.”
“In the evening, around 8 o’clock, we began the journey back to Batavia, under deep and for many of us, undoubtedly ever lasting, impression of the grandiose spectacle that we had just observed.”
Their descriptions of Perboewatan (remember that they were the first to report from here over almost 300 years of history!) indicated that the crater was surrounded at different points by high walls of lava, and which Verbeek later suggested probably formed (at least in part) in the year 1680. It had started at the same place (or very close to) the 1680 eruption. But whereas 1680 caused extensive lava flows, the only mention of any lava being associated with the 1883 events is the black shiny crust deep in the crater. Rather than lava flows, the explosions a week before had formed a crater 1 km across.
No one mentioned this, but what had happened to the peak of Perboewatan? The peak was reported to be 120 meters tall. It seems possible that the crater was in fact the location of the previous, higer peak. A crater 1-km across can have supported a 100 to 200-meter tall edifice, making the mountain over 200 meters tall before the explosion. Such a height fits with the older drawings. The May eruption may therefore have been the demolition of the ‘barren, reddish, sulfurous spot’ of the oldest record: Krakatau had lost one of its summits. That would make the May explosion around 0.1-0.2km3 (DRE).
The eruption continued. There was another explosion on June 19, and when on June 24 the island re-appeared from the dark clouds, a second, stronger column of smoke was present, originating east of Perboewatan, at the foot of Danan – now there were two simultaneous erupting craters. There was no activity from the summit of Danan. The change in appearance of Perboewatan was finally noted: the three rock masses that once formed the summits of this mountain had disappeared. The observations were made from Anjer, from where the island was only intermittently visible because of the weather, so much of the eruption was unobserved.
The last ever visit to Krakatau was made by Captain H. Ferzenaar on 11 August, sent to map the island (a tad late, perhaps). He found three active craters, two near Danan and one at Perboewatan, with 14 bursting fumaroles on the southern slope of Danan. All active sites were on land: there was no evidence for any off-shore activity. The southern summit of Danan seemed to have partly collapsed towards the northwest. He measured this summit at 400 meters – previously it had been 450 meters. Rakata was not active. The ash on the beach was a meter thick. (This may sound a lot but extrapolating suggest that so far less than 1 km3 of ash and tephra had been ejected.) The commonly reported height for Perboewatan may come from his measurements – after it had been demolished. Ferzenaar traveled along the east and north coast of Krakatau. He did not note any change in the coast line, but we don’t know how familiar he was with the area. It is a pity he did not visit or see the western shore south of Verlaten Island where the major eruption later occurred. Neither did any of the earlier parties go there. (it appears that it was not possible to navigate the channel between Verlaten Island and Krakatau.) We don’t know what changes had occurred there before the big eruption.
Over the three months, the number of eruption centres had been increasing. Normally, when eruptions become established they focus on one point: magma always takes the easiest route. The most likely cause is that magma was so close to the surface that for different parts of the magma the easiest path became a different one. This should have been seen as a warning, and in fact after having been there for two days, Ferzenaar declared the island too dangerous to visit. Fifteen days later, the explosions began that would tear Krakatau apart; 36,000 people died from tsunamis and from (unrecognized) pyroclastic flows. It was precisely three months after the excitement of the Krakatau picnic.
The eruption had been intensifying on Aug 26. The explosions became strong enough to cause a rough sea throughout the Sunda Strait. During the night, the tsunami waves began. They threw ships which were anchored at the coast on to the beach; the waves will have been several meters high. The next morning, the first of the big waves arrived at 6:30. One ship reported seeing a town destroyed before their eyes. The darkness came shortly after, lasting for 18 hours. The main event started during this darkness, at 10am, when the rain of pumice near the Java coast became a dense rain of mud, more than 20 kilometers from Krakatau. It covered ships in smelly sea floor. The sulfur smell became stifling and people reported difficulty even breathing. The wind increased and reached storm force, and the big waves followed which reached a run-up height of 30 meters. The mud rain lasted for several hours, before becoming intermittent. The ash and pumice continued until the following morning. Afterwards it was found that there had been two massive explosions, 50 minutes apart, with the last one at 10 am the biggest.
Somehow, the eruption had changed from a decent-sized event (VEI-5? Verbeek called it ‘not unimportant but insignificant’) to something very much larger, the most significant eruption of the past 200 years. The rain of mud shows that the final explosions came not from the island, but from underneath the sea. That was a change as none of the earlier ejecta showed any evidence of interaction with water. The hole left afterwards confirms this shift, as it is centred just off the west coast of old Krakatau. Almost 150 years later, we still don’t really know how this happened.
The traditional explanation for the Krakatau Big Bang is the collapse of the magma chamber. The alternative, that the island collapsed into the sea and that this caused the tsunami was already considered and dismissed in 1885. Some collapses did occur, but the main event does not fit this scenario: instead there was an undersea explosion. But if there was little or no lava, why would the magma chamber collapse? The excavations had all been from the surface, not from the magma chamber. It can’t have been because of pressure reduction, since with a volatile-driven eruption, the pressure goes back to the one before the eruption – not lower. Perhaps the heat in the chamber had melted the roof, but in that case the final event was a bit of an accident and only indirectly related to the Krakatau eruption. There is still a bit of a mystery here.
The answer may be in the lack of data from the west side. And perhaps the 2018 collapse of Anak Krakatau gives us a clue. A major cause of volcanic disasters is flank failure. Flank failure had been suggested as the cause of the tsunamis, but dismissed as it wasn’t mainly directed towards the northwest. However, a flank eruption could still have initiated the final phase. What happened on the west side of Krakatau? Ferzenaar could not visit the west because of the smoke. This may not have been just from the three craters on land: a fourth site could have been hiding itself. And this fourth site was in a dangerous place. I imagine a flank eruption building on the western slope of Danan, similar to what happened in St Helens. The new site was building at or near sea level. It over-inflated, and collapsed. The flank collapse exposed the magma chamber below sea level, which triggered the final explosion. The rest is history. This idea fits the big event, including the mud and the fact that the explosions were not primarily in one direction, as is the case if the main event had itself been the flank explosion.
If Krakatau’s Big Bang was indeed triggered by a flank collapse, it would fit the pattern that flank collapses are far and away the largest cause of casualties from volcanic eruptions. They can turn an eruption from a picnic into a disaster.
An interesting sideline: Verbeek in 1885 predicted that when Krakatau would begin to rebuild, it would do so in-between Danan and Perboewatan. In 1929, that is exactly where Anak Krakatau appeared. Verbeek was the only one ever to understand Krakatau. He later wrote that during the 1880 visit he had found indications for a rift running through the Sunda Strait. (He also complained about the lack of accurate maps of Krakatau. I sympathise!)
The collapse took away half of Rakata. This gave Verbeek the opportunity of a life time to see a volcano’s innards, during his visit in October. The conduit was clearly visible, and Rakata was seen to consist of many separate layers, each 10 meters or more thick. This indicates multiple sequential lava flows, well separated in time. Rakata was not an instant volcano: it had taken time to build. There is an impression that the oldest layers were build up to the east of the later summit. This must clearly have been long before the modern era, because Rakata was inactive and probably extinct by 1600. But how long?
We can get some idea from the rate at which magma is added to the island. Since 1883, all growth has been at Anak Krakatau which grew to a volume of roughly 0.2 km3 before its 2018 collapse. That gives a supply rate of order 0.002 km3 per year – this is not huge, but suffices to explain Anak. At this rate, recovery from the 1883 eruption (20 km3) will take 10,000 years. Rakata may indeed be that old. The old caldera is a few times larger and would take 50,000 years for recovery. These rough numbers suggest that the indicated age of the ancient caldera of 60,000 years is in fact very reasonable.
So it appears that Krakatau, for all its violence, does its violent eruptions only infrequently. The normal mode is of small, cone-building (or cone-destroying) eruptions, similar to how Anak Krakatau build itself up. Collapse events as in 2018 are probably common, but although highly damaging, on the volcanic scale these are small fry. The 1883 eruption dug much deeper.
But there are persistent claims on the web that the formation of the large caldera took place in either 416 or 535 AD. Where does this come from? The answer to this is two-fold.
Let’s first address the claimed 535 AD eruption. This was based on (1) the fact that there was a major eruption somewhere on Earth at this time; (2) that the 416 AD eruption was misdated. If you are waiting for a punch line, there isn’t one: this is all of the evidence. Of course our knowledge has advanced a bit since this claim was made. We now know that the 535 eruption seen in the ice cores was in the northern hemisphere, and that there was a tropical eruption in 540 but there is a good candidate for it in Ilopongo in El Salvador. The 535 Krakatau eruption can be dismissed as fairly wild speculation.
How about 416? This comes from a book called Pustaka Raja Purwa: the book of king Purwa, and was first advocated as describing Krakatau by John Dudd in 1889, Nature 40, 365-363. The Pustaka was written by Raden Ngabehi Ranggawarsita, a famous Javanese ‘pujangga’ (a combination of chronicler and poet) from the Surakarta Sultanate. The Pustaka Raja is the major achievement of a major writer: a massive collection of stories covering the history of the central Java kings, an Indonesian 1001 Nights. The Purwa is part of it, a five-volume introduction to the Pustaka Raja, covering the earliest years in a semi-historical, semi-mythical manner.
The particular story goes as follows:
A thundering sound was heard from the mountain Batuwara which was answered by a similar noise from Kapi, lying westward of the modern Bantam. A great glowing fire, which reached the sky, came out of the last-named mountain; the whole world was greatly shaken and violent thundering, accompanied by heavy rain and storms took place, but not only did not this heavy rain extinguish the eruption of the fire of the mountain Kapi, but augmented the fire; the noise was fearful, at last the mountain Kapi with a tremendous roar burst into pieces and sank into the deepest of the earth. The water of the sea rose and inundated the land, the country to the east of the mountain Batuwara, to the mountain Rajabasa, was inundated by the sea; the inhabitants of the northern part of the Sunda country to the mountain Rajabasa were drowned and swept away with all property. The water subsided but the land on which Kapi stood became sea, and Java and Sumatra were divided into two parts.
Confused? There are two versions of the story, in two different editions of the Purwa. The first edition gives no date whilst the second edition gives the date of 416. We do not know what the story is based on. (The second edition appeared a few years after Krakatau erupted and must have been prepared by someone else as Ranggawarsita had died a decade before the eruption.) It is normally quoted as an ‘ancient Javanese document‘ but the writing dates from the late 19th century, and we don’t really know whether there is any older tradition behind it. So how do you judge the authorative-ness? That is done using several criteria: (1) How reliable is the author? (2) Do the details make sense? (3) Is there independent evidence?
The reliability is not known as none of the stories in the Purwa can be tested. The dates are definitely unreliable as the book in another story gives different dates for the same story. (And for our story, the date comes from a version with uncertain authorship and is not in the ‘authorative’ (i.e. known author) version.) More ancient Javanese documents do not go back nearly this far; we do have some stone inscriptions from the 4th to 6th century but these only refer to acts of kings. As for the details in the story, the separation between Java and Sumatra makes no sense. They were last connected during the ice age and the separation came with the sea level rise 10,000 years ago, not with any volcanic activity. Kapi may or may not be Krakatau. The other locations are around the narrow, northern end of the Sunda Strait. The description of a tsunami seems accurate, suggesting there may well be a historic event behind the story, which affected the north of the Strait. As for independent evidence, there is none. There are no indications for a major eruption around the Strait at this time. Drilling off the southeast coast of Sumatra has found two dacite tephra layers which because of their composition and location can be attributed to Krakatau. One is recent, located in the upper ten centimeters and is attributed to the 1883 eruption. The other is 2.2 meters below the surface, and is tentatively dated to 60,000 years ago. Although there may have been many smaller eruptions in between, there is no indication for anything else at the level of the 1883 eruption, let alone one several times larger.
The conclusion from this is that the large caldera of Krakatau is most likely 60,000 years old. If there is a true story behind the mythology of the Purwa, the eruption that it describes was too small to form a tephra layer in the ocean, and it certainly wasn’t the formation of the Krakatau caldera. An event similar to the 2018 collapse of Anak Krakatau, which generated a very damaging tsunami, can not be excluded: a small (continuous) eruption, collapse into the sea, and a tsunami can fit the description. In addition, the date of the story is highly uncertain. It is beautiful writing – but science requires evidence. And the evidence we have does not support a large, historical eruption in the Sunda Strait other than the 1883 one.
So Krakatau is a dangerous volcano but not a high-volume one. That may seem a surprising conclusion, seeing how frequently Anak erupted before its disappearance. But these eruptions were small ones, driven by the fact that since 1883 the magma has had a fairly easy route to the surface. Look around the Sunda Strait, and you find extinct volcanoes. There is evidence for one or more very large eruptions around 100,000 years ago which formed ignimbrite layers, but not much since. All other island volcanoes in the Strait are inactive. Krakatau is a peculiar exception.
To get a
greip grip, we need to look at Indonesia as a whole. Java is straightforward, a volcanic chain perpendicular to the subduction front. But Sumatra lies at an angle of 40 degrees to the subduction direction. The Great Sumatra Fault runs along the length of the island and takes up the strike motion that come from this angle. It is a highly segmented fault, and where segments are offset, a small basin forms. The Sumatran volcanoes lie along this fault; the basins feed the massive calderas that are characteristic of Sumatra (including Toba). There are also two segments underneath the Sunda Strait, and these have formed a deep subsidence basin. This basin is aligned with the Sumatra Fault close to Sumatra, but bends north-south towards Java. The basin is divided into a west graben and an east graben, with the Tabuan Ridge in the centre. Both grabens are bounded by multiple faults.
There is a ridge on the east side of the east graben, called the Krakatau ridge which runs north-south, and passes to the west of Krakatau. Beyond that, the floor of the Sunda Strait looks fairly featureless. That is surprising, as the Strait formed by Sumatra and Java pulling apart, so a pull-apart basin should run along the length of the Strait. Where is it?
A seismic reflection study found a hidden deep graben, roughly where the letter ‘K’ is of “UKF’ on the figure above. It is 3-6 km deep, less than 20 km wide, and bounded by steep normal faults. But nothing is visible on the surface: it is completely filled with sediment. Somewhat optimistically, the discoverers (Susilohadi et al., 2009 Tectonophysics, 467, 55–71) called it the the ‘Krakatau graben’, a name that has not yet caught on. The study also saw some indication of this graben some 10 km south of Krakatau where they had another trace. Here it was not as well defined. From the two detections, it seems this graben may run north-south, and if it extends as far as Krakatau, the volcano will either be in it or close to its edge. The graben may line up with Lampung Bay on Sumatra but there is currently no evidence it extends that far.
The next part of the puzzle is the line of volcanoes that includes Krakatau. The earthquakes define it as a fracture zone, and the depth of these quakes shows that it is in the bedrock – it is an ancient fault, as already indicated by the fact that its alignment, NNE-SSW is different from that of any recent faults. The volcanic activity is at least a million year old; its presence suggests that the fault was re-activated at some point, but the fact that only Krakatau remains active shows that the fault is being pushed back into retirement.
What happened? The rule of thumb in Asia is that everything is India’s fault. Its crash into Asia deformed the entire continent, and through a chain reaction involving the opening of the Andaman Sea and the rotation of Borneo, caused Sumatra to move northwest and to rotate. The strike-slip motion is currently accommodated by the Sumatra Fault.
The Sumatra fault reaches the Sunda Strait at the Semangka bay. The Lampung Bay further east looks quite similar, and is also bounded by a fault on its northern side. This fault has been argued to continue a short distance across the Strait, in Java, but it has not been traced underneath the Strait. The Lampung bay fault shows evidence for slip-strike movement before around 5 million years ago, but only normal motion since (i.e. before that time there was sideways motion of both sides, since that time the relative motion is up/down). It may have acted as a branch of the Sumatra fault at the time. Movement along this fault could have re-activated the volcanic fracture zone, which begins at this fault.
This makes the history of movements inside the Sunda Strait extraordinary complex. Before 5 million years ago, the area between Lampung Bay and Semangka Bay pulled away from Java, leaving behind a basin with subsidence and thinned crust. After that time, the slip movement here ceased, and the pulling motion now happened southwest of Semangka Bay as the Sumatra Fault took over. The pull-away motion could be origin of the Krakatau graben, present mainly at the southern end because the movement continued there for longer. The sediment-fill is because this was a long time ago.
Now look at Krakatau, It sits where the volcanic fracture zone reaches the Krakatau graben, and just before it hits the Krakatau ridge where it may terminate. In a graben, the crust is thinned and the stress is extensional. This may have given decompression melt, and the low stress made it easy to store the magma and move it up. The composition of the lavas suggest that the magma may be stored a long time in the chambers. The location allowed Krakatau to flourish, while the other volcanoes withered and died as the re-activated fault re-lost its vigour, after the Sumatra Fault stole the northwest movement. There are magmatic no-go areas in all directions from Krakatau: go either way on the fault or on the graben and you find a volcanic dead-end: four volcanic stop signs.
This picture of Krakatau’s cause and origin remains speculative. Most geology research in the region focusses on the oil deposits on Sumatra, and little is done on the Sunda Strait. We don’t know the ages of the faults or volcanoes, the location of the grabens, or even if the Sunda Strait was opened by extension or by rotation (nor where the pivot would be). After all these years, Krakatau’s world still hasn’t been properly mapped.
Krakatau spent centuries or even millennia building up to its explosion. The signs were fumarole activity, drying and moving hot springs, and possibly inflation. After Verbeek briefly visited the island in 1880, he pointed out its peculiar location, where different lines of volcanoes intersect. Had he seen something that had made him uneasy? It is not recorded, and he does not mention any sign of activity apart from the 1680 lava flows, but he later said that, if people had visited more often, signs of an impending eruption might have been spotted. Still, without knowledge of its ancient history it would have been hard to foresee the catastrophe that came from the collapse. It is a typical case of lurking danger not being recognized for want of history.
The main lesson for us is not to rely on apparent inactivity of a volcano. Krakatau may only do its big explosions once every 50,000 years. But with over 1000 active volcanoes in the world, that still means we may expect something this big every 50 years. And Krakatau had a second method to cause disaster, which it probably has done far more frequently. In the volcanic lottery, someone will draw the losing ticket. Only the past can tell us what risk each ticket carries.
And there is one volcano with a behaviour similar to that of Krakatau before its eruption. Iwo Jima has shown centuries of inflation, with fumaroles and hot springs. Nothing may happen – but if it does, we should not call it unexpected. It too is condemned to repeat its past.
Albert Zijlstra, May 2019
There have been previous posts on Krakatau:
After this heavy post, here is some light Escher