Catastrophe: An Investigation Into the Origins of the Modern World (38 page)

The final evidence, however, comes from ice cores drilled ten thousand miles to the south, from deep inside the Antarctic ice cap. There, 660 feet below the windswept surface, scientists discovered evidence of a truly massive volcanic eruption.
⁵
The ice-core material revealed that acid snow had cascaded down on the Antarctic for at least four years running. From the Antarctic ice cores at that time depth there are no accurate dates available—only rough, fifty-year-long ranges of dates. All that can be said is that the four-year-long acid snow episode recorded in the core occurred sometime between 490 and 540.

But by examining the acid traces left by other first-millennium
A
.
D
. eruptions it is possible, through a process of elimination, to conclude that the four-year acid episode must have been associated with the climatic catastrophe and probably with the 535 eruption. This is because the two chronologically adjacent Antarctic acid episodes were, respectively, in the fifty-year brackets 231–281 and 614–664—and because the four-year event that occurred in the 490–540 bracket is by far the biggest event recorded in Antarctica for the whole of the first millennium
A
.
D
.

It is very likely, therefore, that the Greenland and Antarctic ice cores signal the same atmosphere-polluting climate-changing event recorded historically and in tree-ring terms for 535–536.

Alternatively, though much less likely, the four-year Antarctic event could record a second, totally separate (or, indeed, connected) volcanic eruption destabilizing Southern Hemisphere climate in around 540—and helping to further destabilize Northern Hemisphere weather, already thrown into chaos by the big 535 event. The second Greenland acid signal (532–534 +/− 5–8 years) could conceivably, in this alternative though less likely scenario, have been generated by such a 540 second eruption.

But where did the 535 eruption take place? Which volcano was the culprit?
⁶

T H E  B I G  B A N G

T
he first clue as to the location of the 535 eruption is the fact that the event is probably recorded in both the Greenland and the Antarctic ice cores. This double record indicates that the eruption must have been within the tropics; otherwise it would not have shown up as an acid spike at opposite ends of the world. It shows that acid snow was falling on both ice caps and had to have been delivered there by the two totally separate high-altitude wind systems that operate in the Northern and Southern Hemispheres, respectively. Only a tropical eruption could have achieved this to any substantial extent. However, the fact that acid-snow deposition took place for at least twice as long in Antarctica as in Greenland suggests that the eruption occurred in the southern rather than the northern tropics.

Luckily, there are only a limited number of active volcanic areas in the southern tropics: East Africa (including the Comoros Islands), the central Andes, the Galápagos Islands, and the huge chain of volcanoes stretching five thousand miles from the tiny Pacific island of Samoa to the large Southeast Asian island of Sumatra.

Judging by the massive climatic effects and the longevity of the acid spike in Antarctica, the eruption must have been absolutely enormous—bigger, probably substantially bigger, than the 1815 Tambora eruption on the Indonesian island of Sumbawa, which created a caldera over three and a half miles in diameter.

In East Africa, South America, and the Samoa-Sumatra chain, there are fewer than twenty known calderas that are big enough to be candidates—and fourteen of these are in the Samoa-Sumatra complex. However, the eruption dates of five of these are known not to have been in the sixth century.

The search can be further narrowed down by carefully examining the chronology and details of the climatic effects. Of those areas where records were made, the Far East was hit first and worst. That information—together with the fact that 70 percent of the candidate volcanoes lie in the Samoa-Sumatra complex—strongly suggests that the culprit erupted somewhere in that chain. By pure good luck, the suspects can be narrowed down still further, for buried deep in the Chinese
History of the
Southern Dynasties
is a reference to what appears to have been a vast explosion in February 535.

The actual text says that “there twice was the sound of thunder.” Nothing very extraordinary about that, you might think. However, the entry becomes potentially significant because it is one of only three references to “thunder” in the whole of the first half of the sixth century—and is the only reference that does not describe the “thunder” as part of a massive storm or as being associated with lightning. In any fifty-year period, the Chinese chroniclers would have been able to record thousands of thunderclaps—but they didn’t. Only the very severest thunderstorms or those thunderclaps that were unexplainable or mysterious would have been recorded.

It is also the only one of the three thunder incidents in which the chroniclers specifically noted that it was a double event—that the sound was heard twice. Again, this is potentially significant.

Of course, the mere fact that the explosion appears to have been heard in China does not, on its own, pinpoint any particular volcano. But, fortunately, the brief Chinese account also reported that the two bangs came from the southwest. The chronicle was written by scribes based in the south Chinese imperial capital, Nanjing. So if the Chinese account is to be believed, and if the two bangs were indeed volcanically generated, the culprit volcano must have erupted somewhere southwest of Nanjing.

At first sight, that appears to present a problem, because the nearest suitably sized calderas in that direction are located twenty-eight hundred miles away, in the Sumatra/western Java area—presumably too far away to be within earshot. However, volcanic explosions can indeed be heard for thousands of miles. In 1883 Krakatoa was heard four thousand miles away. In the 1815 Tambora volcanic explosion, the sound traveled at least two thousand miles.

The sound of a volcanic explosion is actually transmitted by being bent and bounced through the atmosphere up to twenty times. Those parts of the sound-wave front that travel straight up from the volcano disappear into the far outer atmosphere and are lost. But most parts of the wave move out from the explosion at angles less than the vertical. As wind speed increases with height and because, starting at around seven miles altitude, air temperature also increases, sound waves are bent in much the same way that light is when it passes through a prism.

The bending process is often so pronounced that after some 150 to 200 miles the waves have been refracted to such an extent that they hit the earth’s surface, either the land or the ocean. The low-frequency sound then simply bounces off the surface like a huge echo and heads back into the atmosphere, which bends it a second time. The process is then repeated again and again until finally the energy of the sound wave is dissipated into the ocean, the ground, or the air.

For the sound to travel the twenty-eight hundred miles from a volcano in the Sumatra/western Java area to Nanjing would have taken around four hours, and not all the audible sound would have been lost. In fact, there are several factors that could have substantially strengthened it.

First of all, large volcanic eruptions produce unusually high percentages of low-frequency (i.e., long-wavelength) noise, which is absorbed less well by the atmosphere than is high-frequency (short-wavelength) noise.

And second, because of the refractive effect of the atmosphere, the different parts of the wave front would have traveled along different paths and been accelerated by different wind speeds. The short though very loud sound of a volcanic explosion would therefore have been lengthened into a sound lasting several minutes. However, because so many atmospherically bent sound waves would be echoing off so many parts of the earth’s surface, some waves would reconverge at various points, thus reinforcing each other to produce a plural number of sound peaks within a less audible lengthened-sound phenomenon.

So, if the Chinese chroniclers’ mystery double bang emanated from a volcanic eruption thousands of miles to the southwest, which volcano could it have been?

*    *    *

B
earing in mind that the eruption had to have occurred in the southern tropics, the area pinpointed by the Chinese account narrows the field down to the southern Sumatra/western Java part of the Samoa-Sumatra volcanic chain.

Significantly, there is only one known caldera of appropriate size and vintage in that relatively small (six-hundred-mile-long) area. It surrounds the site of no less notorious a volcano than Krakatoa, the island mountain that brought death and destruction to Java and Sumatra in the 1880s. Could an earlier, bigger eruption of Krakatoa have been responsible for the catastrophe that tormented the world in the mid–sixth century
A
.
D
. and changed its history forever?

Here the evidence takes a fascinating turn. For buried deep in a little-known and normally ignored Indonesian chronicle is an extraordinary passage that may well describe the 535 supereruption itself.

Describing a huge volcanic event in the Sunda Straits area (between Sumatra and Java), where Krakatoa is located, the chronicle says that a “mighty roar of thunder” came out of a local mountain (Mount Batuwara, now called Pulosari).

“There was a furious shaking of the earth, total darkness, thunder and lightning.

“Then came forth a furious gale together with torrential rain and a deadly storm darkened the entire world.”

The chronicle—known as the
Pustaka Raja Purwa,
or
The Book of Ancient Kings,
goes on to state that “a great flood then came from Mount Batuwara and flowed eastwards to Mount Kamula [now called Mount Gede].” It then claims that the eruption was so massive that large areas of land sank below sea level, creating the straits that currently separate Sumatra and Java.

Claiming to describe the dramatic course of events, the chronicle says that “when the waters subsided it could be seen that the island of Java had been split in two, thus creating the island of Sumatra.”

The earliest surviving manuscript of this chronicle dates from 1869.
¹
A second, slightly different manuscript of the same chronicle, dating from the mid- to late 1880s, purports to provide a more detailed description of the event, although some extra information in this second manuscript may be additions inspired by observations of the 1883 eruption of Krakatoa and extrapolated to the earlier event.

This 1880s edition of the chronicle—some of which was potentially contaminated by observations of the 1883 eruption—says that “a great glaring fire which reached to the sky came out of the mountain.”
²

“The whole world was greatly shaken, and violent thundering accompanied by heavy rains and storms took place.

“But not only did this heavy rain not extinguish the eruption of fire, but it made it worse. The noise was fearful. At last the mountain burst into two pieces with a tremendous roar and sank into the deepest of the earth.