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THE STORY OF A VAST EXPLOSION.
The greatest physical convulsion of recent times occurred on the morning of the 27th of August last year, the scene of the catastrophe being a small island in the Sunda Straits, which separate Sumatra and Java. It is a region which there is much reason to regard as one of the intensest foci of volcanic activity on the earth's surface. The main facts connected with this event, although slow in coming to hand, are now fairly within the records of science. Krakatoa, the volcanic island which a year or two ago was seven miles long by five broad, is about thirty miles from the Java coast. When surveyed in 1868-69, the island was found to be clothed from base to summit with a luxuriant growth of forest and tropical vegetation, but uninhabited. A few weeks prior to the eruption, the volcano, which had been dormant for two centuries, gave signs of an awakening. On the 20th of May several shocks, accompanied by loud explosions and hollow reverberations, startled the inhabitants of the towns of Batavia and Buitenzorg, about ninety miles distant. These disturbances continued for the next three months with more or less activity. On the 11th and 18th of August the energy of the volcano increased, and there were symptoms of a crisis. On the 26th and the night following, several eruptions took place, until the climax was reached on the following morning. The submarine base of the mountain then seems, according to all available evidence, to have literally 'caved in.' This was apparently accompanied by an influx of the sea into the molten interior, the instantaneous development of superheated steam, and then an explosion which, for its colossal energy, is unparalleled in the annals of volcanic outbreaks.
The shock of the explosion was felt at a distance of four thousand miles, being equal to an area of one-sixth of the earth's surface--that is, at Burmah, Ceylon and the Andaman Islands to the north-west, in some parts of India, at Saigon and Manila to the north, at Dorey in the Geelvink Bay to the east, and throughout Northern Australia to the south-west. Lloyd's agents at Batavia, in Java, stated that on the eve of this vast explosion, the detonations 'grew louder, till in the early morning the reports and concussions were simply deafening, not to say alarming.' So violent were the air-waves, due to this cause, that walls were rent by them at a distance of five hundred miles, and so great the volume of smoke and ashes, that Batavia, eighty miles off, was shrouded in complete darkness for two hours. Nearly four months after the eruption, masses of floating pumice, each several acres in extent, were seen in the Straits of Sunda.
Paradoxical as it appears, the sound was sometimes better heard in distant places than in those nearer the seat of disturbance. This singular effect has been thus explained--assuming, for example, the presence of a thick cloud of ashes between Krakatoa and Anjer, this would act on the sound-waves like a thick soft cushion; along and above such an ash-cloud the sound would be very easily propelled to more remote places, for instance, Batavia; whereas at Anjer, close behind the ash-cloud, no sounds, or only faint ones, would be heard. Other explanations seem to be less probable, though not impossible.
As may well be imagined, the final outburst by its awful energy gave rise to a succession of air-waves. These we now know went round the earth more than once, and recorded themselves on the registering barometers or barograms at the Mauritius, Berlin, Rome, St Petersburg, Valencia, Coimbra , and other far-distant places. At some points, as many as seven such disturbances were noted; other instruments not so sensitive gave evidence of five, by which time the wave had pretty well spent itself.
Having collected the observations made at all the chief meteorological stations, General Strachey recently read a paper before the Royal Society which, in his opinion, conclusively shows that an immense air-wave started from Krakatoa at about thirty minutes past nine A.M. on August 27th. Spreading from this common centre, the wave went three and a-quarter times round the globe, and those parts of it which had travelled in opposite directions passed through one another 'somewhere in the antipodes of Java.' The velocity of the a?rial undulations which travelled from east to west was calculated at six hundred and seventy-four miles per hour, those moving in the reverse direction at seven hundred and six miles per hour, or nearly the velocity of sound.
But another effect of the eruption was a series of 'tidal waves,' so called--although the term is objected to because not strictly scientific--which, like the air-wave, passed round the world. Whether this was synchronous with the final explosion, it is not possible to say. The highest of these seismic sea-waves, which was over one hundred feet high, swept the shores on either side of the Straits, and wrought terrible destruction to life and property. More than thirty-five thousand persons perished through it; the greater part of the district of North Bantam was destroyed, the towns of Anjer, Merak, Tjeringin, and others being overwhelmed.
In this as in most other cases of volcanic disturbance, electrical phenomena were observed. One vessel in particular, while passing through the Sunda Straits, exhibited 'balls of fire' at her masthead and at the extremities of her yardarms. Further, it was noticed at the Oriental Telephone Station, Singapore, a place five hundred miles from Krakatoa, that on raising the receiving instrument to the ears, a perfect roar as of a waterfall was heard; and by shouting at the top of one's voice, the clerk at the other end of the wire was able just to hear something like articulation, but not a single sentence could be understood. On the line to Ishore, which includes a submarine cable about a mile long, reports like pistol-shots were heard. These noises were considered due to a disturbance of the earth's magnetic field, caused by the explosion, and reacting on the wires of the telephone.
There can now be little doubt but that the green and blue suns and exceptional sunsets observed in Europe, India, Africa, North and South America, Japan, and Australia, were due to the Krakatoa eruption. The enormous volume of volcanic dust and steam shot up into the higher atmospheric zones by this convulsion are adequate to furnish the chromatic effects above mentioned.
FOOTNOTES:
The eruption of May was noticed in a previous article .
BY MEAD AND STREAM.
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