Krakatoa why did it erupt

The best known eruption culminated in a series of massive explosions on August , The eruption ejected more than 25 cubic kilometres of rock, ash, and pumice , and generated the loudest sound ever historically reported — the cataclysmic explosion was distinctly heard as far away as Perth in Australia approx.

Atmospheric shock waves reverberated around the world seven times and were detectable for five days. Near Krakatoa, according to official records, villages and towns were destroyed and seriously damaged, at least 36, official toll people died, and many thousands were injured by the eruption, mostly in the tsunamis which followed the explosion.

The eruption destroyed two-thirds of the island of Krakatoa. New eruptions at the volcano since have built a new island, called Anak Krakatau child of Krakatoa.

Origin and spelling of the name The earliest mention of the island in the Western world was on a map by Lucas Janszoon Waghenaer, who labelled the island "Pulo Carcata. There are two generally accepted spellings, Krakatoa and Krakatau. Another curious circumstance was that at midday at some spots in the city no vibrations were perceived, while in the surrounding buildings they were distinctly experienced.

It was a natural conclusion, however, that an alarming volcanic eruption had taken place; but it was impossible to localize the direction of the sounds, and at the observatory there were no instruments for making such determinations.

The tremblings continued throughout the day and during the forenoon of the 21st. A thin sprinkling of ashes fell at Telok Betong and at Semangko, in Sumatra; whence the ashes came, no one could tell. At Buiteuzorg, thirty miles south of Batavia, the same phenomena were observed; while in the mountains farther to the southwest they were even more pronounced.

By this time general opinion had ascribed to the west or northwest the direction whence the movements were proceeding.

Krakatoa itself was mentioned, but some of the mountains in Sumatra were considered more likely to be the seat of disturbance.

On the evening of May 21st smoke was seen issuing from Krakatoa, and on the 22d it was evident that the volcanic vent was at that place. Shortly afterward the vibrations in Batavia ceased.

During the next eight or nine weeks the eruption continued with great vigor, ejecting masses of pumice and molten stone, and volumes of steam and smoke. Although the prevailing monsoon carried to the westward the greater part of the matter thrown out, a cloud of lighter particles rose higher, and, encountering an easterly current of air, some of the dust fell on the island of Timor, twelve hundred miles distant.

During these weeks vessels passed through extensive fields of pumice spread over the surface of the sea. The soundings at the spot reached two thousand fathoms. It is known that a centre of volcanic disturbance exists in the Keeling Atoll, situated six hundred miles west by south from the mouth of the strait; and it is also known that pumice ejected from the sea bottom rises to the surface.

The currents of the Indian Ocean will show that any flotsam in the region between west and south of Java Head in that longitude could be drifted to the locality in which it was observed in the month of July. In a paper read before the Royal Geographical Society, Mr. Forbes suggested that the sounds heard in Batavia on the 20th of May, which were unnoticed at places so near Krakatoa as Anjer and Merak, and which would be inexplicable if they really originated there, were the result of a submarine eruption in the Indian Ocean, somewhere southwesterly from Java Head; and that the tremors were propagated thither, perhaps, by continuous strata connecting the locale of the outburst with Batavia, Buitenzorg, and more especially with the hills to the southwest, where the manifestations were so distinctly perceived.

If such a submarine outburst did take place, Mr. Forbes suggested that somehow the orifice very soon became blocked after a great inrush of water had taken place, which, becoming transformed into steam under enormous pressure, shaped its course for the nearest old earth scar, and found vent in Krakatoa by an offshoot, probably, of the funnel of the eruption of That such large lumps of pumice should be carried westward seven hundred miles into the Indian Ocean does not seem probable, especially as the earlier outbursts were not of very unusual vigor, for no pieces of any size are reported to have fallen on the neighboring coasts of Java and Sumatra; even after those of August, no ship farther off than one hundred miles speaks of the fall of any but the finest dust and sand.

On the 21st of August the volcano increased in activity. A ship reported being unable to venture into the strait on account of the great shower of pumice and ashes. On the afternoon of the 26th there were violent explosions at Krakatoa, which were heard as far as Batavia.

High waves first retreated, and then rolled upon both sides of the strait. During a night of pitchy darkness these horrors continued with increasing violence, augmented at midnight by electrical phenomena on a terrifying scale, which not only enveloped the ships in the vicinity, but embraced those at a distance of ten to twelve miles.

The lurid gleam that played on the gigantic column of smoke and ashes was seen in Batava, eighty miles away. Some of the debris fell as fine ashes in Cheribon, five hundred miles to the eastward. On the morning of the 27th there was a still more gigantic explosion, heard in the Andaman Islands and in India, which produced along both shores of the strait an immense tidal movement, occasioning that great loss of life recounted in the daily press. The matter expelled rose to an elevation so tremendous that, on spreading itself out, it covered the whole western end of Java and the south of Sumatra for hundreds of square miles with a pall of impenetrable darkness.

Abnormal atmospheric and magnetic displays were observed, compass needles rotated violently, and the barometer rose and fell many tenths of an inch in a minute. Between ten and twelve o'clock in the forenoon of that day the subterranean powers burst their prison walls with a terrific detonation, which spread consternation and alarm among the dwellers within a circle whose diameter lay across nearly three thousand miles.

The description given at the San Francisco Hydrographic Office by Captain Watson, of the British ship Charles Bal, who was in the near vicinity at that time, is especially graphic and thrilling. He says that at "about seven P. There were some cumulus clouds in the sky, but many stars were shining, and from E. The clouds appeared to be edged with a pinkish-colored light; the sky also seeming to have extra light in it, as when the Aurora is showing faintly.

On the morning of the 26th made Java Head light; ahout nine A. We observed a repetition of the noise noted at 3. To us it looked like blinding rain, and had the appearance of a furious squall, of ashen hue. At once shortened sail, to topsails and foresail.

At five the roaring noise continued and was increasing; darkness spread over the sky, and a hail of pumice stone fell on us, of which many pieces were of considerable size and quite warm.

We were obliged to cover up the skylights to save the glass, while our feet and heads had to be protected with boots and sou-westers. Until such a system is in place, it will be vital to get the local community involved in disaster risk management and education. It is also about educating people so that they feel psychologically healthier, more resilient and less anxious about facing the mega tsunamis of the future. I have previously highlighted two examples of proactive community participation in disaster-prone villages in the UK and Japan.

In both cases, residents know how to act in case of a natural disaster without depending on the authorities. It is certain that the decimation of the land and deaths could be reduced if the local communities are well prepared for natural disasters like tsunamis. Following the December Anak Krakatoa tsunami, local researchers and I conducted a detailed field survey of the coastline of Lampung province, on the north side of the strait, and some of the smaller nearby islands. We found a lack of proper tsunami defence structures or any early warning system, and houses and businesses built very close to the coast with no buffer zone.

We identified high ground where residents could run to in case of a tsunami and put up signs with evacuation routes. During this survey, I conducted a series of focus group meetings with local residents and businesses in order to make the communities more resilient and reduce their anxiety about future mega tsunamis in the area.

I developed a tsunami wave propagation model to replicate the tsunami and most plausible future tsunami events, and to identify the most vulnerable coastal stretches, such as the village of Kunjir on the Lampung mainland.