KRAKATOA (krah-kah-ta'a), a small volcanic island in the Sunda strait. At some early period a large volcano rose in the centre of the tract where the Sunda strait now runs. An explo sion blew the mountain away and its base was left as a broken ring of islands. Subsequently small cones were formed within the great crater ring. The most important rose 2,623 ft. above the sea and formed the peak of the volcanic island of Krakatoa. In 168o it appears to have been in eruption; great earthquakes took place and large quantities of pumice were ejected. But the effects of this disturbance had been so concealed by tropical vegetation that the eruption had been called in question. About 1877, earthquakes began to be frequent in the Sunda strait. In 1883 the manifestations of subterranean commotion became more decided, for, in May, Krakatoa broke out in eruption, discharging pumice and dust, with the usual accompaniment of detonations and earthquakes. On Aug. 26, paroxysms began which lasted till the morning of the 28th. The four most violent took place on the morning of the 27th. The whole northern and lower portion of Krakatoa, within the original crater ring, was blown away ; the northern part of the cone of Rakata almost en tirely disappeared, leaving a vertical cliff which laid bare the inner structure of that volcano. Instead of the previous volcanic island, which seems to have had an area of 18 sq.m., and rose from 300 to 1,40o ft. above the sea, there was now left a submarine cavity, with its bottom more than i,000 ft. below sea-level. This was the result of explosions of superheated vapour absorbed in the molten magma within the earth's crust. The vigour and repetition of these explosions may have been caused by sudden inrushes of the ocean as the throat of the volcano was cleared and the crater ring was lowered and ruptured. Access of bodies of cold water to the top of the column of molten lava would probably give minor explo sions, and then chilling of the lava surface would temporarily lessen or stop volcanic eructations. But until the pent-up water vapour in the lava found relief, it would gather strength until it burst through the crust and overlying water, and hurled cooled lava, pumice and dust into the air.
The discharge during the two days was enormous. A large cavity replaced the island, and the sea-bottom was covered with a wide and thick sheet of fragmentary materials ; while surrounding islands had their forests buried and their area increased by masses of the material ejected; also new islands appeared in the sea.
A vast body of the fine dust was carried far and wide by aerial currents, while the floating pumice was transported for many hun dreds of miles on the surface of the ocean. At Batavia, i oo m. from the centre of eruption, the sky was darkened by the quantity of ashes borne across it, and lamps had to be used in the houses at midday. The darkness even reached as far as Bandung, a dis tance of nearly 150 miles, and 2,30o ft. above sea level. It was computed that the column of stones, dust and ashes projected from the volcano shot up into the air for a height of 17 m. or more. The finer particles coming into the higher layers of the atmosphere were diffused over a large part of the surface of the earth, and showed their presence by the brilliant sunrise and sunset glow effects to which they gave rise. Within the tropics they were at first borne along by air-currents at an estimated rate of about 73 m. an hour from east to west, until within a period of six weeks they were diffused over nearly the whole space between the lati tudes 3o° N. and 45° S. Eventually they spread northwards and southwards and were carried over North and South America, Europe, Asia, South Africa and Australasia. In the Old World they spread from Scandinavia to the Cape of Good Hope.
Another remarkable result of this eruption was the world-wide disturbance of the atmosphere. The culminating paroxysm on the morning of Aug. 27 gave rise to an atmospheric wave or oscillation, which, travelling outwards from the volcano as a centre, became a great circle at i8o° from its point of origin, whence it continued travelling onwards and contracting till it reached a node at the antipodes to Krakatoa. It was then reflected or reproduced, travelling backwards again to the volcano, whence it once more returned in its original direction. "In this manner its repetition was observed not fewer that seven times at many of the stations, four passages having been those of the wave travelling from Krakatoa, and three those of the wave travelling from its antipodes, subsequently to which its traces were lost" (Sir. R. Strachey).