The actual sounds of the volcanic explosions were heard over a vast area, especially towards the west. Thus they were noticed at Rodriguez, nearly 3,00o English miles away, at Bangkok (1,413 m.), in the Philippine islands (about 1,450 m.), in Ceylon (2,058 m.) and in West and South Australia (from 1,300 to 2,25o m.). On no other occasion have sound-waves ever been perceived at anything like the extreme distances to which the detonations of Krakatoa reached.
Not less manifest and far more serious were the effects of the successive explosions of the volcano upon the waters of the ocean. A succession of waves was generated which appear to have been of two kinds, long waves with periods of more than an hour, and shorter but higher waves, with irregular and much briefer inter vals. The greatest disturbance, probably resulting from a combina tion of both kinds of waves, reached a height of about 5o ft. The destruction caused by the rush of such a body of sea-water along the coasts and low islands was enormous. All vessels lying in harbour or near the shore were stranded, the towns, villages and settlements close to the sea were either at once, or by successive inundations, entirely destroyed, and more than 36,00o human beings perished. The sea-waves travelled to vast distances from
the centre of propagation. The long wave reached Cape Horn (7,818 geographical miles) and possibly the English channel (11,04o m.). The shorter waves reached Ceylon, and perhaps Mauritius (2,90o m.).
The volcano, now under water, was active in 1928, throwing up lava and ashes, whilst columns of steam and water, 25o to 65o ft. in height were seen to be rising from the surface of the sea. Scien tific expeditions to Krakatoa have been organized from time to time since the eruption and it has been ascertained that a new submarine volcano has formed between Long island and Verlaten island, two of the Krakatoa group, which consists of these and Rakata, or Krakatoa proper.
See R. D. M. Verbeek, Krakatau (Batavia, i886) ; "The Eruption of Krakatoa and Subsequent Phenomena," Report of the Krakatoa Committee of the Royal Society (London, 1888).