xii The Crust of the Earth 225 



explosions. The clq^d reflects the fierce glare of the lava 

 welling up in the crater, from which the explosions and 

 bombardment of heated stones become more frequent, until 

 finally the molten rock surges up to the lip and pours over 

 as a river of fire. The vast quantities of water -vapour 

 meanwhile condense into floods of rain, which convert the 

 dust-strewn slopes into torrents of hot mud, more voluminous 

 and often more important in obliterating the surface features 

 of the scenery than the lava itself. Such a mud deluge 

 destroyed the Roman town Herculaneum when the first 

 recorded eruption of Vesuvius took place in the year 79. 

 Snow-clad volcanoes like Etna and Cotopaxi send down still 

 more serious floods on account of the sudden melting of their 

 snow. 



297. Krakatoa. On 27th August 1883 the volcano of 

 Krakatoa, a small island in the middle of the Strait of 

 Sunda, terminated a set of comparatively quiet eruptions 

 by the most terrific explosions which have ever been wit- 

 nessed. A great crater had been previously formed, and 

 sea -water gained access to the crater full of molten lava- 

 as the mountain walls were gradually broken down. The 

 result was a temporary reduction of activity as the cold 

 water chilled the surface, and then the grand explosion 

 shot out a column of dust and vapour 20 miles high with 

 a roar that was heard at Rodriguez 3000 miles distant, 

 and attracted attention over one-thirteenth of the surface of 

 the globe. The concussion caused by this explosion was 

 severe enough to break windows and crack walls in 

 Batavia I oo miles away, and the disturbance of the air was 

 shown by the records of barographs to have expanded as 

 an air-wave from Krakatoa until it spread round a great 

 circle 180 in diameter, then contracted to the antipodes of 

 Krakatoa, whence it was reflected back, and so continued 

 pulsing round the world four times from the centre of dis- 

 turbance to the antipodes, and three times back again. 

 Two -thirds of the island were blown away, most of the 

 material being deposited in the Strait of Sunda, where 

 several new islands formed of piles of tuff and ashes ap- 

 peared, and after a few months were washed away by the 



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