DESTRUCTION OF VOLCANOES 875 



Where extinct volcanoes have been subject to the attack of 

 the waves of the sea sections are often cut which reveal their struc- 

 ture. This is the case in the island of St. Paul, already noted, and 

 in Vulcanello on the shores of the Island of \'ulcano in the Mediter- 

 ranean. Some of the outlying islands of the Sandwich or Hawaiian 

 group likewise represent partly dissected extinct volcanic cones 

 whose sides, moreover, are deeply gullied into a series of parallel 

 valleys so sharply divided one from the other as to effectively 

 isolate certain of the organisms inhabiting them. (See Chapter 

 XXIX.) 



Finally, the destruction of volcanoes by their own explosive ac- 

 tivity may be noted. Examples are furnished by the Vesuvian 

 eruption of A. D. 79, which shattered the cone of Monte Somma ; 

 by the Japanese volcano Bandai-san, of which a considerable portion 

 was blown out in 1888; and by the Javanese volcano Krakatoa, 

 which was practically blown to pieces on August 26 and 27, 1883, 

 furnishing the most stupendous example of volcanic activity in 

 modern times. "After a series of convulsions, the greater portion 

 of the island was blown out with a succession of terrific detonations 

 which were heard more than 150 miles away. A mass of matter 

 estimated at about iVs cubic miles in bulk was hurled into the air 

 in the form of lapilli, ashes, and the finest volcanic dust. . . . 

 The sea in the neighborhood was thrown into waves, one of which 

 was computed to have risen more than 100 feet above tide-level, 

 destroying towns, villages, and 36,380 people." ( Geikie-9:i'7i'.) 

 The oscillations of the wave were noted at Port Elizabeth, South 

 Africa, 5,450 miles away, having traveled with a maximum velocity 

 of 467 statute miles per hour. The air waves generated traveled 

 from east to west and are supposed to have passed three and a 

 quarter times around the earth (82,200 miles) before they died 

 away. The barometric disturbances, passing round the globe in 

 opposite directions from the volcano, proceeded at the rate of almost 

 700 miles per hour. 



Special Erosion Features. An interesting type of erosion has 

 been observed on some steep-sided volcanoes, such as those of the 

 islands of St. Vincent and Martinique. Vast amounts of dust were 

 deposited during the eruption of May, 1902. and these formed a 

 bed varying from a few inches to many feet in thickness, and 

 extending over an area of 50 square miles on each island. The 

 heavy rains that followed the eruption turned this dust into a 

 cement-like mud which was firm enough to remain in place and 

 which, during the eruptions of September and October of the same 

 year, was covered by a new layer of coarser ejectamenta. In the 



