EXPLOSIVE ERUPTIONS 86i 



Some of the bombs consist of a remarkable mixture of crystals, 

 characteristically developed at great depth within the earth's crust, 

 such as sanidine, olivine, hornblende, garnet, etc. (Walther-41 : 

 lyo-iyi.) 



A modern case of such an explosion without lava extrusion 

 occurred in Japan in 1888, the explosion being a sudden and violent 

 one, and tearing away the side of a volcano which had not been 

 active for at least a thousand years. The air was filled with ashes 

 and debris as in a typical volcanic eruption, and a large tract of 

 the adjacent region was devastated and many lives lost. 



Coon Butte, in Arizona, has also been regarded by Gilbert 

 {iwiS"/) as a possible example of such an explosive eruption — 

 though he also suggests the possibility that it was formed by the 

 impact of a meteorite. Both theories have had their advocates, the 

 former origin being favored by Chamberlin and Salisbury (4:596), 

 while the latter is especially defended by Fairchild (8). 



The cinder cone. While the explosion-craters seen in the Maare 

 represent probably a single eruption, or one which, with slight 

 intervening pauses, lasted only for a comparatively short time, the 

 more general examples of explosive volcanoes last sufficiently long 

 to build up a cinder cone. Such eruptions may be of comparatively 

 limited duration, and may occur at short intervals, as in the volcano 

 Stromboli in the ^olian Islands north of Sicily {Stroniholian type), 

 where the interval of explosion is from i to 20 minutes, as shown 

 by the ''flash" of this "Lighthouse of the IMediterranean" ; or it 

 may be of a more violent character and occur at great intervals 

 with dormant or "strombolian" periods intervening. Such is the 

 case in Vulcano of the same group of islands, and in other violent 

 volcanoes {Vulcanian type) which have an interval of decades 

 (moderate phase), or of centuries (grander phase). 



Material of the cinder cone. This includes the bombs, the 

 lapilli, and the volcanic sand, ash, and dust which fall in the im- 

 mediate vicinity of the crater. Not all the ejected material falls 

 here — much being carried to a distance, this distance increasing 

 with increasing fineness of material. Even large bombs may be 

 hurled beyond the actual radius of the cinder cone, one such, fully 

 three feet in diameter, being hurled to a distance of a mile and a 

 half during the eruption of Vulcano in 1888 (Hobbs-15 :/7p). A 

 remarkable example of the propulsion of volcanic ejecta has been 

 described by Hovey {iy.-,6o) in the eruption of Mont Pelec in 

 1902. Frequent explosions of dust and lava-laden clouds have 

 brought material enough from the crater to fill the gorge of the 

 Riviere Blanche. "The lower portion of the gorge has been entirely 



