SUBMARINE ERUPTIONS 



865 



the west coast of Iceland, where, in the early summer of 1783, 

 arose an island of volcanic nature about thirty miles from Cape 

 Reykjanaes. In less than a year, however, it had again been washed 

 away by the waves, leaving only a submerged reef or shoal from 

 five to thirty fathoms below sea-level. 



Numerous submarine eruptions which never reach the surface 

 no doubt occur over many portions of the ocean floor. In these 

 both cinders and lava enter, sometimes one and sometimes the other 



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V', I'll 



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Fig. 229. Sketch of the submarine volcanic eruption which, in June, 181 1, 

 formed Sabrina Island, off St. Michaels in the Azores. (After 

 De la Beche.) 



predominating. On the floor of some parts of the deep sea volcanic 

 ejectamenta are abimdant, and these are in parv at least due to 

 submarine explosive eruptions. 



Extravasative Eruptions. 



Terrestrial Type — Fissure Eruption. The fundamental charac- 

 teristics of this type are best developed in the great fissure erup- 

 tions which have resulted in the formation of extensive lava fields, 

 and in the broad flat lava domes of the Hawaiian group. The 

 fissures from which the great lava extravasations take place are 

 generally ranged parallel with and near to the coast and seem to 

 be especially prevalent where the edge of the land drops ofif rapidly 



