PHENOMENA OF ERUPTION 



39 



The ejected materials were all fragmentary and of an incredible 

 volume ; ashes were distributed over an area of 300.000 square 

 miles, the greater part falling within a radius of eight miles around 

 the island ; stretches of water that had had an average depth of 

 117 feet were so filled up as to be no longer navigable. Enor- 

 mous masses of pumice floated upon the sea and stopped naviga- 

 tion except for the most powerful steamers. 



These tremendous explosions, even when they do not tear out 

 one whole side of the mountain, as in the case of Krakatoa and 



FIG. 7. — Crater Lake, Oregon. This crater ring is believed to have been formed 

 by a draining away of the lava from below, and not by explosion. (U. S. G. S.) 



Monte Somraa, may blow off the top and thus leave a great 

 crater ring many miles in circumference, within which subse- 

 quent eruptions may build up a new cone. When the volcanic 

 activity dies out, the ring may be filled with water, forming a 

 circular lake. 



Just the opposite extreme from these explosive eruptions is to 

 be found in the volcanoes of the Sandwich Islands, such as Mauna 



