VOLCANOES. 729 



pose the volcanoes of (1) Mount Loa ; (2) the Ltpari Islands ; 

 (3) Vesuvius, and (4) Mt. Shasta, are selected as representatives 

 of the more prominent kinds. 



1. Mount Loa, Hawaii. — In the summer of 1840, the pit or crater 

 of Kilaue'a, after one of its great eruptions, had the depth and form 

 shown in Figs. 1112, 1113. The lava in the great lake (a), 1,000 

 feet in its longest diameter, was seemingly in ebullition over its whole 

 surface, jets of liquid rock 30 to 60 feet in height, occasionally rising 

 to two or three hundred, being in constant play, with ordinarily no 

 sounds but those resembling the muttering of a great boiling cauldron. 

 Toward the middle of the pit, other smaller pools were in similar 

 action. Vapors rose in a great column from the fiery portion of the 

 pit, and spread out in a broad canopy over the crater. The depres- 

 sions or pits occupied by the boiling pools were circular, or nearly so, 

 and evidently because this is the form given by free ebullition. At 

 intervals, the great lake overflowed, or lavas welled up through fissures 

 radiating from it, and the streams spread more or less widely over the 

 bottom of the pit — whose area, it is to be remembered, was large 

 enough to allow of a flow more than two miles long. These ejected 

 lavas speedily blackened with cooling, and in a few hours could be 

 traversed safely and without inconvenience. Thus simple and quiet 

 was the action of the great volcano ; and the same was its usual 

 habit, — though with variations in activity, the boiling sometimes al- 

 most ceasing, sometimes more active and attended by detonations. 

 Through such overflowings at bottom the lower pit was losing its 

 depth. In eight years between 1823 and 1832, and between 1832 and 

 1840, it was nearly obliterated by its reaching the level of the " black 

 ledge" (n o, n' o', Fig. 1113). With the augmented height in the 

 lavas, there was also augmented intensity in the fires ; new boiling 

 lakes opened, and outflows of the lavas became almost incessant, 

 making the wide interior, according to the descriptions given, literally 

 a sea of fire, yet a harmless one to the observer at the brink of the 

 pit. 



Having reached this state, the eruption of 1840 took place; and 

 quietly, like the preparation, the first signal to the natives on the 

 coast being, not an earthquake, but a " fire in the woods." As a con- 

 sequence of the outflow, the lavas sunk 400 feet in the crater, so that 

 there was again a " lower pit " (n p, p' n') ; it escaped, however, by 

 fissures, not by an overflow from the crater. Six miles to the east 

 a fissure opened and some lavas escaped ; in the next seven miles 

 there were other fissures, giving out steam and making small patches 

 of lava. Finally, twelve miles from the sea and twenty-seven from 

 Kilauea, at a height of 1,250 feet above tide level, an outflow began 



