172 J. D. Dana — History of Changes in Mt. Loa Craters. 



Notwithstanding the independence of Kilauea, there may 

 still at times be evidence of some sympathy ; for the two great 

 active lava-columns are only twenty miles apart. 



The evidence does not make it certain, however, that Kilauea 

 originated as early in the history of Hawaii as either Xea or 

 Loa ; for the original fracture extending in that direction from 

 Kea may at first have been sufficient only to let out a flood of 

 lavas, and subsequently have been further opened and crossed 

 by a greater fissure, so as to produce over it the permanent 

 Kilauea vent. 



5 . Whatever the fact as to the relations of Kilauea and Mt. Loa, 

 I believe they still sustain my old conclusion that volcanoes are 

 not safety-valves;^: for "if while Kilauea is open on the flanks 

 of Mount Loa, lavas still rise and are poured out at an elevation 

 of 10,000 feet above it, Kilauea is no safety-valve even for the 

 area covered by the single mountain. Volcanoes are indexes 

 of danger ; they point out the portions of the globe which are 

 most subject to earthquakes." The safer place is somewhere 

 else. And among volcanic mountains, one that is really dead 

 is a preferable neighbor to the volcano that has been smoulder- 

 ing from time immemorial. For the emission of heat by hot 

 springs, geysers or fumaroles within a dozen miles is pretty 

 good evidence, as at Tarawera, !N ew Zealand, that liquid rock 

 is at no very great depth below ; too deep to receive from de- 

 scending waters the moisture that may contribute energy to the 

 fires and produce volcanic activity, but not too deep to be 

 opened on an extreme emergency, so as to give entrance to a 

 flood of waters for the most terrific of eruptions. 



CONTRAST BETWEEN VOLCANOES OF THE MT. LOA AND 

 VESUVIUS TYPES. 



The marked contrast between volcanoes of the Mt. Loa and 

 Vesuvius types based on the liquidity of the lava, making Mt. 

 Loa discharges to be almost solely outflows, and those of Vesu- 

 vius, both upthrows of cinders and outflows of lava, has been 

 sufficiently explained (xxxv, 28). With this exception, the 

 contrast as to their eruptions, as well as to their ordinary ac- 

 tion, is far less than is generally supposed. 



lines at right angles to the sides of the triangle. His map of the Hawaiian 

 Islands, which is covered with triangles, represents one of these lines as merid- 

 ional, and one accordant, consequently, with the mean trend of the group, or 

 nearly so. On page 147 of his work, it is stated that confirmation of his hypothesis 

 is seen in the fact ''that the direction of the longer axis of the elliptical craters of 

 Mokuaweoweo and Kilauea is X. 30° K." But the facts appear to be that the 

 longer axes of the two craters diverge 32° in direction, and that of Kilauea has 

 nearly the course N. 52° K. Moreover, the trend of the island volcanoes of the 

 group varies greatly in going from one end of the range to the other, and in this 

 the Hawaiian is like other ranges over the ocean. 

 X Expl. Exped. Report, p. 221. 



