J. I). Dana — Eruptions of Kilauea and Mt. Loa. 95 



(p. 24); and these so feebly that they did not make themselves 

 generally felt in that city (see map, p. 82). The depth of the 

 oceanic dej^ression between Hawaii and Oahn, which is only 

 500 fathoms where least (between Hawaii and Maui), was 

 sufficient to stop off the vibrations. Further as in the Mt. 

 Loa eruptions, no increase of projectile action was occasioned 

 in the crater by the earthquake disturbance ; the lavas simply, 

 in the quietest way, ran off, leaving the crater empty, still and 

 dark. 



A mountain having within it two great regions of liquid 

 lava thousands of feet in height, each at a temperature above 

 2000° F., and with subterranean waters abundant, at least 

 through the lower two-thirds of the altitude, is well fitted for 

 the production of eruptive crises; and it is remarkable that 

 the eruptions of 1868 and 1887 are the only ones seismically 

 occasioned, or attended, in the past 65 years ; and, further, that 

 in these eruptions, although among the most violent on record, 

 the craters were wholly free from explosive action. 



The violent earthquakes of 1868 and 1887 accomplished noth- 

 ing so far as the eruptions were concerned that is not effected 

 on Hawaii in four eruptions out of five without them. The 

 greatest of the eruptions have had no such aid. In the prep- 

 aration for a discharge, the mountain has reached a dangerous 

 state, because of the elongation upward of the fire column ; then 

 the fracturing agency has done its work ; earthquakes are only 

 a possible incident. With or without them, the conditions and 

 results are the same ; for vibrations necessarily attend fractur- 

 ing, and earthquakes are simply the stronger or perceptible 

 earthshocks. 



4. The rupturing and ejecting forces. — The chief cause of 

 the rupturing is no doubt the elastic force of suddenly gener- 

 ated vapor. So far this is an accepted explanation. As to the 

 conditions under which this vapor is generated, there is not so 

 general agreement. 



The facts show, first, that on Hawaii the vapors are not 

 suddenly generated within the conduit ; for in the event, the 

 lavas slink away from the crater, instead of dashing up wildly 

 to great heights. If not generated within, it must be without, 

 and the most probable region is that of the hot exterior of the 

 conduit, or the hot rocks encasing the liquid column, or else 

 fissures or local fire-places adjoining it. In this view the frac- 

 turing depends on the sudden access of subterranean waters to 

 this outside region of great heat. 



Secondly, the evidence proves that the force makes a fissure 

 or fissures for the discharge of the lava without giving the 

 waters entrance into the conduit. The pressure of the elastic 

 vapor expends itself in breaking the sides of the mountain, and 



