98 PROCEEDINGS OF THE AMERICAN ACADEMY. 



with centrally placed discharge : in both cases vortical motion is observed 

 in the rapidly escaping liquid. *3 Similarly, the vast Kilauean lake of 

 1820 to 1860 is best interpreted as a true lake with solid floor, except 

 for the narrow pipe which has always supplied the heat at this volcano. 

 That pipe is probably the same pipe into which Halemaumau at times 

 discharges its lava and from which the gas issues, to make the foun- 

 tains of " Old Faithful." All the Kilauean lakes have represented over- 

 floivs from that vent or from a few, more temporary, narrow pipes. The 

 fluidity of the lake has, in each case, been preserved for years by the 

 process above outlined for the existing lake. 



Whatever adverse criticism of this conclusion regarding Kilauea may 

 succeed, it is certain that the whole area of either of the Hawaiian 

 sinks cannot be directly taken to represent the size of the conduits. 

 The surface areas of other lava columns active in historic time are all 

 very much smaller. It is doubtful that any one of them, just below 

 the floor of the flaring crater, has been as much as one kilometer. 

 J. D. Dana computed the volume of the 1852 floor from Mauna Loa, 

 which appears to have emptied the conduit to a depth of 2,500 feet, as 

 estimated from the difference of level of the summit lake and of the 

 point of discharge. The result was 10,560,000,000 cubic feet.** This 

 corresponds to the volume in a cylindrical conduit about 2,300 feet or 

 700 meters in diameter. Similar calculations from other lateral out- 

 flows seem to give a mean diameter for the conduit of the same order 

 of magnitude. Such a lateral fissure once opened, it would seem highly 

 probable that the conduit would be emptied almost entirely by the simple 

 outflow of the lava through the fissure ; discharge into " subterranean 

 cavities," would be unlikely. Moreover, it is possible that some of 

 the 1852 lava represents a temporary rise of magma in the conduit, 

 so that only part of the estimated volume of the flow can be used in 

 calculating the average diameter of the Mauna Loa conduit. Thus, 

 the calculation made according to the method outlined, strengthens 

 the suspicion that the lava column of the world's vastest volcano is 

 but a comparatively narrow pipe, perhaps much less than 600 meters 

 in average diameter. 



All of the ancient central vents now exposed as " necks " after pro- 

 longed denudation, are relatively small. (Compare Figure 10.) The 

 average diameter of the pipes recorded in geological literature is well 

 under 500 meters. The largest of the hundreds of deeply eroded lava 

 necks in the Mount Taylor region of New Mexico is said to be not more 



*3 C. H. Hitchcock, Hawaii and its Volcanoes, Honolulu, 1909, p. 254. 

 ** J. D. Dana, Characteristics of Volcanoes, New York, 1891, p. 210. 



