Wood — Effects in Mokuaweoweo of the Eruption of 1911±. 399 



later was built to still higher elevations than when the foun- 

 tain was seen playing. For features then observed were after- 

 ward obliterated or hidden from view from the station at camp. 

 Also the cone eventually was built larger and higher ; and the 

 region of the lava lake of December was in Augustan irregular 

 collapsed area, or pit. See the photograph, fig. 8. 



The evidence of change between stages, cited already, throws 

 light on a very interesting point. Though in some respects a 

 digression, this matter at bottom is pertinent to the present 

 subject. 



During the course of the recent eruption it was noticed from 

 the Hawaiian Volcano Observatory that apparently fumes 

 were emitted at first in great volume: and at night the 

 illumination was both brilliant and widespread ; but that both 

 the emission of fumes and the night illumination rapidly 

 diminished, until on December 8 they had vanished. The glow 

 appeared to diminish in brilliancy as well as in extent. Begin- 

 ning again on December 13 with a glow barely visible from 

 the Observatory, both the fumes and the illumination appar- 

 ently increased until about the end of the month, and then 

 again diminished rapidly until the apparent cessation of erup- 

 tion on January 10, or 11, 1915. 



At the time this behavior was puzzling, and its interpreta- 

 tion presented difficulties. In the iirst place, it was possible 

 that the effect was due to changes in summit meteorological 

 conditions, and so was in no way dependent upon changes in 

 eruptivity. But if a real variation in fuming and illumination 

 were the fact, this still could be understood in two ways — 

 almost diametrically opposed. 



It was a legitimate inference that it might be due to decreas- 

 ing activity, the apparent increase in illumination in that case 

 being- due to a better reflecting fume-cloud. It is well known 

 that when the lava surface falls low in Halemaumau, at Kilauea, 

 great volumes of the gases then emerge from fumaroles at the 

 sides and in the talus slopes as dense white fumes, instead of 

 burning to transparent or translucent products over the molten 

 surface. With this reaction in mind Jaggar wrote: " . . .an 

 increase of fumes is to be looked for, by analogy with the 

 habit of Kilauea, if the fountains in Mokuaweoweo are still 

 diminishing." * 



In regard to this view it is proper to point out that the 

 effect at Kilauea is due to subsidence of the magma level in 

 the Halemaumau pit, — not to diminishing surface action alone ; 

 and that the diminishing of the fountains in Mokuaweoweo 

 without such subsidence of the magma did not produce either 



* Weekly Bulletin of the Hawaiian Volcano Observatory II, 32, p. 178, 

 Honolulu, December 31, 1914. T. A. Jaggar, Jr. 



Am. Jour. Sci.— ^Fourth Series, Vol. XLI, No. 245.— May, 1916. 

 28 



