Jaggar, Jr. — Outbreak of Mauna Loa, Hawaii, 191^. 167 



Art. VIII. — The Outbreak of 21a una Zoa, Hawaii, 19 H; 

 by T. A. Jag gar, Jr. 



The scientific staff of the Hawaiian Volcano Observatory 

 has been awaiting an eruption of Mauna Loa since 1911. On 

 Oct. 1 of that year the writer recorded this expectation and 

 the statistical data on which it was based, as follows :* — "It is 

 fair to expect that Mauna Loa will renew activity with a lava 

 pool at the Mokuaweoweo center, and without tiows at first, 

 before Feb. 1, 1915. After takings and fountains, with inter- 

 vals of retirement of the lava, one outflow is expectable in the 

 course of the five years following the outbreak (average dura- 

 tion since 1868). As the last flow in 1907 was to the south, 

 the next, by the law of alternation which has held since 1868, 

 should be on the north side of the mountain. These N. flows 

 have not commonly been accompanied by strong earthquakes. 

 As the flows on each side, N. and IS., have been progressively 

 higher since 1868 and there is no sign of collapse like that 

 which led to the 1868 crisis, the new flow on the north side 

 may be expected at a higher level than the Dewey crater of 

 1899. Thus the flow may be looked for near the high crater 

 of 1843 KE., or near the' vent of 1859 on the N.W. slope." 



In accordance with such precedent the great lava fountains 

 appeared in the summit crater on Thanksgiving eve, Nov. 25, 

 1914, about 3.45 p. m. Hawaiian Standard Time. This date 

 brings to a close an interval of repose which in length is within 

 two months of equalling the maximum recorded interval of 

 the last half century, namely the eight years from 1888 to 

 1895 inclusive. At that time as at present, the long repose 

 period followed one of the southern outflows. The summit 

 outbreak of April, 1896, inaugurated an active epoch which 

 culminated in the northern outflow of July 4, 1899. 



The four seismographs of the Whitney Laboratory of Seis- 

 mology of the Massachusetts Institute of Technology, in charge 

 of Mr. H. O. Wood, in the basement of the observatory, have 

 abundantly recorded a seismic prelude to this eruption, fifty- 

 six earthquakes, all but one local, being registered in the twenty- 

 one days preceding the outbreak. Moreover, throughout the 

 year there have been strong recurrent seismic spasms, some- 

 times accompanied by strongly felt shocks, especially in the 

 region of the Mauna Loa longitudinal axis. The seismic activ- 

 ity of the above-mentioned twenty-one days was greater than 

 any similar period of the last three years. On Nov. 25 in the 

 early afternoon there w T ere eight or more shocks, beginning 

 shortly after noon with a continuous shaking, having several 



*Keportof the Hawaiian Volcano Observatory, Jan.-March, 1912, Mass. 

 Inst. Tech., Boston. 



