472 F. A. Per ret — Subsidence Phenomena at Kilauea 



influence which is often sufficient to limit the explosive crises 

 to the hours immediately following midnight and midday. At 

 Kilauea, however, there is normally no actual external eruption 

 in the Italian sense of the word ; the ordinary barometric varia- 

 tions are unimportant, while the quantity of gas emitted is 

 often very difficult to gauge correctly, many of the vapors 

 being transparent and that of water — which is present — being 

 absorbed by the atmosphere in the heat from the glowing lake 

 and generally dissipated without subsequent condensation. In 

 three months of observation the writer was unable to trace any 

 indisputable coincidence between the activities of the lava lake 

 and the curves of a barograph installed on the spot. There 

 exists, nevertheless, a well-defined conviction among the 

 residents to the effect that there is greater activity at or after 

 midnight, and for this there must be some foundation. 



But the most powerful of all the forms of external influence 

 upon the height and activity of the lava-column is undoubtedly 

 that of the luni-solar gravitational combinations. Whatever 

 may be the precise mode of action — and the subject cannot be 

 entered upon here — the writer's continued observation of 

 strong eruptive conditions at Vesuvius in 1905 and 1906 ; at 

 Stromboli in 1907; Etna 1908; Teneriffe 1909; Etna 1910 ; 

 Kilauea 1911, and Stromboli in 1912, has convinced him that 

 few facts in volcanology rest upon a firmer basis, providing it 

 is recognized, not as a cause of the volcanic activity, but as a 

 force exerting a certain control over the times of its maximum 

 manifestations. Once an eruption is begun — and this influ- 

 ence is often effective also in initiating the external activity — 

 the eruptive crises almost infallibly coincide with the dates of 

 the luni-solar combinations. The practical advantage to the 

 volcanologist of this knowledge is enormous, enabling him to 

 plan his campaign in advance, to be ready to make the best of 

 the opportunities afforded by the crises ; to employ the inter- 

 vening periods of minor activity in investigation of the more 

 dangerous localities ; to determine with greater precision the 

 end of the eruption, etc. 



In the case of Kilauea not only were the principal interrup- 

 tions and reversals in the course of the subsidence coincident 

 with the luni-solar combinations, as shown by the curve, but 

 the greater fact of the high lava period coinciding with an 

 especially favorable series of planetary positions in the early 

 summer, was foreseen a year previous to the time, and the 

 writer's visit to the island planned accordingly. 



The effects upon the crater basin of so considerable a sub- 

 sidence of the lava could not fail to be remarkable, and these 

 consisted chiefly of a general downfall of the more recent 

 formations, including virtually the entire mass of the black 

 ledge. At the commencement of the subsidence, the lava lake 



