276 H. S. WASHINGTON PERSISTENCE OF VENTS AT STROMBOLI 



above, and covering and masking a more or less precipitous scarp approxi- 

 mately below its upper edge. 



"We have, then, the vents opening from presumably long and narrow 

 conduits very close to the edge of a more or less nearly vertical scarp, 

 about 700 meters above sealevel. They may occupy the site of the former 

 Yanco]'i focus of activity; but, from consideration of the configuration 

 and topography of the remains of the earlier cone, and from analogy with 

 other volcanoes, it is most reasonable to suppose that the chief center of 

 activity has shifted slightly to the southeast, and that the vents have 

 opened on the terrace subsequent to the subsidence of the northwest por- 

 tion of the old Yancori cone. 



In this respect their situation is strikingly like that of some of the 

 small secondary or parasitic vents of Etna, which have opened very close 

 to the edge of the scarp that bounds the great caldera of the Yal del Bove. 

 This scarp is almost precipitous (except for talus and ash) and attains a 

 height of some 2,000 meters. Of these vents may be mentioned Montag- 

 nola, Cisterna, and Eenato. It is to be noted that all these are of recent 

 dates, long subsequent to the formation of the Yal del Bove ; and also that 

 the walls of this are built up of beds of lava and of somewhat compacted 

 agglomerate. 



A similar occurrence is the outbreak of lava in 1832 near the center of 

 the ridge which separates the crater pits of Kilauea and Kilaueaiki,^^ the 

 streams of which flowed down both sides of the ridge, called Byrons 

 Ledge. 



The main characters of the Stromboli vents whose origin we desire to 

 explain are these : 



1. Their persistence in location for a very considerable time. 



2. Their considerable number (6) and contiguity (in spite of their 

 permanence) over a restricted area (about .5 kilometer square). 



3. The want' of synchronism and difference in type of volcanic activity 

 and the consequently deduced non-connection of their conduits. 



4. Their small size and the consequently presumably small diameter 

 of their conduits. 



5. The presumably very considerable depth (of the order of several 

 kilometers) to which their conduits extend. 



6. Their situation near the edge of a scarp about 700 meters high. 

 Taking these characters into consideration, it is clear that no origin 



based on explosive agencies can be postulated — that is, the Stromboli vents 

 can not be ^''explosion diatremes'' — -in the sense of Daubree and Daly,^^ 



S2 W. T. Brigham : Mem. Bishop Mus., vol. ii, 1909, pp. 46 and 90. 



C. H. Hitchcock : Hawaii and its volcanoes, Honolulu, 1911, p. 183. 

 ^ R. A. Daly : Igneous rocks, 1914, p. 252. 



