J. D. Dana — History of the Changes in Kilauea. 289 



great lava-conduit, therefore, has probably its varying phases, 

 like the fires at the surface, and includes extremes in breadth 

 or enlargement as well as in contraction. The widest part 

 should not be at the summit unless the cooling agencies are 

 less effective, or the heat-making causes more so, there than 

 elsewhere. 



3. The metamorphic action of the heat. — Metamorphic action 

 also may be part of the quiet work of the volcano. The lava- 

 column has its enclosing rocks, and at temperatures varying 

 from that just below fusion to that of the outside rocks ; and 

 vapors must be active in the hot regions. The throat of the 

 conduit may well be, therefore, a region of recrystallizations, 

 of the making of geodes, or lining fractures with crystals, out 

 of whatever material was at hand, and differing somewhat 

 according to the temperature. The effects of such meta- 

 morphism are exhibited, beyond question, in the various min- 

 eral crystallizations in the ejected masses of Vesuvius. They 

 are found also at Kilauea and will be mentioned beyond. 



D. Hydrostatic and other Gravitational Pressure. 



1. The hydrostatic pressure of the column of liquid basalt 

 is 2*8-2 9 times that of water, supposing the lavas while in 

 fusion to be mainly in the glassy condition. This pressure 

 was early recognized by Lyell as one of the possible causes of 

 rupture in volcanoes. The cause may have its effects in a 

 quiet way over the bottom of Kilauea, since the lavas often 

 stand in the lakes at a height of 50 to 100 feet above the floor 

 outside of the surrounding cone ; but no facts yet observed can 

 be positively referred to it. 



2. Again, there may be underminings and therefore subsi- 

 dences in the ordinary course of Kilauea changes, through dis- 

 charges following small fractures. But such effects are not at 

 present distinguishable from those of other modes of origin. 



Having thus reviewed the ordinary operations of the crater, 

 that is, those carried forward between times of eruptions in 

 the way of preparation for an eruption, the next enquiry is, 

 What is needed to produce a great eruption of Kilauea ? The 

 power of the rising vapors and that of the ascensive conduit- 

 lavas, the two chief sources of ordinary activity, appear to be 

 too feeble for any such result. Can eruptions take place with- 

 out any increase of their activity within the crater beyond 

 what has been described ? If so, how % 



Before discussing this subject, the history of the summit 

 crater, Mokuaweoweo, may be first reviewed, as its facts afford 

 important illustrations of the eruptive methods. 



[To be continued.] 



