100 J. D Dana — Eruptions of Kilauea and lit. L 



oa. 



charge. I repeat here that after the eruption of 1852, which 

 produced a stream 20 miles long, had closed, the lofty volcano 

 was ready in only 3-J- years for a 26-mile now, that of 1855 ; 

 and in 3J years more, for another still longer, that of 1859, 33 

 miles in length of stream : which is brisk work for the great 

 old mountain. According to these facts the lava-column had 

 risen, after the eruptions, at the rate of at least 100 feet a year 

 so as to reach again the bottom of the crater and be ready for 

 another discharge. 



4r. Kinds of Lama-Streams. Pah.oeh.oe and aa, — The ordi- 

 nary smooth-surfaced lava-stream, the pahoehoe, needs here no 

 further description. The aa-stream is less often seen in 

 process of formation and is more difficult to understand. With 

 reference to an explanation of its origin, I repeat here from 

 volume xxxiv the characteristics of the typical kind (not of the 

 thinner streams that approximate to the pahoehoe), and repro- 

 duce also the sketch of a portion of one to aid the conception 

 of its roughness : the reader's conception of it will be feeble at 

 the best if he has not had a view of chaos already. 



a. The characters of the cooled aa-stream : (1) a mass of 

 rough blocks one foot and less to 1000 cubic feet in size, 

 loosely piled together to a height of twenty to forty feet above 

 the general level ; (2) the blocks bristled with points but not 

 scoriaceous, and less vesiculate than most of the pahoehoe ; 



Portion of an aa lava-stream. 



(3) the material rather brittle, and consequently, when made 

 up of small blocks or pieces easily broken down to a flat sur- 

 face for the site of a house ; (-1) often aa in one part, and 

 pahoehoe for the rest — either the chief part; (5) from one 

 outbreak a pakoehoe-stream in one direction and an aa-stream 

 in another. 



o. The constitution and condition when in motion : (1) a 

 mass of rough blocks outside, precisely like the cooled ; (2) the 

 motion extremely slow, indicating a semifluid condition be- 

 neath : (3) a -red heat often in front among the blocks ; (i) 



