402 W. T. BRIGHAM ON THE VOLCANIC PHENOMENA 



formed craters ten feet high around two of the points where gases were escaping. It was 

 now evident that the escaping gases were not derived from the stream simply, but issued 

 from a vent, which reached to the common reservoir within or under the mountain. From 

 a friend of mine who visited the spot three or four days afterwards, I learn that the fountain 

 had ceased, and that the crater increased only a few feet after we left. 



" Descending by the stream, we were able to follow it on its south side, as a strong wind 

 was blowing from that direction. Here we found good walking, and could with Safety 

 approach within a few feet of the channel. The width of the stream was from twenty to 

 one hundred feet, but its velocity almost incredible. Some of our party thought it one 

 hundred miles per hour. We could not calculate it in any way, for pieces of cold lava 

 thrown into it would sink and melt almost instantly. The velocity certainly seemed as 

 great as that of a railroad car. For eight or ten miles the stream presented a continued 

 succession of cascades, rapids, curves, and eddies, with an occasional cataract, Some of 

 these were formed by the nature of the ground over which it flowed, some by the new lava 

 itself. The stream had built up its own banks on each side, and had added to the depth of 

 ite channel by melting at the bottom. The stream flowed more gracefully than water. In 

 consequence of its immense velocity and imperfect mobility, its surface took the same shape 

 as the ground over which it flowed. It therefore presented not only hollows but ridges. 

 In several places for a few feet the course of the stream was an ascent of five to ten 

 degrees, in one instance of twenty-five. Where the turns in the stream were abrupt, the 

 outside of the stream was much higher than the inside. So much was this the case, that 

 the outride sometimes curved over the inside, forming a spiral. 



" After arriving at the plain between the mountains, we had so much fog and rain that 

 we could explore but little. We however saw pahoehoe or solid lava forming, and also a-a 

 or clinkers. 1 Pahoehoe was formed mostly by small side streams, and always by shallow 

 streams, which flowed freely but slowly. They were derived generally from the overflowing 

 of the main stream. After flowing for some distance they became cooled at the end, 

 and as there was little pressure from behind, gradually stopped. The little ridges which 

 give the pahoehoe a ropy appearance, were caused by the flowing on of the stream for a 

 little after it had cooled forward, and these are circular because the sides of the stream 

 cool first, while the centre moves on a little further. These streams become solid in a 

 short time, cooling through, and not simply coating over. At a subsequent time during 

 the same flow, another layer of pahoehoe may be formed upon the first, as we saw in several 

 instances. 



"The clinkers are always formed by deep streams, and generally by wide ones, which 

 flow sluggishly, become dammed up in front by the cooling of the lava, and in some in- 

 stances cooled over the top, forming as it were, a pond or lake. As the stream augments 

 beneath, the barriers in front and the crust on the surface are broken up, and the pieces are 

 rolled forward and coated over with melted lava which cools and adheres to them more or 

 less. Then from the force of the melted lava behind and underneath, the stream rolls over 

 and over itself. In this way a bank of clinkers ten to forty feet high, resembling the em- 

 bankment of a railroad, is formed. Often at the end of the stream no liquid lava can be 

 seen, and the only evidence of motion is the rolling of the jagged rocks, of all sizes, down 

 the front of the embankment. Sometimes the stream breaks through this embankment 



1 Prof. Haskell does not distinguish between a-a and clinkers ; they are, however, quite different formations. See above, p. 371. 



