134 



THE NATIONAL GEOGRAPHIC MAGAZINE 



None was observed, and the conditions 

 are such as to make their development 

 unlikely for the present. Geysers belong 

 to a declining stage of volcanic activity, 

 while the present region is in a youthful 

 stage. A geyser consists essentially of a 

 column of hot water mixed with steam, 

 which is periodically projected into the 

 air by the sudden formation of the steam 

 from water gradually heating up to the 

 boiling point. 



A geyser can exist, therefore, only in 

 rock cool enough to permit the accumu- 

 lation of the water. The vents of this 

 steaming valley are so hot that they would 

 instantly vaporize any ordinary quantity 

 of water that might find its way into 

 them. One can readily see that if the 

 valley cools off gradually there may come 

 a time favorable for the formation of 

 geysers. 



To attempt any catalogue of the indi- 

 vidual vents or any description of them 

 would be utterly futile. They vary all 

 the way from microscopic jets of gas to 

 mighty columns of smoke which overtop 

 the mountains, To explore 'the valley 

 thoroughly and become acquainted with 

 the characters of the various vents would 

 require a residence of several months. 

 We were continually surprised to find 

 new and interesting features in places 

 with which we thought we were perfectly 

 familiar. The smokes in general, how- 

 ever, may be classed as coming either 

 from craters or fissures. 



THE CRATERS OF THE PLAIN 



The craters are much less numerous 

 than the fissures, but include some of the 

 largest and most active of the vents. All 

 of them are located in the floor of the 

 valley, not around the edges. They aver- 

 age about ioo feet in diameter. The rims 

 are slightly raised above the general level, 

 showing that they were produced by ex- 

 plosive action (see page 135), but the 

 amount of material in these crater rings 

 is, in general, very much less than enough 

 to fill the cavity. Within they are per- 

 fectly conical pits, sloping down into the 

 throat at the bottom. 



The steep sides, standing at the critical 

 angle, remind one of the pits which ant 

 lions dig in the sand. Indeed, little im- 



agination is required to picture the old 

 devil at the bottom waiting to devour 

 whatever slips over the edge ; for the 

 sides are so nearly perpendicular that if 

 any one made the first slip he could never 

 get out again. 



The smoke from these craters comes 

 out in such volume that often the hole is 

 completely filled and its outlines con- 

 cealed, but by waiting a few moments at 

 the windward side one can usually see the 

 inside of the crater, and sometimes for an 

 instant catch a glimpse of the throat at 

 the bottom — usually a perpendicular tube 

 about 10 feet in diameter leading down 

 into the bowels of the earth. On favor- 

 able occasions one may see as much as 

 50 feet below the surface of the plain ; 

 but these momentary glimpses did not 

 give us much information as to the char- 

 acter of the rock at that depth. We could 

 not even be sure whether it differed from 

 the surface mud. 



Many of the craters stand apart from 

 other vents. In other cases they are 

 grouped together in areas with few fis- 

 sures. In a few places the evident rela- 

 tions between craters and fissures furnish 

 perfect models of the relations generally 

 believed to underlie the great lines of 

 volcanic activity that girdle the world. 

 In such a place a long fissure has here 

 and there thrown up craters around 

 points of special activity, forming lines 

 of craters standing up out of the fissure 

 and locally obliterating it without con- 

 cealing their relations to it. 



In the same way such a series of vol- 

 canoes as the Aleutian chain, of which 

 the present district is a part, are sup- 

 posed to be built up around the openings 

 from a continuous fissure in the earth's 

 crust, extending for several hundred miles 

 throughout the length of the chain. 



THE FTSSURES 



Much the greater part of the steam in 

 the valley comes to the surface, not in 

 these craters, but through the innumer- 

 able fissures. There are readily seen to 

 be two sets of these — bands of marginal 

 fissures, several together, running around 

 the edge of the valley in parallel lines, 

 and single central fissures, which criss- 

 cross the floor in all directions (see pages 

 125 and 126). 



