192 



EARTH FEATURES AND THEIR MEANING 



age where the underground water would most naturally reappear 

 at the surface. Their water has penetrated to considerable depths 

 below the surface, but has been chiefly heated by ascending steam 

 or other vapors. The water journey has been chiefly made along 

 fissures, as is shown by the cool springs which often issue near 

 them. Though some hot springs and geysers may disappear from 

 a district, others are found to be forming, and there is no good 

 reason to think that geysers are rapidly dying out, as was at 

 one time supposed. 



The action of a geyser was first satisfactorily explained by the 

 great German chemist Bunsen after he had made studies of the 

 Icelandic geysers, and the mechanics of the eruption was later 

 strikingly illustrated in the laboratory by an artificial geyser con- 

 structed by the Irish physicist Tyndall. In many respects this 

 action is like that of the Strombolian eruption within a cinder 

 cone, since it is connected with the viscosity of the fluid and the 

 resistance which this opposes to the liberation of the developing 

 vapor. In the case of the geyser, a column of heated water stands 

 within a vertical tube and is heated near the bottom of the column. 

 Though the water may at its surface have the normal boiling 

 temperature and be there in quiet ebullition, the boiling point 



for all lower levels is raised by the 

 weight of the column of superin- 

 cumbent liquid, and so for a time 

 the formation of steam within the 

 mass is prevented. In Fig. 202 

 is shown a cross section of the 

 Icelandic Geysir from which our 

 name for such phenomena has been 

 derived, and to this section have 

 been added the actual observed 

 FIG 202. Cross section of Geysir, temperatures of the water at the 



Iceland, with simultaneously ob- ,.,-. ,11 , 



served temperatures recorded at the dlffere nt levels as Well as the tem- 



left, and the boiling temperatures for peratures at which boiling Can 





this it will be seen that at a depth 

 of 45 feet the water is but 2 Centigrade below its boiling point. 

 A slight increase of temperature at this level, due to the con- 

 stantly ascending steam, will not only carry this layer above the 



