528 KIRK BRYAN 



accumulates it may finally overflow through some higher opening 

 and give rise to a periodic spring. Extreme periodicity of flow 

 however, is attained only when the exit tube acts as a siphon so 

 as to drain rapidly the water that has accumulated in the cavity 

 during a considerable time. 



Geysers are hot springs which at regular or irregular intervals 

 emit a stream of mingled steam and hot water. The vent from 

 which eruption takes place usually lies at the bottom of a pool of 

 clear water, situated at the top of a conical mound of siliceous 

 sinter. The sinter is deposited from the water in successive sheets 

 of gelatinous silica, through the aid of living algae. 



The geyser consists of a tube of hot water extending into the 

 ground. The temperature of the water at the surface is about 

 212° F., but that of the water below the surface exceeds the normal 

 boiling-point of water. The water in the lower part of the tube is 

 prevented from boiling by the pressure of the overlying column. 

 When the temperature at any point in the tube exceeds the boiling 

 point for that depth, steam is formed. The expansion and rise of 

 steam bubbles cause the water to overflow at the top. The conse- 

 quent relief of pressure throughout the column of water causes 

 instantaneous formation of steam from the superheated water. 

 The result is an eruption. Of the water thrown out, part is lost 

 and part returns to the tube. The next eruption occurs after 

 the accumulation of sufficient water and an adequate rise in 

 temperature.^ 



The three known geyser regions of the world are in New Zealand, 

 Iceland, and Yellowstone Park, in each of which the geysers are 

 associated with active or relatively recent volcanism. The heat 

 may be attributed with certainty to still uncooled igneous rock. 

 The water, however, may have either a deep-seated or a shallow 

 origin.^ Geyser action is not dependent on the origin of the water 

 but on the existence of proper channels and the requisite tempera- 

 tures. It seems likely that the presence of silica in solution is 



^ Bunsen and Descloiseaux, Compt. Rend., XXIII (1846),, 934, and other papers 

 quoted by Archibald Geikie, Textbook of Geology (New York, 1902), p. 405; also 

 W. H. Hobbs, Earth Features and Their Meaning (New York, 1912), p. 193. 



== Arnold Hague, "The Origin of the Thermal Springs in the Yellowstone National 

 Park," Geol. Soc. Apierica Bull., XXII (1911), 103-22. 



