214 



GEOLOGY 



Water may enter the tube from all sides and at various levels. 

 The heating may precede or follow its entrance into the tube, or 

 both. So far as the water is heated after it enters the tube, the 

 point of most rapid heating may be at the bottom of the tube, or at 

 some point above. If the temperature of the source of heat were 

 high enough to convert the descending water into steam as fast 



Fig. 173. Giant Geyser, Yellowstone National Park. (Wineman.) 



as it enters the tube, the steam would escape continuously, and 

 there would be no geyser; but if the rock is only hot enough to 

 bring the water to the boiling-point after some lapse of time, and 

 after some water has accumulated, an eruption is possible. 



The exact sequence of events which leads up to an eruption is 

 not known, but a definite conception of the principles involved inny 

 perhaps be secured by a definite case. Suppose a geyser-tube full 

 of water and heated at its lower end. As the water is heated below. 

 convection tends to distribute the heat throughout the column 



