Geology 



of rock below. The water at the bottom of this tube 

 becomes heated by contact with the hot rock, and would, 

 under ordinary conditions, circulate by convection until 

 the whole mass reached the boiling point, when ebullition 

 would take place and steam be disengaged at the surface, 

 the point of least pressure. 



Owing chiefly to irregularities in the tube, and partly 

 also, in all probability, to the presence of dissolved silica, 

 the distribution of heat by convection is prevented, or, at 

 all events, seriously hindered, with the result that the 

 water under pressure at the bottom becomes heated up 

 to the boiling point. At first this will be kept in the 

 liquid form by the pressure of the overlying column of 

 water, until at length, as the temperature rises still higher, 

 a small quantity of steam is generated, which by its 

 expansion causes the water to rise in the crater, as we 

 had seen it do before the eruption from which we so 

 narrowly escaped. 



As soon as the water commences to overflow, the 

 pressure on the heated portion of the column below is 

 relieved, and, as its temperature is probably several 

 degrees above the boiling point at normal atmospheric 

 pressure, the water in this lower portion of the pipe at 

 once flashes into steam and drives out the column of 

 cooler water above it with much violence. 



The pipe then slowly fills up again either from below 

 or from above, and the process is repeated. 



In one of the more active of the boiling springs we 

 were able to produce an eruption of the geyser type by 

 throwing in several large stones which probably became 

 jammed in some narrow part of the conduit and provided 

 the necessary check to convection. About ten minutes 



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