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The eruption.— In the geyser basin with an elevation of 7,000 to 8,000 



feet, the theoretical boiling point of water is 198° to 199° Fahrenheit, bat 

 at the bottom of a long geyser tube it would be much higher, and this 

 difference represents the amount of heat available for the sudden gen- 

 eration of steam at the moment when the pressure of water is relieved. 

 In the simplest form of eruption the bubbles of steam at the point of 

 contact with the greatest heat displace a portion of the water in the 

 tube and at once set the geyser in action, but when the weight of water 

 is greater, the steam goes on forming at the bottom until its tension is 

 sufficient to overcome the resistance offered by the column and an equi- 

 librium is established. This may be maintained for a longer or shorter 

 period, owing to the inflow of cold water or the gradual escape of steam, 

 but if the heat be sufficient and the column not too high, a portion of 

 the water will at length be expelled and the crisis ensue as before. In 

 -either case the operation is similar. The water having risen to the top 

 of the bowl or crater and boiling more or less at the surface, large vol- 

 umes of steam begin to rush up by which a considerable quantity of it 

 is displaced and caused to overflow. The weight of water being tlms 

 diminished and the formation of steam at the bottom consequently in- 

 creased, this is quickly followed by still larger volumes and more water 

 is thrown out, and now the whole column, mingled with steam, is lifted 

 several feet into the air and continues rising by successive throes to its 

 full height. The eruption may be continuous until the water is ex- 

 hausted and subside as it rose followed by more or less escape of steam, 

 or it may be suspended for a short interval and reuewed again. It will 

 be readily seen that variation in the character of the tube as to shape, 

 length, direction, &c, would give rise to variations in the character of 

 the geyser, and changes gradually taking place in the tube would 

 also account for changes in its performances. Variations in the quan- 

 tity, manner, and location of the water supply or of the application 

 of heat would have a similar effect, and the limit to which all these 

 may be modified is wide enough perhaps to cover every peculiarity 



i 



noticed amongst the geysers of the Yellowstone Basin. The suspen- 

 sions sometimes occurring during an eruption are, it seems to nie, to 

 be accounted for by the lowering temperature produced by the action 

 itself. As the water escapes from the crater it is quickly cooled by the 



■enormous expansion of steam and consequent absorption of heat which 



takes place, so that the falling spray is quite cold, and as soon as a 

 momentary relaxation in the steam tension is thus brought about, it is 

 furthered by the cool water falling back into the orifice of the crater, 



filling it up. 'Whether a mere coincident or not, further observation 

 must determine, but it was noticed that those geysers having craters 

 which offer great facility for the retain of the water often gave a suc- 

 cession of ejections at short intervals, as in the case of the Giantess 

 and Grand, while those to which the water did not return invariably 

 had but one continuous discharge. The Fan Geyser, for example, throws 



