From this explanation it is apparent that any thing which impedes the circulation of water in the geyser tube will expedite the eruption. The well-known effect of “soaping geysers” may thus be accounted for. As oil thrown upon waves gives a viscosity to the surface, which greatly moderates their violence, so does the addition of soap or lye make the water of the geyser tube less free to circulate, and thus hasten the conditions precedent to an eruption.
The apparently contrary process of violently agitating the water of the geyser, as by stirring it with a stick, sometimes produces the same effect; but this results from the sudden forcing upward of masses of superheated water, instead of allowing them to rise and gradually cool.
That Bunsen’s theory really explains the phenomena of geyser action there can be little doubt. It is true that in no single geyser does one find a perfect example of the theory. But it must be remembered that typical conditions probably never exist. The point of application of heat; the mode of application, whether from the heated surface of rocks or from superheated steam issuing into the tube; the diameter and regularity of the tube; the point of inflow of the cold water; are all matters which influence the eruption and determine its character. In the endless variety of conditions in nature one need not wonder at the varying results. He should rather wonder that in a single instance nature has produced a combination of such perfection as is found in Old Faithful, which, for thousands of years has performed its duty with the regularity of clock work.
There are various other theories, each with some particular merit, which may be briefly referred to. Sir George Mackenzie, who visited Iceland in 1810-11, thought the geyser tube at some point beneath the surface curved to one side and then upward, communicating with a chamber in the immediate vicinity of the source of heat. The water in this chamber becomes heated above the boiling point, and, expanding, forces the water from the chamber into the tube until the chamber is finally emptied to the level of the mouth of the tube. Any further expulsion of water lessens the weight of the column of water above. Bunsen’s theory comes into play, and with the accumulated pressure of the steam in the chamber, produces a violent eruption.
Prof. Comstock, who visited the Park in 1873, thought that there were two chambers, the lower being in contact with the source of heat, and the upper acting as a sort of trap in the geyser tube. After a sufficient force of steam has accumulated in the lower chamber, it ejects the contents of the chamber above.
S. Baring-Gould, who visited Iceland in 1863, observed that if a tube be bent into two arms of unequal length, the shorter of which is closed, and if the tube be filled with water and the shorter arm then heated, all the characteristic phenomena of geyser action result, the water being finally ejected, with explosive violence from the longer tube.
Now, it is probable that in nature each of these theories may find illustration, but it must still be acknowledged that in all cases Bunsen’s theory is the partial explanation, and in many the only adequate one.
The most superficial examination of the geysers in the Park will disclose two widely different characteristics as regards their external appearance and mode of eruption. On this basis they may be divided into two classes—the fountain geysers and the cone geysers.
In the fountain geyser there is no cone or mound, but in its place a considerable pool which in intervals of rest bears perfect resemblance to the larger quiescent springs. The eruption generally consists of a succession of prodigious impulses by which vast quantities of water are thrown up one after another. There is ordinarily no continuous jet. To geysers of this class, Mackenzie’s and Comstock’s theories would seem to find closer application than to any others. Noted examples are the Fountain, the Great Fountain, the Grand and the Giantess Geysers.
The cone geysers, on the other hand, have no pool about the crater, and water is not generally visible in the tube. There is always a self-built cone or mound of greater or less prominence, ranging from a broad gently-sloping mound, like that of Old Faithful, to a huge cone like that of the Castle. The eruptions from these geysers usually take the form of a continuous jet, and are more in accordance with the theory of Bunsen. Prominent examples are the Giant, the Castle, Old Faithful, the Lone Star, and the Union.