The three localities, however, in which they abound in such numbers and magnitude as to attract marked attention are, in the order of their discovery, Iceland, New Zealand, and the Yellowstone National Park. In extent, variety, and magnitude of accompanying phenomena, and in geologic age, the above order is reversed. Iceland has probably the most famous geyser in the world, principally because it was for a long time the only known geyser, and consequently received a great deal of scientific attention; but judging from published descriptions it is clearly inferior to several now known in the Firehole Geyser Basin.
Three notable features of similarity in these geyser regions are the presence of volcanic rocks of remote or recent origin; proximity to the earth’s surface of active sources of subterranean heat; and the presence of a great number of lakes. In all three cases, lava, heat and water are the characteristic geologic and physical accompaniments of those particular phenomena which will now be described more in detail.
GEYSERS.
The hot springs of the Yellowstone National Park may be roughly divided into two classes, eruptive and non-eruptive. To the first the term geyser is applied, while the term hot springs is restricted to the second. These two classes pass into each other by insensible gradations and the line of demarcation it is not possible to draw. The following description will pertain only to those examples about which there is no doubt, and which may be taken as types of their class.
A geyser may be defined as a periodically eruptive hot spring. The name, as might be expected, is of Icelandic origin, and comes from the verb geysa, to gush. The general characteristics of a true geyser, as illustrated by the most perfect example known, Old Faithful in the Yellowstone Park, are the following:
(1.) There is an irregular tube descending from the earth’s surface to some interior source of heat.
(2.) The mouth of this tube may be either a self-built mound or cone (as in the example), or simply an open pool.