The living waters of Geyserland have exercised a hypnotic attraction upon mankind throughout time. Scientific explanation hardly satisfies the love of the magical (common to most of us), inspired by the wonderful sights found in the central thermal arca of New Zealand, an area extending from White Island to Rotorua and Wairakei.

But as curiosity cannot wholly be appeased (although greatly entertained) by the remarkable Maori legends, retailed by the guides, regarding the geyser phenomenon, the following account is given in the hope that it may help visitors to an intelligent understanding of one phase of Nature's tireless energy.

Of all the features of the present stage of New Zealand's volcanic history, the most outstanding is probably the geyser. Geyser-activity is a phase of volcanic action that occurs in many parts of the world. This phenomenon may be seen, for instance, in the sub-artic wastes of Iceland, in the remote uplands of mysterious Thibet, and in the famous Yellowstone Park of North America.

New Zealand, however, possesses the world's greatest geyser-group, and that renowned Thermal District of which Rotorua and Wairakei are the chief centres, displays geyser-activity in endless variety, and in a multiplicity of form such as the older countries cannot offer, and provides a fruitful field for original study and research. Here we may trace the “life history” of the geyser through every stage, from the simple furmarole that is the genesis, to the dry, sinter-ringed orifice that betokens the ultimate extinction of life and action.

In this brief article it is impossible to do more than touch upon the salient features of this spectacular manifestation of thermal energy. I shall therefore endeavour to outline briefly the researches that have developed the present accepted theory of the causes of geyser-action.

The word, “geyser,” is of Icelandic origin, and may be interpreted liberally as “that which gushes, or spouts forth.”

At the headwaters of the White River, and nearly thirty miles from Hecla, the volcano of Iceland, is a group of boiling springs, the three largest of which are called the Great and the Little Geysers, and the Strokr. It is from the two firstnamed that the term is derived, and it is from the scientific investigation of these pools, particularly the Great Geyser, that our present knowledge of the subject is in large measure due.

Scientific Theories.

The first scientific theory advanced to explain the cause of eruption in geysers was that of one Mackenzie, who, in 1811 suggested that the expansion of imprisoned steam brought about the characteristic display. Mackenzie's theory inferred the existence of a subterranean reservoir connected with the geyser. It was submitted that steam collected in the dome-like roof of this underground cavern, and that by reason of the pressure exerted by the weight of the water in the well of the geyser, or by the ingress of further water from below, or because of both, this imprisoned steam expanded until it attained sufficient power to escape violently by means of the well and carry the superincumbent mass of water with it. It is a well-known fact that steam held under pressure expands, and this was considered to be the fundamental principle of geyser activity.

Until comparatively recent times little further progress had been made in the scientific investigation of the geyser, and it was not until the French geologist, Robert, discovered that the water in the depths of the Great Geyser of Iceland registered a temperature considerably above the point at which water boils at the surface, that the earlier and simpler hypothesis was abandoned.

This discovery was supplemented by the researches of Descloiseaux, and the scientific work of Bunsen, Tyndall, and others. Bunsen had demonstrated that water under pressure will remain liquid at a temperature very much above that of the ordinary boiling point. When in this page 54 condition water is said to be superheated, and if the pressure be suddenly reduced is virtually a high explosive. This is a significant fact, and it is now generally recognised that the basic cause of geyser action is the presence of superheated water or steam in the geyser well.

Why Geysers Gush.

Professor J. W. Gregory, a learned authority, puts the matter very clearly and succinctly when he states that “hot water at the bottom of a tube may be prevented from boiling, and thus kept superheated, by the weight of the water in the upper part of the tube. If the pressure be suddenly removed, then the water will burst into steam with explosive violence, and the water in the upper part of the tube will discharge in a geyser-like jet.”

If the water in the bottom of a geyser well is superheated, and either the load be reduced, or the water be heated to a temperature at which the weight of the overlying mass is insufficient to keep the lower water liquid, then the geyser will discharge by a sudden eruption.

The supply of further heated water from subterranean feeding channels to the bottom of the tube will raise the temperature of the water therein above the limit of superheating at that depth and it will therefore burst into steam and lift the whole of the water in the well.

It will be recognised that, given a plentiful supply of superheated water or steam, and a long tube of comparatively small section, geyser-action is probable. Occasionally, however, the conditions may not be conducive to condensation and the steam escapes in a continuous jet. The famous Blow-Hole of Kerapiti at Wairakei is an outstanding example.

In the case of geysers, the water near the surface tends to lose its high degree of temperature and in just such time as is necessary for the superheated steam or waters in the depths of the well to attain sufficient force to overcome the pressure of the heavier surface water, geyser-action is not only possible, but inevitable.

This, then, is the explanation of the more or less regularly intermittent nature of the displays, and the cause of eruption.

A geyser in a state of quiescence or equilibrium may frequently be brought into action in the following ways:

(a) By removing the pressure on the superheated depths through baling out the surface water, or

(b) By lowering the specific gravity of the surface water and its tension. (The popular method is to place soap in the geyser well.)

There are many theories bearing on the origin of the superheated water or steam. Some hold that it is derived from surface percolations which have penetrated deep down into that central magma—the heated “bowels of the earth”—which it is believed forms the core, as it were, of the globe, while others aver that it comes from the primaeval waters imprisoned in that central magma.

Plants that Thrive on Boiling Water.

These waters welling up through the rocks are heavily mineralised, the most common of the ingredients which they contain being silica in various forms. The beautiful coralline formations about the mouth of a geyser are due to the deposition of these silicates. This material is known as siliceous sinter or geyserite, and was once thought to be deposited by the cooling of the waters, but it is now believed that the actual deposition takes place through the agency of living algae—minute living plants of a low order—which have the power of extracting the mineral from the scalding waters in which they live.

Dr. A. S. Herbert, for many years Government Balneologist at Rotorua, sums up the situation thus in his interesting volume “The Hot Springs of New Zealand”: “….the geysers of New Zealand….are fumaroles whose steam has condensed into boiling water in the geyser tubes; and….this water is from time to time superheated by the excess of fresh bursts of steam to a temperature above its boiling point. In some cases, at any rate, the geyser is modified by the cold surface water which exerts a restraining or valve action, and which is in its turn superheated by the steam.”

“Men may fight and lose the battle, and yet that which they fought for may come to pass.”