The periodic explosions of active geysers are due to the following facts—water under heavy pressure requires a much higher temperature to boil than water free from pressure. While the water high up in the geyser pipe may be a little under 212 degrees, that in the lower levels may be standing at 50 or 60 degrees higher, and only kept from expanding into steam by the weight of the column above it. If anything lessens that weight or increases the temperature of the lower water, this latter will explode into steam, and drive the upper waters high into air with the force of its exit from the shaft. This, briefly, is the theory of geyser action.
Rotorua itself, the great focus of the healing forces of Nature in the geyser district, is simply a crust over a mass of hot springs, charged with various minerals. Three feet under earth you will find hot water, in nearly any part of the town. There are hundreds of hot springs in the neighbourhood that have never been analysed. Of the many that are in use in the Government Sanatorium, the “Priest’s Water” and “Rachel Water” are the most famous. The former cures rheumatism, gout, and blood diseases, while “Rachel” makes her patrons “beautiful for ever” by curing all forms of skin trouble, and bestowing a lovely complexion, not to speak of the remarkable effects of the spring on nervous affections. There are also wonderful hot swimming baths, much patronised by the casual tourist; baths of hot volcanic mud, and baths of hot sulphur vapour rising direct from the burning caverns under the earth.
But for people who are in good health, it is the “sights” of Rotorua that are the chief attractions, and these are very many. One of the loveliest, and a welcome change from the countless hot-water springs, is Hamurana, surely the most beautiful river source in the world. It is reached by a journey across one of the lakes in a steamer. All the way the great lake ripples purest turquoise under a high, clear, cloudless sky; green islands rise bright and cool from its shining surface, sharply peaked and shadowed mountains, on the distant shores, stand out in strange hues of crystalline hyacinth unknown to our northern climes. By-and-by the little steamer leaves us on a green wooded shore, and we take boat up a fairy river to a region of enchanted beauty. Blossoming trees line the sun-steeped banks; the water is of the strangest colours—jade-green, clear molten sapphire, silver/ emerald, and transparent as a great highway of rock crystal. Enormous trout, weighing up to twenty pounds, rush from under our keel; grass-green and rose-red water weeds quiver far beneath the oar. Wild fuchsias, wild cherries, loaded with scarlet fruit, snowy-flowered tea-tree, arum lilies, yellow broom, and pink dog-roses, hang out over the water. But a few hundred yards, and the big lovely river comes to a sudden end, walled in by blossoming bushes, and apparently cut short in the strangest’ of culs-de-sac. In reality it is the source we have reached; here the whole Hamurana stream springs full-grown from the earth. A great rift in the bed of the glassy river is visible, where the water wells up under our keel in wavering masses of amber, aquamarine, and deep blue, shot with glancing arrows of prismatic light. Five million gallons are poured forth from this deep cold cavern every twenty-four hours—each drop as clear as a diamond, and as pure. The force of the upspringing stream is so great that pennies can be thrown in from the boat without sinking, to the bottom of the cavern—the water sends them back, and casts them out into the shallows about the edge of the rift. Sometimes a small silver coin will slip down into depths, and lie glittering many fathoms below, magnified conspicuously by the transparent water. The Maori natives, who are marvellous divers, have tried time and again to reach-this tempting store of treasure; but no man can stem the uprushing torrent of water, and if the coins were gold, they would be as safe as they are now from being taken by human hands. The most determined suicide could not drown himself in the Hamurana River source, for the stream about the source is shallow, and the cavern water itself would not permit him to sink, however willing he might be.
The Valley of Tikitere, some ten miles from Rotorua, is the greatest contrast that could possibly be conceived to Hamurana’s enchanted loveliness. Enchanted indeed this valley also plight be, but by a spell of evil. It is the nearest possible approach to the familiar conception of hell. A stretch of white siliceous soil, streaked here and there with the blood-coloured stains of hematite, or the livid yellow of sulphur, is pitted all over with lakes, pools, and small deep pot-holes of boiling mud, sometimes thick, sometimes thin, but always scalding, bubbling, spirting, and threatening. Chief of all the horrors is the well-named lake, “Gates of Hell.” Standing upon a bank of white earth that is warm underfoot, and seamed with steaming cracks, one looks down upon a ghastly hellhole of a seething cauldron, slimy black in colour, and veiled with stinging mists that only now and then lift sufficiently to show the hideous surface of the lake. The foul broth of which it is composed bubbles and lifts ceaselessly, now and then rising into ominous heights and waves that seem about to break upon the banks above. The heat reaches our faces, as we stand half-stifled on the pathway. Just beside us, a large pool of bubbling mud, which stands constantly at 2120 Fahrenheit—ordinary boiling point—seems almost cool in comparison. Little wonder that is so; for the “Gates of Hell” is largely composed of sulphuric acid, and its surface temperature is 232°.
Beyond lies a perfect wilderness of boiling mud-holes of every kind. Here, there is a pond of mud as thick as porridge; there, one fluid as cream. Here, the deadly, scalding surface lies innocently smooth and unrippled; there, it leaps and thunders like a young volcano in action.
At one corner we come suddenly upon an ugly black archway, leading to no inviting interior; nothing can be seen within; but the loud gurglings and chokings of the seething depths inside restrain any desire for closer observation, “The Heavenly Twins,” derisively so-named, are two boiling mud-lioles not a foot apart, but quite unconnected; one boils the thickest of brews, while its twin concocts the thinnest.
One must follow the guide closely and carefully about these ghastly wonders. One step off the pathway, and a horrible death awaits the careless walker. Even the path itself is only cool and solid on the outside skin. The guide stops now and then to dig his stick into the whitey-brown earth for a couple of inches, and turn up a clod all glittering on the under-side with fresh crystals of sulphur. This under-side is so hot that one can hardly touch it with the unprotected hand.