THE GEYSERS

Hokitika Guardian, 1 March 1929, Page 2

THE GEYSERS

(By J. DHU.AfM.ONI), F.L.S., lOZ.S in “Lyttelton Times.”)

It is somewhat .strange that, although countless newspaper articles and many pamphlets have been written oil the Rotorua district, its geological history has still to ho written. This history, recorded in the mitks in a very complicated style is ‘ not easily read, a fact that may account for the absence of the Rotorua district from New Zealand’s splendid geological library, which includes Mount Cook, the glaciers, the Southern sounds and wild places visited by few except geologists, prospectors and explorers.

Spectacularly, the* fevers are Rotorun.s greatest feature. They arc the most spectacular phenomenon in the whole of New Zealand. They arc worth going a lone way to see, as, while hot springs are plentiful, geysers are rare. In well-developed forms, they are found in only three parts of the world, name" ]y, New Zealand, .Iceland, and America’s Yellowstone National Park. When Waimangu was at the height of its activity, it hi Id the record as the world’s largest' geyser. - At times it spouted a <n!umii <if dark, muddy water 1000 feet high. It is a new geyser. It is in the line of the giganlie rift opened hy life Tarawera eruption. some forty-two years ago. Waimangu has a large, circular mouth, shaped like a crater. On account of its youth, it has not lined its tube with siliceous material, otherwise, the waters would tie-as clepr as -water of Old Faithful, the most notable geyser in the Yellowstone Park. Old Faithful plays regularly. Waimangu. like most geysers, played irregularly. It arose from a pond, innocent enough

to all appearances when the geyser was at rest, but treacherous in character.

Geysers arc gushing hot springs. Hot water and steam that supply hot

springs may come from water in contact with hot rocks below the surface., nr from water given off as fleam front rock which results from the action of lire and which is solidifying. The essential mechanism of a geyser is impie. hut it is seldom present, and 'cyseis are rare. There must he a subterranean supply of steam or water limited to a point well above the surface hoiling-poiut. There must he a tube communicating verHeally. or [ almost vertically, from tin- supply to the surface. 'I here was a belief formerly that the intervention of a subterranean cavern was a necessary part of a geyser’s mechanism, to act as a re-ervoir for the water and to offer with its domed roof place for an elastic cushion of steam. Yo cavern now is deemed necessary, all hough one extinct geyser had a cave'll. With sufficient water of sufficient temperature. and a .sufficiently long tube from the subterranean supply to the siir- j face, geyser action is inevitable. If heavy objects are thrown into the tube, the wafer is s'-irre.l. .‘■•mu* of it rises, the pressure on it is reduced, it boils, and there is an eruption.

A premature eruption is induced by tile trick of throwing soap into a gey.■•ey’.s mouth. This increases the stickiness of tin' water on the surface. The size of the steam-bubbles is increased. They cause a greater disturbance of the water, stirring and lit ting: it as they rise, and there is further boiling. Impatient tourists now are not allowed to sown geysers in tlie Yellowstone Park, as it is believed that too much soaping causes geysers, in time, to. cease oruptiifg. Somewhat similar tricks are played upon hot springs and fiimarnles, or steam-jets. If a piece of lighted paper is held over ilie mouth of a languid blow-hole, it starts into

brisk activity. The healed air from the llaming paper rises and causes a momentary lessening of (.he atmospheric pressure.

The most notable features of a. | geyser, briefly described by Dr A. S. j llepbcrt, are that, it shoots boiling water info the air, that the action is intermittent, and that in -some cases the action is repeated with clockwork regularity; but this regular intermission is not a necessary feature; some geysers, like Old Faithful, are almost continuous in their action. W-atelling the Rotorua geysers. Dr Herbert in a few words, described the feelings of most people in the presence of those toys of Nature. “One almost iorgets,” ho. stated, “that it is not a phenomenon of inanimate nature, but rather feels that one is in the presence of some monstrous, beautiful, living tiling, rising terrible in its wrath.”

A correspondent has asked as to th means by which a remarkable outcrop of limestone at Warn, near AYhangaref, has Ihoen tinted, chiselled, and carved into blocks. This is the weath-

ering work of rain. A drop of water on the surface of a rock has no noticeable effect; hut when drop follows drop for almost limitless time, the effect sometimes is .startling. Rain softens liard rocks by working into their pores. The activity of rain-water results mainly from the chemical and solvent action of dissolved substances. Rain-water, descending on lands, is charged with carbon dioxide and oxygen captured from the air. As it works its way into the soil it takes more from decayed plants and animals. Charged with these substances, water, slowly decomposes the rocks on which it falls. The solution of limestone is a result of the simplest action of rain-water. Tt is’se< n on all outcrops of pure limestone. Their furrowed surfaces are caused hy rainwater collecting as streams and deep-

ening the grooves in which it Hows. | In passing down through rock rainwater makes its way along natural i crevices or joints. These, when somo- • what widely spaced, separate compact ! blocks of rock, which weather slowly on all their surfaces.' As sharp angles ; ni those block's are attacked from two I ides, they .are rounded off. As the , wenticred layers around the outside i become thicker, the diminishing cores j become rounder. They stand for j plieroidal weathering. They are I abundant in places, and when some of j lie clay is washed away they may be n. the surface, hut Dr C. A. Cotton, from whom this account of spheroidal veathering is taken, slates that they ■mist not lie mistaken for steam-worii :el>i>ios. He explains that tors, huge .'■ouiilers which sometimes resemble ruined masonry, and which surmount winy plateaux formed of granite rocks had the same origin. There are typi<al tors near the Summit Road along t lie ridge of the Port Hills.

Rain,, in its destructiveness, does •lost work m;'lianically, not chenni ally. It lubricates unconsolidated material and causes soil < n >| pas Lo < reop down hill; it, washes dust out of the atmosphere and deposits it, on the surface of the earth; it removes the finer material of soils and leaves behind the coarser material. It is a Instructive agent, but not exclusively so ns it slightly builds up land affected hy the dosposition of dust from the atmosphere. In that way it is constructive. Rain-wash sculptures the bare ground into many small ridges and val leys closely spaced and with steep sides. This type of country is “budhinds:.” Perhaps the clearest demonstration of the erosive action of rain is in the earth pillars it cuts, simply !>v ruin-drops falling vertically. The drops fail • on clay with embedded boulders. As the surface is won: clown idle boulders protect the clay immediately below them from the inpact

of falling drops, an doach boulder caps a clay colowmn until if fa lies off. The best—or the worst— work of rain is done when the drops are large and arc driven by the wind. The impact then is great or.