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Page:Popular Science Monthly Volume 21.djvu/387

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of the tube R, and fail to prevent the temperature of the whole water-column from finally rising under the influence of the constant flow of superheated water from the streams, W’. The strata of water in the middle of the tube finally reach the temperature of the boiling-point at that depth. This water is then converted into steam, and thereby the pressure upon the lower strata is diminished. Then the strata of water still deeper in the tube are also converted into steam, and this throws the masses of water above it energetically out of the geyser-tube. The water being cooled somewhat in the air, a part of it falls back in the tube, and, producing a reduction of temperature, causes a short interruption of the formation of steam, but that is resumed again as the superheated water flows in, and continues till the whole column has been so reduced in temperature, by the water that falls back, that the liquid strata no longer reach the boiling-point corresponding with the pressure upon them, and the eruption ceases.

According to the theory of Lang, the Great Geyser occupies a space in the interior of the earth in shape somewhat like Fig. 3. The tube

PSM V21 D387 Theoretical structure of the bjarnafell great geyser.jpg
Fig. 3.

R, by which the waters are connected with the surface, is bent upward at x, to be bent downward again at y into the tube Z, which, reaching the depths of the earth, is connected with the channels V. These channels conduct to Z hot water mixed with steam, while R is supplied by the streams S, which lie near the surface, with cold water. The geyser-tube becomes stopped at x by the accumulation from these two sources, and the steam rising from Z, deprived of an outlet, collects at y. Its elasticity being augmented by the masses of steam that keep coming up, and by the continued accession of heat from Z, it forces away the water that is in contact with it, and gradually fills the connecting passage x y and a part of Z, while it interposes a separation