The epoch-marking visit of Professor Bunsen proved, by soundings, the Geysir to be a regular tube, 60 to 74 feet deep, with a diameter of 10 feet 4 inches: he found the temperatures by termometres à deversement varying to a maximum of 270° (F.), or 58° above boiling point; and Mr Bryson (1864) verified these observations, making the bottom of the pipe 240°, and the centre 270°. Superheated water loses the cohesion of its particles with the expulsion of air, and, if pressure be removed, “flashes into steam;” this well-known fact at once suggested the chemist’s explanation. Thus M. Müller was able to make an artificial Geysir; M. Douay of Ghent corked a straight brass tube, and caused explosion by heating it at the bottom and at half length; and Professor Tyndall followed with his pipe of galvanised iron, 6 feet long, surmounted by a basin, and girt about the centre with burning gas. Even the detonations were imitated; those of the model were explained by steam being condensed in the saucer, whose diameter is 52 to 60 feet, and whose contents are cooled by abundant evaporation—the same phenomenon on a small scale will be observed if water be heated in a bottle. Whilst the far-famed Werner held that volcanoes were caused by the burning of coal-beds, George Stephenson, a great and original mechanical genius, more Wernerian in this point than the master himself, was so impressed by the rhythm and regularity of movements as he first sighted a volcano that he at once referred them to steam and superheated water.
But presently observers raised the valid objection that if air were liberated in large quantities, the Geysir surface would be ever boiling like that of the “Strokkr.” Hence Baring-Gould suggested that an angle in the pipe is sufficient to produce all the phenomena, and he calls the following experiment “merely an adaptation of Sir George Mackenzie’s theory.” Bend an iron tube to 110°, making one arm half the length of the other; fill with water, and place in the fire. For a minute the liquid will remain quiet; presently it begins to quiver; steam generated in the shorter section causes a slight overflow, without signs of ebullition, till the bubble turns the angle: the column of the longer arm is then suddenly forced high in the air, and a jet of eighteen feet can be produced with a tube, whose long arm measures two feet, and whose bore is three-eighths of an inch. The bending pipe is given by Forbes (p. 252), but he has drawn no conclusions from it.
Finally, Dr Hochstetter (Revue Hebdomadaire de Chimie), whose highly interesting experiments throw much light upon volcanic action, can almost dispense with a pipe. When sulphur is melted under water, with a pressure of forty-five pounds to the square inch, the mineral absorbs part of the fluid, and as the former cools, the latter is driven out as steam accompanied by explosions. When the quantity of sulphur is excessive, upheavals take place, craters are formed, and melted brimstone is ejected.
Evidently the several theories require reconciling. A friend wrote to me: “Your suggestion of emptying the Geysir can be done only by a force pump. The long arm of a syphon would require to measure upwards of a hundred yards to find a lower level than the bottom of the tube, which lies eighty-six feet below the upper basin-rim. And even if you succeed, we shall learn very little more than what we already know, or we have reason to assume.” I rejoin that the position of the spring which fills the Geysir after each explosion, and which keeps up the constant flow over its saucer, is a matter of the greatest importance.
Ólafsson produced a new “Gusher,” by simply piercing through eighteen feet of sulphur ground at Krísuvík; and in Tuscany there are artificial soffioni, one of which has been driven 168 metres into strata showing 145° (Centig.). In the present state of science we evidently need not despair of being able to create a Great Geysir upon the grandest scale: these eruptions come from earth’s skin not from her intestines; and the subterranean laboratories of metallic bases are readily opened to oxidation.
Remains now only to walk over the ground, which divides itself into four separate patches: the extinct, to the north-west, below and extending round the north of the Laugarfjall buttress; the Great Geysir; the Strokkr and the Thikku-hverar to the south.
In the first tract earth is uniformly red, oxidised by air, not as in poetical Syria by the blood of Adonis. The hot, coarse bolus, or trachytic clay, soft and unctuous, astringent, and adhering to the tongue, is deposited in horizontal layers: snowy-white, yellow-white, ruddy, light-blue, blue-grey, mauve, purple, violet, and pale-green, are the Protean tints; often mixed and mottled, the effect of alum, sulphuric acid, and the decomposition of bisulphide of iron. The saucer of the Great Geysir is lined with Geysirite (silica hydraté), beads or tubercles of grey-white silica; all the others want these fungi or coral-like ornaments. The dead and dying springs show only age-rusty moulds and broken-down piles, once chimneys and ovens, resembling those of Reykir, now degraded and deformed to couthless heaps of light and dark grey. Like most of the modern features, they drained to the cold rivulet on the east, and eventually to the south. The most interesting feature is the Blesi (pronounced Blese), which lies 160 feet north of the Great Geysir. This hot-water pond, a Grotta Azurra, where cooking is mostly done, lies on a mound, and runs in various directions. To the north it forms a dwarf river-valley flowing west of the Great Geysir; eastward it feeds a hole of bubbling water which trickles in a streak of white sinter to the eastern rivulet and a drip-hole, apparently communicating underground with an ugly little boiler of grey-brown, scum-streaked, bubbling mud, foul-looking as a drain. The “beautiful quiescent spring” measures forty feet by fifteen,[110] and is of reniform or insect shape, the waist being represented by a natural arch of stone spanning the hot blue depths below the stony ledges which edge them with scallops and corrugations. Hence the name; this bridge is the “blaze” streaking a pony’s face. Blesi was not sealed by deposition of silex; it suddenly ceased to erupt in A.D. 1784, the year after the Skaptár convulsion, a fact which suggests the origin of the Geysirs. It is Mackenzie’s “cave of blue water;” and travellers who have not enjoyed the lapis lazuli of the Capri grotto, indulge in raptures about its colouration. North-west of the Blesi, and distant 300 feet, is another ruin, situated on a much higher plane and showing the remains of a large silicious mound: it steams, but the breath of life comes feebly and irregularly. This is probably the “Roaring Geyser” or the “Old Geyser,” which maps and plans place eighty yards from the Great Geysir.
The Great Geysir was unpropitious to us, yet we worked hard to see one of its expiring efforts. An Englishman had set up a pyramid at the edge of the saucer, and we threw in several hundredweights, hoping that the silex, acted upon by the excessive heat, might take the effect of turf; the only effects were a borborygmus which sounded somewhat like B’rr’rr’t, and a shiver as if the Foul Fiend had stirred the depths. The last eruption was described to us as only a large segment of the tube, not exceeding six feet in diameter. About midnight the veteran suffered slightly from singultus. On Monday the experts mispredicted that he would exhibit between eight and nine A.M., and at one A.M. on Tuesday there was a trace of second-childhood life. After the usual eructation, a general bubble, half veiled in white vapour, rose like a gigantic glass-shade from the still surface, and the troubled water trickled down the basin sides in miniature boiling cascades. Thence it flowed eastwards by a single waste-channel which presently forms a delta of two arms, the base being the cold, rapid, and brawling rivulet: the northern fork has a dwarf “force,” used as a douche, and the southern exceeds it in length, measuring some 350 paces.
We were more fortunate with the irascible Strokkr, whose name has been generally misinterpreted. Dillon calls it the piston, or churning-staff; and Barrow the “shaker:” it is simply the “hand-churn” whose upright shaft is worked up and down—the churn-like column of water suggested the resemblance. This feature, perhaps the “New Geyser” of Sir John Stanley and Henderson, formerly erupted naturally, and had all the amiable eccentricity of youth: now it must be teased or coaxed. Stanley gave it 130 feet of jet, or 36 higher than the Great Geysir; Henderson, 50 to 80; Symington, 100 to 150 feet; Bryson, “upwards of a hundred;” and Baring-Gould, “rather higher than the Geysir.” We found it lying 275 feet (Mackenzie, 131 yards) south of the big brother, of which it is a mean replica. The outer diameter of the saucer is only 7 feet, the inner about 18; and it is too well drained by its silex-floored channel ever to remain full. A funnel or inverted cone, whereas the Great Geysir is a mound and a cylinder, it gives the popular idea of a crater: the upper bore is 8 feet 4 inches to 9 feet, the depth 44 to 49, and about half-way down it narrows to 11 inches. The surface is an ugly area of spluttering and even boiling water. A “fulminating dose” of twenty-four turfs and stones, with three by way of “bakhshísh,” brought on the usual tame display of “bouquets d’eau in sheaves, gerbes, lanceolations, and volutes,” the highest rising at most 40 feet: travellers give twelve minutes for the operation, others see it “almost instantaneously;” we had to wait more than an hour. Bryson explains (pp. 44, 45) the action of turf by its organic matter causing violent ebullition, like the mucus or albumen of eggs, which make the pot boil over, or like the vesicles in foam or custard-confining atmospheric oxygen. But a second experiment with stones only, and the want of suddenness in the outburst, made us fall back upon the homely old theory, namely, that stopping the narrow tube enables the water to overcome the pressure of the upper column. The French expedition, after duly “activising it,” fired a shotted gun at the surface of the Strokkr, which is said at once to have ceased boiling.
The most interesting part to us was the fourth or southern tract. It is known as Thikku-hverar, thick caldrons (hot springs), perhaps in the sense opposed to thin or clear water. Amongst its “eruptiones flatuum,” the traveller feels that he is walking