Ultima Thule; or, A Summer in Iceland. vol. 2/2

by Sir Richard Francis Burton

The sulphur on the top of the cone occurs in such quantity in the cracks and fissures, often lining them to the thickness of more than half-an-inch, that the question naturally arises whether the sulphur could not be worked with advantage.

Although in the immediate neighbourhood of the crater, where the fissures are numerous, the ground seems to be completely penetrated with sulphur; this is so evident in other parts, only a few feet lower, where the surface is unbroken. There are, however, some reasons which seem to promise that a search might be successful. In eruptive cones, like that of Barren Island, there is always a central tube or passage, connecting the vent in the crater with the volcanic action in the interior. In this tube the sulphur, generally in combination with hydrogen, rises in company with the watery vapour, and is partly deposited in the fissures and interstices of the earth near the vent, the remainder escaping through the apertures.

If in the present case we admit the sensible heat of the ground of the upper third of the cone to be principally due to the condensation of steam—a process of which we have abundant evidence in the stream of hot water rushing out from underneath the cold lava—it is not improbable that the whole of the upper part of the interior of the cone is intersected with spaces and fissures filled with steam and sulphurous vapour, these being sufficiently near the surface to permit the heat to penetrate. It is therefore not unlikely that at a moderate depth we should find sulphur saturating the volcanic sand that covers the outside of the cone.

I only speak of the outside, as we may conclude from the evidence we have in the rocks of lava in the crater, and those bulging out on the side, that the structure of the cone is supported by solid rock nearly to its summit, the ashes covering it only superficially.

From what has been said above, the probability of sulphur being found near the surface, disposed in such a way as to allow of its being profitably exhausted, will depend on the following conditions:

First, That the communication of the central canal, through which the vapours rise, with its outlets, be effected not through a few large but through many and smaller passages, distributed throughout the thickness of the upper part of the cone.

Second, That some of these passages communicate with the loose cover of ashes and stones which envelops the rocky support of the cone.

Although I have mentioned some facts which seem to indicate the existence of such favourable conditions, and which are moreover strengthened by an observation by Captain Campbell, who saw vapour issuing, and sulphur being deposited near a rocky shoulder, about two-thirds of the height, on the eastern descent of the cone; still their presence can only be ascertained satisfactorily by experimental digging....

If a preliminary experiment should make it appear advantageous to work the cone regularly, the material about the apex, after being exhausted of the sulphur that is present, could, by blasting and other operations, be disposed in such a way as to direct the jets of vapour in the most convenient manner through uncharged portions of ground. If the sulphur should aggregate in periods of not too long duration, it would be possible to carry on the work of filling up new ground on one side, and taking away saturated earth on the other at the same time—so that, after working round the whole circumference, the earth that had been first put on would be ready to be taken away.

If the periods should prove too long to allow the work permanently to be carried on, an interval of time might be allowed to pass before resuming operations.