Page:Popular Science Monthly Volume 17.djvu/471

Rh Pacific Ocean is a vast circle of ignivomous mountains—the western coasts of America, the Aleutian Islands, Kamtchatka, the Kuriles, Japan, the Philippines, Molucca, down to the Sunda Islands and New Zealand, being comprised therein. Aside from this immense belt only isolated groups are found, but they are always disposed around the borders of the sea, or near some large body of water. Does not this geographical distribution force us to the conclusion that there exists an intimate connection between volcanic phenomena and water? Shall not we say that infiltration of water is a necessary condition of eruptions, and that the force which expels the torrents of lava is due to the pressure of steam?

This view finds a confirmation in the recent discoveries of the chemical constitution of the gases emitted by volcanoes. According to M. Charles Sainte-Claire Deville, the clouds that emanate from volcanoes consist principally of the vapor of water. M. Fouqué estimated at over 2,000,000 cubic metres the quantity of water thrown out from Etna in a gaseous form during the eruption of 1865. The clouds of vapors issuing from a crater in eruption often condense and fall in delude-like rains, which make torrents of mud of the volcanic ashes. The streams of lava are, moreover, so charged with vapors that they acquire a remarkable fluidity. These vapors are rapidly disengaged as the streams descend, and sometimes in suddenly escaping they occasion miniature eruptions in the middle of a torrent of solidifying lava. Marine salt and other elements of sea-water are found in the gaseous products of eruptions and in the deposits of fumaroles as well; and M. Fouqué's researches on the chemical composition of the emanations from Vesuvius, Etna, and the volcano of Santorin, show that they are in part the result of the decomposition of sea-water.

Such accumulated proofs no longer allow us to doubt the constant agency of water in the production of volcanic phenomena. It would seem that sea-water passes into the subterranean reservoirs either by percolation through fissures or by transudation under, the enormous pressure it sustains. Coming in contact with the incandescent lava at a great depth, it is vaporized, and the accumulation of steam causes from time to time an explosion of these subterranean boilers. Although the heat of the lava-streams is rapidly dissipated by contact with the air, the temperature of the incandescent mass at the bottom of the crater may be estimated at 2,000°, for refractory metals are known to melt in contact with the molten lava. Were it not over 1,200°, the pressure of the steam generated by matter thus heated would be ample to account for the explosive force of eruptions. It is not necessary, indeed, to assume so great a depth as twenty kilometres for the seat of this force, in order to explain the existence of matter in fusion, for there is nothing to militate against the supposition that the earth's crust is thinner in volcanic regions than elsewhere. It is quite probable that the inner surface of this crust is furrowed and fissured,