Open main menu

Page:Popular Science Monthly Volume 61.djvu/283

This page has been proofread, but needs to be validated.
277
THE ANTILLEAN VOLCANOES.

the futility of attempting escape) to photograph the swirling tongue of flame by which the cloud was rent, and this picture must some day tell whether the fire was lightning or the combustion of inflammable gas.

Other external features of the Vulcanean throes, especially in Mont Pelee, were the detonations heard 200 miles away (those of Krakatoa were audible over 1,000 miles in all directions, almost 3,000 in one); the seismic tremors felt throughout most of the Lesser Antilles; the magnetic shock noted by suitably equipped laboratories from Paris to Honolulu, or a full third of the way about the globe; and especially the solid and gaseous ejectamenta discharged skyward and distributed hundreds of miles in every direction. At Fort de France it was estimated that the greater discharges rose six miles from the crater, seven miles above the level of the sea; by triangulation Bernadou determined the height of the minor discharge of May 30 at 15,500 feet, or something less than three miles (the mean estimate of the height of the Krakatoan discharge in 1883 was 17 miles). The cloud of steam and other gases, with their burden of rock-powder, spread in typical mushroom shape with such rapidity that neighboring islands up to a hundred miles away were darkened, and the dust-rain began to fall within three hours; on Barbados, 100 miles from La Souffriere and 125 from Mont Pelee, the dust-rain reached a depth of a quarter of an inch, and brought down sulphurous gases. The early analyses indicate that the greater part of this material is a crystalline hypersthene-andesite, i. e., the heavier portion of a rather acidic lava of which the more glassy portions are thought by Teall Ho have been vanned away and deposited elsewhere' (Nature, Vol. 66, p. 130); while according to Diller and Steiger some of the grains collected 275 miles southeast of St. Vincent have the astonishingly high specific gravity of 3.3, and the insoluble dust contained.11 per cent, of sulphur, while the dust collected on Barbados was notable for the abundance of magnetite (Science, Vol. XV., pp. 947-950). Nearer the crater of Mont Pelee, the dust—'ashes' of the press reports, 'lapilli' of the books—lies like snow in drifts and sheets sometimes several feet in depth, and is mingled with fragments of pumice or bombs of denser rock, perhaps torn from the throat of the crater. Naturally the rock-rain was cool at Barbados and other remote stations; on St. Vincent, after the outbreak of La Souffriere, and on Martinique under each eruption of Mont Pelee, the falling rock was warm, even hot; an officer of one of the vessels wrecked in the roadstead of St. Pierre escaped the first shock only to be smitten down by a falling mass of half-molten rock; Russell found indications that some of the falling dust was hot enough to scorch the skin of victims but not to fire cotton garments; and a correspondent of Nature reiterates the incredible report that the sand