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surably greater than was requisite to the elevation to the surface of the contents of any one of the strata that can be supposed to have been thrown up at a single effort. The whole mass of a mountain, however great in weight, was to be lifted at once. Of the materials of a stratum forced up in a continuous current, like the waters of a spring or the lava of a volcano, only a small portion was to be supported at the same time. The weight at any moment, for example, of the column of lava borne upwards in the cavity of Etna or Hecla, at a period of the most violent eruption, is but that of a feather to the mountain itself, compared to the vast and inconceivable weight that was uplifted at the elevation of the Alps from the fathomless abysses of the earth in which their massy granites were elaborated. The lofty pinnacles and mounds of that range are themselves, indeed, but trifles, probably, in comparison of the vast bed extending down an immense depth in which they are rooted, that must have been elevated at the same moment along with them. Agents, then, have in fact been acting in the depths of the planet, and elevating the substances deposited there to the surface, that were of even greater energy than is ordinarily exerted in volcanoes, and than was necessary to the gradual ejection of the materials of the strata in the long series of ages that was occupied in their formation.
The forces, however, that are exerted in volcanic eruptions, and the volume of matter ejected by them on the surface in brief periods, is sometimes immense. Thus the current of lava thrown up in 1783 by Skaptar Jokul, one of the principal volcanoes of Iceland, was like that of a great river, and soon filled up deep valleys and spread over extensive plains.
"On the 11th of June, Skaptar Jokul threw out a torrent of lava which flowed down into the river Skapta and completely dried it up. The channel of the river was between high rocks, in many places from 400 to 600 feet in depth, and near 200 in breadth. Not only did the lava fill up this great defile to the brink, but it overflowed the adjacent fields to a considerable extent. The burning flood, on issuing from the rocky gorge, was then arrested for some time by a deep lake which formerly existed in the course of the river between Skaptardal and Aa, which it entirely filled. ... On the 18th of June, another ejection of this liquid lava rushed from the volcano, which flowed down with amazing velocity over the surface of the first stream. By the damming up of the mouths of some of the tributaries of the Skapta, many villages were completely overflowed with water, and thus great destruction of property was caused. The lava, after flowing for several days, was precipitated down a tremendous cataract called Stapafoss, where it filled a profound abyss, which that great waterfall had been hollowing out for ages, and after this the fiery current again continued its course.
"On the 2d of August, fresh floods of lava still pouring from the volcano, a new branch was sent off in a new direction; for the channel of the Skapta was now so entirely choked up, and every opening to the west and north so obstructed, that the melted matter was forced to take a new course, so that it ran in a southeast direction, and discharged itself into the bed of the river Haverfisfliot, where a scene of destruction scarcely inferior to the former was occasioned. These Icelandic lavas—like the ancient streams that are met with in Auvergne and other provinces of central France—are stated to have accumulated to a prodigious depth in narrow rocky gorges; but where they came to wide alluvial plains, they spread themselves out into broad burning lakes, sometimes from twelve to fifteen miles wide, and one hundred feet deep. When the fiery lake which filled up the lower portion of the valley of the Skapta had been augmented by new supplies, the lava flowed up the course of the river to the foot of the hills from whence the Skapta takes its rise. . . . The eruption did not entirely cease till the end of two years.
"The extraordinary volume of the melted matter produced in this eruption, deserves the particular attention of the geologist. Of the two branches which flowed in nearly opposite directions, the greater was fifty, and the lesser forty miles in length. The extreme breadth which the Skapta branch attained in the low countries, was from twelve to fifteen miles ; that of the other about seven. The ordinary height of both currents was 100 feet, but in narrow defiles it sometimes amounted to 600."—Lyell's Principles, vol. i., pp. 342-344.
The matter thrown out of this volcano principally in a few days of a single season, was thus enough probably to spread a stratum ten or twelve feet in thickness over six or seven thousand square miles.
The eruptions from Kilauea, Hawaii, are also on a vast scale:
"The discharge from the large lake during the night of the 17 th, must have been equal to fifteen million cubic feet of melted rock. This undoubtedly found cavities to receive it on the line of the eruption. It is impossible to calculate the discharge from the smaller, or Judd's lake, but supposing it had continued as rapid as it was at the first filling, it would have thrown out, by the time I was there next day, upwards of two hundred million cubic feet of lava. It will readily be perceived, with such a flood, it would be possible within the lapse of a period comparatively short, geologically speaking, for a mound the size of Mauna Loa to be heaped up. However large the above numbers may seem to be, we have reason to suppose from appearances, that the 'boiling up' and overflow of the terminal crater of Mauna Loa must have been far greater ; so much so, indeed, that the outpourings of Kilauea cannot bear a comparison with it. Its whole height of more than six thousand feet above the plain of lava, appears to be entirely owing to the accumulation of ejected matter."—Wilkes's Narrative of the U. S. Exploring Expedition, vol. iv., p. 178.
In an eruption which commenced on the 30th of May, 1840, and continued three weeks, a far greater mass was ejected.
"The first appearance of the lava at the surface occurred in a small crater about six miles from Kilauea. The next day another outbreak was distinguished farther towards the coast. Other openings followed, and by Monday, the 1st of June, the large flow had begun which formed a continuous stream to the sea, where it reached on the 3d of June, destroying the small village of Nanawale. This flood issued from several fissures along its whole course, instead of being an overflow of lavas from a single opening ; the lowest being at an elevation of 1,244 feet, as determined by Captain Wilkes, at a point twenty-seven miles distant from Kilauea, twenty-two miles from the first outbreak, and twelve from the shores. . .
"The lavas rolled on sometimes sluggishly and sometimes violently, receiving at times fresh force from new accessions to the fiery stream, and then almost ceasing its motion. It swept away forests in its course, at times parting and inclosing islets of earth and shrubbery, and at other times undermining and bearing away masses of rock and vegetation on its surface. Finally, it plunged into the sea with loud detonations. The burning lava on meeting the waters was shivered, like melted glass, into millions of particles, which were thrown up in clouds that darkened the sky, and fell like a storm of hail over the surrounding country. Vast columns of steam and vapors rolled off before the wind, whirling in ceaseless agitation, and the reflected glare of the lavas formed a fiery firmament overhead. For three weeks this terrific river disgorged itself into the sea with little abatement. Night was converted into day on all eastern