The quantity of lava which Skaptar Jokul emitted during this eruption was almost beyond belief. The two principal branches were respectively forty and fifty miles long. The branch which crossed the Skapta was from twelve to fifteen miles wide; the width of the other was seven miles. The usual depth was one hundred feet; but two and three hundred were frequent; and where the streams dashed across gorges or narrow valleys the depth was six or seven hundred. It would be quite safe to estimate the average depth at one hundred and fifty feet. These two principal streams were, then, sufficient to cover one thousand square miles to a depth of one hundred and fifty feet. Contrast with this the twenty million cubic meters estimated to have been poured forth in one of the great Vesuvian eruptions. This last would cover one square mile to a depth of twenty-five feet. Vesuvius sinks to an insignificance that is pitiable; its great outbreak produced but one-six thousandths as much as the single eruption of Skaptar Jokul! Such calculations may give us a comparative estimate of the two; but no figures can give us any conception of the force required to elevate such a stream of melted rock through the crust of the earth. And if we compare the resultant fatality, it is clear that this great convulsion, in a very sparsely settled island, destroyed more lives than all the outbursts of Vesuvius in its densely populated neighborhood.
This eruption of Skaptar was preceded by several outbreaks in the sea; some of them close to the shore; some many miles from land. Such phenomena have become tolerably familiar. Livy informs us that a disturbance of this kind near Sicily, occurring with similar phenomena at the time of Hannibal’s death, so terrified the Romans as to induce them to proclaim a day of supplication to the gods to avert their displeasure. Santorin in the Grecian Archipelago is a similar production. And in 1831 an island was thrown up to the southwest of Sicily, where previous soundings had shown a depth of six hundred feet. It was preceded by a violent spouting of steam and water. The sea around was filled with floating pumice and dead fish. The crater reached a height of two hundred feet, being three miles in circumference. Its circular basin was full of boiling, dingy, red water. It continued active three weeks, and then slowly sank, leaving a dangerous reef eleven feet below the surface; while a single black volcanic rock projected from the sea near the center of the reef. It is known as Graham’s Island. Thus we see that volcanic action is not confined to the land, and that the areas affected are continually shifting.
Jorullo, in Mexico, affords an example of the way in which new volcanoes are constantly being formed. In the parallel of the City of Mexico exist five volcanoes, extending in a line across the country as if thrown up along some immense fissure or subterranean fault, extending from sea to sea. Of these Popocatepetl is perhaps the largest, and Jorullo the most recent.
There formerly existed in Mexico an extensive plain of remarkable fertility, covered with fields of cane, cotton and indigo, and watered by irrigation from the reservoirs in the basaltic mountains that bounded it. This region, the Malpays, had no volcano within eighty miles, and lay twenty-six hundred feet above the sea. In June, 1759, alarming rumblings were heard in the earth, which were succeeded by severe earthquakes. These phenomena lasted several weeks, to the great consternation of the inhabitants. In September it seemed that quiet was restored, when suddenly, on the night of the 28th, a fearful subterranean noise was again heard; fissures opened, and hot stones were thrown out. Part of the plain rose up like
JORULLO.
an immense bubble to the height of sixteen hundred feet. Imagine the astonishment of the natives when morning showed them a mountain where the night before was a level plain! It almost seemed as though some magic had transported them to another land. Smoke and ashes spouted forth; five smaller cones were thrown up, the least of which was three hundred feet in height. The plain was dotted with thousands of small conical mounds, called by the natives hornitos, or ovens. Each emitted vapor for a time; but at length all the upheavals, save Jorullo, ceased action, though the plain remained so hot as to be uninhabitable for many years. Jorullo continued to throw out lava several months, and has been in more moderate action ever since.