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instance of the origin of a volcanic mountain suddenly elevated one thousand six hundred and ninety-five feet above the plain, (four thousand two hundred and sixty-five feet above the ocean,) more than one hundred miles distant from the sea, and quite remote from any active volcano. It occurred on the plain of Malpais, west of the city of Mexico, in the year 1759. In the month of June of that year, alarming subterranean noises, with frequent earthquakes commenced and continued about fifty days. After a period of apparent tranquillity, on the night of the 28th of September the inhabitants were compelled to leave the convulsed plain, in which a tract of four square miles heaving like an agitated sea, was raised to a height five hundred and twenty-four feet; flames were seen to issue, and fragments of burning rock were thrown to great heights. Two rivers were precipitated into the chasms, increasing the fury of the flames. Thousands of small cones rose up on the plain from six to ten feet high, called by the Indians, ovens (hornitos) emitting sulphureous vapors and smoke. In the midst of these fumaroles, stood six large conical

masses rising from three hundred to one thousand six hundred feet above the plain. The largest of these was Jorullo which continued burning and throwing up immense quantities of lava containing fragments of granite rock.

The annexed diagram presents the outline of the elevated plain; a is the cone Jorullo, and b the plain loping from the base of the cones at an angle of 6o.

Fig. 24.

a

Jorullo.

58. Kilauea, in Hawaii, Sandwich Islands, is an ever active, and most remarkable volcano. It is situated, not on the summit, but on the south-eastern flank of Mount Loa, at an elevation of three thousand nine hundred and seventy feet above the sea, while the summit is nine thousand seven hundred and ninety feet higher. Instead of slender walls around a deep crater, liable in most conical craters to be demolished by the explosions of an eruption, the summit of this volcano is nearly a plain, and its crater a deep abrupt pit, seven and a half miles in circuit, of an oval figure, embracing about four square miles. At a depth of six hundred and fifty feet below the brim of this pit, a narrow plain of hardened lava, called the "black ledge," projects like a vast terrace or gallery around the whole interior; and within this gallery, below another similar precipice of three hundred and forty feet, lies the bottom, a vast plain of volcanic rock, more than two miles in length. In this plain are pools of boiling lava, which vary at different times in num

ber and extent, one of which, in November, 1840, was fifteen hundred feet long by one thousand broad. The lava boils in these pools with various degrees of energy, sometimes flowing over, cooling, and thus raising a rim, or passing in glowing streams to distant parts of the crater. At times, the activity of the ebullition is such as to throw up jets of the lava thirty or forty feet high. The overflowing of the pools raises cones, sometimes one hundred feet high, with central cavities, from which vapors issue.

The adjoining figure represents a singular spire of lava, resembling a petrified fountain. From small vents, the liquid lava, thrown up in jets, falls over, raising a conical

Fig. 25.

froduard by reas of guse

Lava Spire at Kilauea.

base. The column is built up by the successive drops of lava which fall upon each other, as they are tossed up. These spires vary in height from a few inches to forty feet, and are miniature craters of eruption.*

59. Four eruptions of Kilauea have occurred since A. D. 1789. That of 1840 was most extraordinary. For several years previous, the lava had been rising in the crater, until it stood about fifty feet above the "black ledge." The immense pressure of the lava and gases opened fissures in the sides of the crater, and the molten flood flowing in a subterranean channel six miles, emerged in an ancient wooded crater, rising in it to the height of three hundred feet; from this again, passing sometimes under ground for miles, and then upon the surface, filling the valleys, melting the hills, and consuming the forests along its path, it poured itself for three weeks with loud detonations into the sea. The length of the stream from Kilauea to the ocean was about forty miles: it accomplished the passage in three days. The breadth of the stream varied from one to four miles, and its depth from ten to two hundred feet. The coast was extended by it a quarter of a mile into the ocean. The whole area covered by it is estimated at fifteen square miles, and the amount of lava at six thousand millions of cubic feet. The waters of the ocean were so heated that the shores were covered for twenty miles with dead fish. Night was converted into day, its glare being visible more than one hundred miles at sea, and at the distance of forty miles fine print could be read at midnight. The lava in Kilauea fell four hundred

* Prof. Dana, in the "Geology of the United States Exploring Expedition."

feet, showing that the eruption was a disgorgement of the The Sandwich Islands present re

lava of that crater.

markable regions of volcanic action, in which several craters occur within a few miles.

Fig. 26.

Diamond Hill and adjacent Volcanic Cones in Oahu, Sandwich Islands.

60. The phenomena of submarine volcanoes are influenced by the pressure of the water of the ocean, which may at certain depths entirely suppress any exhibition of volcanic agency exerted at the bottom. History abounds with authentic instances of the rise of islands. The Grecian Archipelago is studded with them, and the origin of many of the Aleutian islands is within recorded observation. The structure of others (some of them large, as Hawaii, which covers four thousand square miles, and whose summit is nearly fourteen thousand feet above the ocean,) reveals their history. Teneriffe, St. Helena, and the Azores have the same origin. In the year 1811, an island (Sabrina) arose out of the ocean, near the Azores, to the height of three hundred feet, with a circumference of one mile, and after remaining six months, disappeared.

A remarkable volcanic island appeared in the Mediterranean sea, in the month of July, A. D. 1831, which remained visible above the water about three months. A fortnight previously, shocks were experienced on board a ship passing the spot, which produced an impression like

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