CHAPTER VI

OTHER VOLCANOES OF THE MEDITERRANEAN

The relative positions of the other volcanic mountains of the Mediterranean Sea; i. e., Etna, Stromboli, and the volcanoes of the Santorin group of the Grecian Archipelago, are shown in the map, Fig. 12.

We will begin with the volcanic mountain of Etna, under which, according to mythology, the angry gods had buried the rebellious Typhoon.

Etna is situated on the island of Sicily, immediately southwest of Italy. It is a much larger mountain than Vesuvius, rising, as it does, from a circular base about eighty-seven miles around, to a height of 10,840 feet above the level of the Mediterranean. It forms a conspicuous object when seen either from the Mediterranean, or from distant parts of Italy.

The height of Etna is so great that its slopes can be divided into three distinct climatic zones or belts. The lowest of these lies between the sea and a height of 2,500 feet. In this zone the mountain slopes are covered with cultivated fields, olive groves, orchards, and vineyards. The middle zone lies between 2,500 feet and 6,270 feet. This zone is covered with forests of chestnuts, oaks, beeches, and cork trees. The third and highest zone includes the rest of the mountain, and may be called the desert zone, since it is a sterile region, covered with huge blocks of lava and scoriæ, and terminating, in the higher portions, in a snow-covered plain, from which the central cone rises.

Etna is continually sending up columns of steam and sulphur vapor. Every now and then it starts in eruption, throwing out large quantities of lava either from the crater on its summit, or from some of the 200 smaller cones or craters that occupy portions of its slopes. On account, probably, of its height the eruptions are most frequently on the sides. Etna affords a magnificent example of a huge volcanic pile of the Vesuvian type, which has been slowly built up by the gradual accumulation of materials that have escaped from its craters.

One of the most interesting features of the higher regions of Etna is an immense chasm rent in a side of the cone near the summit, and known as the Val del Bove. This chasm forms a vast amphitheater.

The great force that removed such an immense mass of matter from the cone could not have been the eroding power of water, since the materials of the cone are too porous to permit streams of any size to rush down the slopes. The force is most probably to be found in some explosive eruption of the mountain, when a portion of the crater was suddenly blown off, just as was done in Vesuvius when a large part of the old crater of Somma was blown away. What is especially interesting about the Val del Bove is the opportunity it affords for studying the interior structure of the mountain, for it practically enables one to enter to almost the heart of this great volcano.

The Val del Bove has the shape of a great pit five miles in diameter. It has almost vertical walls, the height of which varies with their position. Those which reach highest up the mountain vary from 3,000 to 4,000 feet in height.

Like Vesuvius, Etna has been split or fissured into great crevices that have been filled with lava during the many eruptions of its central crater. On hardening, these lava streams form what are known as dikes. As the sides of the mountain are worn away by erosion, the dikes, being harder than the rest of the cone, project from its sides like huge walls. An excellent opportunity for seeing them is afforded in the walls of the Val del Bove.

Sir Charles Lyell, the English geologist, who has carefully studied Mt. Etna, asserts that this mountain began to be formed during a geological period known as the Tertiary Age, through a crater that opened on the floor of the Mediterranean Sea. The material thus thrown out, collected around the crater and produced a mountainous pile that gradually emerged above the level of the sea, and on fresh materials continuing to be thrown out, at length reached its present height. It would appear that at some former time in its history, there were two vents near the top of the mountain, the second crater being formed immediately under the Val del Bove. Soon, however, the second and lower crater was closed, the upper one alone remaining active. The mountain, therefore, continued to be slowly raised in the air by the materials brought out through this opening. Then came the great explosive eruption during which the side of the mountain was blown off to form the great chasm of the Val del Bove.

Because of its almost constant activity, Mt. Etna must have been well known to the ancients, who described some of its most violent eruptions. The following brief notes concerning these eruptions have been taken from Lyell.

According to Diodorus Siculus, an eruption that occurred before the Trojan war, caused the people living in districts near the mountain to seek new homes. Thucididies, the Greek historian, states that in the sixth year of the Peloponnesian war, which would be about the spring of 425 B. C., a lava stream caused great destruction in the neighborhood of Campania, this being the third eruption that had occurred in Sicily since it had been settled by the Greeks.

Seneca, during the first century of the Christian Era, calls the attention of Lucullus to the fact that during his time Mt. Etna had lost so much of its height that it could no longer be seen by boatmen from points at which it had before been readily visible.

But passing by these very early eruptions of Etna we come to the great eruption of 1669. This eruption was preceded by an earthquake that destroyed many houses in a town situated in the lower part of the forest zone, about twenty-five miles below the summit of the mountain, and ten miles from the sea at Catania. During this eruption two deep fissures were opened near Catania. From these such quantities of sand and scoriæ were thrown out, that, in the course of three or four months, a double cone was formed 450 feet high, which is now known as Monte Rosso. But what was most curious was the sudden opening, with a loud crash, of a fissure six feet broad reaching down to unknown depths that extended in a somewhat crooked course to within a mile of the summit of Etna. This great fissure was twelve miles in length and emitted a most vivid light. Five other parallel fissures of considerable length opened, one after another, throwing out vapor, and emitting bellowing sounds which were heard at a distance of forty miles. These fissures were afterwards filled with molten rock, and in this manner were formed the long dikes of porphyry and other rocks that are seen to be passing through some of the older lavas of Mt. Etna.

The great lava streams which flowed down the side of the mountain during this eruption, destroyed fourteen towns and villages, and at length reached Catania. A great wall had been raised around this city to prevent the lava from entering it. The molten rock, however, accumulated, until it rose to the top of the wall, which was sixty feet high, and then pouring over it in a fiery cascade, overwhelmed part of the city. It is said that during the first part of its journey, the lava streams moved over thirteen miles in twenty days, or at the rate of 162 feet an hour. Beyond this, after the lava had thickened by cooling, it had a velocity of only twenty-two feet per hour.

Fig. 14 represents a plan of Mt. Etna reduced from a map by the Italian Government. During the eruption of 1865, a rent was made in the mountain extending from Mount Frumento (B in the preceding map) for one and one-half miles, and six cones from 300 to 350 feet in height were formed along the fissure.

During the eruption of 1874, great fissures three miles in length were formed in the mountain.

There exists on the slopes of Mt. Etna vast subterranean grottoes formed by the sudden conversion into steam of great quantities of water that were overwhelmed by the molten mass. These immense volumes of steam produced enormous bubbles in the molten lava. When the lava hardened irregular grottoes were left. Lyell describes one of these as follows:

"Near Nicolosi, not far from Monte Rosso, one of these great openings may be seen, called the _Fossa della Palomba_, 625 feet in circumference at its mouth and seventy-eight deep. After reaching the bottom of this, we enter another dark cavity, and then others in succession, sometimes descending precipices by means of ladders. At length, the vaults terminate in a great gallery ninety feet long, and from fifteen to fifty broad, beyond which there is still a passage, never yet explored, so that the extent of these caverns remains unknown. The walls and roofs of these great vaults are composed of rough bristling scoriæ of the most fantastic forms."

Besides the eruptions mentioned there have been many others, such as those of 1811, 1819, and 1852. The last of these was greater than any eruption except that of 1669. It began in August, 1852, and continued until May, 1853, and was remarkable for the immense quantity of lava thrown out.

We come now to the volcano of Stromboli. Stromboli, one of the Lipari islands, is situated about sixteen miles west of the Straits of Messina. Its general appearance is shown in Fig. 15. The form of the mountain is that of an irregular four-sided pyramid, which rises about 3,090 feet above the level of the Mediterranean, and stands on the bottom of the sea in water about 3,000 feet deep.

If you carefully examine the appearance of Stromboli, as shown in the preceding figure, you will notice that the flat cloud which hangs over the island is made up of a number of globular masses of vapor, formed during the peculiar action of the volcano.

When examined by night Stromboli presents a still more curious appearance. Since the mountain stands alone, its height permits it to be seen readily at sea for distances of at least a hundred miles. At night a curious glow of red light may be seen on the lower surfaces of the cloud. This light is not continuous, but increases in intensity from a faint glow to a fairly bright red light, then gradually decreases, and finally dies away completely. After awhile the light again appears, again gradually decreases, and disappears, and this continues until the rising sun prevents the red glow from being any longer visible. Stromboli, therefore, acts not unlike the flashing lighthouses so common on the sea coasts of all parts of the world. Indeed, it is actually used by sailors in the Mediterranean for the purpose of showing them their direction. For this reason Stromboli is commonly called "The Lighthouse of the Mediterranean."

As Judd remarks, from whom much of the information concerning some of the volcanic districts of the Mediterranean has been obtained, the flashing light of Stromboli differs from that of the ordinary flashing light in two important respects; viz., in the intervals that elapse between the successive flashes, and in the intensity of the light emitted. As you know, it is necessary that the different lighthouses placed near one another on a coast must have their lights of such a nature that they can be readily distinguished. In order to do this, the flashing light has been devised. In flashing lighthouses, the lights only appear at intervals, one lighthouse being distinguished from another in its neighborhood by the intervals between successive flashes, or, sometimes, indeed, by the color of some of the flashes. Now, in the case of Stromboli, the intervals between the successive glowings of the red lights are very irregular, varying between one and twenty flashes per second. Moreover, the intensity of the light also varies greatly from time to time.

You naturally inquire as to the cause of these flashes of light that are emitted by Stromboli. If, as Judd suggests, you should climb to the summit of the mountain, during the daytime, and look down the inside of the crater, you could see its black slag bottom crossed by many cracks and fissures. From most of the smaller fissures the vapor of water is quietly escaping. This vapor rises in the air in which it soon disappears. There are, however, larger cracks on the bottom of the crater from which, at more or less regular intervals, masses of steam are emitted with loud snorting puffs not unlike those produced by a locomotive. From some of the openings molten matter is seen slowly oozing out, collecting in parts of the crater and moving up and down in a heaving motion. Every now and then a bubble is formed on the surface of this liquid. The bubble swells to a gigantic size, and suddenly bursts. The steam it contained escapes, carrying fragments of scum which are thrown high into the air. The masses of steam, formed below the surface of the sticky, boiling, lava, in endeavoring to escape, force their way through the mass, blow huge bubbles, which, on bursting, produce the roaring sounds that are heard, and throwing great columns of vapor in the air, produce the rounded masses of clouds you can see floating high up in the air over the mountain. At the same time the scum is partially removed from the red hot surface, its light illumines the lower surface of the overhanging cloud, which flings it back again to the earth. With the bursting of each bubble, and the clearing of the scum from the surface of the red hot mass, the light begins, increases in intensity, and then as the scum again begins to collect on the surface, decreases, and finally disappears, and not until the bursting of the next bubble is it again visible.

But let us make a study of some of the peculiarities of Vulcano, another of the Lipari islands, which lies north of Sicily.

Vulcano affords a curious example of a volcano that has been harnessed by man, or made to do work for him. All volcanoes bring from inside of the earth different kinds of chemical substances, in the form of vapors, gases, or molten materials. Now, these materials acting on one another, produce chemical substances some of which, such as sal ammoniac, sulphur, and boracic acid, possess commercial value. This is especially true in the case of Vulcano, and since the eruptions are not generally violent, a chemical works has actually been erected by a Scotch firm on the side of the mountain, where the materials are collected from the crevices.

This effort to harness a volcano was for a time so successful that the same people contemplated the building of great leaden chambers over the principal fissure at the bottom of the crater, so that the large volumes of ejected vapors might be condensed and collected. But Vulcano, like all other volcanoes, could not be relied on continually to keep the peace. One day it suddenly burst forth more fiercely than usual, so that the workmen were compelled to abandon the factory and fly down the mountain for their lives, but not, however, before some of them were severely injured by the explosions.

Vulcano is an instance of a volcano in an almost exhausted or dormant condition. It has had, however, many eruptions during the past few centuries, some of which have been very violent, for example, that of 1783, and that of 1786.

There still remains to be considered the volcanic region of the Santorin group of the Grecian Archipelago. The island of Santorin or Thera, is the southernmost of the Cyclades. It is an exceedingly curious island, being a submerged volcano, with most of the top of the crater remaining above the waters, so that the entire island has the shape of an irregular circle or crescent broken at several points. Its formation is, probably, due to the gradual sinking of a volcanic mountain until its crater has been almost completely submerged, only the higher parts of the edges of the crater being left above the surface of the waters. Suppose, for example, a mountain like Vesuvius at the time the crater Somma existed, was sunk below the level of the Mediterranean until only the highest parts of the crater remained above the waters. If, now, one or more volcanic eruptions occurred, producing craters or volcanic islands inside the submerged rim, you would have a condition of affairs seen in the island of Santorin.