Etna: A History of the Mountain and of its Eruptions

by G. F. Rodwell

On reaching the summit we noticed that a quantity of steam and sulphurous acid gas issued from the ground under our feet, and in some places the cinders were so hot that it was necessary to choose a cool place to sit down upon. A thermometer inserted just beneath the soil from which steam issued registered 182° F. For a short time we anxiously awaited the rising of the sun. Nearly all the stars had faded away; the vault of heaven was a pale blue, becoming a darker and darker grey towards the west, where it appeared to be nearly black. Just before sunrise the sky had the appearance of an enormous arched spectrum, extremely extended at the blue end. Above the place where the sun would presently appear there was a brilliant red, shading off in the direction of the zenith to orange and yellow; this was succeeded by pale green, then a long stretch of pale blue, darker blue, dark grey, ending opposite the rising sun with black. This effect was quite distinct, it lasted some minutes, and was very remarkable. This was succeeded by the usual rayed appearance of the rising sun, and at ten minutes to 5 o'clock the upper limb of the sun was seen above the mountains of Calabria. Examined by the spectroscope the Fraunhofer lines were extremely distinct, particularly two lines near the red end of the spectrum.

The top of the mountain was now illuminated, while all below was in comparative darkness, and a light mist floated over the lower regions. We were so fortunate as to witness a phenomenon which is not always visible, viz., the projection of the triangular shadow of the mountain across the island, a hundred miles away. The shadow appeared vertically suspended in space at or beyond Palermo, and resting on a slightly misty atmosphere; it gradually sank until it reached the surface of the island, and as the sun rose it approached nearer and nearer to the base of the mountain. In a short time the flood of light destroyed the first effects of light and shadow. The mountains of Calabria and the west coast of Italy appeared very close, and Stromboli and the Lipari Islands almost under our feet; the east coast of Sicily could be traced until it ended at Cape Passaro and turned to the west, forming the southern boundary of the island, while to the west distant mountains appeared. No one would have the hardihood to attempt to describe the various impressions which rapidly float through the mind during the contemplation of sunrise from the summit of Etna. Brydone, who is by no means inclined to be rapturous or ecstatic in regard to the many wonderful sights he saw in the course of his tour, calls this "the most wonderful and most sublime sight in nature." "Here," he adds, "description must ever fall short, for no imagination has dared to form an idea of so glorious and so magnificent a scene. Neither is there on the surface of this globe any one point that unites so many awful and sublime objects. The immense elevation from the surface of the earth, drawn as it were to a single point, without any neighbouring mountains for the senses and imagination to rest upon, and recover from their astonishment in their way down to the world. This point or pinnacle, raised on the brink of a bottomless gulph, as old as the world, often discharging rivers of fire and throwing out burning rocks with a noise that shakes the whole island. Add to this, the unbounded extent of the prospect, comprehending the greatest diversity and the most beautiful scenery in nature, with the rising sun advancing in the east to illuminate the scene."

When the sun had risen we had time to examine the crater, a vast abyss nearly 1000 feet in depth, and with very precipitous sides. Its dimensions vary, but it is now between two and three miles in circumference. Sometimes it is nearly full of lava, at other times it appears to be bottomless. At the present time it is like an inverted cone; its sides are covered with incrustations of sulphur and ammonia salts, and jets of steam perpetually issue from crevices. Near the summit we found a deposit, several inches in thickness, of a white substance, apparently lava decomposed by the hot issuing gases. Hydrochloric acid is said to frequently issue from the crater; the gases that were most abundant appeared to be sulphurous acid and steam. The interior of the crater appeared to be very similar to that of the Solfatara near Puzzuoli. During the descent from the cone we collected various specimens of ash and cinder, some red, others black and very vesicular, others crystalline, some pale pink. The steep slope of the cone was well shown by the fact that, although the surface is either extremely rugged owing to the accumulation of masses of lava, or soft and yielding on account of the depth of cinders, a large mass of lava set rolling at the top rushes down with increasing velocity until it bounds off to the level plain below.

View of the Val del Bove

The great cone is formed by the accumulation of sand, scoriæ, and masses of rock ejected from the crater; it is oval in form, and has varied both in shape and size in the course of centuries. When we saw it, it was not full of smoke or steam; but it was possible to see to the bottom of it, in spite of small jets of steam which issued from the sides. It presented the appearance of a profound funnel-shaped abyss; the sides of which were covered with an efflorescence of a red or yellow, and sometimes nearly white, colour. The crater presented the same appearance when it was seen by Captain Smyth in 1814, but he was so fortunate as to witness it in a less quiescent state. "While making these observations," he writes, "on a sudden the ground trembled under our feet, a harsh rumbling with sonorous thunder was heard, and volumes of heavy smoke rolled over the side of the crater, while a lighter one ascended vertically, with the electric fluid escaping from it in frequent flashes in every direction. . . . During some time the ground shook so violently that we apprehended the whole cone would tumble into the burning gulf (as it actually had done several times before) and destroy us in the horrible consequences; however, in less than a couple of hours all was again clear above and quiet within." When Mr. Gladstone ascended in 1838, the volcano was in a slight state of eruption: "The great features of this action," he writes, "are the sharp and loud claps, which perceptibly shook from time to time the ground of the mountain under our feet; the sheet of flame which leapt up with a sudden momentary blast, and soon disappeared in smoke; then the shower of red-hot stones and lava. At this time, as we found on our way down, lava masses of 150 or 200 pound weight were being thrown a distance of probably a mile and a half; smaller ones we found even more remote. These showers were most copious, and often came in the most rapid succession. Even while we were ascending the exterior of the cone, we saw them alighting on its slope, and sometimes bounding down with immense rapidity within, perhaps, some thirty or forty yards of our rickety footing on the mountain side. They dispersed like the sparks of a rocket; they lay beneath the moon, over the mountain, thicker than ever the stars in heaven; the larger ones ascended as it were with deliberation, and descended, first with speed and then with fury. Now they passed even over our heads, and we could pick up some newly fallen, and almost intolerably hot. Lastly, there was the black grey column, which seemed smoke, and was really ash, and which was shot from time to time out of the very bowels of the crater, far above its edge, in regular unbroken form."

At the Casa Inglesi we remounted the mules, and made a slight detour to the east in order to look down into the Val del Bove, which is here seen as a gigantic valley, bounded on the north by the precipitous cliffs of the Serra delle Concazze, and on the South by the Serra del Solfizio. It is believed by Lyell and others that in the Balzo di Trifoglietto, at which point the precipices are most profound and abrupt, there was a second permanent crater of eruption. The Torre del Filosofo, a ruined tower, traditionally the observatory of Empedocles, stands near the Casa Inglesi. Not far from this a great deposit of ice was found in 1828. It was preserved from melting by a layer of ashes and sand, which had covered it, soon after its first existence, as a glacier: a stream of lava subsequently flowed over the ashes, and completely protected the ice; the non-conducting power of the ashes prevented the lava from melting the ice. The snow which falls on the mountain is stowed away in caves, and used by the Sicilians during summer. A ship load is also sent to Malta, and the Archbishop of Catania derives a good deal of his income from the sale of Etna snow.

During our descent from the mountain we were much struck by the apparent nearness of the minor cones beneath us, and of the villages at the base of the mountain. They seemed to be painted on a vertical wall in front of us, and although from ten to fifteen miles distant they appeared to be almost within a stone's throw. This curious effect, which has often been observed before, is due to refraction. At the summit of Etna we have left one-third of the atmosphere beneath us, and the air is now pressing upon the surface of the earth with a weight of ten pounds on the square inch, instead of the usual fifteen pounds experienced at the level of the sea. In looking towards the base of the mountain we are consequently looking from a rarer to a denser medium; and it is a law of optics, that when light passes from a denser to a rarer medium it is refracted away from the perpendicular, and thus the object, from which it emanates, appears raised, and nearer to us than it really is. The objects around Etna appear near to us and raised vertically from the horizon for the same reason that a stick plunged in water appears bent.

We reached Nicolosi again about noon, having left it eighteen hours before. The ascent of the mountain, although it does not involve much hard walking, is somewhat trying on account of the extremes of temperature which have to be endured. In the course of the morning of our descent we had experienced a difference equal to more than 40° F. As to the ascent, you are moving upwards nearly all night; you have six hours of riding on a mule, some of it in a bitterly cold atmosphere; you get very much heated by the final steep climb of 1100 feet, and you find at the summit a piercing wind; of course there is no shelter, and you sit down to wait for sunrise on cinders which are gently giving off steam and sulphurous acid; the former condenses to water as soon as it meets the cold air, and you find your great coat, or the rug on which you have sat down, speedily saturated with moisture.