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MIDDLE AND VALLEY LAKE CRATERS, MOUNT GAMBIER, SOUTH AUSTRALIA.

CHAPTER VI.

VOLCANOES.

Volcanic Mountains-Extinct and Active Craters-Their Size-Dangerous Craterexplorations-Dr. Judd in the Kilauea Pit-Extinct Craters-Their BeautyThe Crater of Mount Vultur in Apulia-Volcanoes still constantly formingJorullo and Isalco-Submarine Volcanoes-Sabrina and Graham's IslandSantorin-Number of Volcanoes-Their Distribution-Volcanoes in a constant state of eruption-Stromboli-Fumaroles-The Lava Lakes in Kilauea—Volcanic Paroxysms-Column of Smoke and Ashes-Detonations-Explosion of Cones-Disastrous Effects of Showers of Ashes and Lapilli-Mud StreamsFish disgorged from Volcanic Caverns-Eruption of Lava-Parasitic ConesPhenomena attending the Flow of a Lava Stream-Baron Papalardo-Meeting of Lava and Water-Scoria-Lava and Ice-Vast Dimensions of several Lava Streams-Scenes of Desolation-Volcanoes considered as safety-valves-Probable Causes of Volcanoes.

VOLCANOES

OLCANOES are vents which either have communicated, or still communicate, by one or several chimney-like canals or shafts, with a focus of subterranean fire, emitting, or having once emitted, heated matter in a solid, semi-liquid, or gaseous state. The first eruption of a volcano necessarily leaves a mound of scoriæ and lava, while numerous eruptions at length raise mountains, which are frequently of an amazing extent and height. These mountains, which are generally called volcanoes, though in reality they are but an effect of volcanic action situated far beneath their base, are called extinct when for many centuries they have exhibited no signs of combustion-active, when, either perpetually or from time to time, eruptions or exhalations of lava, scoriæ, or gases take place from their summits, or from vents in their sides. Their shape is generally that of a more or less truncated cone; but while some, like Cotopaxi or the Peak of Teneriffe, rise with abrupt declivities in the shape of a sugar-loaf, others, like Mauna Loa in the island of

Hawaii, gradually, and almost imperceptibly, ascend from a vast base embracing many miles in circuit.

Their heights also vary greatly. While some, like Madana in Santa Cruz, or Djebel Teir on the coast of the Red Sea, scarcely raise their summits a few hundred feet above the level of the ocean, others, like Chuquibamba (21,000 feet), or Aconcagua (22,434 feet), hold a conspicuous rank among mountains of the first class.

The summit of a volcano generally terminates in a central cavity or crater, where the eruptive channel finds its vent. Craters are sometimes regularly funnel-shaped, descending with slanting sides to the eruptive mouth, but more commonly they are surrounded with high precipitous rock-walls, while their bottom forms a plain, which is frequently completely horizontal, and sometimes of a considerable extent. Its surface is rough and uneven, from the mounds of volcanic sand, of scoriæ, or of hardened lava with which it is covered, and generally exhibits a scene of dreadful desolation, rendered still more impressive by the steam and smoke, which, as long as the volcano continues in an active state, issue from its crevices.

Within this plain, the eruptive orifice or mouth of the volcano is almost universally surrounded by an elevation, composed of ejected fragments of scoria thrown from the vent. Such cones are forming constantly at Vesuvius, one being no sooner destroyed by any great eruption, before another begins to take shape and is enlarged, till often it reaches a height of several hundred feet.

Thus the crater of an active volcano is the scene of perpetual change-of a continual construction and re-construction, and the sands of the sea do not afford a more striking image of inconstancy.

The various craters are of very different dimensions. While the chief crater of Stromboli has a diameter of only fifty feet, that of Gunong Tenger, in Java, measures four miles from end to end; and, though the depth of a crater rarely exceeds 1,000 or 1,500 feet, the spectator, standing on the brink of the great crater of Popocatepetl, looks down into a gulf of 8,000 feet.

From the colossal dimensions of the larger craters, it may

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well be imagined that their aspect exhibits some of the sublimest though most gloomy scenery in nature-the picture of old Chaos with all its horrors.

The volcano Gunong Tjerimai, in Java, which rises to the height of 9,000 feet, is covered with a dense vegetation up to the crater's brink. On emerging from the thicket, the wanderer suddenly stands on the verge of an immense excavation encircled with naked rocks. He is obliged to hold himself by the branches of trees, or to stretch himself flat upon the ground, so as to be able to look down into the yawning gulf. The deep and inaccessible bottom of the crater loses itself in misty obscurity, and glimmers indistinctly through the vapours which are there slowly and incessantly ascending from its mysterious depths. All is desolate and silent, save when a solitary falcon, hovering over the vast chasm, awakes with her discordant screech the echoes of the precipice. Through a telescope may be seen, in various parts of the huge crater walls, swarms of small swallows, which have there built their nests, flying backwards and forwards. The eye can detect no other signs of life, the ear distinguish no other sound.

Humboldt describes the view down the crater of the RucuPichincha -a volcano which towers above the town of Quito to a height of 15,000 feet-as the grandest he ever beheld during all his long wanderings. Guided by an Indian, he ascended the mountain in 1802, and after scaling, with great difficulty and no small danger, its steep and rocky sides, he at length looked down upon the black and dismal abyss, whence clouds of sulphurous vapour were rising as from the gates of hell.

The descent into the crater of an active volcano is at all times a difficult and hazardous enterprise, both from the steepness of its encircling rock walls, and the suffocating vapours rising from its bottom; but it is rare indeed that a traveller has either the temerity or the good fortune to penetrate as far as the very mouth of the eruptive channel, and to gain a glimpse of its mysterious horrors. When M. Houel visited Mount Etna in 1769, he ventured to scale the cone of stones and ashes which had been thrown up in the centre of the crater, where thirty years before there was only a prodigious chasm or gulf. On ascending this mound, which

emitted smoke from every pore, the adventurous traveller sunk about mid-leg at every step, and was in constant terror of being swallowed up. At last, when the summit was reached, the looseness of the soil obliged him to throw himself down flat upon the ground, that so he might be in less danger of sinking, while at the same time the sulphurous exhalations arising from the funnel-shaped cavity threatened suffocation, and so irritated his lungs as to produce a very troublesome and incessant cough. In this posture the traveller viewed the wide unfathomable gulf in the middle of the crater, but could discover nothing except a cloud of smoke, which issued from a number of small apertures scattered all around. From time to time dreadful sounds issued from the bowels of the volcano, as if the roar of artillery were rebellowed throughout all the hollows of the mountain. They were no doubt occasioned by the explosions of pent-up gases striking against the sides of these immense caverns, and multiplied by their echoes in an extraordinary manner. After the first unavoidable impression of terror had been overcome, nothing could be more sublime than these awful sounds, which seemed like a warning of Etna not to pry too deeply into his secrets.

Dr. Judd, an American naturalist, who, in 1841, descended into the crater of Kilauea, on Mauna Loa, in Hawaii, wellnigh fell a victim to his curiosity. At that time, the smallest of the two lava pools which boil at the bottom of that extraordinary pit appeared almost inactive, giving out only vapours, with an occasional jet of lava at its centre. Dr. Judd, considering the quiet favourable for dipping up some of the liquid with an iron ladle, descended for the purpose to a narrow ledge bordering the pool. While he was preparing to carry out his plans, his attention was excited by a sudden sinking of its surface; the next instant it began to rise, and then followed an explosion, throwing the lava higher than his head. He had scarcely escaped from his dangerous situation, the moment after, by the aid of a native, before the lava boiled up, covered the place where he stood, and, flowing out over the northern side, extended in a stream a mile wide to a distance of more than a mile and a half!

In extinct volcanoes, the picture of desolation originally

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