MOUNT HEKLA, FROM THE VALLEY OF HEVITA.
The extremities of the valleys, where they approach the ocean, are the principal theatres of volcanic activity. At the northern end the best-known volcano is that of Hekla, which has attained a sinister repute from the terrific character of its eruptions. Of these six-and-twenty are recorded, the last having occurred in 1845–46. One lasted for six years, spreading devastation over a country which had formerly been the seat of a prosperous colony, burying the fields beneath a flood of lava, scoriæ, and ashes. During the eruption of September 2, 1845, to April 1846, three new craters were formed, from which columns of fire sprang to the height of 14,000 feet. The lava accumulated in formidable hills, and fragments of scoriæ and pumice-stone, weighing two hundredweight, were thrown to a distance of a league and a half; while the ice and snow which had lain on the mountain for centuries were liquefied, and poured down into the plains in devastating torrents.
But the eruption of another of these terrible volcanoes, the Skaptá Jokul, which broke out on the 8th of May 1783, and lasted until August, was of a still more awful character. At that time the volcanic fire under Europe must have raged most violently, for a tremendous earthquake shattered a wide extent of Calabria in the same year, and a submarine volcano had flamed fiercely for many weeks in the ocean, thirty miles from the south-west cape of Iceland.
Its fires ceased suddenly; a series of earthquakes shook the island; and then Skaptá broke forth into sudden and destructive activity.
For months the sun was hidden by dense clouds of vapour, and clouds of volcanic dust were carried many hundreds of miles to sea, extending even to England and Holland. Sand and ashes, raised to an enormous height in the atmosphere, spread in all directions, and overwhelmed thousands of acres of fertile pasturage. The sulphurous exhalations blighted the grass of the field, and tainted the waters of river, lake, and sea, so that not only the herds and flocks perished, but the fish died in their poisoned element.
The quantity of matter ejected by the rent and shivered mountain was computed at fifty or sixty thousand millions of cubic yards. The molten lava flowed in a stream which in some places was twenty to thirty miles in breadth, and of enormous thickness; a seething, hissing torrent, which filled the beds of rivers, poured into the sea nearly fifty miles from its points of eruption, and destroyed the fishing on the coast. Some of the island-rivers were heated, it is said, to ebullition; others were dried up; the condensed vapour fell in whirls of snow and storms of rain. But dreadful as was the eruption itself, with its sublime but awful phenomena, far more dreadful were its consequences. The country within its range was one wide ghastly desert, a fire-blighted wilderness; and, partly from want of food, partly owing to the unwholesome condition of the atmosphere, no fewer than 9336 men,[10] 28,000 horses, 11,461 cattle, and 190,000 sheep, were swept away in the short space of two years. Even yet Iceland has scarcely recovered from the blow.
At the northern end of the great central valley the focus of igneous phenomena is found in a semicircle of volcanic heights which slope towards the eastern shore of the Lake Myvatr. Two of these are very formidable,—namely, Leirhnukr and Krabla on the north-east. After years of inaction, they suddenly broke out with tremendous fury, pouring such a quantity of lava into the Lake Myvatr, which measures twenty miles in circuit, that the water was in a state of ebullition for many days. On the sides of Mount Krabla, and at the base of this group of mountains, are situated various caldrons of boiling mineral pitch, the ruined craters of ancient volcanoes; and from their depths are thrown up jets of the molten matter, enveloped in clouds of steam, and accompanied by loud explosions at regular intervals.
But the most singular phenomena in this singular country, where frost and fire are continually disputing the pre-eminence, are the Geysers, or eruptive boiling springs. These all occur in the trachytic formation, are characterized by their high temperature, by holding siliceous matter in solution, which they deposit in the form of siliceous sinter, and by evolving large quantities of sulphuretted hydrogen gas.
Upwards of fifty geysers have been counted in the space of a few acres at the southern end of the great valley. Some are constant, some periodical, some stagnant, some only slightly agitated. The grandest and most celebrated are the Great Geyser and Strokr, thirty-five miles north-west from Hekla. These, at regular intervals, hurl into the air immense columns of boiling water, to the height of one hundred feet, accompanied by clouds of steam and deafening noises. In the case of the Great Geyser, the jet issues from a shaft about seventy-five feet deep, and ten in diameter, which opens into the centre of a shallow basin, about one hundred and fifty feet in circumference. The basin is alternately emptied and filled: when filled, loud explosions are heard, the ground quivers, and the boiling water is forced upwards in gigantic columns. Thus the basin is emptied, and the explosions cease until it is refilled.