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base towards the east, extending from Thrándar jökull to
In this belt lie the following principal volcanoes—Krafla and Leirhuukr, both near Myvatn ; Trölladyngja, in the Odathahraun; Skapta and Oroefa, the westernmost points of the enormous Watna jökull, Katla or Kötlugjá, and its twin mountain Myrdals jökull, and Hekla. The total number of recorded eruptions is:— Eldborg, date uncertain. 894. Katla erupted for the first time. 934. Katla for the second time.
Seventh eruption at sea.
Hekla. Eighth eruption.
1311 or 1332. Katla. Fourth eruption.
Eruption of the Oroefajökull.
Fourth eruption of Trölladyngja.
the third of the western head.
Hekla. Eleventh eruption.
1510. Hekla. Fourteenth eruption; at the same time the second eruption of Herthubreith, and the sixth of Trölladyngja. 1554. Hekla. Fifteenth eruption, from a side crater. 1580. Sixth eruption of Katla, which then formed the huge rift between itself and Myrdals jökull. The volcano has since been called Kötlugjá. 1588. Tenth eruption in the sea off Reykjanes; and the sixteenth of Hekla. 1587. Bursting of ground near Thingvalla lake; clouds of smoke and streams of lava gushed forth. 1597. Seventeenth eruption of Hekla. 1612. Eruption of Eyjafjallajökull. 1619. Eighteenth eruption of Hekla. 1625. Seventh eruption of Katla. In the same year, the nineteenth of Hekla. 1636. Hekla. Twentieth eruption. 1660. Kátla. Eighth eruption. 1693. Hekla. Twenty-first eruption. 1716. Eruption of ash and smoke from Ball jökull. 1717. Eyjafjallajökull. Second eruption. 1720. Fourth eruption of the Ordefa. 1721. Ninth eruption of Katla. 1724–30. Eruption of Krafla, near Myvatn. 1725. Eruption of lava in a grass-grown plain at Hitaholl, near Myvatn; followed by a similar outburst in the grass-land of Bjarnaflag. In the same year, an eruption of Leirhnukr; and also of Skeitharārjökull, west of the Ordefa. That of Leirhnukr lasted till 1729. 1727. Second eruption of Skeitharārjökull, and the fifth from Oroefajökull. 1727–28. Tenth eruption of Katla. 1728. Second eruption in the grass-land at Bjarnaflag, and, in the same year, a slight outburst from Hekla. Another eruption of lava took place in Horsadalr, near Myvatn, and filled the valley; at the same time, the earth opened near Reykjahlith and threw up ash, fire, and lava. Sithu jökull, in the south, also erupted. 1748–52. The Hversjall was thrown up. 1753. Second eruption of Sithu jökull. 1754. Hekla. Twenty-third eruption. 1755. Eleventh eruption of Katla. 1766. Four-and-twentieth eruption of Hekla. 1772. Hekla. Twenty-fifth eruption.
1788. Eleventh eruption off Cape Reykjanes. In the same year occurred the most appalling eruption on record — that of Skapta. 1821. Third eruption of Eyjafjallajökull. 1823. Katla. Twelfth eruption. 1845–46. Hekla. Twenty-sixth eruption. 1860. Katla. Thirteenth eruption. 1861. Skapta threw up ash and sand. 1862. Trôlladyngja erupted ash. There is much uncertainty about this explosion. From the above-given list it will be seen that the number of eruptions from— Hekla, since 1004, inclusive, have been 26. Katla, since 894, inclusive, have been 13. At sea, since 1210, inclusive, have been 11. Trôlladyngja, since 1150, inclusive, have been 7. Oroefa, since 1832, inclusive, have been 5. There have been eighty-six eruptions, including outbreaks of lava, mentioned in some of the Icelandic histories, but the date of which it is impossible with accuracy to determine. These outbursts have taken place from twenty-seven different spots. Some of these vents have been active at several different periods, whilst others have erupted but once. The intervals between these explosions have been most irregular. Those of Hekla have varied from six to seventy-six years, and the intervals between the eruptions of Katla from six to three hundred and eleven years. At periods of peculiar activity more volcanoes than one have vomited simultaneously, as, for instance, in the year 1840, when the Oroefa, Hekla, Mósfell, Herthubreith, and Trôlladyngja erupted together; or, in 1510, when Hekla, Herthubreith, and Trölladyngja poured forth fire and molten rock at the same time. From 1724–30 was the period of greatest activity, twelve eruptions having taken place in those six years. The interval of greatest length between outbreaks of subterraneous fire was between the eruptions of Trölladyngja, in 1510, and Hekla, in I554, a period of forty-four years. Between those of Hekla and Trölladyngja, in 1436 and 1475 respectively, thirty-nine Nears elapsed. Lava breaks forth not only from mountain sides, but from the gorass-land under foot. The earth gapes and pours forth a flood of fire or casts up scoriae, where meadows had previously existed. Such eruptions took place near Myvatn, in 1725, and at Thingwellir, in 1587.
Lava and obsidian.
The traveller notices many instances of the lava having thus welled up and overflowed older strata. Beds of lava of this nature exist in the midst of the Storisandr, at Olfus, and throughout the Gullbringu sysla. Immediately after an eruption has taken place, the volcanoes of Iceland relapse into quiescence, and no smoke or steam rises from them, as it does from Vesuvius and Etna. The great majority have no circular craters; some have split themselves in the fury of explosion, and the lava has flowed from their sides, whilst the fire and water have found vent at the gashed crown. The perfectly symmetrical craters are Eldborg, Hverfjall, Wilingafjall, Borg in Withidal, and every mountain named Skál. The lava stream from Eireks jökull we distinctly traced to the mountain roots. It had not flowed from the summit, but from a chasm at the base. The Odatha Hraun is the most extensive lava bed, covering a space of 1,160 square miles. It has flowed from Trôlladyngja and Herthubreith, and its recesses are quite unknown. It extends farther north than has been represented by Gunnlaugson, and reaches indeed as far as Burfell. The second largest bed is more broken and intercepted by hills and lakes. It extends from Skjaldbreith and Hlöthufell to Reykjanes, a distance of seventy-three miles. The tract around Hekla covers an area twenty-five miles long by ten broad. Obsidian has flowed from some of the volcanoes, as well as lava. The most important streams are near Krafla, Hekla, and at As, in Hvítárdalr. I found coarse obsidian on Ök. As already stated, the great mountain system of Iceland is formed of Palagonite tuff. The principal places where this rock has been pierced by trachyte are Baula, Thorishöfthi in Kaldidalr, a portion of Ok, and Laugarfjall, above Geysir. One of the most singular formations in Iceland is the surturbrand, a species of lignite, which lies in beds between clinkstone and trap. The wood is brightly glossed and black, free from all admixture of sulphur, very splintery in fracture. . Logs and branches are preserved with their knots and roots; the circles denoting the age of the tree are very distinct at the ends of the fragments. In several places a layer of leaves overlies the coal in beds of four to six inches in thickness. The impression of the leaves, with all their delicate fibres, is perfect and very beautiful. The leaves belong to the poplar, willow, and birch. The alternation of basalt and surturbrand deserves peculiar attention from geologists, as the existence of leaves, and absence of marine shells in the deposit, seems to point out that there