The Volcanoes of Iceland


    DURING the past year the Danish Government despatched the well-known geologist, Prof. Johnstrup, to Iceland, for the purpose of making a thorough scientific investigation of the scene of the recent volcanic disturbances. A short time since he laid before the Danish Parliament a report of his journey, with a brief account of the results so far obtained. The first part of the expedition was devoted to the volcanoes in the Dyngju Mountains, encircling the valley of Askja, and was accompanied with many difficulties resulting from the conformation of the region and the prevalence of violent snow-storms. The mountains themselves are not of volcanic origin, but consist of basalt and palagonite-breccia. In former times the Askja Valley was evidently much deeper than at present. Repeated flows of lava have gradually filled it up, and these Prof. Johnstrup believes to have occurred within the historic period, although no mention of volcanic disturbances in this district is to be found in the annals of the island. Along the outer edge of the Dyngju Mountains are numerous craters, some of considerable size, which have contributed most of the Java covering the plain of Odadahrann to the extent of sixty square geographical miles. Part of this enormous quantity of lava had its origin in the neighbouring volcano of Trölladyngja. It is, however, sharply distinguished from the twisted, contorted, masses of the former, by its more regular character and smooth crusts, In the neighbourhood of the newly-formed craters the earth is covered to the distance of over a mile with the bright yellow pumice-stone ejected during the eruption of March 29, 1875. Most of the pieces are seven to eight inches in diameter; many contained two to three cubic feet. In places where the pumice-stone is several feet in depth, it covers a layer of snow twenty-five feet deep, which fell in the winter of 1874–1875, and has been protected from the effects of solar warmth by the feeble conductive power of the pumice-stone. It is fortunate for the land that the outbreak was of this nature, for from its lightness the pumice-stone can be easily removed from the surface of the country. The party examined the most northerly of the craters, which was 300 feet wide and 150 feet deep. It was filled with steam, which was driven out with such force as to give rise to a most deafening roar. No solid matter, however, was borne along with the vapour. Not far from the crater an extensive depression in the valley of Askja has taken place, and the fresh surfaces of rock exposed thereby give a clear picture of the peculiar formation of the valley by successive deposits. It presents a remarkable similarity to the basalt and dolerite formations so prevalent in the mountain ranges of Iceland.

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    The Volcanoes of Iceland . Nature 16, 105–106 (1877).

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